[j-nsp] GigE: M10 <-> Cisco Catalyst 6509: oversized and corrupted frames

Josef Buchsteiner josefb at juniper.net
Fri Mar 28 09:01:12 EST 2003

At 07:14 AM 3/28/2003, Matti Saarinen wrote:
>Josef Buchsteiner <josefb at juniper.net> writes:
> >> Both ends complain about the packets they are seeing. On M10, the
> >> number in oversized frames counter increases.
> >
> > this might be normal if you use tagged interface connections
> > and the frame is longer then 1518 including FCS. Although all
> > works perfect the counter is increasing as oversizd frames.
>      Thanks, now I'm able to iterpret the counters a little bit
>      better. I do indeed use tagged frames.
> >>  The 6509 complains about corrupted IP packets, too.
> >
> > so you get checksum error when you ping the interface address
> > of the cisco ?  is this consistent ?
>      No, I don't get any errors and the errors do show up a few times
>      in a day. The interval between the errors isn't contant.
>      I attached an analyser to a another GigE port on Cisco and
>      configured the switch to copy all the traffic it receives from
>      M10 to that port. The analyser has now been scanning the packets
>      for a three days and it has seen no errors. I could be that the
>      Cisco doesn't mirror packet containing errors.

We need to differentiate between L2/L1 errors and L3 errors. In your
case it is L3. Which means also that your Analyser needs to perform
a data integrity check to catch a corrupted IP packet. It would be
good to understand if the ip header or the ip payload is corrupted
and if your Analyzer is really checking the payload for corruption.
When you performed the  mirror function have you still seen that the
6509 complains about corrupted IP packets ?

>      Still, I think that there's nothing wrong in a way Juniper sends
>      the packets. The errors must be caused by some other equipment.
>      Thanks,
>- Matti -

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