Question about migrating to IPv6 with multiple upstreams.

Ray Soucy rps at
Tue Jun 14 12:04:11 CDT 2011

Today you're probably correct.  If you want to have more than one
provider reliably you pretty much need to be doing BGP; or have some
sort of primary-backup setup to fail over from one to the other; or
give each host a global address from each provider (really not
desirable in the majority of networks).

I think in the long term telling everyone to jump into the BGP table
is not sustainable; and not operationally consistent with the majority
of SMB networks.

A better solution; and the one I think that will be adopted in the
long term as soon as vendors come into the fold, is to swap out
RFC1918 with ULA addressing, and swap out PAT with NPT; then use
policy routing to handle load balancing and failover the way most
"dual WAN" multifunction firewalls do today.


Each provider provides a 48-bit prefix;

Internally you use a ULA prefix; and setup prefix translation so that
the prefix gets swapped appropriately for each uplink interface.  This
provides the benefits of "NAT" used today; without the drawback of
having to do funky port rewriting and restricting incoming traffic to
mapped assignments or UPnP.

The firewall keeps track of if a connection is up or down and keeps
policy routing up to date;

You can choose to set it up to either load balance per-flow or as a
primary and backup interface.

You can handle DNS by using RFC 2136 updates for a sub-domain with a
short TTL on a hosted server to keep names up to date in the event of
a link drop.

This doesn't require cooperation from the provider; it doesn't require
knowledge of routing protocols; and it is easy to understand for
people used to the "NAT" environment.

Last time I checked, Linux still needs some work to handle ECMP
routing for IPv6, but once that is in place; combined with patches for
Network Prefix Translation (NPT), it should be trivial to implement.

My guess is within the next year we'll see something pop up that does this.


On Mon, Jun 13, 2011 at 8:48 PM, Owen DeLong <owen at> wrote:
> The vastly better option is to obtain a prefix and ASN from ARIN and merely trade BGP with your
> upstream providers.
> Prefix translation comes with all the same disabilities that are present when you do this in IPv4.
> In IPv4, everyone's software expects you to have a broken network (NAT) and there is lots of extra
> code in all of the applications to work around this.
> In iPv6, it is not unlikely that this code will eventually get removed and you will then have a high
> level of application problems in your "prefix-translated" environment.
> Owen
> On Jun 12, 2011, at 11:46 AM, Randy Carpenter wrote:
>> Prefix translation looks to be exactly what we need to do here. Thanks for all of the replies.
>> -Randy
>> On Jun 12, 2011, at 2:42, Seth Mos <seth.mos at> wrote:
>>> Op 12 jun 2011, om 03:50 heeft Randy Carpenter het volgende geschreven:
>>>> I have an interesting situation at a business that I am working on. We currently have the office set up with redundant connections for their mission critical servers and such, and also have a (cheap) cable modem for general browsing on client machines.
>>> So basically policy routing?
>>>> The interesting part is that the client machines need to access some customer networks via the main redundant network, so we have a firewall set up to route those connections via the redundant connections, and everything else via the cheaper, faster cable modem. NAT is used on both outbound connections.
>>> Yep that sounds like policy routing.
>>>> With IPv6, we are having some trouble coming up with a way to do this. Since there is no NAT, does anyone have any ideas as to how this could be accomplished?
>>> Sure there is NAT, you can use prefix translation to translate your Global Address Range from the redundant ISP to the Cable ISP Global address range when leaving that interface. I've run a similar setup with 3 independent ISPs with IPv6 netblocks.
>>> Whichever connection the traffic went out it got the right GUA mapped onto it. Note that this is 1:1 NAT and not N:1.
>>> In my case there was no primary GUA range, I used a ULA on the LAN side of things, and mapped the corresponding GUA onto it when leaving the network. I had 3 rules, 1 for each WAN and mapped the ULA/56 to the GUA/56.
>>> In your case you already have a primary connection of sorts, so I'd suggest using that on the LAN side and only map the other GUA onto it when it leaves the other interfaces.
>>> The policy routing rules on your firewall can make all the routing decissions for you.
>>> If you search google for "IPv6 network prefix translation" there will be a firewall listed that can do this somewhere in the middle of the page.
>>> Cheers,
>>> Seth

Ray Soucy

Epic Communications Specialist

Phone: +1 (207) 561-3526

Networkmaine, a Unit of the University of Maine System

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