Ip Nat

Hi guys,
I was wondering if I can do NATing on a Cisco router if it is configured with two IPs on the same interface.
I have an interface configured with two IPs, one private IP and one public IP. I want just the public IP to be advertised by the routing protocol.
I'd like to use NAT so that devices having private IPs can access the devices on the other side of router without being advertised. Can I do this?
Any help is appreciated.

 

hi

1 i cant understand u r question
2 there r 2 interface ,in interface 1 public ip and interface 2 private ip
where do u want the second ip to configure in interface 1 r in in terface 2 in both ways it can be done

regards
karthik

 

Hey Karthik,
I'd like to configure two IP addresses on the same interface say interface 1.
ip address x.x.x.x 255.255.255.0
ip address y.y.y.y 255.255.255.0 secondary
x.x.x.x is private IP
y.y.y.y is public IP
now my question is: Can I do NATing for just the private IP? I'd like to advertise the public IP through some routing protocol and make it accessible from anywhere and at the same time employ NAT for private IP.

 

By "public" and "private" IPs are you referring to your internal and external gateways?

 

Yes. I have two sets of devices out of which one set will have 'private' internal address and the other set will have 'public' global addresses. these two sets of devices are connected to a router's interface on which two IP addresses are configured to route the traffic beween the two sets and also to the outside world. I'd like to know if I can employ NAT on the router's interface.

 

From what I've read up on, it is possible to NAT only a portion of a network without affecting the other hosts. For your second question (will the NATed host's IPs remain hidden even when communicating with the public IP-assigned hosts on the network) all instincts tell me yes. Seeing as how any traffic outbound from any host will need to pass through the router/switch before going anywhere. I haven't had much experience configuring NAT tables, but I did find this site that gives a pretty darn thorough rundown of what you can and can't do with NAT. http://www.dslreports.com/faq/cisco/40.1_NAT_VPN_ACL_CBAC_Firewall

Hope it helps! Good luck.

 

Thanks for your reply. That was a good site but it did not talk about configuring multiple IP addresses (private and public) on the same interface. So are you saying that I can NAT only a portion without affecting other hosts?

 

Yes, you should be able to.

 

Alright. I will give it a try. Can I use a routing protocol and advertise just the public subnet?