[c-nsp] Large GLBP installations

[Church, Charles]

Would it be possible to increase the hello and dead timers you're using
for the GLBP so that you're sending hellos 1/2 as often, and you declare
a neighbor dead after 1 more missed hello than what you're currently
using?  Seems like processing half as many hellos would help the CPU,
and waiting for one extra missed hello would help the flapping.  I had
that help in HSRP situations, haven't dealt with GLBP a whole lot.

Chuck

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Ross Vandegrift
Sent: Tuesday, June 10, 2008 11:00 AM
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] Large GLBP installations


Hello everyone,

What is the general feeling on the list of GLBP as well as GLBP on
the SUP720-3BXL?

For the past few months(!) I've been working with TAC to troubleshoot
a perplexing issue.  We have a pair of 6500/SUP720-3BXLs that aggregate
a few thousand customer VLANs and provide first-hop gateway service.
Around 1000 of those VLANs are configured with GLBP.  The rest use
HSRP.

GLBP interfaces are constantly flapping which switch is the active
master of the GLBP group.  The flapping is not service impacting,
doesn't elevate CPU, but floods the logs constantly with useless
garbage.  HSRP interfaces behave perfectly well.

RP CPU utilization on these switches is somewhat high for what they
do.  It averages between 40-50% with constantly spiking over 95%.  TAC
has blamed the GLBP problem on high CPU causing packets to drop from
input queues.  This explanation is hard to swallow, since this would
affect both HSRP and GLBP.

We have another pair of switches that are similarly configured, except
that they do not use any GLBP.  There are fewer VLANs on the second
pair, but each of those VLANs carries much more traffic.  CPU on these
switches averages 15-20%.  BGP Scanner, OSPF/STP recalcs are the only
things that cause CPU to cross the 95% mark.

Am I crazy for thinking GLBP is the problem here?  Has anyone else had
experience with around 1000 GLBP groups on a 6500?

-- 
Ross Vandegrift
ross at kallisti.us

"The good Christian should beware of mathematicians, and all those who
make empty prophecies. The danger already exists that the mathematicians
have made a covenant with the devil to darken the spirit and to confine
man in the bonds of Hell."
	--St. Augustine, De Genesi ad Litteram, Book II, xviii, 37
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