NAT explanation

Unanswered Question
Apr 30th, 2012

ip nat inside source static tcp 80 80 extendable

I have this problem too.
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Dan-Ciprian Cicioiu Tue, 05/01/2012 - 01:27


It will translate the packet arrived on

              a) outside interface with the destination IP port 80/TCP to inside port 80/TCP.

              b) inside interface with the source IP port 80/TCP that has as destination interface outside

You are NATing the inside host. Extendable will allow you to use more the one static pat (port address translation ) with the same public ip.


omerpal1190 Tue, 05/01/2012 - 01:41

ip nat inside source static

is ther any difference between this command and above-mentioned command ?

Dan-Ciprian Cicioiu Tue, 05/01/2012 - 01:50


This will allow you to

               - use the public ip only for this translation

               - translate any traffic from and to the inside host ( ) to the public ip


Peter Paluch Tue, 05/01/2012 - 12:47

Hello Dan,

Correct me please if I am wrong here but in this case:

ip nat inside source static tcp 80 80 extendable

the extendable keyword actually does nothing, as this translation is already fully specified by addresses, protocols and ports. The extendable keyword was more used with plain IP-to-IP translation and to be completely honest, to this day I have not fully understood its usage.

Best regards,


Dan-Ciprian Cicioiu Tue, 05/01/2012 - 13:14

Hi Peter,

My understanding about the extendable option is that allows you to do PAT using the same outside global.

I do now that this option is available also on ip-ip and network-network static nat...but I do not see how could you apply the extandable in those cases ( ip-ip and net-net ).

I've done a quick test :

interface FastEthernet0/0

ip address

ip nat inside

ip virtual-reassembly



interface Loopback0

ip address

ip nat outside

ip virtual-reassembly



ip route

Commands :

R1(config)#ip nat inside source static tcp 80 80

R1(config)#ip nat inside source static tcp 81 81



R1#sh run | i nat

ip nat outside

ip nat inside

ip nat inside source static tcp 80 80 extendable

ip nat inside source static tcp 81 81 extendable


The extendable keywork was automatically added.

I opened the NAT overview :

"The extendable keyword allows the user to configure several ambiguous static translations, where an ambiguous translations are translations with the same local or global address."



ricmazuru Mon, 07/22/2013 - 00:29


Guys i have a 2911 Router with 3 interfaces (GIG) and 4 wic 10/100 which is connected to my lan and the 3 interfaces are connected to 3 ISP i want the correct NAT and Access-list to send emails from my mail server on using ISP 3 who is on Gig0/2


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