Home > Articles > Cisco Network Technology > General Networking > Cisco NX-OS and Cisco Nexus Switching: Unified Fabric

Cisco NX-OS and Cisco Nexus Switching: Unified Fabric

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Apr 26, 2013.

Chapter Description

This chapter shows the basic Nexus 5x00 and Nexus 7000 configurations necessary to provide a Unified access method for LAN data traffic and SAN storage traffic. The multiple technologies that can be used with Unified Fabric such as NPV, NPIV FCOE-NPV, Storage VDCs, and shared interfaces are illustrated, and various use cases are discussed.

Enabling Technologies

Ethernet represents an ideal candidate for I/O consolidation. Ethernet is a well-understood and widely deployed medium that has taken on many consolidation efforts already. Ethernet has been used to consolidate other transport technologies such as FDDI, Token Ring, ATM, and Frame Relay networking technologies. It is agnostic from an upper layer perspective in that IP, IPX, AppleTalk, and others have used Ethernet as transport. More recently, Ethernet and IP have been used to consolidate voice and data networks. From a financial aspect, there is a tremendous investment in Ethernet that also must be taken into account.

For all the positive characteristics of Ethernet, there are several drawbacks of looking to Ethernet as an I/O consolidation technology. Ethernet has traditionally not been a lossless transport and relied on other protocols to guarantee delivery. In addition, a large portion of Ethernet networks range in speed from 100 Mbps to 1 Gbps and are not equipped to deal with the higher-bandwidth applications such as storage.

New hardware and technology standards are emerging that will enable Ethernet to overcome these limitations and become the leading candidate for consolidation.

10-Gigabit Ethernet

10-Gigabit Ethernet (10GbE) represents the next major speed transition for Ethernet technology. Like earlier transitions, 10GbE started as a technology reserved for backbone applications in the core of the network. New advances in optic and cabling technologies have made the price points for 10GbE attractive as a server access technology as well. The desire for 10GbE as a server access technology is driven by advances in computer technology in the way of multisocket/multicore, larger memory capacity, and virtualization technology. In some cases, 10GbE is a requirement simply for the amount of network throughput required for a device. In other cases, however, the economics associated with multiple 1-G ports versus a single 10GbE port might drive the consolidation alone. In addition, 10GbE becoming the de facto standard for LAN-on-motherboard implementations is driving this adoption.

In addition to enabling higher transmission speeds, current 10GbE offerings provide a suite of extensions to traditional Ethernet. These extensions are standardized within IEEE 802.1 Data Center Bridging. Data Center Bridging is an umbrella referring to a collection of specific standards within IEEE 802.1, which are as follows:

  • Priority-based flow control (PFC; IEEE 802.1Qbb): One of the basic challenges associated with I/O consolidation is that different protocols place different requirements on the underlying transport. IP traffic is designed to operate in large wide area network (WAN) environments that are global in scale, and as such applies mechanisms at higher layers to account for packet loss, for example, Transmission Control Protocol (TCP). Because of the capabilities of the upper layer protocols, underlying transports can experience packet loss and in some cases even require some loss to operate in the most efficient manner. Storage area networks (SANs), on the other hand, are typically smaller in scale than WAN environments. These protocols typically provide no guaranteed delivery mechanisms within the protocol and instead rely solely on the underlying transport to be completely lossless. Ethernet networks traditionally do not provide this lossless behavior for a number of reasons including collisions, link errors, or most commonly congestion. Congestion can be avoided with the implementation of pause frames. When a receiving node begins to experience congestion, it transmits a pause frame to the transmitting station, notifying it to stop sending frames for a period of time. Although this link-level pause creates a lossless link, it does so at the expense of performance for protocols equipped to deal with it in a more elegant manner. PFC solves this problem by enabling a pause frame to be sent only for a given Class of Service (CoS) value. This per-priority pause enables LAN and SAN traffic to coexist on a single link between two devices.
  • Enhanced transmission selection (ETS; IEEE 802.1Qaz): The move to multiple 1-Gbps connections is done primarily for two reasons:
    • The aggregate throughput for a given connection exceeds 1 Gbps; this is straightforward but is not always the only reason that multiple 1-Gbps links are used.
    • To provide a separation of traffic, guaranteeing that one class of traffic will not interfere with the functionality of other classes. ETS provides a way to allocate bandwidth for each traffic class across a shared link. Each class of traffic can be guaranteed some portion of the link, and if a particular class doesn’t use all the allocated bandwidth, that bandwidth can be shared with other classes.
  • Congestion notification (IEEE 802.1Qau): Although PFC provides a mechanism for Ethernet to behave in a lossless manner, it is implemented on a hop-by-hop basis and provides no way for multihop implementations. 802.1Qau is currently proposed as a mechanism to provide end-to-end congestion management. Through the use of backward congestion notification (BCN) and quantized congestion notification (QCN), Ethernet networks can provide dynamic rate limiting similar to what TCP provides only at Layer 2.
  • Data Center Bridging Capability Exchange Protocol extensions to LLDP (IEEE 802.1AB): To negotiate the extensions to Ethernet on a specific connection and to ensure backward compatibility with legacy Ethernet networks, a negotiation protocol is required. Data Center Bridging Capability Exchange (DCBX) represents an extension to the industry standard Link Layer Discovery Protocol (LLDP). Using DCBX, two network devices can negotiate the support for PFC, ETS, and Congestion Management.

