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Securing the Management Plane on Cisco IOS Devices

Chapter Description

This chapter, prep for CCNA Security exam 640-554, introduces the concept of the management plane (which is a collection of protocols and access methods we use to configure, manage, and maintain a network device) and examines how to protect it.

Foundation Topics

Securing Management Traffic

It is tricky to fix a problem if you are unaware of the problem. So, this first section starts by classifying and describing management traffic and identifying some of the vulnerabilities that exist. It also identifies some concepts that can help you to protect that traffic. This chapter then provides implementation examples of the concepts discussed earlier.

What Is Management Traffic and the Management Plane?

When you first get a new router or switch, you connect to it for management using a blue rollover cable that connects from your computer to the console port of that router or switch. This is your first exposure to the concept of management traffic. By default, when you connect to a console port you are not prompted for a username or any kind of password. By requiring a username or password, you are taking the first steps toward improving what is called the management plane on this router or switch.

The management plane includes not only configuration of a system, but also who may access a system and what they are allowed to do while they are logged in. The management plane also includes messages to or from a Cisco router or switch that is used to maintain or report on the current status of the device, such as a management protocol like Simple Network Management Protocol (SNMP).

Beyond the Blue Rollover Cable

Using the blue rollover cable directly connected to the console port is fairly safe. Unfortunately, it is not very convenient to require the use of a console port when you are trying to manage several devices that are located in different buildings, or on different floors of the same building. A common solution to this problem is to configure the device with an IP address that you can then use to connect to that device remotely. It is at this moment that the security risk goes up. Because you are connecting over IP, it might be possible for an unauthorized person to also connect remotely. The management plane, if it were secure, would enable you to control who may connect to manage the box, when they may connect, what they may do, and report on anything that they did. At the same time, you want to ensure that all the packets that go between the device being managed and the computer where the administrator is sitting are encrypted so that anyone who potentially may capture the individual packets while going through the network could not interpret the contents of the packets (which might contain sensitive information about the configuration or passwords used for access).

Management Plane Best Practices

When implementing a network, remember the following best practices. Each one, when implemented, improves the security posture of the management plane for your network:

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  • Strong passwords: Make passwords very difficult to break. Whenever you use passwords, make them complex and difficult to guess. An attacker can break a password in several ways, including a dictionary and/or a brute force attack. A dictionary attack automates the process of attempting to log in as the user, running through a long list of words (potential passwords); when one attempt fails, the attack just tries the next one (and so on). A brute-force attack doesn’t use a list of words, but rather tries thousands or millions of possible character strings trying to find a password match (modifying its guesses progressively if it incorrectly guesses the password or stops before it reaches the boundary set by the attacker regarding how many characters to guess, with every possible character combination being tried.). A tough password takes longer to break than a simple password.
  • User authentication and AAA: Require administrators to authenticate using usernames and passwords. This is much better than just requiring a password and not knowing exactly who the user is. To require authentication using usernames and passwords, you can use a method authentication, authorization, and accounting (AAA). Using this, you can control which administrators are allowed to connect to which devices and what they can do while they are there, and you can create an audit trail (accounting records) to document what they actually did while they were logged in.
  • Role-based access control (RBAC): Not every administrator needs full access to every device, and you can control this through AAA and custom privilege levels/parser views. For example, if there are junior administrators, you might want to create a group that has limited permissions. You could assign users who are junior administrators to that group; they then inherit just those permissions. This is one example of using RBAC. Another example of RBAC is creating a custom privilege level and assigning user accounts to that level. Regardless of how much access an administrator has, a change management plan for approving, communicating, and tracking configuration changes should be in place and used before changes are made.
  • Encrypted management protocols: When using either in-band or out-of-band management, encrypted communications should be used, such as Secure Shell (SSH) or Hypertext Transfer Protocol Secure (HTTPS). Out-of-band (OOB) management implies that there is a completely separate network just for management protocols and a different network for end users and their traffic. In-band management is when the packets used by your management protocols may intermingle with the user packets (considered less secure than OOB). Whether in-band or OOB, if a plaintext management protocol must be used, such as Telnet or HTTP, use it in combination with a virtual private network (VPN) tunnel that can encrypt and protect the contents of the packets being used for management.
  • Logging: Logging is a way to create an audit trail. Logging includes not only what administrators have changed or done, but also system events that are generated by the router or switch because of some problem that has occurred or some threshold that has been reached. Determine the most important information to log, and identify logging levels to use. A logging level simply specifies how much detail to include in logging messages, and may also indicate that some less-serious logging messages do not need to be logged. Because the log messages may include sensitive information, the storage of the logs and the transmission of the logs should be protected to prevent tampering or damage. Allocate sufficient storage capacity for anticipated logging demands. Logging may be done in many different ways, and your logging information may originate from many different sources, including messages that are automatically generated by the router or switch and sent to a syslog server. A syslog server is a computer that is set up to receive and store syslog messages generated from network devices. If SNMP is used, preferably use Version 3 because of its authentication and encryption capabilities. You can use SNMP to change information on a router or switch, and you can also use it to retrieve information from the router or switch. An SNMP trap is a message generated by the router or switch to alert the manager or management station of some event.
  • Network Time Protocol (NTP): Use NTP to synchronize the clocks on network devices so that any logging that includes time stamps may be easily correlated. Preferably, use NTP Version 3, to leverage its ability to provide authentication for time updates. This becomes very important to correlate logs between devices in case there is ever a breach and you need to reconstruct (or prove in a court of law) what occurred.
  • Secure system files: Make it difficult to delete, whether accidentally or on purpose, the startup configuration files and the IOS images that are on the file systems of the local routers and switches. You can do so by using built-in IOS features discussed later in this chapter.

Password Recommendations

Using passwords is one way to provide access. Using passwords alone is not as good as requiring a user ID or login name associated with the password for a user.

Here are some guidelines for password creation:

  • It is best to have a minimum of eight characters for a password; bigger is better. This rule can be enforced by the local router if you are storing usernames and passwords on the router in the running config. The command security passwords min-length followed by the minimum password length enforces this rule on new passwords that are created, including the enable secret and line passwords on the vty, AUX, and console 0. Preexisting passwords will still operate even if they are less than the new minimum specified by the command.
  • Passwords can include any alphanumeric character, a mix of uppercase and lowercase characters, and symbols and spaces. As a general security rule, passwords should not use words that may be found in a dictionary, because they are easier to break. Leading spaces in a password are ignored, but any subsequent spaces, including in the middle or at the end of a password, literally become part of that password and are generally a good idea. Another good practice is using special characters or even two different words (that are not usually associated with each other) as a passphrase when combined together. Caution should be used to not require such a complex password that the user must write it down to remember it, which increases the chance of it becoming compromised.
  • Passwords in a perfect environment should be fairly complex, and should be changed periodically. The frequency of requiring a change in passwords depends on your security policy. Passwords changed often are less likely to be compromised.
  • From a mathematical perspective, consider how many possibilities someone would need to try to guess a password. If only capital letters are used, you have 26 possibilities for each character. If your password is one character long, that is 261, or 26 possible variants. If you have a two-character password, that is 262, or 676 possible variants. If you start using uppercase (26) and lowercase (26), numerals (10), and basic special characters (32), your starting set becomes 94 possible variants per character. Even if we look at using an eight-character password, that is 948 or 6,095,689,385,410,816 (6.1 quadrillion) possibilities.

Using AAA to Verify Users

Unauthorized user access to a network creates the potential for network intruders to gain information or cause harm or both. Authorized users need access to their network resources, and network administrators need access to the network devices to configure and manage them. AAA offers a solution for both. In a nutshell, the goal of AAA is to identify who users are before giving them any kind of access to the network, and once they are identified, only give them access to the part they are authorized to use, see, or manage. AAA can create an audit trail that identifies exactly who did what and when they did it. That is the spirit of AAA. User accounts may be kept on the local database or on a remote server. The local database is a fancy way of referring to user accounts that are created on the local router and are part of the running configuration.

