[c-nsp] C7600 / WS-X6724-SFP interface flapping

[Kristofer Sigurdsson]

Hi list,

I've got a pretty unusual setup at one site, where I have a 7606
router (Sup720-3BXL, if that matters) with a 24 x SFP line card
(WS-X6724-SFP).  IOS 12.2(18)SXF, Advanced IP Services.

The unusual part is, that I've got 2 "loops", i.e. an interface on the
linecard connected to another interface on the same linecard.  Those
two loops are both L3 links, routed.

One loop is connected with LX fiber, the other one with copper SFP's. 
As, by default, those LAN ports have the same mac address, I changed
the mac address on all four ports involved in the loops.

Now, the problem is, that both loops flap every once in a while.  The
LX one does it every couple of days, goes down and converges back
again within about 30 secs.

The copper one, however, is worse.  Only one interface goes down, the
other one stays up (!!!).  The only way of fixing it is re-seating one
of the SFP's (doesn't seem to matter which, and this has been
happening to both SFP's, i.e. it's not always the same SFP who's
interface goes down).  Re-seating either SFP seems to bring the link
back up.

We tried replacing one of the copper SFP's, the one that had most
problems, we've had at least one failure since...that time, the new
SFP interface stayed up, the other one showed interface down.

Now I've changed the copper loop to other ports on the linecard (from
22 and 23 to 15 and 16), hoping it's a faulty chip in the line card...

The other loop is on ports 20 and 21.  We've been using port 24 for
connecting to a switch, no flaps there, and various other ports on the
line card, not participating in loops, but connecting to other devices
(copper, LX, SX, ZX) are just fine.

Has anyone seen this before?  Any points?

Thanks in advance,
Kristo