Re: High EIGRP Pending routes

On 10 Jan, 17:49, sonic31ss <sonic3...@xxxxxxxxxxx> wrote:
Most of the documentation I can find on "Pending routes" from show ip
eigrp interfaces comes directly from Cisco and is not that helpful.
Their definition is "Number of routes in the packets sitting in the
transmit queue waiting to be sent."
The reason for this question is that we have an EIGRP meltdown on our
core routers (6500s - Sup720) about every three months.  We created
scripts to collect more data from the router on a 5 minute interval
and the early indication that EIGRP was in trouble was that there were
52 out of approximately 300 EIGRP interfaces that had as many as 8000
pending routes.  The remainder of the interfaces had zero pending
routes.  The IP routing table is approximately 4000 routes.
The CPU utilization was 34% at 5 sec with 11% consumed by EIGRP PDM.
Five minutes later the  CPU was at 100% and Pending routes were as
high as 100,000 on some of the EIGRP interfaces.  All interfaces with
EIGRP neighbors had tens of thousands of pending routes.
This core router (Core_01) has another core router attached (Core_02)
and it did not record a high number of Pending routes.
There was no indication in the syslog of any significant topology
change leading up to or during this event.
So my questions to the group are;
1. Does anyone have a better definition of Pending routes?
2. How often are the counters from show ip eigrp interface updated by
the IOS?
3. Does 8000 Pending routes seem to high considering that there are
only 4000 routes in the IP routing table?

Caveat - I am not an EIGRP expert. In fact I don't
know much about it at all and have basically
zero operational experience.

Answers:-
1.
I understand that EIGRP requires that routing
updates are acknowledged by the neighbour.
Most acknowledged protocols send some information
then wait on that being acknowledged before
sending more. I guess that pending routes are
routes waiting on previously sent routes being
acknowledged. This could be caused by
communications problems with the neighbours or
CPU overoload on the neighbours.

2.
I don't have a clue about these specific counters.
The bytes in/out etc counters are updated
quite infrequently on some platforms - 20 seconds
is the longest I have seen. From memory it is either
15sec or 20sec on the 6500.

3.
Yes. EIGRP sends *routes*. Perhaps the router has
decided to send one set of updates and then before
they can be sent successfully something triggers
another update. It may be no co-incidence that
8000 = 2 * 4000.

eigrp sends every route out of every interface
(except for split horizon) so you expect to see
(nearly) all routes.

I would approach this as follows:-
Check out if there is something in common
with the 52 interfaces that get the queues first.

Then I would get back to basics.

Check the whole network for
Interface errors on infrastructure ports.
Zero is good.

sh ip eigrp nei
shows srtt and I think also counts missed hellos.
worth a look.

I am not really sure of the significance of this
but I woud fancy checkig that all routers
with more than one link to any destination
have a feasible successor to that destination
or are load sharing.

Remember that with dynamic routing
protocols the key thing is the performance of
your feeblest router. It has to be able to
deal with all of the requests made of it.

The other thing that might go wrong is that
on a slow link updates might not be completed
before another is required. Have you any slow links?
Work out how much data is required to send the 4000
route update and figure out how long
it takes to send it on your slowest link.

Perhaps you could describe the network further.
How many routers are in the EIGRP AS.
How many EIGRP processer are there?
Are you doing summarisation?
Do you manage all of the routers?
Is the network "well designed" or
are new devices and links whacked in
as required? (you dont need to answer that:)

300 EIGRP ports sounds like quite a lot to me.

I'll stop there:)
.

Relevant Pages

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    ... eigrp interfaces comes directly from Cisco and is not that helpful. ... Their definition is "Number of routes in the packets sitting in the ... The reason for this question is that we have an EIGRP meltdown on our ... This core router has another core router attached ...
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