Fibre Channel over Ethernet

Fibre Channel over Ethernet (FCoE) represents the latest in standards-based I/O consolidation technologies. FCoE was approved within the FC-BB-5 working group of INCITS (formerly ANSI) T11. The beauty of FCoE is in its simplicity. As the name implies, FCoE is a mechanism that takes Fibre Channel (FC) frames and encapsulates them into an Ethernet. This simplicity enables for the existing skillsets and tools to be leveraged while reaping the benefits of a Unified I/O for LAN and SAN traffic.

FCoE provides two protocols to achieve Unified I/O:

  • FCoE: The data plane protocol that encapsulates FC frames into an Ethernet header.
  • FCoE Initialization Protocol (FIP): A control plane protocol that manages the login/logout process to the FC fabric.

    Figure 8-1 provides a visual representation of FCoE.

    Figure 8-1

    Figure 8-1. Fibre Channel over Ethernet

When Fibre Channel frames are encapsulated in an Ethernet, the entire Fibre Channel frame, including the original Fibre Channel header, payload, and CRC are encapsulated in an Ethernet. Figure 8-2 depicts this.

Figure 8-2

Figure 8-2. Fibre Channel Frame Encapsulated in an Ethernet

The ANSI T11 specifies the frame format for FCoE. It is a standard Ethernet frame with a new EtherType of 0x8906. Also note that the new Ethernet frame has a new Frame Check Sequence (FCS) created rather than using the FCS from the Fibre Channel frame. Figure 8-3 illustrates the FCoE frame format.

Figure 8-3

Figure 8-3. FcoE Frame Format

FCoE standards also define several new port types:

  • Virtual N_Port (VN_Port): An N_Port that operates over an Ethernet link. N_Ports, also referred to as Node Ports, are the ports on hosts or storage arrays used to connect to the FC fabric.
  • Virtual F_Port (VF_Port): An F_port that operates over an Ethernet link. F_Ports are switch or director ports that connect to a node.
  • Virtual E_Port (VE_Port): An E_Port that operates over an Ethernet link. E_Ports or Expansion ports are used to connect Fibre Channel switches together; when two E_Ports are connected the link, it is an interswitch link (ISL).

To facilitate using FCoE an additional control plane protocol was needed and thus FCoE Initialization Protocol (FIP) was developed. FIP helps the FCoE perform VLAN discovery, assists the device in login (FLOGI) to the fabric, and finds key resources such as Fibre Channel Forwarders (FCFs). FIP is its own Ethertype (0x8914), which makes it easier to identify on a network and helps FIP Snooping devices identify FCoE traffic. Figure 8-4 depicts where FIP starts and ends and where FCoE takes over.

Figure 8-4

Figure 8-4. FIP Process

FIP can be leveraged by native FCoE-aware devices to help provide security against concerns such as spoofing MAC addresses of end nodes and helps simpler switches, such as FIP Snooping devices, learn about FCoE traffic. This awareness can provide security and QoS mechanisms that protect FCoE traffic from other Ethernet traffic and can help ensure a good experience with FCoE without the need to have a full FCoE stack on the switch. Currently the Nexus 4000 is the only Nexus device that supports FIP snooping.

Single-Hop Fibre Channel over Ethernet

Single-hop FCoE refers to an environment in which FCoE is enabled on one part of the network, frequently at the edge between the server and the directly connected network switch or fabric extender. In a single-hop topology the directly connected switch usually has native Fibre Channel ports which in turn uplink into an existing SAN, although you can have a complete network without any other fibre channel switches. Single-hop FCoE is the most commonly deployed FCoE model because of its double benefit of seamless interoperability into an existing SAN and the cost savings with a reduction in adapters, cabling, and optics to servers.

