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Field Notice 70545

Cisco NEXUS with Fabric Extenders connected to UCS, what is the best design?

Cisco NEXUS with Fabric Extenders connected to UCS, what is the best design?

We recently implemented a new network backbone, the NEXUS 6004, with Fabric Extenders. Our UCS fabrics are connected to the FEX (not direct to the 6004) I have been unable to find any documentation that takes into account the NEXUS FEX’s.

Attached are 5 different designs, what would the recommended one be? And reasons why?

We have a mix (we have multiple UCS fabrics) of designs on different fabrics trying to find out what is the most ideal. We have been getting some network anomalies here and there and have been unable to point pint why,

Any help is appreciated


Walter Dey

Best practise: connect UCS FI uplinks with 10G non oversubscribed to a North bound switch (n5k, N6k); no FEX !

FEX might be used to connect many (max 160) rack mount servers (C-series) to a UCS FI. There you might tolerate some more oversubscription per server.

Agreed. You would want to PO straight into the 6K from the FIs. Where the external Fexs are used to connect rack mount servers. Below is diagram to show that part (minus the native FC you had)

I agree with the design of direct attached of the FIs to the 6Ks using port-channels (vPC from the 6Ks). The potential traffic from the FIs is quite large and you want to avoid risking over-subscription and bottleneck issues.

BTW - the last design " straight_thrugh.jpg" is the least recommended since traffic between servers that are pinned to different FIs will cross the vpc peer-link and as a best practice you would like to avoid that and keep the peer-link "free of traffic" as much as possible. it also might cause packet drops in some cases when traffic from the wan directed to the blades.

Thank you for the responses, just to clarify in my diagram the FEX 2000 are the ones designed for the NEXUS 6000, not for UCS! ( specifically this model ) we are not using any UCS FEX’s

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