[c-nsp] MPLS, MTU and POS (STM-1) "problems"

[Primoz Jeroncic]

On Wed, 14 Sep 2005, Primoz Jeroncic wrote:

> On Tue, 13 Sep 2005, Mikael Abrahamsson wrote:
>
> > On Tue, 13 Sep 2005, Primoz Jeroncic wrote:
> >
> > Do something like "mpls mtu 1546" on all interfaces you're running MPLS
> > on.
>
> Now while this is working on my fastethernet on test 7206vxr in my lab it
> doesn't look like it would be working in real life.
> When I finished pretty much every possible scenario on my test network I tried
> to put this in real life (instead of fastethernet I have Gigabitethernet on
> 7206vxr), I still have same problem. From all other routers in network it's
> working now, but everything what goes through 7206vxr still can't access GSR (P4)
> on other side of STM-1, even though mpls mtu is set to 1546 (and 1524 on 7206vxr)
> all over the path (on mpls enabled ports of course)

Don't bother with this problem anymore :) I guess I figured it out what was
the problem.
In lab I had routers connected with x-over cables, while in real network I
had few Catalysts inbetween. After changing mtu on Catalysts to 1546 all of
a sudden it started to work :) Based on first tests everything is running
normal but if guys on helpdesk will be complaining to me tomorrow that they
are getting bunch of calls, and I won't find any solution I will be back :)
Thanks again for all your help :)

Have fun, Primoz

>
> > > Hi everyone
> > >
> > > I know I'm probably missing something really basic here, but at 10pm after
> > > bugging with this for whole day my mind is probably not really clear
> > > anymore :)
> > > My core was pure IPv4 before and after turning on MPLS I have few
> > > strange problems. Current config (really short and stripped one) could
> > > look like this (sorry for my ascii "art"):
> > > CE1
> > > |
> > > PE1(c2811)
> > > |
> > > P1 (c7206vxr) -- PE2(c7401) -- CE2
> > > |
> > > P2 (gsr) -- P3 (gsr) -- PE3 -- CE3
> > > |
> > > P4 (gsr)
> > >
> > > All connections between CE's, PE's and P's are fastethernet or gigabitethernet
> > > links, except between P2 and P4 where I have STM-1. I have also normal (ipv4)
> > > clients connected to all PE and P's. Now I have some strange problem (at
> > > least for me at this time of day). When I try to ping with 1500bytes/packet
> > > (and DF bit set to 1) from any client it works fine from client (ipv4 client
> > > not CE) all the way to P3. But when I try to ping P4 (over STM-1) it doesn't
> > > go. When i set route-map which sets DF bit to 0 on ingress port from client to
> > > my router it works (which is right anyway). Only problem I have with this is,
> > > that I can't set those route-maps on every single ingress port I have all over
> > > my network.
> > > I would also understand this won't work if it would be constant all the way
> > > through network, but not that only problem is on STM-1 link (with MTU set to 4470
> > > bytes) while on ethernet links everything is working fine.
> > > I would appreciate if someone can suggest some solution or at least tell me
> > > it's normal that it doesn't work :)
>
>
>
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Primoz Jeroncic
Support - IP Connectivity & Routing
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