We have four isp routers and one CSS connected to a layer 2 switch. The CSS is configured with four equal cost default routes to the routers. Since all incoming traffic is entering from the same interface of the CSS, how does the CSS know which routers to send the reply packets to?
We are experiencing problems with return packets not being sent back to the right
router. However if we reduce the isp routers to 3 from 4, things seems to work. We were told that we just got lucky with the ecmp hashing algorithm but
we could not convince others in our organization that was the case. Can you share some insights how the ecmp hashing algorithm works. And why 3 routers works better than 4 routers in our topology.