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AAA Components

Providing network and administrative access in a Cisco environment—regardless of whether it involves administrators managing the network or users getting access through network resources—is based on a modular architecture composed of the following three functional components:

  • Authentication: Authentication is the process by which individuals prove that they are who they claim to be. The network environment has a variety of mechanisms for providing authentication, including the use of a username and password, token cards, and challenge and response. A common use is authenticating an administrator’s access to a router console port, auxiliary port, or vty lines. An analogy is a bank asking you to prove that you are who you say you are before allowing you to make a transaction. As an administrator, you can control how a user is authenticated. Choices include referring to the local running configuration on the router to look for the username, going to an external server that holds the username and password information, and other methods. To specify the method to use, you create an authentication “method list” that specifies how to authenticate the user. There can be custom named method lists or default method lists. Examples of each are shown later in this chapter.
  • Authorization: After the user or administrator has been authenticated, authorization can be used to determine which resources the user or administrator is allowed to access, and which operations may be performed. In the case of the average user, this might determine what hours that user is allowed on the network. In the case of an administrator, it could control what the administrator is allowed to look at or modify. An analogy is a bank (after having already authenticated who you are) determining whether you are authorized to withdraw some amount of money (probably based on your balance in your account at the bank). You can create authorization method lists to specify how to authorize users on the network.
  • Accounting and auditing: After being authenticated and possibly authorized, the user or administrator begins to access the network. It is the role of accounting and auditing to record what the user or administrator actually does with this access, what he accesses, and how long he accesses it. This is also known as creating an audit trail. An analogy is a bank documenting and debiting your account for the money you withdraw. You can create and assign accounting method lists to control what is accounted for and where the accounting records will be sent.
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Options for Storing Usernames, Passwords, and Access Rules

Cisco provides many ways to implement AAA services for Cisco devices, many of which use a centralized service to keep usernames, passwords, and configured rules about who can access which resources. Over the years, there have been many names and access methods associated with the central server, including calling it an authentication server, AAA server, ACS server, TACACS server, or RADIUS server. These all refer to the same type of function: a server that contains usernames, passwords, and rules about what may be accessed. A router or switch acts like a client to this server and can send requests to the server to verify the credentials of an administrator or user who is trying to access a local router or switch. The following list describes a few of these centralized server types:

  • Cisco Secure ACS Solution Engine: This is a dedicated server that contains the usernames, their passwords, and other information about what users are allowed to access and when. In the past, this was sold as a server appliance with the Access Control Server (ACS) software preinstalled. A router or switch becomes a client to the server. The router can be configured to require authentication from a user or administrator before providing access, and the router sends this request to the ACS server and lets the ACS server make the decision about allowing the user or administrator to continue. The protocol used between the router and the ACS server is normally TACACS+ if you are authenticating an administrator who is seeking command-line access. The protocol used between the router and the ACS server is normally RADIUS if you are authenticating an end user for network access. These are not hard-and-fast rules, and you can use either of the two protocols for similar features in many cases.
  • Cisco Secure ACS for Windows Server: This software package may be used for user and administrator authentication. AAA services on the router or network access server (NAS) contact an external Cisco Secure ACS (running on a Microsoft Windows system). This is an older flavor of ACS, but may still be relevant to the certification exams.
  • Current flavors of ACS functionality: The most common way that ACS services are implemented today is through a virtual machine running on some flavor of VMware. Another up-and-coming service to support similar services to ACS is called the Cisco Identity Services Engine (ISE), which can be bundled in a single physical or logical device or appliance.
  • Self-contained AAA: AAA services may be self-contained in the router itself. Implemented in this fashion, this form of authentication and authorization is also known as local authentication and authorization. The database that contains the usernames and passwords is the running configuration of the router or IOS device, and from a AAA perspective is referred to as the local database on the router. So, if you create a user locally on the router, you can also say that you created a user in the local database of the router. It is the same thing. In this case, because the router is acting as its own AAA server, you do not use TACACS+ or RADIUS as a protocol to connect to a remote ACS server, because you are not using an ACS server.
Authorizing VPN Users

One common implementation of AAA is its use in authenticating users accessing the corporate LAN through a remote-access IPsec VPN.

Let’s see how authentication and authorization applies to users who are trying to access our network through a VPN. The first step is to authenticate users to find out who they are, and after we find out who they are, we can then control what they are authorized for. For example, if a user connects via a VPN, that user may or may not be allowed access to certain portions of the network based on who the user is. This type of access is sometimes called packet mode, as in a user attempting to send packets through the network instead of trying to get a command-line interface (CLI) like an administrator would. A user connecting over a dial-up connection (older technology) could very likely be authenticated via a PPP connection using the same concepts. In either case, we authenticate the users by asking for their username and password, and then check the rules to see what they are authorized to access. If we use the remote Access Control Server (ACS) server for the authentication and authorization for an end user, we would very likely use the RADIUS protocol between the router and the AAA server.

AAA access control is supported using either a local username-password database or through a remote server (such as an ACS server). To provide access to a small group of network users, or as a backup in case the ACS server cannot be reached, a local security database can be configured in the router using the username command.

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Router Access Authentication

Note that we must choose authentication first if we want to also use authorization for a user or administrator. We cannot choose authorization for a user without knowing who that user is through authentication first.

Typically, if we authenticate an administrator, we also authorize that administrator for what we want to allow him to do. Administrators traditionally are going to need access to the CLI. When an administrator is at the CLI, that interface is provided by something called an EXEC shell. If we want to authorize the router to provide this CLI, that is a perfect example of using AAA to first authenticate the user (in this case, the administrator) and then authorize that user to get a CLI prompt (the EXEC shell) and even place the administrator at the correct privilege level. This type of access (CLI) could also be referred to as character mode. Simply think of an administrator at a CLI typing in characters to assist you in remembering that this is “character” mode. With the administrator, we would very likely authenticate his login request and authorize that administrator to use an EXEC shell. If we were using a remote ACS server for this authentication and authorization of an administrator, we would very likely use TACACS+ (between the router and the ACS server) because it has the most granular control, compared with RADIUS, which is the alternative. TACACS+ and RADIUS are both discussed in another chapter of this book in greater detail.

Table 6-2 identifies some of the terms that refer to the type of access and the likely protocols used between the router acting as a client and the ACS server acting as the AAA server.

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Table 6-2 AAA Components to Secure Administrative and Remote LAN Access

Access Type Mode

Mode

Where These Are Likely to Be Used

AAA Command Element

Remote administrative access

Usually TACACS+ between the router and the ACS

Character (line or EXEC mode)

Lines: vty, AUX console, and tty

login, enable, exec

Remote network access end users

Usually RADIUS between the router and the ACS

Packet (interface mode) such as an interface with PPP requiring authentication

Interfaces: async, group-async, BRI, PRI, Other functionality: VPN user authentication

ppp, network, vpn groups

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The AAA Method List

To make implementing AAA modular, we can specify individual lists of ways we want to authenticate, authorize, and account for the users. To do this, we create a method list that defines what resource will be used (such as the local database, an ACS server via TACACS+ protocol or an ACS server via RADIUS protocol, and so forth). To save time, we can create a default list or custom lists. We can create method lists that define the authentication methods to use, authorization method lists that define which authorization methods to use, and accounting method lists that specify which accounting method lists to use. A default list, if created, applies to the entire router or switch. A custom list, to be applied, must be both created and then specifically referenced in line or interface configuration mode. You can apply a custom list over and over again in multiple lines or interfaces. The type of the method list may be authentication, authorization, or accounting.

The syntax for a method list is as follows:

aaa type {default | list-name} method-1 [method-2 method-3 method-4]

The commands for a method list, along with their descriptions, are shown in Table 6-3.

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Table 6-3 Method List Options

Command Element

Description

type

Identifies the type of list being created. Relevant options are authentication, authorization, or accounting.

default

Specifies the default list of methods to be used based on the methods that follow this argument. If you use the keyword default, a custom name is not used.

list-name

Used to create a custom method list. This is the name of this list, and is used when this list is applied to a line, such as to vty lines 0–4.

method

At least one method must be specified. To use the local user database, use the local keyword. A single list can contain up to 4 methods, which are tried in order, from left to right.

