[c-nsp] jumbo MTU on WS-X6704-10GE

[Dave Temkin]

Are you positive the traffic is being thrown away?

I'm sure that someone here can give more detail, but I remember it being
standard for that oversize counter to increment even if the traffic was
still being passed for stuff over the standard MTU size.  I believe it
would be counted as an error if it wasn't being forwarded.

-Dave

On Wed, 5 Jul 2006 A.L.M.Buxey at lboro.ac.uk wrote:

> hi,
>
> run into an interesting one, wonder if someone can help.
>
> we have several 10GbE links, run from WS-X6704-10GE modules
> on Sup720 powered 6509e chassis.  2 of them dont have any requirement
> to carry jumbo frames...and on those we see no problem. however,
> one of the links is taking over from a 1GbE link (fed from WS-X6724-SFP
> modules) which had 9000 MTU traffic running through it. from the
> specs, the 10GbE module has a max of 9216..which is what the
> system jumbomtu has been set for..as well as an instruction on the
> interface to handle...so, the config for the interface looks like:
>
> interface TenGigabitEthernet2/1
>  description 10GbE jumbomtu interlink
>  mtu 9216
>  no ip address
>  logging event link-status
>  switchport
>  switchport trunk encapsulation dot1q
>  switchport trunk native vlan 708
>  switchport trunk allowed vlan 100,120,280,708,736
>  switchport mode trunk
>
> however, in the counters, we see this:
>
> 32 bit counters:
>  0.                   rxCRCAlignErrors = 0
>  1.                   rxUndersizedPkts = 0
>  2.                    rxOversizedPkts = 203234
>  3.                     rxFragmentPkts = 0
>  4.                          rxJabbers = 0
>  5.                       txCollisions = 0
>  6.                         ifInErrors = 37
>  7.                        ifOutErrors = 0
>  8.                       ifInDiscards = 37
>  9.                  ifInUnknownProtos = 37
> 10.                      ifOutDiscards = 0
> 11.            txDelayExceededDiscards = 0
> 12.                              txCRC = 0
> 13.                         linkChange = 0
> 14.                   wrongEncapFrames = 37
>
>
> on our other links, which dont have jumbo/mtu , all these values are
> a nice , beautiful '0'..which is exactly what we like to see :-)
>
> can anyone shed some info on this peculiarity?  IOS is 12.2(17d)SXB
> on all involved routers (ie those with happy 10GbE and those with errors)
>
> alan
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