Junos Asymmetric Routing

Fri May 28 21:27:28 UTC 2010

* Ken Gilmour:

> 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.

You cannot use Juniper's software forwarding platforms in this
scenario.  This may sound like a drastic verdict, but I think it's a
pretty accurate summary of the situation.

Perhaps you can coax the software forwarding platforms into packet
mode (instead of flow mode), but from the documentation, I get the
feeling that Juniper doesn't want you to do that (at least on
J-series).  You also lose some functionality if you do that.  Moving
the filters to a different box doesn't help, either.

So you either have to buy real Juniper routers (and the necessary
service modules to implement this), or switch vendors.