speed links balanced according to a predefined algorithm. See Chapter 7 for more information on how EtherChannel hashing works. With four 10 Gbps uplinks, we can assign 12 ports to each 10 Gbps link, giving us an oversubscription ratio of 1.2:1. That's a potential four-to-one improvement in uplink speed. Sounds like a great idea. The downside of this increase in usable uplink is that should one of the uplinks fail, all 12 of the pinned ports will also be down. There is no dynamic healing like there is with an EtherChannel when pinning fabric ports. Pinning can be done with one, two, or four links. On a 48-port FEX, the breakdown is as follows: Pinning one All host ports use one uplink. This is the method used with an EtherChannel uplink. Pinning two The first 24 ports use the first link and the second 24 ports use the second uplink. Pinning four Each 12-port group uses its own uplink. When using a FEX with all four uplinks bonded together, we must use a pinning of one, configured within the FEX configuration block: fex 101 pinning max-links 1 Nexus Design Features description FEX0101 type "Nexus 2148T" If we wanted to abandon the idea of using an EtherChannel and instead get the most out of our bandwidth, we would use pinning four: fex 101 pinning max-links - 4 description FEX0101 type "Nexus 2148T" You will get an error if you try to configure your uplinks into a channel when pinning is set higher than one: NX-5K-1(config-if-range)# channel-group - 10 command failed: port not compatible [FEX pinning max-links not one] FEX fabric uplinks using vPC To configure a single FEX cross-connected to two Nexus 5000s (cross-connect design), we must use a vPC to bond the links together: NX-5K-1: interface port-channel 20 switchport mode fex-fabric vpc 20 fex associate 101 speed 10000 NX-5K-2: interface port-channel 20 switchport mode fex-fabric vpc 20 fex associate 101 speed 10000 If this is confusing, read on, as vPCs are covered in the next section. Remember that the FEX configuration should be identical on both 5000s, or