This reduction in cabling and adapters is accomplished through the use of a new adapter: Converged Network Adapter (CNA). CNAs have the capability to encapsulate Fibre Channel frames into Ethernet and use a 10GbE Ethernet interface to transmit both native Ethernet/IP traffic and storage traffic to the directly connected network switch or fabric extender. The CNA’s drivers dictate how it appears to the underlying operating system, but in most cases it appears as a separate Ethernet card and separate Fibre Channel Host Bus Adapter (HBA).

Figure 8-5 shows how a CNA appears in Device Manager of a Microsoft Windows Server.

Figure 8-5

Figure 8-5. CNA in Device Manager

Using CNAs in a server, a typical single-hop FCoE topology would look like Figure 8-6 where a server is connected to Nexus 5x00 switches via Ethernet interfaces. The Nexus 5x00 switches have both Ethernet and native Fibre Channel interfaces for connectivity to the rest of the network topology. The fibre channel interfaces connect to native fibre channel ports on the Cisco MDS switches, and the Ethernet interfaces connect to the Ethernet interfaces on the Nexus 7000 switches. The FCoE traffic is transported only across the first or single hop from the server to the network switch. The current implementation of the Cisco Unified Computing System (UCS) uses single-hop FCoE between the UCS blade servers and the UCS Fabric Interconnects.

Figure 8-6

Figure 8-6. Single-Hop FCoE Network Topology

Multhop Fibre Channel over Ethernet

Building on the implementations of single-hop FCoE, multihop FCoE topologies can be created. As illustrated in Figure 8-6, native fibre channel links exist between the Nexus 5x00 and the Cisco MDS Fibre Channel switches, whereas separate Ethernet links interconnect the Nexus 5x00 and Nexus 7000. With multihop FCoE, topologies can be created where the native fibre channel links are not needed, and both fibre channel and Ethernet traffic use Ethernet interfaces.

The benefit of multihop FCoE is to simplify the topology and reduce the number of native fibre channel ports required in the network as a whole. Multihop FCoE takes the same principles of encapsulating fibre channel frames in Ethernet and uses it for switch-to-switch connections, referred to as Inter-Switch Links (ISL) in the Fibre Channel world, and uses the VE port capability in the switches.

Figure 8-7 shows a multihop FCoE topology where the server connects via CNAs to Nexus 5x00s, which in turn connect to Nexus 7000 series switches via the Ethernet carrying FCoE. The storage array is directly connected to the Nexus 7000 via FCoE as well.

Figure 8-7

Figure 8-7. Multihop FCoE Topology

Storage VDC on Nexus 7000

One of the building blocks in a multihop FCoE topology is the storage Virtual Device Context (VDC) on the Nexus 7000. VDCs are discussed in detail in Chapter 1, “Introduction to Cisco NX-OS,” and the focus in this chapter is on the Storage VDC and its use in a multihop FCoE topology. VDC is a capability of the Nexus 7000 series switches that enables a network administrator to logically virtualize the Nexus 7000 into multiple logical devices. The storage VDC is a special VDC that enables the virtualization of storage resources on the switch. This enables in essence a “virtual MDS” inside the Nexus 7000 that participates fully in the FCoE network as a full fibre channel forwarder (FCF).

With a Storage VDC network, administrators can provide the storage team a context that allows the storage team to manage their own interfaces; configurations; and fibre channel-specific attributes such as zones, zonesets, and aliases. Figure 8-8 shows how a storage VDC can be implanted in an existing topology where single-hop FCoE was initially deployed and then multihop FCoE was added. The storage VDC was created with VE ports connecting downstream to the Nexus 7000 and VE port to the Cisco MDS fibre channel director.

Figure 8-8

Figure 8-8. Storage VDC on the Nexus 7000

The storage VDC has some requirements that are unique to this type of VDC as storage traffic is traversing it. The first requirement is that the storage VDC can support only interfaces hosted on the F1 or F2/F2e series of modules. These modules support the capability to provide lossless Ethernet and as such are only suitable for doing FCoE. The VDC allocation process in NX-OS does not allow for other types of modules to have interfaces in a VDC that has been defined as a storage VDC.

In addition to requiring F1 or F2/F2e series modules, the storage VDC cannot run nonstorage related protocols. You cannot enable features such as OSPF, vPC, PIM, or other Ethernet/IP protocols in the storage VDC. The only features allowed are directly related to storage. Finally, the default VDC cannot be configured as a storage VDC.

3. N-Port Virtualization | 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.


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.


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.


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.


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


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


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.


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.


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