Mac Flaps on VM Host with uplinks to different switches

[Terence Lockette]

Hello,

We are currently using 3750-X switches for a top-of-rack solution that will eventually connect to a pair of 6807-XL switches running in VSS.  As of now, these switches connect to standalone 6500s.  Some of the servers connected to the 3750-Xs have one uplink going to 1 switch and a second uplink going to another.  None of the 3750s are stacked.  The config on the switchport for the server in question is simple:

Interface GigabitEthernet1/0/3

 switchport mode access

 switchport nonegotiate

 spanning-tree portfast

 spanning-tree bpduguard enable

This particular server is a MS 2008 or 2012 server as a Hyper-V host.  There are currently 8 mac addresses behind one interface on switch A connecting this server, and about 5 mac addresses on the other interface on switch B.  I'm getting mac flap notifications and I'm not sure if it's completely due to a reboot of the server.  We use WUG to monitor server status and I didn't see a notification around the time my syslog server caught the mac flap notifications.  Is there anything that I can do, configuration wise, to eliminate or avoid getting these mac flaps either when the server reboots or for some other reason?  Thanks!

Regards,

Terence

[johnd2310]

Hi,

How are the NICs on the server setup? Are they teaming?

Thanks

John

[Terence Lockette]

Hi John,

That would be a question I would have to ask my server admin.  I only handle the network side so my knowledge of VM NIC teaming isn't great.  I'm not sure if these NICs are teaming or not but when I get an answer from the admin, I'll update the discussion.  If they are teaming, what info would you need?  If they're not teaming, what info would you need?

Regards,

Terence

[johnd2310]

Hi,

I guess you will need to find out from the server admins how they have configured the NICs.  Is the mac-flap happening constantly or was this a one-off event?

Thanks

John

[Terence Lockette]

Hello John,

The server admin did state that the NICs are teamed.  As for specifics, I don't have that info.  However, the mac flaps don't occur on a regular basis.  This event was once but I have seen it in the past.  So far, I haven't been able to correlated to a reboot or something else at this point.

Regards,

Terence

[johnd2310]

Hi,

I suspect the server admins were doing some configuration or re-configuration on the server NICs and created the issue. You will have to check what  server configuration was happening at that time.

Thanks

John 

[Terence Lockette]

Hello John,

I know a lot of maintenance work is done in a 24/7 production network in the late hours but I don't think so in this case.  The server admin would've told me he was doing some work since this happened at 1:20am on Sunday morning.  We typically don't like making changes on the weekends in the event something happens then there goes our weekend if the fix isn't quick.  However, the server could have gone through a Windows update and quickly rebooted.  I haven't seen mac flaps since posting this discussion but I'll certainly keep my eye on it.  Thanks!

Regards,

Terence