Fusion has made a lot more sense since Juniper changed the
licensing model from every switch AND the MX to just the MX.
We've deployed it in some of our sites. It is very cool from a
forwarding plane perspective, but from a control plane
standpoint it's very...meh. For example, you can't get SNMP oids
for light levels or even read them right from the CLI. You have
to log into the satellite switch like you would log into an FPC
just to get light levels. That's probably the dumbest thing
we've dealt with though. I've also heard you can have them do
local L2 forwarding, which can be nice for latency and
conserving uplink bandwidth, but we don't do any L2 that way so
I wouldn't know the implications. From what we can tell though,
it does give you Trio L3 performance and features with a MUCH
cheaper port cost which is exactly what we were looking for, the
extended reach of the chassis was just a fantastic bonus.
We also REALLY like that we can have one pair of MX dists
for a whole data center with hundreds of thousands of square
feet of raised floor and deploy QFX5100 or EX4300 switches in
every pod and haul back over just a few pairs of fiber. Saves
a lot of time because all that's required to turn up a new
connection is a cross connect in the pod. It also allows us to
offer copper ports very far away from the MX device, which
would normally require media converters.
We've wanted to experiment with doing this over dark fiber
in the metro as well, but we want to feel out any kinks
locally before we add additional failure modes.
Very interested in hearing about other's experiences with
Fusion, good, bad, and ugly.