[c-nsp] ASR1k to ASR9k CLNS MTU problems

[Pshem Kowalczyk]

Hi,

ASR 9k calculates the MTU differently to ASR 1k. We've settled on the
9k way of calculating MTU and adjust all other platforms with "clns
mtu". Our network runs mostly on ~9100, so XR uses 9114 as interface
MTU and 9097 as CLNS MTU (calculated by XR). On other platforms (xe
and classic ios) we apply interface MTU of 9100 with "clns mtu 9083".
I'm guessing that XR takes the source/destination MAC and ethertypes
field into consideration for CLNS frames (14 bytes), but other
platforms don't. I'm not sure where the initial 9097 comes from
though.

kind regards
Pshem


On 28 May 2013 00:35, Adam Vitkovsky <adam.vitkovsky at swan.sk> wrote:
> Hi Folks,
> Has anyone encountered ISIS/CLNS MTU issues between ASR1k and ASR9k please?
>
> sh isis int / sh clns int
> - shows MTU:  9177 on both ends.
>
> debug isis adj-packets / debug isis adj det
> - shows that both routers are sending IIHs with Length 9177 -though they do
> not receive any IIHs from each other.
>
> Only after I have instructed both routers to never pad IIHs (no to check
> mtu) the adjacency came up.
> So they clearly have problems with CLNS MTU.
>
> A1k  XE 15.3(1)S1
> interface GigabitEthernet0/0/2
>  mtu 9180
>
> A9k XR 4.2.3
> interface Bundle-Ether201.3206
>  mtu 9198
>
>
> adam
>
>
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