Nexus 5000 - FWM-2-STM_LOOP_DETECT
In a previous post, I mentioned problems we were having with one of our Nexus 5000 switches. During all of the Nexus 1000v issues, it was throwing these messages continually:
I couldn't tell if it was actually affecting anything, since VLAN 801 was being used as a FCoE VLAN. Looking at MAC addresses bound to VLAN 801 would reveal one MAC address in particular that would move around:
But what was this MAC address? After a little bit of digging, I finally found it:
But how did this come about? Well, before we installed our FCoE storage, we were using vPC's off of the Nexus 5000s to each of our ESX hosts. When we installed the storage, EMC told us we could not use FCoE across our vPC's. I can't find any evidence that this advice was accurate, but it is what it is. The Management ports had originally been assigned internally routable IP addresses, and the vPC Keep-Alive was built on top of that. That means that the default VRF would have learned the address from the management VRF at some point in time. Upon removing the vPC configuration, it just never un-learned it apparently.
2011 Mar 29 05:22:13 N5K-2 %FWM-2-STM_LEARNING_RE_ENABLE: Re enabling dynamic learning on all interfaces
2011 Mar 29 05:22:20 N5K-2 %FWM-2-STM_LOOP_DETECT: Loops detected in the network among ports Eth1/10 and Eth1/2 vlan 801 - Disabling dynamic learn notifications for 180 seconds
I couldn't tell if it was actually affecting anything, since VLAN 801 was being used as a FCoE VLAN. Looking at MAC addresses bound to VLAN 801 would reveal one MAC address in particular that would move around:
N5K-2(config)# sho mac add vlan 801
Legend:
* - primary entry, G - Gateway MAC, (R) - Routed MAC, O - Overlay MAC
age - seconds since last seen,+ - primary entry using vPC Peer-Link
VLAN MAC Address Type age Secure NTFY Ports
---------+-----------------+--------+---------+------+----+------------------
* 801 0005.9b7a.8800 dynamic 0 F F Eth1/7
But what was this MAC address? After a little bit of digging, I finally found it:
N5K-2(config)# sho int mgmt0There it is, but why is it being learned? The interface is down (and the MAC still remained even when Admin Down). After opening a TAC case and collecting debugs over and over again, the Engineer opened a Bug for the issue. Which was then terminated. Solution? Stop the leak of the MAC address and reload the switch. Fun.
mgmt0 is down (Link not connected)
Hardware: GigabitEthernet, address: 0005.9b7a.8800 (bia 0005.9b7a.8800)
But how did this come about? Well, before we installed our FCoE storage, we were using vPC's off of the Nexus 5000s to each of our ESX hosts. When we installed the storage, EMC told us we could not use FCoE across our vPC's. I can't find any evidence that this advice was accurate, but it is what it is. The Management ports had originally been assigned internally routable IP addresses, and the vPC Keep-Alive was built on top of that. That means that the default VRF would have learned the address from the management VRF at some point in time. Upon removing the vPC configuration, it just never un-learned it apparently.
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