Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

IPv6 LAN to IPv4 Internet

Hi Guys,

We have a 881G router which is connecte to internet through 3G (IPv4 DHCP).

I have been given a requirement to translate the communication from the IPv6 clients to IPv4 internet.

I have configured the DHCP part.. but I am stuck translating the IPv6 to the outgiong interface (Dialer - internet) and vice versa.

Any help would be appreciated.




IPv6 LAN to IPv4 Internet

Hi, Have you seen this configuration guide on NAT-PT?

Don't forget to rate posts that are helpful.



New Member

IPv6 LAN to IPv4 Internet

Hi Sean,

Thanks for the reply..

Yes, I have gone through that doc.

My requirement is for a NAT-PT which can translate the LAN IPs to the internet with dynamic  IPv4 (Dialer interface).

The methods shown there is from a pool of IPv6 to pool of IPv4.



New Member

IPv6 LAN to IPv4 Internet

Waaooww.. Is it not possible at all??

New Member

IPv6 LAN to IPv4 Internet

Yes, it is possible, but it is not clear what you want to do.

Do you want to translate IPv4 Outside Source to an IPv4 Outside Destination to a given inside destination?

In that case is static nat outside.

If you want to use your IPv6 to Internet connection you will have to use NAT overload exactly like you would do it for v4 in v4.

Also you might want to consider tunnelling IPv6 in IPv4 and in that case you can map your inside network (let's say 192.168.1.x) automatically to pubblicly routable IPv6 space (let's call you /64 prefix  gggg:faba:a0a0:1234::/64) you can map with nat anything coming let's say to gggg:faba:a0a0:1234:3434. to your Outgoing traffic will have the source reverse mapped. But this is inside v4 outside v6.



New Member

IPv6 LAN to IPv4 Internet

Thanks for the reply.

I want my IPv6 hosts connected at the LAN side to be able to access IPv4 Internet.

So guess it is obvious that I need the router in the middle to act as a converter and if that is the case, need to know the way to perform the config.

I have gone through the guide below, but none expalin the config for my scenario..

New Member

IPv6 LAN to IPv4 Internet

Hello Arjun,

The solution is in the document you linked:

Port Address Translation or Overload

Port Address Translation (PAT), also known as Overload, allows a single IPv4 address to be used among multiple sessions by multiplexing on the port number to associate several IPv6 users with a single IPv4 address.

This is exactly what you need. It is the equivalent of NAT Overload for IPv4 where the inside address is an IPv6 rather than an (non routable) IPv4.

This are the steps:

Configuring PAT for IPv6 to IPv4 Address Mappings

Perform this task to configure PAT for IPv6 to IPv4 address mappings. Multiple IPv6 addresses are mapped to a single IPv4 address or to a pool of IPv4 addresses and using an access list, prefix list, or route map to define which packets are to be translated.


1. enable

2. configure terminal

3. ipv6 nat v6v4 source {list access-list-name | route-map map-name} pool name overload


ipv6 nat v6v4 source {list access-list-name | route-map map-name} interface interface name overload

4. ipv6 nat v6v4 pool name start-ipv4 end-ipv4 prefix-length prefix-length

5. ipv6 nat translation [max-entries number] {timeout | udp-timeout | dns-timeout | tcp-timeout | finrst-timeout | icmp-timeout} {seconds | never}

6. ipv6 access-list access-list-name

7. permit protocol {source-ipv6-prefix/prefix-length | any | host source-ipv6-address} [operator [port-number]] {destination-ipv6-prefix/prefix-length | any | host destination-ipv6-address}

If any of these are misterious, please read about configuring NAT in

Configuring Network Address Translation: Getting Started



P.S. Please rate useful answers.

CreatePlease login to create content