[c-nsp] converting cmts from pure ip routing to mpls pe - uBR7246VXR

[Jean-Francois.Dube at videotron.com]

Hi Aaron,

It sounds like you may be having MTU issue.

At least that is my experience when you can ping and only  browse "some"
websites.

Your CMTS is running IOS and your ASR9K is running IOS-XR.

In IOS-XR you need to account for the L2 header of 14 bytes so the
"default" MTU is 1514.

If you are running MPLS you'll need to increase the MTU even higher to
account for the extra headers/labels.

That means your CMTS interfaces should be using something like 1516 and
your ASR9K would be 1530.

Cheers,

JF

Jean-François Dubé
Technicien, Opérations Réseau IP
Ingénierie Exploitation des Réseaux
Vidéotron

cisco-nsp-bounces at puck.nether.net a écrit sur 2013-03-28 15:24:42 :

> De : "Aaron" <aaron1 at gvtc.com>
> A : <cisco-nsp at puck.nether.net>,
> Date : 2013-03-28 15:31
> Objet : [c-nsp] converting cmts from pure ip routing to mpls pe -
uBR7246VXR
> Envoyé par : cisco-nsp-bounces at puck.nether.net
>
> I have (5) cmts's (uBR7246VXR) ..4 operational and 1 in lab for testing.
>
>
>
> We have a new mpls network comprised of asr901's, me3600's and asr9k's
> functioning as p's and pe's.
>
>
>
> I wanted to move my cmts's off my traditional routed/switched network to
my
> new mpls network.  I wanted to have cmts's function as pe's so as to
> potentially take advantage of the mpls LxVPN's
>
>
>
> I successfully converted one of my cmts's to pe and it's running nicely,
> uplinked into p box (me3600).  What I did was basically convert wan
uplink
> to mpls, remove igp and replace with core mpls network igp process, and
then
> bring up the expected mp-ibgp and vrf stuff, and then convert all those
> traditional routing interfaces and services (ntp, logging, aaa and
tacacs)
> to be vrf based..works.
>
>
>
> Now for the second cmts that I wanted to convert to pe, I've tried twice
now
> and have seen similar strange behavior. wan uplink utilization drops to
> about 50% of what was previously seen before change..cpu utilization
drops
> from 30-40% utilization to about 0-10%....given those observations on the
> first attempt last week, I left it that way, thinking not too much of it
as
> it was 2:30 a.m. in the morning and was thinking that low utilization at
> that hour is conceivable. later I got woken up with a phone call from one
of
> my front-line noc network analysts at 7:15 a.m. saying that we had
several
> subs calling in saying that they could not get to most internet web pages
> but only some were reachable.. (I think the web pages they could get to
were
> our local company web site hosted on-net, and some of our local Akamai
and
> other cached pages)..strangely I could ping and trace to and from those
> subnets on that cmts to and from internet route server (looking glass)
test
> locations.. I didn't know what to make of this..i couldn't find a
problem,
> so was forced to hurry up and throw the cmts back to old switched/routed
> network.
>
>
>
> ..i tried again a few nights ago and saw similar drop in wan utilization
and
> cpu load..not knowing what to make of it, and concerned that subs would
be
> unable to get to web sites that following morning, I moved it back.  I
don't
> have a test modem off of this cmts to test with but will need to get one
out
> there if I try again.
>
>
>
> .I have a tac case open, and I am going to try to reproduce this in the
test
> cmts. (but all previous tests on the lab cmts show good results.and as I
> mentioned, the other cmts is running fine in mpls net)
>
>
>
> Difference between the one that worked and the one that doesn't is one is
> uplinked into me3600 (working one) and the one that didn't work is
uplinked
> into asr9k
>
>
>
> Interestingly, the module in the asr9k that I uplink that second cmts
into,
> crashed a couple weeks ago..it took a double ecc error and ios xr showed
a
> forced reset on that module..strange.. tac ios xr team said that it's
> probably an isolated (transient) error and shouldn't happen again, but if
it
> does, they will RMA that 2/20 module in that asr9k.   ..several
connections
> are still working on that asr9k linecard and so I didn't think that this
> second cmts being mpls uplinked through there would be an issue..but I
had
> to mention it since I'm seeing weirdness..
>
>
>
> Any thoughts or input would be appreciated.
>
>
>
> Aaron
>
>
>
>
>
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