Home > Articles > Cisco Network Technology > General Networking > Cisco Firewall Configuration Fundamentals

Cisco Firewall Configuration Fundamentals

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Jul 8, 2011.

Chapter Description

This chapter describes the configuration fundamentals for IOS and ASA-based firewalls, highlighting the similarities between the product families.

From the Book

Cisco Firewalls

Cisco Firewalls

$69.99

Remote Management Access to ASA and FWSM

The examples presented so far have considered that there was physical access to the console port of the appliance (or to the hosting Catalyst 6500 for the FWSM). This section examines management connections that rely on remote access protocols (Telnet, SSH, and HTTPS).

Telnet Access

Telnet is a classic terminal access protocol that has received much criticism because of its clear text nature. It is highly recommended you replace it with SSH, which provides confidentiality.

At any rate, Telnet can still be useful for testing purposes mainly during initial setup. The commands shown in Example 3-15 specify the following:

  • Telnet access is accepted only when it is initiated from source addresses on network 192.168.1.0/24. Further, the packets must arrive through the logical interface called mgmt.
  • The authentication of users who have permission to Telnet to the firewall is done using the LOCAL database. (LOCAL is a reserved keyword for ASA and FWSM.)
  • The username admin is included in the LOCAL database.

Example 3-15 also displays a sample Telnet session coming from address 192.168.1.201.

Example 3-15. Configuring and Verifying Telnet Access

! Creating a local user
username admin password cisco123 privilege 15
!
! Telnet access is authenticated using the LOCAL Data Base
aaa authentication telnet console LOCAL
!
! Defining source addresses that can initiate Telnet Access to the Firewall
telnet 192.168.1.0 255.255.255.0 mgmt
!
! Initiating a Telnet session to ASA
DMZ# telnet 192.168.1.2
Trying 192.168.1.2 ... Open
User Access Verification
Username:admin
Password: ********
Type help or '?' for a list of available commands.
ASA5505>enable
Password: *****
ASA5505#
!
! Displaying connections to the Firewall
ASA5505# show conn all | include Identity
TCP mgmt 192.168.1.201:35313 NP Identity Ifc 192.168.1.2:23, idle 0:00:00, bytes 1017, flags UOB
!
ASA5505# who
         0: 192.168.1.201

SSH Access

If remote CLI access to the firewalls is needed, SSH is the protocol of choice. It provides the same terminal services that Telnet does but with the significant advantage of encrypting traffic between client and server (the firewall receiving the connection).

Because SSH uses RSA public keys to encrypt the sessions, you need to have consistent timing information. Example 3-16 shows not only how to manually adjust and verify timing information, but also how to create a domain name and generate RSA keys.

Example 3-17 shows how to visualize SSH-related information in the Running-config. Notice that the default timeout value for SSH sessions is 5 minutes.

Example 3-16. Recommended Tasks Before Starting SSH Configuration

! Setting Local Time (before generating the cryptographic keys)
ASA5505# clock set 19:05:00 november 15 2009
!
! Verifying Time Information
ASA5505# show running-config clock
clock timezone BRT -3
!
ASA5505# show clock detail
19:18:00.569 BRT Sun  Nov 15 2009
Time source is user configuration
!
! Configuring a domain-name
ASA5505(config)# domain-name mylab.lab
!
! Removing (if needed) any previously generated RSA keys
ASA5505(config)# crypto key zeroize rsa
WARNING: All RSA keys will be removed.
WARNING: All device digital certificates issued using these keys will also be removed.
Do you really want to remove these keys? [yes/no]: yes
!
! Generating new RSA Cryptographic Keys
ASA5505(config)# crypto key generate rsa modulus 1024
INFO: The name for the keys will be: <Default-RSA-Key>
Keypair generation process begin. Please wait...
!
! Displaying the RSA Public Keys
ASA5505# show crypto key mypubkey rsa
Key pair was generated at: 19:24:29 BRT Nov  15 2009 Key name: <Default-RSA-Key>
 Usage: General Purpose Key
 Modulus Size (bits): 1024
 Key Data:
  30819f30 0d06092a 864886f7 0d010101 05000381 8d003081 89028181 008e60c4
  bce3e63a 47aa12c4 e78c0a76 f2faf41c 5d8d461a 4978a5f6 0a4ac11b 26585f61
  d6b5adcb f5ce2430 a96c6fb9 d09f2187 3525255a 349e015e 37d0dd79 90e2b2f1
  5e968993 b9bb9cde 557ba395 e0b20f7c 0049b0d8 5d901902 fe8269ce 74f06a7f
  16713eea 8fe2a0a8 9ddeb2c3 1d258249 d16e6fc4 5a3b4fb6 be977bbf 55020301 0001

