Routing and NAT in same subnet

[Darren Durbin]

Hi,

I have the following; a Cisco 877 connected to an ADSL line with a public /29.

What I've been asked to do is make 2 of the 5 usable IP's non-NATed so they can assigned to 2 devices and then NAT 3 of the other IP's on to the 192.168.x.y internal LAN.

I assume I can create 2 VLAN's - one for the /29 and one for the internal LAN, but can I NAT ( or possibly PAT, I guess ) 3 addresses from the /29 so that they are translated on to servers that sit in the LAN ?

If I can't I guess I'll have to go

ISP ---> Cisco 877  ---> Switch ---> NATing Router ---> LAN

            (Routing the /29)         |

                                                       |

                                                Servers with public IP's

But if I can do it all on one device, all the better!

Thanks!

Darren

[Phillip Remaker]

You don't NEED to route; you can do one-to-one NATs for the two external-facing fixed-address devices in question and give them IPs on the internal network.  Then you can use an overload NAT (NAT-PT or PAT) for the rest of the subnet.  Or you can use VLANs. Or you can mix routing and NAT - all of these things are possible.  I think the one-to-one NAT for the fixed external addresses is the simpler configuration.  Or is there a reason to isolate the external servers from the inside?

In short, not only is it possible, but there are several ways to do it depending on your specific needs.