[j-nsp] Load Balancing Per Flow

[Kashif.Khawaja at Broadwing.com]

Hi All,

Have a situation where I have two links (equal cost) between two routers. On the juniper
(w/ IP II) I have per flow (the per-packet command acting on all protocols and layer-2,
layer-3 keywords under the hash-key section, all the good stuff) load balancing. After
replacing one of the FPCs, which does not even home these two links, the traffic
distribution shifted from pretty much even to 30/70. Barring the possibility of the hash
algorithm doing the least likely (experiencing an inordinate numbers of collisions) OR a
group of flows carrying heavy traffic on the highly utilized link, is there anything else
I can look at to find out where the issue resides?

The forwarding table correctly sees that it has two equal cost paths available. I enabled
per-dest. load balancing (which changed the distribution to 40/60) and then changed back
to per-flow but it did not help. Obviously, I wouldn't prefer forcing a re-hash in a way
which could impact service (at this time there is no service impact at all) especially
without first determining the root cause.

I see kb article 18082 says Juniper has seen instances where router would change to 30/70
for a short period of time (about 2 hrs.) and switch back to an almost 50/50 distribution
but in my case it has been about 2x10 hrs since this started.

As always, any suggestions would be greatly appreciated.

-Kashif.
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