Sign up ×
Server Fault is a question and answer site for system and network administrators. It's 100% free, no registration required.

I've got two internet accessible /24 subnets, lets say and which I want to pass to servers using a private subnet behind a PIX 506E

e.g. requests to and either both get sent to or one gets sent to and the other to (don't need to use all 254 IPs internally, can reconfigure as in future if that changes).

The subnet is already configured and working, but I can't get the PIX to do anything with the addresses.

Configuration is as follows.


  • name / ip / vlan / hardware
  • inside native eth1
  • outside native eth0
  • outside2 vlan1 eth0


  • inside > static
  • inside > static


  • outside

Access rules allow all ip and icmp traffic on (will lock those down later)

Any suggestions for where I should be looking, or further information I need to provide? Thanks.

share|improve this question
every time i see someone using vlan1 in production i die a little inside. – Zypher Jul 12 '11 at 18:12
how about explaining why this is a bad idea and helping me to make better choices, instead of just being a smart a***. – thelem Jul 14 '11 at 7:09

1 Answer 1

up vote 1 down vote accepted
  1. The PIX has no hope of figuring out what you want to do if you try and point both a 11.x.x.x and 44.x.x.x IP to the same internal IP. It has to pick one IP or the other to respond with. If you are doing raw static mapping and not port level stuff, then keep to one outside to one inside.

  2. If you are using VLAN1 then your switch had better be able to peel that off and get the packets where they need to go. And if that place is a second router then it probably won't ever work. You can only have one default route. You can't ever get random traffic from the web to go back out the interface it came in on, it always goes out the default. You gotta move up to stuff like BGP to beat that.

  3. Alternately, does the router at also route 44.55.66/24? If so, you probably don't need the VLAN1 interface and the outside2 interface. The PIX will just route the packets there. As long as that router knows to send that subnet to the PIX the static lines will be enough for the PIX to answer and pass-thru.

If 3. is the case, you should be able to drop the outside2 interface and the overlapping statics and it should just work.

share|improve this answer
1. OK, we'll go for different internal IPs then. 2. It's not our switch, it's the data centre switch. 3. We tried that but it didn't work, let me check which configuration we had for that – thelem Jul 13 '11 at 11:00
Thanks - this is now working perfectly, no vlans in sight! Turns out one of the many previous configs we'd had was right, but the data centre hadn't set it up correctly at their end! Your answer helped me understand what was happening though. – thelem Jul 13 '11 at 11:49

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.