In the case of an authentication method list, methods include the following:

enable: The enable password is used for authentication. This might be an excellent choice as the last method in a method list. This way, if the previous methods are not available (such as the AAA server, which might be down or not configured), the router times out on the first methods and eventually prompts the user for the enable secret as a last resort.

krb5: Kerberos 5 is used for authentication.

krb5-telnet: Kerberos 5 Telnet authentication protocol is used when using Telnet to connect to the router.

line: The line password (the one configured with the password command, on the individual line) is used for authentication.

local: The local username database (running config) is used for authentication.

local-case: Requires case-sensitive local username authentication.

none: No authentication is used.

group radius: A RADIUS server (or servers) is used for authentication.

group tacacs+: A TACACS+ server (or servers) is used for authentication.

group group-name: Uses either a subset of RADIUS or TACACS+ servers for authentication as defined by the aaa group server radius or aaa group server tacacs+ command.

Role-Based Access Control

The concept of role-based access control (RBAC) is to create a set of permissions or limited access and assign that set of permissions to users or groups. Those permissions are used by individuals for their given roles, such as a role of administrator or a role of a help desk person and so on There are different ways to implement RBAC, including creating custom privilege levels and creating parser views (coming up later in this section). In either case, the custom level or view can be assigned the permissions needed for a specific function or role, and then users can use those custom privilege levels or parser views to carry out their job responsibilities on the network, without being given full access to all configuration options.

Custom Privilege Levels

When you first connect to a console port on the router, you are placed into user mode. User mode is really privilege level 1. This is represented by a prompt that ends with >. When you move into privileged mode by typing the enable command, you are really moving into privilege level 15. A user at privilege level 15 has access and can issue all the commands that are attached to or associated with level 15 and below. Nearly all the configuration commands, and the commands that get us into configuration mode, are associated by default with privilege level 15.

By creating custom privilege levels (somewhere between levels 2 and 14, inclusive), and assigning commands that are normally associated with privilege level 15 to this new level, you can give this subset of new commands to the individual who either logs in at this custom level or to the user who logs in with a user account that has been assigned to that level.

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Limiting the Administrator by Assigning a View

Working with individual commands and assigning them to custom privilege levels is tedious at best, and it is for that reason that method is not used very often. So, what can be done if we need users to have a subset of commands available to them, but not all of them? In an earlier chapter, we looked at how Cisco Configuration Professional (CCP) could restrict the visibility of the features in the navigation pane by using user profiles. This technique, however, did not protect the router against a user connecting with Telnet or SSH, and if that user had level 15 permissions, the router would once again be unprotected at the CLI.

A solution to this is to use parser views, also referred to as simply a view. You can create a view and associate it with a subset of commands. When the user logs in using this view, that same user is restricted to only being able to use the commands that are part of his current view. You can also associate multiple users with a single view.

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Encrypted Management Protocols

It is not always practical to have console access to the Cisco devices you manage. There are several options for remote access via IP connectivity, and the most common is an application called Telnet. The problem with Telnet is that it uses plain text, and anyone who gets a copy of those packets can identify our usernames and passwords used for access and any other information that goes between administrator and the router being managed (over the management plane). One solution to this is to not use Telnet. If Telnet must be used, it should only be used out of band, or placed within a VPN tunnel for privacy, or both.

Secure Shell provides the same functionality as Telnet, in that it gives you a CLI to a router or switch; unlike Telnet, however, SSH encrypts all the packets used in the session. So, with SSH, if a packet is captured and viewed by an unauthorized individual, it will not have any meaning because the contents of each packet are encrypted and the attacker or unauthorized person will not have the keys or means to decrypt the information. The encryption provides the feature of confidentiality.

With security, bigger really is better. With SSH, Version 2 is bigger and better than Version 1. Either version, however, is better than the unencrypted Telnet protocol. When you type in ip ssh version 2, (to enable version 2), the device may respond with a Version “1.99” is active. This is a function of a server that runs 2.0 but also supports backward compatibility with older versions. For more information, see RFC4253, section 5.1. You should use SSH rather than Telnet whenever possible.

For GUI management tools such as CCP, use HTTPS rather than HTTP because it encrypts the session which provides confidentiality for the packets in that session.

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Using Logging Files

I still recall an incident on a customer site when a database server had a failed disk and was running on its backup. It was like that for weeks until they noticed a log message. If a second failure had occurred, the results would have been catastrophic. Administrators should, on a regular basis, analyze logs, especially from their routers, in addition to logs from other network devices. Logging information can provide insight into the nature of an attack. Log information can be used for troubleshooting purposes. Viewing logs from multiple devices can provide event correlation information (that is, the relationship between events occurring on different systems). For proper correlation of events, accurate time stamps on those events are important. Accurate time can be implemented through Network Time Protocol (NTP).

Cisco IOS devices can send log output to a variety of destinations, including the following:

  • Console: A router’s console port can send log messages to an attached terminal (such as your connected computer, running a terminal emulation program).
  • vty lines: Virtual tty (vty) connections (used by SSH and Telnet connections) can also receive log information at a remote terminal (such as an SSH or Telnet client). However, the terminal monitor command should be issued to cause log messages to be seen by the user on that vty line.
  • Buffer: When log messages are sent to a console or a vty line, those messages are not later available for detailed analysis. However, log messages can be stored in router memory. This “buffer” area can store messages up to the configured memory size, and then the messages are rotated out, with the first in being the first to be removed. When the router is rebooted, these messages in the buffer memory are lost.
  • SNMP server: When configured as an SNMP device, a router or switch can generate log messages, in the form of SNMP traps and send them to an SNMP manager (server).
  • Syslog server: A popular choice for storing log information is a syslog server, which is easily configured and can store a large volume of logs. Syslog messages can be directed to one or more syslog servers from the router or switch.

A syslog logging solution consists of two primary components: syslog servers and syslog clients. A syslog server receives and stores log messages sent from syslog clients such as routers and switches.

Not all syslog messages are created equal. Specifically, they have different levels of severity. Table 6-4 lists the eight levels of syslog messages. The higher the syslog level, the more detailed the logs. Keep in mind that more-detailed logs require a bit more storage space, and also consider that syslog messages are transmitted in clear text. Also consider that the higher levels of syslog logging consume higher amounts of CPU processing time. For this reason, take care when logging to the console at the debugging level.

Table 6-4 Syslog Severity Levels

Level

Name

Description

0

Emergencies

System is unusable.

1

Alerts

Immediate action needed.

2

Critical

Critical conditions.

3

Errors

Error conditions.

4

Warnings

Warning conditions.

5

Notifications

Normal, but significant conditions.

6

Informational

Informational messages.

7

Debugging

Highly detailed information based on current debugging that is turned on.

The syslog log entries contain time stamps, which are helpful in understanding how one log message relates to another. The log entries include severity level information in addition to the text of the syslog messages. Having synchronized time on the routers, and including time stamps in the syslog messages, makes correlation of the syslog messages from multiple devices more meaningful.

Understanding NTP

Network Time Protocol (NTP) uses UDP port 123, and it allows network devices to synchronize their time. Ideally, they would synchronize their time to a trusted time server. You can configure a Cisco router to act as a trusted NTP server for the local network, and in the same way, that trusted NTP server could turn around and be an NTP client to a trusted NTP server either on the Internet or reachable via network connectivity. NTP Version 3 supports cryptographic authentication between NTP devices, and for this reason its use is preferable over any earlier versions.

One benefit of having reliable synchronized time is that log files and messages generated by the router can be correlated. In fact, if we had 20 routers, and they were all reporting various messages and all had the same synchronized time, we could very easily correlate the events across all 20 routers if we looked at those messages on a common server. A common server that is often used is a syslog server.

Protecting Cisco IOS Files

Similar to the computers that we use every day, a router also uses an operating system. The Cisco operating system on the router is called IOS. When a router first boots, it performs a power-on self-test, and then looks for an image of IOS on the flash. After loading the IOS into RAM, the router then looks for its startup configuration. If for whatever reason an IOS image or the startup configuration cannot be found or loaded properly, the router will effectively be nonfunctional as far as the network is concerned.

