Junos Asymmetric Routing

Fri May 28 14:13:52 UTC 2010

Firewalls that can route and service properly multiple "untrusts"?

Good luck. Hit or miss. Constant flux.

Place a router in front of it and that will get you a ways there.

Ken Gilmour wrote:
> Hi all,
>
> I have a very peculiar situation here that i seem to have difficulty
> explaining in such a way for people to understand. I just got off the phone
> to the Juniper Devs after about 4 hours with no result. They understand the
> problem but can't seem to think of a working solution (last solution led to
> the primary firewall hard crashing and then failing over after a commit
> (which also makes me wonder what made the primary crash and not the
> secondary)). I am wondering if there is anyone "creative" on the list who
> has encountered and worked around this problem before...
>
> Here goes *sigh*
>
> ISP1 - 1.1.1.0/24
> ISP2 - 2.2.2.0/24
>
> 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.
>
> So look at it this way:
>
> SYN comes from client at 3.3.3.3 aimed at 2.2.2.2, packet is received by the
> firewall. Firewall sends a SYN/ACK but the firewall at 1.1.1.1 sees it in
> TCPDump, the firewall at 2.2.2.1 never sees it.
>
> Here's a log snippet (I can send you more if you need:
>
> May 27 21:38:49 21:38:48.1509569:CID-1:RT:  route lookup: dest-ip 3.3.3.3 *orig
> ifp reth3.0* *output_ifp reth2.0* orig-zone 19 out-zone 19 vsd 3
>
> You will see that the orig and out zones are the same zone, however this was
> a last ditch effort (putting both interfaces into one zone, effectively
> creating a swamp).
>
> Our current (non-preferred) solution is to put match-all rules on our
> Catalyst 6513s and put both providers into a swamp and the switch will then
> intercept the packets if they are destined for the wrong interface and send
> them out the right one based on a bunch of boolean.
>
> We've tried setting up a virtual instance on the offending interface and a
> firewall filter, but this had little to no effect (at one point it stopped
> passing the packets to the end machine altogether). We're using small SRX
> 650ies. Why do we want to do it this way you ask? In the event of a BGP
> session failure we need to be able to use our statically routed IPs and rely
> on someone else.
>
> Thanks!
>
> Ken
>
>