Is there a way that Cisco IOS can be configured to do conditonal NAT operations?
For example, as a default I want to NAT traffic coming into the router from some private IP space destined for most public space. But if the traffic on the private side needs to talk to some particular address on the public side of the router, such as a DHCP server (by IP address and/or by port), I'd like to keep the traffic un-NAT'ed.
ip address 22.214.171.124 255.255.255.192
ip nat outside
ip address 10.33.0.1 255.255.0.0
ip helper-address 126.96.36.199
ip nat inside
ip nat pool NAT-POOL 188.8.131.52 184.108.40.206 prefix-length 26
ip nat inside source list NAT-LIST pool NAT-POOL overload
ip access-list standard NAT-LIST
permit 10.33.100.0 0.0.0.255
Let's say I want to send traffic to the DHCP server at 220.127.116.11 coming from 10.33.100.0/24, but I do not want it NAT'ed. Can I play some some of trick to make an exception to the normal NAT'ing rule? I've seen some discussion that this might be done with a route-map statement, but I'm wondering if someone might be able to provide a working example.
College of William and Mary
You can use an extended ACL instead of a standard ACL and within the extended ACL deny the traffic sourcing from the group of addresses destined to the networks you don't want to NAT.
ip access-list extended NAT-LIST
deny ip 10.33.100.0 0.0.0.255 host 18.104.22.168
permit ip 10.33.100.0 0.0.0.255 any