Example 3-17. SSH Configuration

ASA5505# show running-config | include ssh
aaa authentication ssh console LOCAL
ssh 192.168.1.0 255.255.255.0 mgmt
ssh timeout 5

HTTPS Access Using ASDM

The Adaptive Security Device Manager (ASDM) is an intuitive and easy-to-use GUI that accompanies every member of the ASA family. The interface provides a nice graphical abstraction for the actual commands that are used not only to implement the features but also to verify their operation, thus allowing users who are already familiar with classic firewall concepts (even from other vendors) to easily adapt their knowledge to the new GUI and immediately start working.

Documenting ASDM usage with its uncountable configuration and monitoring screens is beyond the scope of this book. However, the preparation of firewall devices to accommodate ASDM management is covered.

ASDM uses the HTTPS protocol for communications between the management station and the firewall. After properly loading the ASDM image on the device's flash memory, a web browser can be employed for the first access to the device, with the underlying goal of installing the ASDM launcher application on the administrator's PC.

Example 3-18 shows the preliminary tasks for enabling HTTPS access and assumes that the remote user has been granted the highest privilege level (priv-lvl = 15) and that the requests arrive though the logical interface called mgmt. In the example, the user named admin is authenticated against the LOCAL database and should start the management session from a host that belongs to the 192.168.1.0/24 subnet. The example also contains information about location of the ASDM image in the device flash (disk0: in this case) and how to find it within the show version output.

Example 3-18. Enabling HTTPS Access on ASA

! Assigning the highest privilege level (15) to the HTTPS user
usernameadmin password ****** privilege 15
!
! Defining allowed source IP Addresses. Authentication using the LOCAL Data Base

   http 192.168.1.0 255.255.255.0 mgmt

   aaa authentication http consoleLOCAL
!
! Enabling the HTTPS server

   http server enable
!
! Defining the location of the ASDM image

   asdm image disk0:/asdm-621.bin
!
! Verifying Operating System and ASDM versions
ASA5505# show version | include Version
Cisco Adaptive Security Appliance Software Version  8.2(1)
Device Manager Version 6.2(1)

Figure 3-4 portrays the web browser access to the HTPPS server on the device whose management interface is configured with the address 192.168.1.2 (https://192.168.1.2).

Figure 3-4

Figure 3-4 First HTTPS Access and Initial ASDM Page

From this screen, select the Install ASDM Launcher and Run ASDM option and follow these steps:

  • Step 1. Authenticate with the credentials configured in Example 3-18 when the Connect to 192.168.1.2 window displays.
  • Step 2. From the File Download - Security Warning window, save the ".msi" file locally.
  • Step 3. Run the ".msi" file and install the ASDM Launcher application.
  • Step 4. After starting the ASDM Launcher, fill in the IP address (192.168.1.2 in this case) and the credentials (username/password).
  • Step 5. After accepting the device certificate, the main ASDM page displays (Figure 3-5). This screen summarizes information for the device, including available licenses, interface status, and system resources status.
    Figure 3-5

    Figure 3-5 ASDM Home Page - Device Dashboard

Figure 3-6 depicts the base ASDM screen for Interface Configuration on an ASA 5505 appliance. Notice that the full path to this particular screen, Configuration > Device Setup> Interfaces, displays on the top of the right pane.

Figure 3-6

Figure 3-6 Base ASDM Page for Interface Configuration

Figure 3-7 shows a sample ASDM screen that helps perform the Monitoring task of verifying the ARP table. The complete path for viewing this table is represented at the top of the right pane (Monitoring > Interfaces > ARP Table).

Figure 3-7

Figure 3-7 Base ASDM Page for ARP Table Monitoring

5. IOS Baseline Configuration | Next Section Previous Section

Cisco Press Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Cisco Press and its family of brands. I can unsubscribe at any time.

Overview

Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Cisco Press products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@ciscopress.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security

Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children

This site is not directed to children under the age of 13.

Marketing

Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out

Users can always make an informed choice as to whether they should proceed with certain services offered by Cisco Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.ciscopress.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links

This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020