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NAT outside and inside


We need to configure double nat on a router, to mask inside hosts to outside

and viceversa, but it doesn't work.

If we perform ony one direction nat all work properly.

Situation is:


we need that real host connect to real host using

source natted ip and destination natted ip

This is show run

interface FastEthernet0/0

ip address

ip nat inside


interface FastEthernet0/1

ip address

ip nat outside


ip nat pool CAD netmask

ip nat inside source static

ip nat outside source list 1 pool CAD

ip classless

ip route

ip route


access-list 1 permit

I've sniffed packets on destination, and there come three packets, when I try to establish a telnet session

1) src --> dst SYN

2) src --> dst SYN ACK

3) src --> dst RST

NAT seems to work properly, but I don't understand why sender Reset connection..




Re: NAT outside and inside

To mask the outside address to the inside network, use "ip nat outside source" command and map the outside address to any private address.This will map the outside public address to the inside private network.

Since you want your outside global outside address to, use the following cmd ip nat ouside source "outside global address(use the respective ip address)" will mask the public ip address from the private network while packets arrive from global to local.

Community Member

Re: NAT outside and inside

Yes, I've configured the router in this way...

ip nat outside source to mask outside address to inside hosts, and ip nat inside source static to permit external machine to access inside machines with natted ip...

but it doesn't work, it seems to mask properly the addresses, but when I try to establish a tcp connection, it RESET immediatly...

I've sniffed traffic on destination server, there it come:

1) SYN

2) ACK

3) RST

I don't understand....

Re: NAT outside and inside

Here is a real good link to help understand the inside outside source issue.

Always make sure you have the proper routing. I have noticed sometimes a default route will not work.

Rate if it helps.



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