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Nexus 5548UP not forwarding packets over vPC link

igor.hamzic81
Level 1
Level 1

Hi everybody,

 

just to give a broad view of the infrastructure before going further into details. We have a pair of Nexus 5548UP connected over a vPC between them. To them are connected 4 FEXs redundantly to which the ESX infrastructure is connected(one link per FEX). On the secondary Nexus(port itself is routed) we have a remote location connected via a L2 link. We have HSRP established for all VLANs that are on the Nexus switches.

 

And now for the problem. We have a rather odd situation with one of our remote locations when it tries connecting to a server on virtual infrastructure connected to a pair of Nexus switches. When trying to connect to this server there are problems in bringing up the connection to the server from user computers in the remote location as it time outs. This lasts until we try a ping from the user computer and then the connection to the server succeeds.

 

We have have been capturing traffic on several points in the path(on user computer, on the secondary Nexus - link towards remote location and on the server itself) and have found that SYN packets are received on the server, the server sends a SYN-ACK packet but this packet is never seen on the link to the remote location.

 

Traffic flow looks like this traffic from remote location:

 

remote location -> L2 link -> Nexus 2 -> link to FEX -> FEX -> L2 trunk(multiple VLANs) -> ESX host -> virtual server

 

Traffic flow from server to remote location:

 

virtual server -> ESX host -> L2 trunk(multiple VLANs) -> FEX -> link to FEX ->  Nexus 1 -> vPC link -> Nexus 2 -> L2 link -> remote location

 

From all of these we guess that either the packets are dropped either on Nexus 1 or on the vPC between Nexus switches.

Another problem is that we cannot see any drops on any of the interfaces on the infrastructure and  cannot see anything in the logs itself.

Does anybody have a clue what could be causing this strange behavior and only to this specific server?

 

Edit: I have entered the correct traffic flows from and to remote location.

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