 Please note that spanning tree port type is changed to "network" port type on vPC peer-link. This will enable spanning tree Bridge Assurance on vPC peer-link provided the STP Bridge Assurance (which is enabled by default) is not disabled. A vPC domain is the area in which vPCs reside. The domain must be the same for each switch participating in the vPC. Remember, there can be only two switches in the main. In our example, each 5K is assigned vPC Domain 1. This may seem daunting, but the good news is that all of these vPC commands need only be entered once. Once the pair of Nexus switches is configured to support vPCs, adding a vPC is very simple. Adding a vPC With everything else ready to go, the EtherChannels on each 5K that are to be linked into a single vDC must be tagged with a vPC ID. The ID is up to you, but a good rule to follow is to tag the EtherChannel with the same number as the channel itself. Virtual Port Channel Technically, you could bond port channel 10 on 5K1 with port channel 20 on 5K2, and tag it with vPC ID 30, but if you do, every networking engineer who works on the switches after you will want to hunt you down and kill you. Let's endeavor to keep them all the same. First the configuration on NX-5K-1: NX-5K-1 (config)# int po 10 NX-5K-1 (config-if)#vpc 10 And the same configuration on NX-5K-2: NX-5K-2 (config)# int po 10 NX-5K-2 (config-if) #vpc 10 Though the concept can be difficult to grasp, once you've set up the original vPC ar- chitecture, the configuration for adding a vPC is that simple. There are limitations with vPCs that we'll see in Chapter 18, the most important having to do with how fabric extenders are connected. Since vPCs create a single data link across two separate switches, the switches must agree that the vPC is possible. To do so, they communicate with each other and will refuse to bring up a vPC if the two switches are configured differently. Luckily, there is a quick way to see if there is a problem. Using the show vpc consistency-parame ters command will show you if 