Cisco 2921 destination NAT for transparent proxy

Question

Hi All,
I can successfully destination-nat all outbound port 80 and 443 connections to a remote proxy server without issue, provided I use a PBR first to push any of these connections off to a Linux box.
In iptables its easy:
iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j DNAT --to <proxy ip>:80
iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 443 -j DNAT --to <proxy ip>:443
iptables -t nat -A POSTROUTING -o eth0 -d <proxy ip> -j SNAT --to <linux box IP>
I am however, trying to work out a way to do this without the need of a Linux box, except it seems at this stage that the Cisco 2900 series (IOS 15.0(1r)M16) is incapable of doing this. I just wanted to confirm from some of the experts in here if this is actually the case.
So to reiterate - I'm trying to intercept any outbound packets with destination port tcp 80 or 443 and change the destination IP to point to the remote proxy server.
The source address also needs to be changed to that of the outside interface of the router it is exiting (obviously).
Any ideas guys? I'm stuck.
Cheers,
Jordan.

Answer 1

Sounds like you need a route-map to change the next IP hop?
This would be the best way to do it which will also verify the remote proxy server is available as well.
ip sla monitor 1
type echo protocol ipIcmpEcho <ip address of your proxy server>
timeout 3000
frequency 3
ip sla monitor schedule 1 life forever start-time now
track 123 rtr 1 reachability
interface FastEthernet0/1
ip address <x.x.x.x x.x.x.x>
ip policy route-map REDIRECT-TO-PROXY
ip access-list extended webtraffic
! Deny traffic from your proxy server from redirecting
  deny tcp host <ip address of your proxy server> any eq www
  deny tcp host <ip address of your proxy server> any eq https
  permit tcp <your ip network> <subnet mask> any eq www
  permit tcp <your ip network> <subnet mask> any eq https
route-map REDIRECT-TO-PROXY permit 10
match ip address webtraffic
set ip next-hop verify-availability <ip address of your proxy server> 1 track 123
If you don't already have a NAT rule setup to translate this traffic to the outside here is an example of that:
Here is how my router is configured.
interface FastEthernet0/0
 ip address dhcp hostname home-rtr-1
 ip nat outside
interface FastEthernet0/1
 ip address 10.235.x.x 255.255.255.252
 ip nat inside
ip nat inside source list 10 interface FastEthernet0/0 overload
access-list 10 permit <your ip network> <your ip subnet>
HTH