[j-nsp] Strange IS-IS Problem

Eric Van Tol eric at atlantech.net
Mon Mar 8 14:01:14 EST 2010

> -----Original Message-----
> From: juniper-nsp-bounces at puck.nether.net [mailto:juniper-nsp-
> bounces at puck.nether.net] On Behalf Of Chuck Anderson
> Sent: Monday, March 08, 2010 12:55 PM
> To: Juniper-Nsp
> Subject: Re: [j-nsp] Strange IS-IS Problem
> On Mon, Mar 08, 2010 at 11:57:55AM -0500, Eric Van Tol wrote:
> > Both MTUs are consistent and always have been.  I started out with
> > 9216 physical MTU and 1500 inet MTU, but have since just deleted the
> > custom MTU and went with the defaults.  I am quite sure now that
> > this is not an MTU issue, but rather a deficiency with the EX2500.
> > I've opened up a JTAC case and will let the list know what the
> > problem turns out to be.
> But you didn't have the iso mtu set.  Which means iso was probably
> using 9216-6-6-4-2-3 = 9195 (or 9192-6-6-4-2-3 = 9171) by default for
> a VLAN encapsulated 802.2 LLC frame. Changing the inet MTU doesn't
> affect any non-IP protocols' MTUs.

Another person had previously suggested setting iso MTU, which I did, and that did not change anything.  The issue seems to be that the EX2500 is dropping the ISIS hellos upon ingress.  I've updated the JTAC case and they are attempting to replicate it in the lab.  

- evt

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