[nsp] PPP Multilink problem.

Gert Doering gert at greenie.muc.de
Mon Mar 17 12:11:07 EST 2003


On Mon, Mar 17, 2003 at 12:02:46PM +0100, Gert Doering wrote:
> On Tue, Mar 18, 2003 at 03:52:10AM +0530, mahesh_s wrote:
> > I have a very basic question, We have a multilink configured for 
> > 2*E1 links & the issue is the 5 min input/output on the multilink
> > interface is double the sum of indivudal interface.
> Sounds good to me.  What about this is worrying you?

Ah.  Non-native speaker, not enough coffee, too fast fingers.  Sorry.

You are right, this is not how things should be.  Your input rates look

  5 minute input rate 197000 bits/sec, 182 packets/sec

individual E1:
  5 minute input rate 96000 bits/sec, 109 packets/sec
  5 minute input rate 96000 bits/sec, 109 packets/sec

(the figures do not add up perfectly, but this might be normal due to 
the way the average is calculated.  But "roughly" it fits).

The output values are bogus:

  5 minute output rate 2153000 bits/sec, 200 packets/sec

individual E1:
  5 minute output rate 614000 bits/sec, 116 packets/sec
  5 minute output rate 463000 bits/sec, 83 packets/sec

- so from the individual rates, one should expect something along the line
of about 1100000 bits/sec for the multilink (plus minus a few per cent).

There could be a few reasons why this is happening - but most likely
you're just hitting an IOS bug.  The "5 minute output rate" counters are
something that's broken quite regularily.

I personally have had good experience with the rates on multilink
interfaces in recent 12.0S IOS versions (only bundling 64kbit BRIs,
though).  Earlier releases in all trains (11.2 12.0, 12.0S, 12.1, 12.2) 
have had all variants of broken counters.

We do not use the "5 minute ... rate" values for accounting anymore, as
they are just to unreliable (the "show int" and SNMP values for the same
interface manage to differ up to 30% - how do they do that???).  We get
the byte count values, and calculate the average values ourselves.

There are other bugs in the byte counters (counters going backwards,
counters getting "stuck" and only counting non-IP traffic) but Cisco seems
to finally get the hang on those - recent 12.0 and 12.1 mainline IOSes
seem to have fixed that, and even 12.0S seems to get there ("show int"
counters don't get stuck anymore, but for a change the SNMP counters do).


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Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert.doering at physik.tu-muenchen.de

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