[c-nsp] ME3600 BFD session to A9K breaks after upgrade to 15.3(3)S1a

[Mark Tinka]

On Thursday, November 14, 2013 07:39:14 PM Jason Lixfeld 
wrote:

> The root cause was due to a fix implemented in 15.3(3)S1a
> for CSCtl54835.  Essentially, the CLNS mtu is now
> properly calculated from the L3 interface MTU whereas
> before, the CLNS MTU was always 1497 no matter what the
> L3 interface MTU was set to.  This fix was not listed in
> the list of resolved caveats for that release, but it is
> now.

Hmmh, interesting.

I've always worked with the impression that the IS-IS MTU is 
inherited from the interface MTU, both on Cisco and Juniper 
(although if my ageing photographic memory is anything to go 
by, a "show clns" might be playing back sights of 1,497 
bytes across ports that certainly had a higher physical 
MTU).

There is a special case I've encountered on a Juniper where 
this is not the case, on some SDH ports on the MX104, i.e., 
all address families supported on an interface do not 
inherit the physical interface's MTU, and end up doing their 
own thing; workaround is to set the MTU at the address 
family/protocol level. I think this was a bug that is being 
fixed.

Good to hear that Cisco have finally fixed this, although 
I'm not sure if this is specific to the ME3600X, or whether 
it affects other IOS-based platforms (might explain a few 
inconsistent things I've seen with IS-IS MTU, Hello Padding, 
e.t.c. over the years with IOS systems).

Thanks for the tip, Jason.

Cheers,

Mark.
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