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New Member

Public IP through NAT device

I want to be able to give a server on the network a public routable IP and not a private natted IP. I thought I was on the right track here, but it didn't work. I am obviously missing something.

I have the following config:

interface FastEthernet0

ip address a.b.c.d secondary

ip address

ip nat inside

speed auto


interface Serial0

ip address w.x.y.z

ip nat outside


ip nat inside source list 2 interface Serial0 overload

ip classless

ip route

no ip http server


access-list 2 permit

a.b.c.d is the public IP to be on the inside network.

w.x.y.z is the global IP address.

I am using as the private network.

Hall of Fame Super Bronze

Re: Public IP through NAT device

Can you ping the Fa0 secondary IP from the server ?

What's the server default gateway ?

Can you ping out to the internet when sourcing from Fa0 secondary IP ?

New Member

Re: Public IP through NAT device


Hall of Fame Super Bronze

Re: Public IP through NAT device


Can you elaborate a bit more ?

New Member

Re: Public IP through NAT device

I perform the ping with the following results.

Router#ping source

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:

Packet sent with a source address of


Success rate is 0 percent (0/5)


New Member

Re: Public IP through NAT device

This should have been a reply to a different message


Re: Public IP through NAT device

Depends on what address your sample ping implies

You should be able to ping with a source of a.b.c.d If this does not work then your ISP has the routing messed up.

Now if you are tring to ping between a.b.c.d and w.x.y.z you are going to have a number of issues. Partially it is that it is hard to test using the router interfaces because of how nat works. You also have issues running nat when the inside and outside interface are the same interface. This configuration is called nat on a stick but I would not recommend it as other than a last option.

It should be possible to talk between 192.168.10.x and a.b.c.d network if you have your gateways and subnets setup correctly.