Nexus 5010/2248 dual-homed FEX scenario - question about "switchport mode fex-fabric" and BA/STP

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Sep 1st, 2010
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Hello -


Was wondering what other experiences have been in the field with dual-homed FEX 2248s against two vPC peer-enabled 5010s. 


We're using this configuration on the latest 4.2(1)N2(1) code and seeing 5-10 second failover times when "pulling the uplink" on our FEX physical uplink to 5010-A.  Surprisingly, the same test when re-connecting and then pulling the uplink to 5010-B is less than 1 second.


Each 2248 has a single 10Gb connection back to each 5010 (total of two per 2248) - and at the N5K level each 5010 is configured to have a single-10Gb port-channel (vpc-enabled) back to the FEX.


Is there a STP/BA issue going on here?  STP shows no blocked ports at the 5010 level.  STP doesn't even show active for our FEX interfaces which I assume is inherited through the use of the "switchport mode fex-fabric" command.


Has anyone else seen this issue?  or is this simply expected behavior?


Thanks !

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sgober Tue, 09/07/2010 - 11:34
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Where are you connected when you are watching this?  Are you watching a device connected to the 2k?

mcarter@egroup-... Tue, 09/07/2010 - 17:51
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Yes - that's right.  Pretty sure we've identified this as a FEX module ejection/reinsertion issue based on the messages that register with the parent switch.

sgober Thu, 09/09/2010 - 08:34
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Just curious have you tried having your client in both sides of the 2k?  Say the client is in port 1 of the 2k now have you moved it to the other side say port 48.  Im curious if its just failing over after dividing your 2k in to two halves with the first half going over FEX1 and the second going over FEX2. 


The reason I think this is that i issued the pinning max-links 2 command on mine and it works by dividing the 2k in to two halves.  1-24 run over FEX1 and 25-48 run over FEX2.  If FEX2 goes down in this config it takes manual intervention IE issuing pinning max-links 1 in order to bring 25-48 back up.  The reason I did this is that I read somewhere that if you dont issue the pinning max-links 2 links you will only utilize one FEX link and the other will not be used. 

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