To help protect a router from accidental or malicious tampering of the IOS or startup configuration, Cisco offers a resilient configuration feature. This feature maintains a secure working copy of the router IOS image and the startup configuration files at all times. Once enabled, the administrator cannot disable the features remotely (but can if connected directly on the console). The secure files are referred to as a secure bootset.

Implement Security Measures to Protect the Management Plane

The first section of this chapter covered some best practices to protect the management plane. With that in mind, you can now leverage what you have learned and look at some practical examples of implementing those best practices. It requires both the understanding and implementation of these best practices to secure your networks.

Implementing Strong Passwords

The privileged EXEC secret (the one used to move from user mode to privileged mode) should not match any other password that is used on the system. Many of the other passwords are stored in plain text (such as passwords on the vty lines). If an attacker discovers these other passwords, he might try to use them to get into privileged mode, and that is why the enable secret should be unique. Service password encryption scrambles any plaintext passwords as they are stored in the configuration. This is useful for preventing someone who is looking over your shoulder from reading a plaintext password that is displayed in the configuration on the screen. Any new plaintext passwords are also scrambled as they are stored in the router’s configuration.

Example 6-1 shows the use of strong passwords.

Example 6-1 Using Strong Passwords

! Use the "secret" keyword instead of the "password" for users
! This will create a secured password in the configuration by default
! The secret is hashed using the MD5 algorithm as it is stored in the
! configuration
R1(config)# username admin secret CeyeSc01$24

! At a minimum, require a login and password for access to the console port
! Passwords on lines, including the console, are stored as plain text, by
! default, in the configuration
R1(config)# line console 0
R1(config-line)# password k4(1fmMsS1#
R1(config-line)# login
R1(config-line)# exit

! At a minimum, require a login and password for access to the VTY lines which
! is where remote users connect when using Telnet
! Passwords on lines, including the vty lines, are stored as plain text, by
! default, in the configuration
R1(config)# line vty 0 4
R1(config-line)# password 8wT1*eGP5@
R1(config-line)# login

! At a minimum, require a login and password for access to the AUX line
! and disable the EXEC shell if it will not be used
R1(config-line)# line aux 0
R1(config-line)# no exec
R1(config-line)# password 1wT1@ecP27
R1(config-line)# login
R1(config-line)# exit

! Before doing anything else, look at the information entered.
R1(config)# do show run | include username
username admin secret 5 $1$XJdX$9hqvG53z3lesP5BLOqggO.
R1(config)#
R1(config)# do show run | include password
no service password-encryption
  password k4(1fmMsS1#
  password 8wT1*eGP5@
  password 1wT1@ecP27
R1(config)#

! Notice that we can not determine the admin user's password, since
! it is automatically hashed using the MD5 algorithm because of using
! the secret command, however, we can still see all the other plain text
! passwords.

! Encrypt the plain text passwords so that someone reading the configuration
! won't know what the passwords are by simply looking at the configuration.
R1(config)# service password-encryption

! Verify that the plain text passwords configured are now scrambled due to the
! command "service password-encryption"
R1(config)# do show run | begin line
line con 0
  password 7 04505F4E5E2741631A2A5454
  login
line aux 0
  no exec
  login
  password 7 075E36781F291C0627405C
line vty 0 4
  password 7 065E18151D040C3E354232
  login
!
end

User Authentication with AAA

Example 6-2 shows the use of method lists, both named and default.

key-topic.jpg

Example 6-2 Enabling AAA Services and Working with Method Lists

! Enable aaa features, if not already present in the running configuration
R1(config)# aaa new-model

! Identify a AAA server to be used, and the password it is expecting with
! requests from this router. This server would need to be reachable and
! configured as a TACACS+ server to support R1's requests
R1(config)# tacacs-server host 50.50.4.101
R1(config)# tacacs-server key ToUgHPaSsW0rD-1#7

! configure the default method list for the authentication of character
! mode login (where the user will have access to the CLI)
! This default method list, created below has two methods listed "local"
! and "enable"

! This list is specifying that the local database (running-config) will
! be used first to look for the username. If the username isn't in the
! running-config, then it will go to the second method in the list.
! The second method of "enable" says that if the user account isn't found
! in the running config, then to use the enable secret to login.
! This default list will apply to all SSH, Telnet, VTY, AUX and Console
! sessions unless there is another (different) custom method list that is
! created and directly applied to one of those lines.
R1(config)# aaa authentication login default local enable

! The next authentication method list is a custom authentication
! method list named MY-LIST-1.This method list says that the first attempt
! to verify the user's name and password should be done through one of the
! tacacs servers (we have only configured one so far), and then if that server
! doesn't respond, use the local database (running-config), and if the
! username isn't in the running configuration to then use the enable secret
! for access to the device. Note: this method list is not used until
! applied to a line elsewhere in the configuration.
R1(config)# aaa authentication login MY-LIST-1 group tacacs local enable

! These next method lists are authorization method lists.
! We could create a default one as well, using the key
! word "default" instead of a name. These custom method lists for
! authorization won't be used until we apply them
! elsewhere in the configuration, such as on a VTY line.
! The first method list called TAC1 is an authorization
! method list for all commands at user mode (called privilege level 1).
! The second method list called TAC15 is an
! authorization method list for commands at level 15 (privileged exec mode).
! If these method lists are applied to a line, such as the
! console or VTY lines, then before any commands
! are executed at user or privileged mode, the router will check
! with an ACS server that is one of the "tacacs+" servers, to see if the user
! is authorized to execute the command. If a tacacs+ server isn't
! reachable, then the router will use its own database of users (the local
! database) to determine if the user trying to issue the command
! is at a high enough privilege level to execute the command.
R1(config)# aaa authorization commands 1 TAC1 group tacacs+ local
R1(config)# aaa authorization commands 15 TAC15 group tacacs+ local

! The next 2 method lists are accounting method lists that will record the
! commands issued at level 1 and 15 if the lists are applied to a line, and
! if an administrator connects to this device via that line.
! Accounting method lists can have multiple methods, but can't log to the
! local router.
R1(config)# aaa accounting commands 1 TAC-act1 start-stop group tacacs+
R1(config)# aaa accounting commands 15 TAC-act15 start-stop group tacacs+

! Creating a user with level 15 access on the local router is a good idea,
! in the event the ACS server can't be
! reached, and a backup method has been specified as the local database.
R1(config)# username admin privilege 15 secret 4Je7*1swEsf

! Applying the named method lists is what puts them in motion.
! By applying the method lists to the VTY lines
! any users connecting to these lines will be authenticated by the
! methods specified by the lists that are applied
! and also accounting will occur, based on the lists that are applied.
R1(config)# line vty 0 4
R1(config-line)# login authentication MY-LIST-1
R1(config-line)# authorization commands 1 TAC1
R1(config-line)# authorization commands 15 TAC15
R1(config-line)# accounting commands 1 TAC-act1
R1(config-line)# accounting commands 15 TAC-act15

! Note: on the console and AUX ports, the default list will be applied,
! due to no custom method list being applied
! directly to the console or AUX ports.

Using debug as a tool to verify what you think is happening is a good idea. In Example 6-3, we review and apply AAA and perform a debug verification.

