[c-nsp] MTU / BGP

[James Bensley]

On 20 July 2015 at 21:33, CiscoNSP List <CiscoNSP_list at hotmail.com> wrote:
> Well...I was on the right track with MTU, and disabling path discovery..but, Id only ever soft reset the sessions

Cool, glad its fixed. Yeah it needs a hard clear to reset the TCP session.


On 21 July 2015 at 07:43, Gert Doering <gert at greenie.muc.de> wrote:
> Hi,
>
> On Mon, Jul 20, 2015 at 08:33:10PM +0000, CiscoNSP List wrote:
>> Side note - It would be nice to be able to set mtu per neighbour purely for bgp (i.e. not have to change the physical Interface, or disable path mtu discovery)...
>
> Side note - if you have a network where path mtu discovery fails and BGP
> sessions die as a consequence, something in your network is seriously broken.
>
> Normally, even if MTUs on different links are different, pMTU discovery
> gets it sorted out nicely.
>
> Typical issues that are very much a recipe for trouble is when you have
> a single layer2 network where different devices have different layer 3
> MTUs.  Always ensure that *all* adjacent L3 devices agree on the
> IP/IPv6/MPLS MTU (and take into account the subtle differences between
> IOS, IOS XR and JunOS...).
>
> gert
>
> --
> USENET is *not* the non-clickable part of WWW!
>                                                            //www.muc.de/~gert/
> Gert Doering - Munich, Germany                             gert at greenie.muc.de
> fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de

This is more or less what I was going to say, there is an underlying
MTU problem in your network. Although an MTU setting per neighbour
knob would be nice, its only really needed as a bit of a fudge. Its
more ideal to have consistent MTUs everywhere.

Cheers,
James.