[c-nsp] SFP-10G-LRM in Nexus 5000

[Crist J. Clark]

On our campus, we have a pair of Nexus 5596 cores connected to
5548s at the distro layer using SFP-10G-LRM optics. We ran into
some of the layer 3 limitations inherent in the 5596s and are
moving to a Catalyst 6880X core. To be safe, we just copied the
existing design and put in SFP-10G-LRM optics to link the 6880
to the 5548s. It did not go well.

The links flap at the 5548 side and eventually drop into the
"linkFlapErrDisabled" state... most of the time. Given enough
retries, minutes or hours later, they all seem to eventually
come up. And once they come up, they look OK.

Before we started, we verified the SFP-10G-LRM was supported on
6880s. After a lot of troubleshooting, we eventually realized
that the optics are NOT listed as supported for 5548s or 5596s.
That is despite the fact we've been running our campus on that
for the last three years.

We're obviously looking at getting new optics, but we're wondering
why what we have works and if it still isn't possible to get
the Nexus 5548 and Cat 6880X links to behave better.

We're working with TAC and our Cisco reps, but wonder if other
customers have experience with 5000s and SFP-10G-LRM modules.
-- 
Crist J. Clark