NAT problem, two external IPs - how ?

[Valent]

I have wireless router, with one external and one internal network interface.
external interface - ra0 - 10.31.6.31
internal interface - eth0 - 10.31.31.1

clients in internal network use IP's 10.31.31.2-40 with default gateway 10.31.31.1

I have NAT setup with:
iptables -t nat -A POSTROUTING -s 10.31.31.0/24 -o ra0 -j MASQUERADE

is it possible to make one new client (10.31.31.39) have a different external IP (10.31.6.41) ?

I tried adding virtual interface:
ifconfig ra0:1 10.31.6.41 netmask 255.255.255.0

and adding more NAT rules:
iptables -t nat -A PREROUTING -d 10.31.6.41 -j DNAT --to-destination=10.31.31.39
iptables -t nat -A POSTROUTING -s 10.31.31.39 -j SNAT --to-source=10.31.6.41

but that doesn't work, it seams that first NAT rule overwrites all other.

So how can I setup TWO independent external IP adresses in my internal network?

I would like this:
10.31.31.1-10 to have external IP of 10.31.6.31 and
10.31.31.39 to have external IP of 10.31.6.41

Thank you in advance.

[Brian1]

Pulled this from http://www.linuxhomenetworking.com/w...Using_iptables

# PREROUTING statements for 1:1 NAT
# (Connections originating from the Internet)

iptables -t nat -A PREROUTING -d 97.158.253.26 -i eth0 \
        -j DNAT --to-destination 192.168.1.100

# POSTROUTING statements for 1:1 NAT
# (Connections originating from the home network servers)

iptables -t nat -A POSTROUTING -s 192.168.1.100 -o eth0 \
         -j SNAT --to-source 97.158.253.26

Read the sections on post routing 1 to 1 and many to 1. Since using AliasIP for the addtional IP leave out the -o eth0 in the example. Iptables does not handle Alias IP structure like eth0:0. For that use use the IP and all is fine there.

Brian
Brian

[mediator]

for having 2 ips u first need 2 NICs.

[Brian1]

You can have multiple IPs on the same nic. It is called IP Aliasing.
Don't know why I did not include this link but might help you out. http://www.faqs.org/docs/Linux-mini/IP-Alias.html

Brian

[mediator]

Yea, but IP-aliasing is for same network i.e like 10.10.10.xx , but for 2 different networks u need to have 2 NICs. But in @Valent's case IP-aliasing is possible.