Example 6-3 Another Example of Creating and Applying a Custom Method List to vty Lines

! Creating the method list, which has 3 methods. First the local database
! (if the username exists in the configuration, and if not
! then the enable secret (if configured), and if not then no
! authentication required
! (none)
R2(config)# aaa authentication login MY-AUTHEN-LIST-1 local enable none

! Applying the method list to the VTY lines 0-4
R2(config)# line vty 0 4
R2(config-line)# login authentication MY-AUTHEN-LIST-1
R2(config-line)# exit

! Creating a local username in the local database (running-config)
R2(config)# username bob secret ciscobob

! Setting the password required to move from user mode to privileged mode
R2(config)# enable secret ciscoenable
R2(config)# interface loopback 0

! Applying an IP address to test a local telnet to this same local router
! Not needed if the device has another local IP address that is in use
R2(config-if)# ip address 2.2.2.2 255.255.255.0
R2(config-if)# exit

! Enable logging so we can see results of the upcoming debug
R2(config)# logging buffered 7
R2(config)# end

! Enabling debug of aaa authentication, so we can see what the router is
! thinking regarding aaa authentication
R2# debug aaa authentication
AAA Authentication debugging is on

R2# clear log
Clear logging buffer [confirm]


! Telnet to our own address
R2# telnet 2.2.2.2
Trying 2.2.2.2 ... Open

User Access Verification

Username: bob
AAA/BIND(00000063): Bind i/f
AAA/AUTHEN/LOGIN (00000063): Pick method list 'MY-AUTHEN-LIST-1'
Password: [ciscobob] password not shown when typing it in

R2>

! We can see that bob is connected via line vty 0, and that from the debug
! the correct authentication list was used.
R2>who
   Line        User      Host(s)          Idle       Location
  0 con 0                2.2.2.2          00:00:00
* 2 vty 0      bob       idle             00:00:00 2.2.2.2
R2> exit

! If we exit back out, and remove all the users in the local database,
! (including bob) then the same login authentication will fail on the first
! method of the "local" database (no users there), and will go to the second
! method in the list, which is "enable", meaning use the enable secret if
! configured.

! As soon as I supply a username, the router discovers that there are no
! usernames
! configured in running configuration (at least none that match the user
! who is trying to
! login), and fails on the first method "local" in the list
! It then tries the next method of just caring about the enable secret.

R2# telnet 2.2.2.2
Trying 2.2.2.2 ... Open
User Access Verification

AAA/BIND(00000067): Bind i/f
AAA/AUTHEN/LOGIN (00000067): Pick method list 'MY-AUTHEN-LIST-1'

! Note: bertha in not a configured user in the local database on the router
Username: bertha
Password: [ciscoenable} not shown while typing. This is the enable secret
 we set.
AAA/AUTHEN/ENABLE(00000067): Processing request action LOGIN
AAA/AUTHEN/ENABLE(00000067): Done status GET_PASSWORD

R2>
AAA/AUTHEN/ENABLE(00000067): Processing request action LOGIN
AAA/AUTHEN/ENABLE(00000067): Done status PASS
R2> exit

! One more method exists in the method list we applied to the VTY lines.
! If the local fails, and the enable secret fails (because neither of these
! is configured on the router, then the third method in the method list
! 'MY-AUTHEN-LIST-1' will be tried. The third method we specified is none,
! meaning no authentication required, come right in. After removing the
! enable secret, we try once more.

R2# telnet 2.2.2.2
Trying 2.2.2.2 ... Open

User Access Verification
AAA/BIND(00000068): Bind i/f
AAA/AUTHEN/LOGIN (00000068): Pick method list 'MY-AUTHEN-LIST-1'
Username: doesn't matter
R2>
AAA/AUTHEN/ENABLE(00000068): Processing request action LOGIN
AAA/AUTHEN/ENABLE(00000068): Done status FAIL  secret not configured
R2>
! No password was required.   All three methods of the method list were
! tried.
! The first two methods failed, and the third of "none" was accepted.

Using the CLI to Troubleshoot AAA for Cisco Routers

One tool you can use when troubleshooting AAA on Cisco routers is the debug command. You may use three separate debug commands to troubleshoot the various aspects of AAA:

key-topic.jpg
  • debug aaa authentication: Use this command to display debugging messages for the authentication functions of AAA.
  • debug aaa authorization: Use this command to display debugging messages for the authorization functions of AAA.
  • debug aaa accounting: Use this command to display debugging messages for the accounting functions of AAA.

Each of these commands is executed from privileged EXEC mode. To disable debugging for any of these functions, use the no form of the command, such as no debug aaa authentication.

Example 6-4 shows an example of debugging login authentication, EXEC authorization, and commands at level 15 authorization. As shown in the example, you can use debug not only for verification, as in the preceding example, but also as a troubleshooting method.

key-topic.jpg

Example 6-4 Using debug Commands

! R4 will have a loopback, so we can telnet to ourselves to test
R4(config-if)# ip address 4.4.4.4 255.255.255.0
R4(config-if)# exit

! Local user in the database has a privilege level of 15
R4(config)# username admin privilege 15 secret cisco

! This method list, if applied to a line, will specify local authentication
R4(config)# aaa authentication login AUTHEN_Loc local

! This next method list, if applied to a line, will require authorization
! before giving the administrator an exec shell. If the user has a valid
! account in the running configuration, the exec shell will be created for
! the authenticated
! user, and it will place the user in their privilege level automatically
R4(config)# aaa authorization exec AUTHOR_Exec_Loc local

! This method list, if applied to a line, will require authorization for
! each and every level 15 command issued. Because the user is at
! privilege level 15 the router will say "yes" to any level 15 commands
! that may be issued by the user
R4(config)# aaa authorization commands 15 AUTHOR_Com_15 local

! Next we will apply the 3 custom method lists to vty lines 0-4, so that
! when anyone connects via these vty lines, they will be subject to the
! login authentication, the exec authorization, and the level 15 command
! authorizations for the duration of their session.

R4(config)# line vty 0 4
R4(config-line)# login authentication AUTHEN_Loc
R4(config-line)# authorization exec AUTHOR_Exec_Loc
R4(config-line)# authorization commands 15 AUTHOR_Com_15
R4(config-line)# exit
R4(config)#
R4(config)# do debug aaa authentication
AAA Authentication debugging is on
R4(config)# do debug aaa authorization
AAA Authorization debugging is on
R4(config)# exit

! Now test to see it all in action.
R4# telnet 4.4.4.4
Trying 4.4.4.4 ... Open
User Access Verification

Username: admin
Password: [cisco] password not displayed when entering

! It picked the login authentication list we specified
AAA/BIND(00000071): Bind i/f
AAA/AUTHEN/LOGIN (00000071): Pick method list 'AUTHEN_Loc'

! It picked the authorization list we specified for the exec shell
R4#
AAA/AUTHOR (0x71): Pick method list 'AUTHOR_Exec_Loc'
AAA/AUTHOR/EXEC(00000071): processing AV cmd=
AAA/AUTHOR/EXEC(00000071): processing AV priv-lvl=15
AAA/AUTHOR/EXEC(00000071): Authorization successful

! It picked the command level 15 authorization list, when we issued the
! configure terminal command, which is a level 15 command.
R4# config t
Enter configuration commands, one per line. End with CNTL/Z.
R4(config)#
AAA/AUTHOR: auth_need : user= 'admin' ruser= 'R4' rem_addr= '4.4.4.4' priv=
 15 list=
'AUTHOR_Com_15' AUTHOR-TYPE= 'command'
AAA: parse name=tty2 idb type=-1 tty=-1
AAA: name=tty2 flags=0x11 type=5 shelf=0 slot=0 adapter=0 port=2 channel=0
AAA/MEMORY: create_user (0x6A761F34) user='admin' ruser='R4' ds0=0
 port='tty2'
rem_addr='4.4.4.4' authen_type=ASCII service=NONE priv=15 initial_task_
 id='0',
vrf= (id=0)
tty2 AAA/AUTHOR/CMD(1643140100): Port='tty2' list='AUTHOR_Com_15'
 service=CMD
AAA/AUTHOR/CMD: tty2(1643140100) user='admin'
tty2 AAA/AUTHOR/CMD(1643140100): send AV service=shell
tty2 AAA/AUTHOR/CMD(1643140100): send AV cmd=configure
tty2 AAA/AUTHOR/CMD(1643140100): send AV cmd-arg=terminal
tty2 AAA/AUTHOR/CMD(1643140100): send AV cmd-arg=<cr>
tty2 AAA/AUTHOR/CMD(1643140100): found list "AUTHOR_Com_15"
tty2 AAA/AUTHOR/CMD(1643140100): Method=LOCAL
AAA/AUTHOR (1643140100): Post authorization status = PASS_ADD
AAA/MEMORY: free_user (0x6A761F34) user='admin' ruser='R4' port='tty2'
rem_addr='4.4.4.4' authen_type=ASCII service=NONE priv=15 vrf= (id=0)
R4(config)#
! It made a big splash, with lots of debug output, but when you boil it all
! down it means the user was authorized to issue the configure terminal
! command.

