[j-nsp] Verifying Juniper ECMP

[Chris Woodfield]

I've learned that the EX platform only allows 8 equal-cost routes. How many proxies are in your setup?

The behavior you're describing should only happen when one of the ECMP routes is either withdrawn or a new route is advertised. 

Followup question: is the flow-hashing algorithm on the EX platform a consistent hash (ring hash)? If so, only flows that were being mapped to the withdrawn route, or that would be hashed to the new route, would be affected. If it's not a consistent hash, then all flows would be re-mapped to new routes whenever there's a change in the available next-hops.

-C

On Aug 9, 2014, at 9:00 AM, ryanL <ryan.landry at gmail.com> wrote:

> oh man... this might be the answer to a long standing problem i've been having with the EX4500's at my core. they do BGP to a bunch of proxy machines (exabgp) that advertise the same /32 (as a VIP). once every so often (becoming more often as traffic grows), a TCP packet is forwarded by the EX to one of the machines which has no knowledge of the original flow. that machine of course sends back a RST and breaks the whole flow.
> 
> i've done exhaustive packet captures for juniper on this, thinking that somehow the EX was actually duplicating a packet incorrectly out one interface. but this stateless ECMP rehash for all flows every time a new flow is added or taken away makes a lot more sense to me, and also really sucks if true.
> 
> case 2014-0123-0781, if anyone at juniper is listening. that case is _still_ open.