We have two ISP connections for our office. I would like to use one ISP (ISP A) as the primary ISP for both outgoing and incoming traffic. I would like to use the Secondary ISP (ISP B) as a backup only.
I am accepting only default route from both ISPs and advertising only our "/24" prefix to both the ISPs. I use local preference to make sure ISP A is used for all outbound traffic and I use AS prepend on updates to ISP B to ensure that ISP A is used for all incoming traffic.
But, I found that some incoming traffic uses ISP B. I tried increasing the number of prepends and still see some traffic coming through ISP B. I spoke to ISP B and they say that their uplink service provider does not honor AS prepends. Hence this problem.
My question is, has anyone else come across this issue and were you able to solve the problem? (communities, etc. ).