There is also a test aaa command that is very useful when verifying connectivity with a remote ACS server.

This section walked you through the details of AAA using the command line with very exact examples because you need to understand how it works. Now that you have taken a look at how it works, you should know that you can also use CCP as a GUI to implement the AAA.

Let’s take a moment to review where you can find the AAA elements inside CCP. In the configuration section, using the navigation pane on the left, go to Configure > Router > AAA > AAA Summary. You will see there an overview of what authentication policies have been created on a router and any authorization or accounting policies, as shown in Figure 6-1.

Figure 6-1

Figure 6-1 Using CPP to View AAA Policies

If you wanted to add, edit, or modify your authentication policies, you just navigate to Configure > Router > AAA > Authentication Policies > Login, as shown in Figure 6-2.

Figure 6-2

Figure 6-2 Using CCP to See Method Lists for Login

If you want to see which method lists were applied to your vty lines, just navigate to Configure > Router > Router Access > VTY, as shown in Figure 6-3.

Figure 6-3

Figure 6-3 Using CCP to See Which Methods Have Been Applied to the vty Lines

From here, you can also modify which AAA policies are applied to vty lines by clicking Edit, which prompts the opening of an Edit VTY Lines dialog, as shown in Figure 6-4.

Figure 6-4

Figure 6-4 Using CPP to Edit vty Line Properties, Including AAA Method Lists Applied

RBAC Privilege Level/Parser View

You may implement RBAC through AAA, with the rules configured on an ACS server, but you may implement it in other ways, too, including creating custom privilege levels and having users enter those custom levels where they have a limited set of permissions, or creating a parser view (also sometimes simply called a view), which also limits what the user can see or do on the Cisco device. Each options can be tied directly to a username, so that once users authenticate they may be placed at the custom privilege level, or in the view that is assigned to them.

Let’s implement a custom privilege level first, as shown in Example 6-5. The example includes explanations throughout.

key-topic.jpg

Example 6-5 Creating and Assigning Commands to a Custom Privilege Level

! By default, we use privilege level 1 (called user mode), and privilege
! level 15 (called privileged mode). By creating custom levels, (between
! 1-15) and assigning commands to those levels, we are creating custom
! privilege levels
! A user connected at level 8, would have any of the new commands
! associated with level 8, as well as any commands that have been custom
! assigned or defaulted to levels 8 and below. A user at level 15 has
! access to all commands at level 15 and below.
! This configuration assigns the command "configure terminal" to privilege
! level 8
R2(config)# privilege exec level 8 configure terminal

! This configuration command assigns the password for privilege level 8
! the keyword "password" could be used instead of secret, but is less secure
! as the "password" doesn't use the MD5 hash to protect the password
! The "0" before the password, implies that we are inputting a non-hashed
! (to begin with) password. The system will hash this for us, because we
! used the enable "secret" keyword.
R2(config)# enable secret level 8 0 NewPa5s123&
R2(config)# end
R2#
%SYS-5-CONFIG_I: Configured from console by console

! To enter this level, use the enable command, followed by the level you want
! to enter. If no level is specified, the default level is 15
R2# disable
! Validate that user mode is really privilege level 1
R2> show privilege
Current privilege level is 1
! Context sensitive help shows that we can enter a level number after the
! word enable
R2> enable ?
  <0-15>  Enable level
  view    Set into the existing view
  <cr>

R2> enable 8
Password: [NewPa5s123&] ! note: password doesn't show when typing it in
R2# show privilege
Current privilege level is 8
! We can go into configuration mode, because "configure terminal" is at our
! level
R2# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
! Notice we don't have further ability to configure the router, because
! level 8 doesn't include the interface configuration or other router
! configuration commands.
R2(config)# ?
Configure commands:
  beep     Configure BEEP (Blocks Extensible Exchange Protocol)
  call     Configure Call parameters
  default  Set a command to its defaults
  end      Exit from configure mode
  exit     Exit from configure mode
  help     Description of the interactive help system
  netconf  Configure NETCONF
  no       Negate a command or set its defaults
  oer      Optimized Exit Routing configuration submodes
  sasl     Configure SASL
  wsma     Configure Web Services Management Agents

If we are requiring login authentication, we can associate a privilege level with a given user account, and then when users authenticate with their username and password they will automatically be placed into their appropriate privilege level. Example 6-6 shows an example of this.

Example 6-6 Creating a Local User and Associating That User with Privilege Level 8 and Assigning Login Requirements on the vty Lines

! Create the user account in the local database (running-config) and
! associate that user with the privilege level you want that user to use.
R2(config)# username Bob privilege 8 secret Cisco123
R2(config)# line vty 0 4

! "login local" will require a username and password for access if the "aaa
! new-model" command is not present. If we have set the aaa new-model,
! then we would also want to create a default or named method list that
! specifies we want to use the local database for authentication.
R2(config-line)# login local

! Note: Once bob logs in, he would have access to privilege level 8 and
! below, (including all the normal show commands at level 1)
key-topic.jpg

Implementing Parser Views

To restrict users without having to create custom privilege levels, you can use a parser view, also referred to as simply a view. A view can be created with a subset of privilege level 15 commands, and when the user logs in using this view, that same user is restricted to only being able to use the commands that are part of his current view.

To create a view, an enable secret password must first be configured on the router. AAA must also be enabled on the router (aaa new-model command).

Example 6-7 shows the creation of a view.

key-topic.jpg

Example 6-7 Creating and Working with Parser Views

! Set the enable secret, and enable aaa new-model (unless already in
! place)
R2(config)# enable secret aBc!2#&iU
R2(config)# aaa new-model
R2(config)# end

! Begin the view creation process by entering the "default" view, using the
! enable secret
R2# enable view
Password: [aBc!2#&iU] note password not shown when typed

R2#
%PARSER-6-VIEW_SWITCH: successfully set to view 'root'.
R2# configure terminal

! As the administrator in the root view, create a new custom view
R2(config)# parser view New_VIEW
%PARSER-6-VIEW_CREATED: view 'New_VIEW' successfully created.

! Set the password required to enter this new view
R2(config-view)# secret New_VIEW_PW

! Specify which commands you want to include as part of this view.
! commands "exec" refer to commands issued from the command prompt
! commands "configure" refer to commands issued from privileged mode
R2(config-view)# commands exec include ping
R2(config-view)# commands exec include all show
R2(config-view)# commands exec include configure

! This next line adds the ability to configure "access-lists" but nothing
! else
R2(config-view)# commands configure include access-list
R2(config-view)# exit
R2(config)# exit

! Test the view, by going to user mode, and then back in using the new view
R2# disable
R2>enable view New_VIEW
Password: [New_VIEW_PW] Password not shown when typed in

! Console message tells us that we are using the view
%PARSER-6-VIEW_SWITCH: successfully set to view 'New_VIEW'.

! This command reports what view we are currently using
R2# show parser view
Current view is 'New_VIEW'

! We can verify that the commands assigned to the view work
! Note: we only assigned configure, not configure terminal so we have to
! use the configure command, and then tell the router we are configuring
! from the terminal. We could have assigned the view "configure terminal"
! to avoid this
R2# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.

! Notice that the only configuration options we have are for access-list,
! per the view
R2(config)# ?
Configure commands:
   access-list  Add an access list entry
   do           To run exec commands in config mode
   exit          Exit from configure mode

We could also assign this view to a user account, so that when users log in with their username and password, they are automatically placed into their view, as shown in Example 6-8.

