Tuning GLBP...

Unanswered Question
Dec 5th, 2007

Hello,


I am doing testing for our GLBP setup and notice when I shutdown a vlan on the active device it takes in the neighbourhood of 5 minutes for the secondary device to start passing the traffic for that vlan again.


I will assume there are some tuning "best practices" that are out there to reduce this time to recover??


Any help would be appreciated. :)

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nordick26 Thu, 12/06/2007 - 04:12

Hello William,

When you shutdown your vlan on your GLBP active router, will your GLBP standby router recognize this?

You can debug it, or check with "show glbp brief" and you'll see something like this, if you standby router changed his status:


Router#show glbp brief

Interface Grp Fwd Pri State Address Active router Standby router

Fa0/0 1 - 100 Active 10.1.1.100 local unknown



By default, the timers for GLBP are as follows:

Hello time 3 sec, hold time 10 sec.


You can change them by this command " glbp 1 timers X Y" Where 1 is GLBP group, which have to match on active and standby routers, X is hello timer and Y is holddown timer.


If you have bigger or complex network architecture, try to check other L2 isues, e.g. STP configuration.


Or maybe search for eventual IOS release bugs (try your test on different IOS)


Hope this helps :)


Regards


[rate any helpful posts]



william.briere Thu, 12/06/2007 - 11:57

Hello,


I seem to see a delay of 5 minutes when the device with "preempt" on the vlan has its vlan shutdown.


I am watching it and find that if I leave it down, it stays down for 5 minutes then comes backup, on the secondary device. If I continue to leave it down... in five more minutes, after being up, it goes down again??


Is this a Spanning-Tree issue or GLBP? (I guess the thought of Spannnig-Tree being the issue come from the 300 second aging timer)


I can post my configs on each if needed...

william.briere Thu, 12/06/2007 - 12:53

Anyone know what is going on here?


I now believe it is GLBP...


When I shut the Vlan on the "preempt" device, and keep it down, The Vlan goes down then up then down then up (All with 5-10 minutes in between changes in state)


Why will the backup device not takeover... And stay active until the the "preempt" device becomes available again?


Please Help :)

william.briere Thu, 12/06/2007 - 13:36

Hello,


Thought I would update...


This odd behavior only happens when I'm shutting down layer 3 vlans...


If I shut any combination of interfaces... Say for example all the interfaces on the primary or secondary device that holds the GLBP config... Things failover in seconds...


Why does this odd behaviour only happen when it is me shutting down an individual vlan interface on one of the two devices?


Hopefully someone has an explaination...


Anyone... Bueller?? LOL

nordick26 Fri, 12/07/2007 - 00:43

Hello William,


can you provide an output of following (from both devices)?


sh run int vlan XY;

sh glbp brief;

sh vlan;


Do you have any loggs from the VLAN going up and down? You could find a possible reason of this mystery :)







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