Junos Asymmetric Routing

Jack Bates jbates at brightok.net
Fri May 28 13:08:32 UTC 2010

Ken Gilmour wrote:
> ISP1 is the default gateway, ISP2 is a backup provider but which is always
> active. Client comes in on ISP1's link, traffic goes back out on ISP1s link.
> Client comes in on ISP2's link (non default gateway) but for some reason,
> the packets seem to be going back out through the link for ISP1.

Your BGP config with ISP2 is probably unideal. This has lead to packets 
coming in via ISP2 despite the fact you prefer to use ISP1. Often, 
people only do AS Prepend to alter traffic patterns. However, if a 
packet finds it's way to your directly connected ISP, an AS Prepend is 
not enough. It will be sent to you based on local preference. Setting 
appropriate communities with your ISP can often override this preference 
so they will send the packet towards your ISP1 instead of direct.


More information about the NANOG mailing list