Forum Discussion

Dazzla_20011's avatar
Icon for Nimbostratus rankNimbostratus
Nov 26, 2010

Help Major network outage involving F5 LTM




I'm really hoping someone can help me. Last Friday we had a major problem which affected access to all our Core Systems. The initial problem was caused due to a bug within the Cisco Nexus IOS which caused loopguard to block the vlans on a port-channel and then unblock them.



The 3 vlans used by the F5 (real, virtual servers and heartbeat) between our two LTM's became blocked for a few microseconds.



2010 Nov 19 14:31:43 GR_Core2 %STP-2-LOOPGUARD_BLOCK: Loop guard blocking port port-channel1 on VLAN0205. 2010 Nov 19 14:31:43 GR_Core2 %STP-2-LOOPGUARD_UNBLOCK: Loop guard unblocking port port-channel1 on VLAN00205



We have two LTM's, in active (data centre1) - standby (data centre2).



When we came to investigate why users couldn't access the systems it was because the servers couldn't reach their default gateway which is a floating ip on the F5 LTM. To solve the problem I pressed update on the F5 self ip used as the DG. Suddenly the servers could reach their DG and access to systems was restored. I'm interested to know what this would have done. I suspect it sent out a gratuitous arp?



Having checked the logs the Standby LTM became Active. The LTM also reported address conflicts for some of the IP's which are used for the Virtual Servers.



Any help to determine the cause will be very much appreciated as we are new to the F5 world so troubleshooting is difficult as we are used to Cisco products. our support company isn't being very helpful.



One thing I have noticed as that we are not using MAC masquerade.



Many Thanks



16 Replies