n9k arp entry with vpc domain - help what is the normal behavior

selina-scheuermann · ‎04-27-2018

Hello Guys

Sorry for asking but i didn't find the correct answer to my question.

Network Design:

2 Nexus Switches n9k which are members in vpc domain, two port-channel 101-102

which are connected to the FI A und FI B (behind UCS System/ESX Host/DVS/Port-Gruppe/VM)

Currently i see two different kind of arp entries.

1. VLAN140 in this Case both entries are marked with "+" -> primary entry using vPC Peer-Link

switch-one# sh mac address-table vlan 140 | i 0050.56a9.53a0
+ 140 0050.56a9.53a0 dynamic 0 F F Po101

switch-two# sh mac address-table vlan 140 | i 0050.56a9.53a0
+ 140 0050.56a9.53a0 dynamic 0 F F Po101

2. VLAN851 in this Case one entry is marked with "+" -> primary entry using vPC Peer-Link on switch-one and on switch-two with "*" -> primary entry

switch-one# sh mac address-table vlan 851 | i 0050.56a9.dabe
* 851 0050.56a9.dabe dynamic 0 F F Po102

switch-two# sh mac address-table vlan 851 | i 0050.56a9.dabe
+ 851 0050.56a9.dabe dynamic 0 F F Po102

Is one of them not the correct way how should the nexus switch install the mac address?

I'm asking because we had a forwarding issue and based on that i think it was a mac learning/synchronization issue but i'm not sure. The problem was solved when we shut down one port-channel to the FI.

Thx a lot and BR

Kirk J · ‎04-27-2018

Greetings.

Are both FIs actually learning that mac as well? There are a couple of bugs, and other scenarios that could trigger that?

Is this just an isolated incident or do you have a lot like this?

Please confirm the interfaces on each FI that shows the same macs be learned.

Thanks,

Kirk...

selina-scheuermann · ‎04-27-2018

Hello Kirk

It is very strange and make me confusing. It seems we have two different problem and it would be super complicated if I have to explain both of them but both of them could be related to each other.

At first, the forwarding issue appears when we change something on our network such as, configure a new vlan and redirect this explizit traffic to the new vlan.

I think it's not a problem on FI because we had this problem also from those nexus switches to c-240 rackserver (without FIs) which are also connected over 2 port-channels. Therefore can you please answer my question above that would be great. I would like to start step by step but before i have to unterstand what i should expect for arp entry in my environment and of sure i will check the mac entries as well on FIs (thanks for this Input)