UCS and Mixed vPC / Non vPC VLANs

A great feature added to the Cisco UCS V2+ is the ability to map VLANs to specific Port Channel uplinks and/or Ethernet uplinks. This seems pretty straight forward, but this was not available in V1 and I am finding customers who are not aware of this capability…

Many deployments of UCS use vPC links from Nexus core networks to the UCS Fabric Interconnects, and by default, both vPC trunks presented to the UCS are used for all VLAN traffic without any pinning of VLANs to specific Port Channels or Ethernet uplinks.

Due to a “feature” of the Nexus platform, there is an issue using vPC backed VLAN(s) for routing Edge traffic from an NSX environment and the solution is to add non vPC uplinks from the Nexus core to the UCS Fabric Interconnects. As I have seen, if VLAN pinning is not being used, then adding a new uplink without preparation will create a “black hole” for all vPC VLANs given the new non vPC uplink(s) are automatically another path to use for all VLANs.

Brad Hedlund does a great job of describing the issues surrounding routing across vPC trunks and the requirement to provide a non vPC back uplinks: http://lostdomain.org/2014/02/13/design-guide-deploying-vmware-nsx-with-cisco-ucs-and-nexus-7000/

Attached UCS configuration guide speaks to pinning traffic: http://www.cisco.com/c/en/us/td/docs/unified_computing/ucs/sw/gui/config/guide

So simply, before creating new uplinks for non vPC traffic on the UCS, ensure existing vPC VLANs are mapping to existing vPC Port Channels or Ethernet interfaces. Once this is in place, adding a new uplink will not create a “black hole” for existing VLAN’s, and the new VLAN required for Edge Traffic can then be created and mapped to the two (Fabric A and B) non vPC uplinks/port groups.

If you have not mapped VLAN’s to Port Croups/Ethernet Interfaces, the LAN Uplinks Manager configuration option available by right clicking on any Port Channel or Ethernet Interface under LAN configuration:

Screen Shot 2015-04-24 at 3.13.38 PM

From LAN Uplinks Manager, you can then select VLAN Manager:

Screen Shot 2015-04-24 at 3.14.00 PM

Remember to perform this configuration for both Fabric A and B Port Channels/Ethernet Interfaces. In the example below, VLAN’s have been mapped to Ethernet Interfaces Fabric A 1/17, 1/18, Fabric B 1/17, 1/18.

Screen Shot 2015-04-24 at 3.14.17 PM

UCS is a awesome platform, but care must be taken to ensure you fully understand how VLANs map from the Fabric Interconnects to the core network before changes are made to enable new uplinks.

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