Matthew had a link aggregation question:
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I have had the following question from one of my partners Solution Architects;
Can you let me know if I am correct in thinking that you don't need SmartLink if a VC module is LACP connected to two Cisco switches if they are using vPC?
(Couldn’t find a VC to Nexus 5000 version, so imagine the server is a VC FlexFabric module with LACP, and that the Nexus 2000 aren’t there. The link between the Nexus 5000 is VCP peer, as per http://www.cisco.com/en/US/prod/collateral/switches/ps9441/ps9670/configuration_guide_c07-543563.html.)
I think they are correct but I am no expert on the matter, and I haven’t been able to find any documentation to say one way or the other.
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Reply from Vincent:
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Short answer: just enable SmartLink
Long answer: the interest of SmartLink is somewhat independent of whether the upstream switches are joined at the hip with vPC or not, although vPC makes it less likely that SmartLink will kick in. You presumably still have uplinks coming out of 2 VC modules, and therefore 2 port-channels on the Cisco side since VC doesn’t do distributed LACP yet. On the VC side you can either create 2 VC networks (or SUS), one for each port-channel, that’s an Active/Active config, or a single network (or SUS) with both port-channels, that’s an Active/Standby config. In the Active/Active case, you want SmartLink enabled to trigger a NIC failover in the server if a port-channel goes down (although that’s unlikely to occur because your port-channel is distributed on 2 different physical switches). In the Active/Standby case, SmartLink is less useful because the failover happens at the VC level, and it could be slightly harmful because if all uplinks go down on both sides (which would trigger SmartLink), it would cut off downlinks on both sides as well and therefore cut off even communication between blades in the enclosure, but if that happens your servers can no longer communicate with the outside anyway and that’s probably a bigger problem.
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Other comments or suggestions?
