[nsp] High latency

[Streiner, Justin]

On Wed, 12 Nov 2003, Kevin wrote:

> Yes I'm running BGP on the router with full routes, here's the output
> from "sh proc cpu hist"
> I am running CEF on the router also.

>                CPU% per minute (last 60 minutes)
>               * = maximum CPU%   # = average CPU%
>
> It does look like bgp scanner is running at the inteveral,
> How do I reduce the IP Input load?

Those snapshots show a picture very similar to what I saw on a
7206VXR/NPE300 shortly before I upgraded it to an NPE-G1 ;-)

If you're running CEF and all of your interfaces are configured for CEF
switching, the only other things to look at would be optimizing or
removing excess access-lists (if there are any), the possibility of
flapping interfaces that are driving the CPU load up, especially if
they're running a routing protocol.  Also look for things you don't need,
like unused features that may be on be default...

You can verify that all of your interfaces are actually running CEF by
doing a "show ip int".  If you see any that show flags like "No CEF", then
the router is process-switching or using another slower switching path to
handle packets on that interface.  That can definitely tear up CPU.
Depending on the IOS version/feature set/train, some interfaces may not be
compatible with CEF, like 802.1q trunks.

Also, are you running anything like NAT on this router?  NAT at high
traffic levels can make routers do strange things.

jms

> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net
> [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Streiner, Justin
> Sent: Wednesday, November 12, 2003 12:54 PM
> To: cisco-nsp at puck.nether.net
> Subject: Re: [nsp] High latency
>
>
> On Wed, 12 Nov 2003, Kevin wrote:
>
> > I'm having a really strange Issue with my 7513,
> > It seems like the 7513 will make the latency on any link
> > Jump up to a peak of 100ms to 400ms for a few packets then settle down
>
> > to below 1ms Then after a little while (30sec to 1min) it'll do the
> > same thing, The cpu load when this happens is around 30%-40% (this
> > load is constant during the day),
> > None of the interfaces are overloaded, it happens on all the
> interfaces.
> > Is there anything else I can do to diagnose the problem?
> > It's a 7513 with an RSP4 and 12.2(14)s3.
>
> Are you running BGP on this router?  If so, during these times of high
> latency, does the "BGP Scanner" process tear up lots of CPU when you
> look at a "sho proc cpu"?
>
> If you do a "sho proc cpu hist", do you see lots of regular spikes up to
> around 100%?
>
> If so, I'll bet what you're seeing is the BGP Scanner process walking
> the RIB.  If your router is heavily loaded and/or you're taking multiple
> full feeds this process can eat up lots of CPU and produce the latency
> you're seeing.
>
> Running CEF won't specifically cure this problem, but it can help reduce
> the amount of CPU your router spends on other tasks, particularly IP
> Input.
>
> jms
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