On Fri 2015-Jun-05 19:11:16 +0300, Yuriy B. Borysov <yokod...@yokodzun.kiev.ua> 
wrote:

Hello!

I got a strange problem with Filter Based Forwarding on SRX 220.

I have two uplink:

show configuration interfaces ge-0/0/0.14
description uplink1;
vlan-id 14;
family inet {
   mtu 1500;
   address x.x.x.82/29;
   address x.x.x.85/29;
   address x.x.x.86/29;
}

show configuration interfaces ge-0/0/0.18
description uplink2;
vlan-id 18;
family inet {
   mtu 1500;
   address y.y.y.114/28;
   address y.y.y.117/28;
}


Default route on ge-0/0/0.14 (x.x.x.81).

I configure destination nat on y.y.y.114:
show security nat destination rule-set port-redirect rule test
match {
   destination-address y.y.y.y/32;
   destination-port 2555;
}
then {
   destination-nat pool test;
}



Run telnet y.y.y.114 2555 and I see a strange picture:

run show security flow session destination-port 2555
Session ID: 133327, Policy name: untrust-to-trust/11, Timeout: 14, Valid
 In: 213.160.143.26/21722 --> y.y.y.114/2555;tcp, ****If: ge-0/0/0.14****, 
Pkts: 2, Bytes: 120
 Out: 10.100.0.252/25 --> 213.160.143.26/21722;tcp, If: ge-0/0/0.100, Pkts: 3, 
Bytes: 180
Total sessions: 1


Why inbound interface is ge-0/0/0.14 but not ge-0/0/0.18???


This is an issue with the interaction between FBF and flow route caching. When the packet ingresses ge-0/0/0.18, a route lookup is done for the source address within the routing table to which ge-0/0/0.18 belongs. As you mentioned, the default route for that VR/table is out ge-0/0/0.14, so the cached flow route entry is entered as such and the flow session gets installed with ge-0/0/0.14 as the "outside" interface.

I haven't found a way around this outside of sticking ge-0/0/0.18 in a totally separate virtual-router with a default route via ge-0/0/0.18's gateway and then leaking interface routes between instances as needed. With ge-0/0/0.18 in its own VR with a default gateway pointing to its next-hop, the route lookup on initial packet ingress will pick up ge-0/0/0.18 as the egress interface on the return path. It gets kinda messy, though, and I haven't really run it in production.

My past pings on this fell on deaf ears:
http://forums.juniper.net/t5/SRX-Services-Gateway/SRX110-Asymmetric-routing-with-FBF-and-remote-sourced-traffic/m-p/199115


Thanks!


No problem.



--
WBR, Yuriy B. Borysov
YOKO-UANIC | YOKO-RIPE  
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--
Hugo
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