Example 6-8 Associating a User Account with a Parser View

R2(config)# username Lois view New_VIEW secret cisco123

SSH and HTTPS

Because Telnet sends all of its packets as plain text, it is not secure. SSH allows remote management of a Cisco router or switch, but unlike Telnet, SSH encrypts the contents of the packets to protect it from being interpreted if they fall into the wrong hands.

To enable SSH on a router or switch, the following items need to be in place:

  • Hostname other than the default name of “router”
  • Domain name
  • Generating a public/private key pair, used behind the scenes by SSH
  • Requiring user login via the vty lines, instead of just a password. Local authentication or authentication using an ACS server are both options.
  • Having at least one user account to log in with, either locally on the router, or on an ACS server

Example 6-9 shows how to implement these components, along with annotations and examples of what happens when the required parts are not in place. If you have a non-production router or switch handy, you might want to follow along.

key-topic.jpg

Example 6-9 Preparing for SSH

! To create the Public/Private key pair used by SSH, we would issue the
! following command.   Part of the key pair, will be the hostname and the
! domain name.
! If these are not configured first, the crypto key generate command will
! tell you as shown in the next few lines.
Router(config)# crypto key generate rsa
% Please define a hostname other than Router.
Router(config)# hostname R1
R1(config)# crypto key generate rsa
% Please define a domain-name first.
R1(config)# ip domain-name cisco.com

! Now with the host and domain name set, we can generate the key pair
R1(config)# crypto key generate rsa
The name for the keys will be: R1.cisco.com
Choose the size of the key modulus in the range of 360 to 2048 for your
  General Purpose Keys. Choosing a key modulus greater than 512 may take
  a few minutes.

! Bigger is better with cryptography, and we get to choose the size for the
! modulus
! The default is 512 on many systems, but you would want to choose 1024 or
! more to improve security. SSH has several flavors, with version 2 being
! more secure than version 1. To use version 2, you would need at least a
! 1024 size for the key pair
How many bits in the modulus [512]: 1024
% Generating 1024 bit RSA keys, keys will be non-exportable...[OK]

R1(config)#
%SSH-5-ENABLED: SSH 1.99 has been enabled
! Note the "1.99" is based on the specifications for SSH from RFC 4253
! which indicate that an SSH server may identify its version as 1.99 to
! identify that it is compatible with current and older versions of SSH.

! Create a user in the local database
R1(config)# username Keith secret Ci#kRk*ks
! Configure the vty lines to require user authentication
R1(config)# line vty 0 4
R1(config-line)# login local

! Alternatively, we could do the following for the requirement of user
! authentication
! This creates a method list which points to the local database, and then
! applies that list to the VTY lines
R1(config)# aaa new-model
R1(config)# aaa authentication login Keith-List-1 local
R1(config)# line vty 0 4
R1(config-line)# login authentication Keith-List-1

! To test this we could SSH to ourselves from the local machine, or from
! another router that has IP connectivity to this router.

R1# ssh ?
  -c    Select encryption algorithm
  -l    Log in using this user name
  -m    Select HMAC algorithm
  -o    Specify options
  -p    Connect to this port
  -v    Specify SSH Protocol Version
  -vrf  Specify vrf name
  WORD  IP address or hostname of a remote system

! Note: one of our local IP addresses is 10.1.0.1
R1# ssh l Keith 10.1.0.1

Password: <password for Keith goes here>

R1>
! to verify the current SSH session(s)
R1>show ssh
Connection Version Mode Encryption  Hmac       State            Username
0          2.0     IN   aes128-cbc  hmac-sha1  Session started  Keith
0          2.0     OUT  aes128-cbc  hmac-sha1  Session started  Keith
%No SSHv1 server connections running.
R1>

Perhaps you want to manage a router via HTTPS. If so, you can use CCP or a similar tool and implement HTTPS functionality, as shown in Example 6-10.

Example 6-10 Preparing for HTTPS

! Enable the SSL service on the local router. If it needs to generate
! keys for this feature, it will do so on its own in the background.
R1(config)# ip http secure-server

! Specify how you want users who connect via HTTPS to be authenticated
R1(config)# ip http authentication ?
  aaa     Use AAA access control methods
  enable  Use enable passwords
  local   Use local username and passwords

R1(config)# ip http authentication local

! If you are using the local database, make sure you have at least one user
! configured in the running-config so that you can login. To test, open
! a browser to HTTPS://a.b.c.d where a.b.c.d is the IP address on the
! router.

Implementing Logging Features

Logging is important as a tool for discovering events that are happening in the network and for troubleshooting. Correctly configuring logging so that you can collect and correlate events across multiple network devices is a critical component for a secure network.

Configuring Syslog Support

Example 6-11 shows a typical syslog message and how to control what information is included with the message.

Example 6-11 Using Service Time Stamps with Syslog Events

R4(config)# interface fa0/0
R4(config-if)# shut
%LINK-5-CHANGED: Interface FastEthernet0/0, changed state to administratively
 down
%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed
 state to down
R4(config-if)#

! If we add timestamps to the syslog messages, those timestamps can assist it
! correlating events that occurred on multiple devices
R4(config)# service timestamps log datetime
R4(config)# int fa0/0
R4(config-if)# no shutdown

! These syslog messages have the date of the event, the event (just after
! the %) a description, and also the level of the event. The first is 3,
! the second is 5 in the example shown
*Nov 22 12:08:13: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state
   to up
*Nov 22 12:08:14: %LINEPROTO-5-UPDOWN: Line protocol on Interface
   FastEthernet0/0, changed state to up

To configure logging, you just tell CCP what the IP address of your syslog server is and which level of logging you want to do to that IP address. As a reminder, level 7, also known as debug level, sends all syslog alerts at level 7 and lower. To configure logging, navigate to Configure > Router > Logging, as shown in Figure 6-5.

Figure 6-5

Figure 6-5 Viewing the Logging Configuration

To modify any of the logging settings, click the Edit button, as shown in Figure 6-6.

Figure 6-6

Figure 6-6 Using CCP to Edit the Logging Settings

In Figure 6-6, we have configured level 7 logging (debugging level) to a syslog server at the IP address of 10.1.0.25, and we have specified that the logging level to the buffer on the router is level 6 (informational level). The memory buffer to hold syslog messages is 8192 bytes. Beyond the 8192 bytes worth of messages in memory, any new messages will replace the oldest messages in a first in, first out (FIFO) manner. An example of a syslog server is syslog software running on a PC or dedicated server in your network.

The CCP (for the preceding scenario) creates the equivalent output at the CLI, as shown in Example 6-12.

Example 6-12 CLI Equivalent Generated by CCP

logging 10.1.0.25
logging trap debugging
logging buffered 8192 informational

Figure 6-7 shows the syslog output from the router being collected on the syslog server computer.

Figure 6-7

Figure 6-7 Sample Output Viewed on a Syslog Server

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SNMP Features

Simple Network Management Protocol (SNMP) has become a de facto standard for network management protocols. The intent of SNMP is to manage network nodes, such as network servers, routers, switches, and so on. SNMP versions range from version 1 to 3, with some intermediate steps in between. The later the version, the more security features it has. Table 6-5 describes some of the components of SNMP.

Table 6-5 Components of SNMPv1 and SNMPv2c Network Management Solutions

Component

Description

SNMP manager

An SNMP manager runs a network management application. This SNMP manager is sometimes called a Network Management Server (NMS).

SNMP agent

An SNMP agent is a piece of software that runs on a managed device (such as a server, router, or switch).

Management Information Base

Information about a managed device’s resources and activity is defined by a series of objects. The structure of these management objects is defined by a managed device’s Management Information Base (MIB). This can be thought of as a collection of unique numbers associated with each of the individual components of a router.

An SNMP manager can send information to, receive request information from, or receive unsolicited information (called a trap) from a managed device (a router). The managed device runs an SNMP agent and contains the MIB.

Even though multiple SNMP messages might be sent between an SNMP manager and a managed device, consider the three broad categories of SNMP message types:

  • GET: An SNMP GET message is used to retrieve information from a managed device.
  • SET: An SNMP SET message is used to set a variable in a managed device or to trigger an action on a managed device.
  • Trap: An SNMP trap message is an unsolicited message sent from a managed device to an SNMP manager. It can be used to notify the SNMP manager about a significant event that occurred on the managed device.

