CFS Fabric Lock – Cisco CCNP and CCIE

When you configure (first-time configuration) a Cisco NX-OS feature (or application) that uses the CFS infrastructure, that feature starts a CFS session and locks the fabric. When a fabric is locked, the Cisco NX-OS software does not allow any configuration changes from a switch to this Cisco NX-OS feature, other than the switch holding the lock, and issues a message to inform the user about the locked status. The configuration changes are held in a pending database by that application.

If you start a CFS session that requires a fabric lock but forget to end the session, an administrator can clear the session. If you lock a fabric at any time, your username is remembered across restarts and switchovers. If another user (on the same machine) tries to perform configuration tasks, that user’s attempts are rejected.

A commit operation saves the pending database for all application peers and releases the lock for all switches. In general, the commit function does not start a session; only a lock function starts a session. However, an empty commit is allowed if configuration changes were not previously made. In this case, a commit operation results in a session that acquires locks and distributes the current database.

When you commit configuration changes to a feature using the CFS infrastructure, you receive a notification about one of the following responses:

Images One or more external switches report a successful status: The application applies the changes locally and releases the fabric lock.

Images None of the external switches report a successful state: The application considers this state a failure and does not apply the changes to any switch in the fabric. The fabric lock is not released.

CFSoIP and CFSoFC

A mixed fabric of different platforms such as the Cisco Nexus 7000 Series, Cisco Nexus 5000 Series, and Cisco MDS 9000 Series can interact with each other using CFS over IP (CFSoIP) and/or CFS over FC (CFSoFC).

You can configure CFS to distribute information over IP for networks containing switches that are not reachable over Fibre Channel. CFS distribution over IP supports the following features:

Physical distribution over an entirely IP network.

Physical distribution over a hybrid Fibre Channel and IP network with the distribution reaching all switches that are reachable over either Fibre Channel or IP.

Distribution over IP version 4 (IPv4) or IP version 6 (IPv6).

Keepalive mechanism to detect network topology changes using a configurable multicast address.

Compatibility with Cisco MDS NX-OS Release 4.x.

Distribution for logical scope applications is not supported because the VSAN implementation is limited to Fibre Channel.

The switch attempts to distribute information over Fibre Channel first and then over the IP network if the first attempt over Fibre Channel fails. CFS does not send duplicate messages if distribution over both IP and Fibre Channel is enabled.

Figure 8-19 shows a network with both Fibre Channel and IP connections. Node A forwards an event to node B over Fibre Channel. Node B forwards the event to nodes C and D using unicast IP. Node C forwards the event to node E using Fibre Channel.

Figure 8-19 Network Example 1 with Fibre Channel and IP Connections

Figure 8-20 is the same as Figure 8-19 except that nodes D and E are connected using Fibre Channel. All processes are the same in this example because node B has node C and node D in the distribution list for IP. Node C does not forward to node D because node D is already in the distribution list from node B.

Figure 8-20 Network Example 2 with Fibre Channel and IP Connections

Figure 8-21 is the same as Figure 8-20 except that nodes D and E are connected using IP. Both nodes C and D forward the event to node E because node E is not in the distribution list from node B.

Figure 8-21 Network Example 3 with Fibre Channel and IP Connections

CFS over IP can also be used with static IP peers. In this case, dynamic discovery over IP multicast is disabled, and CFS distribution is done only on the peers configured statically. CFS uses the list of configured IP addresses to communicate with each peer and learn the peer switch WWN. After learning the peer switch WWN, CFS marks the switch as CFS-capable and triggers application-level merging and database distribution.

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