NAT Problem

[UnaBomber]

I was having a dissusion with another engineer at my work today regarding NAT. Specifically Static NAT, for example:

ip nat inside source static [local-addr] [global-addr]

int fa0/0
ip nat inside

int s0/0
ip nat outside


The situation is that the inside is actually a public ip address and the outside is a private ip address. Dont ask, extranet type thing

Now a packet going from [local-addr] to a destination global address, will be translated on the router from the [local-addr] to the [global-addr], and our ospf routing picks up the packet and routes it to its destination with a sources address o [global-addr]. Normal right?

Now I was told that in this situation a server with a global ip address could establish a session with a local server, ie bi-directional NAT, when a packet is sent to the [global-addr] .

This to me seems wrong. If I wanted this to happen I would do another nat statement:

ip nat outside source static [global-addr] [local-addr]

Has anyone tested this?

 

[UnaBomber]

Figured it out anyway. And he was correct..

 

[fartingfrog]

Is the server with a global address on your LAN? That is a strange NAT, by the way---bass ackwards.

Tim

 

[UnaBomber]

I know, we need to give IP addresses to customers to access our network, on occasion. They nat to public IP address then we nat the public's to our network, it works.

The local address is on their network, the global address is a routable /28 address from our network, and the server is on our network with a private ip address.

UnaBomber
ccnp mcse2k

 

[fartingfrog]

Interesting. Never came across that scenario, but it sounds like it is not all that uncommon. Thanks for the info.

Tim