Paul, if I get your meaning on this I haven't seen a lot of discussion on this topic; however I have this running on my own network. Essentially you want one address assigned to each server which you can do through a NAT inside source command, this will send the packet to the correct server. However when that server replies it will exit through the default nat pool and the address assigned to it. This is unacceptable for most Internet protocols since the host that sent the packet is receiving a response from another IP address.
In order to make this work you will need to create a NAT pool for each public address you want to use, for instance:
ip nat pool 123.123.123.98 123.123.123.98 netmask 255.255.255.248
ip nat pool 123.123.123.99 123.123.123.99 netmask 255.255.255.248
ip nat pool 123.123.123.100 123.123.123.100 netmask 255.255.255.248
ip nat pool 123.123.123.101 123.123.123.101 netmask 255.255.255.248
Next you will need to assign an access list to each of these NAT pools with the following commands
ip nat inside source list 101 interface GigabitEthernet0/1 overload <-------
ip nat inside source list 102 pool overload
ip nat inside source list 103 pool overload
ip nat inside source list 104 pool overload
ip nat inside source list 105 pool overload
The secret to making this work is building the access list correctly, what I generally will do is I will create a private address space on the lan to assign each public address to, for instance I will segment the network into blocks of 16 private addresses to each public address except for the default pool which is generally what is left over. For instance I will segment the network like this:
10.10.10.17 - 10.10.10.31 assigned to 123.123.123.98
10.10.10.33 - 10.10.10.47 assigned to 123.123.123.99
10.10.10.49 - 10.10.10.63 assigned to 123.123.123.100
10.10.10.65 - 10.10.10.79 assigned to 123.123.123.101
10.10.10.81 - 10.10.10.254 assigned to 123.123.123.102 <-------.
.
Given this the assess list would look something like this:
access-list 101 deny ip 10.10.10.16 0.0.0.15 any
access-list 101 deny ip 10.10.10.32 0.0.0.15 any
access-list 101 deny ip 10.10.10.48 0.0.0.15 any
access-list 101 deny ip 10.10.10.64 0.0.0.15 any
access-list 101 permit ip 10.10.10.0 0.0.0.255 any
access-list 102 deny ip 10.10.10.32 0.0.0.15 any
access-list 102 deny ip 10.10.10.48 0.0.0.15 any
access-list 102 deny ip 10.10.10.64 0.0.0.15 any
access-list 102 permit ip 10.10.10.16 0.0.0.15 any
access-list 103 deny ip 10.10.10.48 0.0.0.15 any
access-list 103 deny ip 10.10.10.64 0.0.0.15 any
access-list 103 permit ip 10.10.10.32.0 0.0.15 any
access-list 104 deny ip 10.10.10.64 0.0.0.15 any
access-list 104 permit ip 10.10.10.48 0.0.0.15 any
access-list 105 permit ip 10.10.10.64 0.0.0.15 any
This should accomplish what you are looking for, if you want to have multiple servers on an IP this becomes easy. Just assign a private address within the range you want for the given public address.
Cheers,
Sam
