Руководство По Проектированию для Cisco Cisco Nexus 5010 Switch

 

 

Design Guide 

© 2010 Cisco and/or its affiliates. All rights reserved. This document is Cisco Public Information. 

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vPC Configuration Synchronization 

A vPC allows two links that are physically connected to two Cisco Nexus switches to appear as a single PortChannel. 

Some configurations must be identical on both switches for vPCs to forward traffic. Such configurations include port 

mode, channel mode, speed, and duplex. 

The config-sync command simplifies the management of vPCs by synchronizing vPC configurations between 

primary and secondary vPC peers. 

vPC config-sync is currently available on the Cisco Nexus 5000 Series starting from Cisco NX-OS 5.0(2)N1(1). 

The config-sync feature uses the concept of the configuration profile. The switch profile is the construct that allows 

configurations to be applied both locally and on the config-sync peer. The config-sync peer definition is independent 

of the vPC peer definition and is specified in the switch profile configuration mode as follows: 

Nexus5000(config-sp)# sync-peers destination {destination IPs}+ [source <source IP> 
|  vrf <vrf>] 

Note:   Even if the config-sync peer is the same as the vPC peer device, the config-sync infrastructure has been 
designed so that it can be decoupled from vPC. Thus, you need to define the config-sync peer even in presence of a 

vPC configuration. 

After the config-sync peer has been defined, the configuration that uses vPC config-sync appears as follows: 

Switch# config sync 

Switch(config-sync)# switch-profile profiledefinition 

Switch(config-sp)# interface Port-channel100 

Switch(config-sp-if)# interface Ethernet1/1 

Switch(config-sp-if)# channel-group 100 

Switch(config-sp-if)# exit 

Switch(config-sp)# commit 

Configurations are applied only after the user enters a commit command. The configuration is synchronized with the 

remote peer through the mgmt0 interface using routable Cisco Fabric Service protocol over IP. If the remote peer 

cannot be reached, the configuration is applied only locally. 

All commit operations follow the two-phase commit approach: If the config-sync peer is reachable, either the 

configuration is fully committed on both peers or it is rolled back on both. If the config-sync peer is not reachable, then 

the configuration is applied only locally. When the peer becomes reachable, the configurations are merged. 

One of the most important forwarding rules for vPC is that a frame that enters the vPC peer switch from the peer link 

cannot exit the switch from a vPC member port. 

Figure 13 shows switches 3 and 4 connected to 5k01 and 5k02 with vPCs Po51 and Po52. If one of the hosts 

connected to switch 4 sends either an unknown unicast or a broadcast, this traffic may get hashed to port eth2/2 on 

PortChannel 52. 5k02 receives the broadcast and needs to forward it to the peer link for the potential orphan ports on 

5k01 to receive it. 

Upon receiving the broadcast, 5k01 detects that this frame is coming from the vPC peer link. Therefore, it does not 

forward it to port 2/9 or 2/10; if it did, a duplicate frame on switch 3 or 4, respectively, would be created. 

If a host on switch 4 sends a broadcast, 5k02 will correctly forward it to Po51 on port 2/9 and place it on the peer link. 

5k01 will prevent this broadcast frame from exiting onto port 2/9 or 2/10 because this frame entered 5k01 from a vPC 

peer link. Should eth2/2 on switch 3 go down, port 2/9 on 5k01 would become an orphan port and as a result will 

receive traffic that traverses the peer link.