mac flapping between multiple ports

[multiplexer002]

Hello,

I am facing a problem that has to do with mac flapping between ports in a specific vlan. 

Just to inform you I am working on a Data Center environment and the implementation is using VPC and port-channels and all ports are configured in such a way to support it. There is no loop effect with this implementation.

Beside that I am letting you know that we use FEX and their ports are connected to the servers. 

With the use of the command sh log last x I get the output that a specific host in a specific vlan is flapping between several ports.

Is there any idea why this is happening?

Please advice accordingly.

Thanks in advance.

John 

[Mark Malone]

Hi

This can really depend on whet the device is an what way its physically setup , what is the host is it a bonded device connected to multiple fexes or just 1 , I have seen this before with the 3020 blades in the chassis when there connected to the fexes in vpc design , the issue on the 3020 was it wasn't bonded correctly on that side logically , another instance I seen it the portchannel wasn't set right and the links were acting individually in the etherchannel on an enhanced vpc device design

[multiplexer002]

Hi Mark,

Thank for your reply.

We use two fexes 2224 in vpc design that connect with blade servers in a chassis for management. 

I am not sure about the port-channel configurations due to the fact that they weren't done by me and I am not in position to check their validity. If there is a workaround for that reason, please advice.

Can you explain me also a little bit the phrase " I have seen this before with the 3020 blades in the chassis when there connected to the fexes in vpc design , the issue on the 3020 was it wasn't bonded correctly on that side logically"?

Best Regards

John

[Mark Malone · Accepted solution]

Hi

So that sounds like same as our setup is there an A and B side 3020 blades , Im not in systems team so I cant go into the exact detail on the bonding on their side in the Linux but they bond on the actual OS in software too and if its not done right can cause issues like mac flaps , they kept pushing it back on the  network but we checked everything it turns out it was them had incorrect settings on their end behind the 3020 in the OS bit

in terms of the cisco to cisco config this is what we have setup and it works fine , I have also seen mac flaps when the lacp individual statement was missing on our end , we caused it that time

I think really you need to double check your cisco config make sure your right and then tie in with the user that setup the chassis side , it will be very difficult to determine the issue when you only have access to certain parts unless the fault is on your end

5k side A side this would also be mirrored on the second 5k for the B side of the chassis for the other 3020

example of one of our setups A and B side 3020 directly connected to 2 fexes , A side is Fex118 and B side fex 117 which is identical

interface Ethernet118/1/13
  description xxxxxxxxxxx
  switchport mode trunk
  switchport trunk allowed vlan 1-1005,1226
  channel-group 26 mode active

interface Ethernet118/1/15
  description xxxxxxxxxxxxx
  switchport mode trunk
  switchport trunk allowed vlan 1-1005,1226
  channel-group 26 mode active

interface port-channel26
  description xxxxxxxxxx
  switchport mode trunk
  no lacp suspend-individual
  switchport trunk allowed vlan 1-1005,1226

&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&7

3020 side

interface Port-channel52
 description xxxxxxxxxxxxxxxxxxxxxxxxx
 switchport trunk allowed vlan 1-1005,1226
 switchport mode trunk
 link state group 1 upstream
 spanning-tree bpdufilter enable
end
!
interface GigabitEthernet0/17
 description xxxxxxxxxxxxxx
 switchport trunk allowed vlan 1-1005,1226
 switchport mode trunk
 channel-group 52 mode active
end

interface GigabitEthernet0/18
 description xxxxxxxxxxxxxxxx
 switchport trunk allowed vlan 1-1005,1226
 switchport mode trunk
 channel-group 52 mode active
end