Back to Back vPC - Why is it not possible?

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Oct 14th, 2014
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Good Evening!

I'm studying for CCDP and am currently sitting on page 271 for those of you that have the official book (642-874). 

Similar topology to book here.

If I understand correctly, in an Active/Active FEX design two Cisco Nexus 5000s plug into two Cisco Nexus 2000s which in turn plug into the server. There is a two way vPC between the 2000s and 5000s (it doesn't look like that's shown in the picture though). However, because there is a vPC between the FEXs and the Nexus 5000 you cannot have a vPC between the FEXs and the servers. Why is this? Any clarification on at a conceptual level of how an Active/Active FEX configuration works is also appreciated. I've read the section, but since I haven't had hands on with any of this equipment I'm having some trouble conceptualizing everything. Thanks for your time.

Grant

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InayathUlla Sharieff Thu, 10/16/2014 - 04:56
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  • Cisco Employee,

Question:

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 However, because there is a vPC between the FEXs and the Nexus 5000 you cannot have a vPC between the FEXs and the servers. Why is this?

Answer: No you can have VPC between the Fex and the servers.

https://communities.cisco.com/thread/21567?tstart=0

 

2)

good document on VPC:

http://www.cisco.com/c/en/us/products/collateral/switches/nexus-5000-ser...

Video on the same:

http://www.ine.com/all-access-pass/training/playlist/ccie-data-center-ne...

 

HTH

Gurpreet Kochar Sat, 10/18/2014 - 06:10
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When you have a vpc between fex and parent switch, you do not need to create a custom vpc between the fex and the server. The fex ports by default are in vpc which is created automatically when you dual home the fex port to the same server.

"show vpc" should list all the vpcs which comprise of your fex ports.

 

What you are referring to is probably the feature where you can assign custom vpc numbers to port-channels between fex and the server and as i remember, this feature is supported after a certain code and one certain platforms ( will have to check the details for this ).

 

 

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