Unfortunately, the ability to get information from or send configuration information to a managed device poses a potential security vulnerability. Specifically, if an attacker introduces a rogue NMS into the network, the attacker’s NMS might be able to gather information about network resources by polling the MIBs of managed devices. In addition, the attacker might launch an attack against the network by manipulating the configuration of managed devices by sending a series of SNMP SET messages.

Although SNMP does offer some security against such an attack, the security integrated with SNMPv1 and SNMPv2c is considered weak. Specifically, SNMPv1 and SNMPv2c use community strings to gain read-only access/read-write access to a managed device. You can think of a community string much like a password. Also, be aware that multiple SNMP-compliant devices on the market today have a default read-only community string of “public” and a default read-write community string of “private.”

The security weaknesses of SNMPv1 and SNMPv2c are addressed in SNMPv3. SNMPv3 uses the concept of a security model and a security level:

  • Security model: A security model defines an approach for user and group authentications.
  • Security level: A security level defines the type of security algorithm performed on SNMP packets. Three security levels are discussed here:
    • noAuthNoPriv: The noAuthNoPriv (no authentication, no privacy) security level uses community strings for authentication and does not use encryption to provide privacy.
    • authNoPriv: The authNoPriv (authentication, no privacy) security level provides authentication using Hashed Message Authentication Code (HMAC) with message digest algorithm 5 (MD5) or Secure Hash Algorithm (SHA). However, no encryption is used.
    • authPriv: The authPriv (authentication, privacy) security level offers HMAC MD5, or SHA authentication and also provides privacy through encryption. Specifically, the encryption uses the Cipher Block Chaining (CBC) Data Encryption Standard (DES) (DES-56) algorithm.

As summarized in Table 6-6, SNMPv3 supports all three of the previously described security levels. Notice that SNMPv1 and SNMPv2 support only the noAuthNoPriv security level.

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Table 6-6 Security Models and Security Levels Supported by Cisco IOS

Security Model

Security Level

Authentication Strategy

Encryption Type

SNMPv1

noAuthNoPriv

Community string

None

SNMPv2c

noAuthNoPriv

Community string

None

SNMPv3

noAuthNoPriv

authNoPriv

authPriv

Username

MD5 or SHA

MD5 or SHA

None

None

CBC-DES (DES-56)

Through the use of the security algorithms, as shown in Table 6-6, SNMPv3 dramatically increases the security of network management traffic as compared to SNMPv1 and SNMPv2c. Specifically, SNMPv3 offers three primary security enhancements:

  • Integrity: Using hashing algorithms, SNMPv3 can ensure that an SNMP message was not modified in transit.
  • Authentication: Hashing allows SNMPv3 to validate the source of an SNMP message.
  • Encryption: Using the CBC-DES (DES-56) encryption algorithm, SNMPv3 provides privacy for SNMP messages, making them unreadable by an attacker who might capture an SNMP packet.

To configure SNMP on the router is simple, especially with CCP. If you know the community strings to use, and the IP address of the SNMP manager, you can configure it on the router by navigating to Configure > Router > SNMP and from there use the Edit button to add, change, or remove any of the SNMP-related settings. CCP enables command-line editing through the Utilities menu, but currently the SNMP Properties window does not support the configuration of SNMPv3. You can configure the basic SNMPv1 information, as shown in Figure 6-8.

Figure 6-8

Figure 6-8 Using CCP to Configure SNMPv1 Information

The command-line output for this GUI would look similar to that shown in Example 6-13.

Example 6-13 Output Created by CCP for Implementing SNMPv1

snmp-server location 10.1.0.26
snmp-server contact Bubba Jones
snmp-server community super-secret RW
snmp-server host 10.1.0.26 trap cisK0tRap^

Configuring NTP

Because time is such an important factor, you should use Network Time Protocol (NTP) to synchronize the time in the network so that events that generate messages and time stamps can be correlated. You can use CCP to implement the NTP in addition to using the CLI. Let’s take a look at both right now.

To configure the NTP, you first need to know what the IP address is of the NTP server you will be working with, and you also want to know what the authentication key is and the key ID. NTP authentication is not required to function, but is a good idea to ensure that the time is not modified because of a rogue NTP server sending inaccurate NTP messages using a spoofed source IP address.

Armed with the NTP server information, in CCP you go to Configure > Router > Time > NTP and SNTP and click Add and put in the information about the server you will be getting the time from. When done, you click OK to close the dialog box. It may take anywhere between 5 and 15 minutes for the router to synchronize its clock. In Figure 6-9, this router is being told that the NTP server is at 55.1.2.3, that it should source the NTP requests from its IP address on its local Fast Ethernet 0/0 interface, and that it should use key number 1, and the password associated with that key. If multiple NTP servers were configured, the Prefer option is used to identify the preference of which NTP server to use.

Figure 6-9

Figure 6-9 Configuring a Router to Use an NTP Server

NTP supports authentication on a Cisco router because the router supports NTPv3. Example 6-14 shows the effective equivalent syntax that is created and delivered to the router.

Example 6-14 Using Authentication via Keys with NTPv3

ntp update-calendar
ntp authentication-key 1 md5 pAs5w0rd!3@
ntp authenticate
ntp trusted-key 1
ntp server 55.1.2.3 key 1 source FastEthernet0/0 prefer

To verify the status on this router acting as a NTP client, you could use the commands from the CLI as shown in Example 6-15.

Example 6-15 Verifying Synchronization from the NTP Client

R2# show ntp status
Clock is synchronized, stratum 4, reference is 55.1.2.3
nominal freq is 250.0000 Hz, actual freq is 250.0000 Hz, precision is 2**24
reference time is D27619E3.7317ACB3 (12:53:55.449 UTC Tue Nov 22 2011)
clock offset is 0.0140 msec, root delay is 0.00 msec
root dispersion is 0.97 msec, peer dispersion is 0.43 msec
loopfilter state is 'CTRL' (Normal Controlled Loop), drift is 0.000000053 s/s
system poll interval is 64, last update was 130 sec ago.

R2# show ntp association
  address    ref clock     st   when   poll   reach   delay   offset   disp
*~55.1.2.3   127.127.1.1   3    4      64     77      0.000   14.090   190.28
 * sys.peer, # selected, + candidate,  outlyer, x falseticker,
   ~ configured
R2#

Securing the Cisco IOS Image and Configuration Files

If a router has been compromised, and the flash file system and NVRAM have been deleted, there could be significant downtime as the files are put back in place before restoring normal router functionality. The Cisco Resilient Configuration feature is intended to improve the recovery time by making a secure working copy of the IOS image and startup configuration files (which are referred to as the primary bootset) that cannot be deleted by a remote user.

To enable and save the primary bootset to a secure archive in persistent storage, follow Example 6-16.

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Example 6-16 Creating a Secure Bootset

! Secure the IOS image
R6(config)# secure boot-image
%IOS_RESILIENCE-5-IMAGE_RESIL_ACTIVE: Successfully secured running image

! Secure the startup-config
R6(config)# secure boot-config
%IOS_RESILIENCE-5-CONFIG_RESIL_ACTIVE: Successfully secured config archive
 [flash:.runcfg-20111222-230018.ar]

! Verify the bootset
R6(config)# do show secure bootset
IOS resilience router id FTX1036A13J

IOS image resilience version 12.4 activated at 23:00:10 UTC Thu Dec 22 2011
Secure archive flash:c3825-advipservicesk9-mz.124-24.T.bin type is image
 (elf) []
  file size is 60303612 bytes, run size is 60469256 bytes
  Runnable image, entry point 0x80010000, run from ram

IOS configuration resilience version 12.4 activated at 23:00:18 UTC Thu Dec
 22 2011
Secure archive flash:.runcfg-20111222-230018.ar type is config
configuration archive size 1740 bytes

! Note: to undo this feature, (using the "no" option in front of the command)
! you must be connected via the console. This prevents remote users from
! disabling the feature.
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