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Mike S


How do SOHO routers auto-configure with IPv6?

I am trying to understand how SOHO routers will auto configure with native ISP provided IPv6. I have configured a few Cisco routers with IPv6 but it has always been a completely manual process.

Do they just receive the prefix on the WAN port, assign a full address to that port and another address to the LAN side, then start broadcasting router advertisements to the LAN?

Thanks for any clarification.

Raleigh, NC

1 recommendation

It depends *entirely* on the ISP... TR-069, PPPoE, DHCPv6, etc. IPv6 is a totally different animal. With IPv4, they're only giving you one address (in most cases), and that's set via DHCP or PPPoE. With IPv6 however, they have to feed you a LAN segment (*minimum* of a ::/64) as there's no NAT, in addition to whatever your router's link address. How all of that is communicated and how the end-user equipment uses it is completely undefined at this point.

(DHCPv6 has "prefix-deligation", but if you're handed a ::/56 (the generally agreed standard), how is your router going to use that space?)

Mike S

Interesting, so it seems that everything is so new that all the details have yet to be worked out how consumer access routers will act.

I found a thread over in the Comcast fourm about there IPv6 rollout.
»Re: [IPv6] Deployment of IPv6 Begins

It seems they are going with DHCPv6 on from the ISP and assuming stateless autoconfig on the LAN side. I'm guessing that this means that the WAN will have the generated address and the LAN will take the prefix and just append ::1 to it?



2 recommendations

In the preliminary testing that I've done with a DIR-655 and a cable modem system, this is what I saw:
The router requests a /64 for the wan address, and then a /56 for a Prefix Delegation scope (PD). It then hands out IPv6 addresses from the PD scope to devices on the LAN (and takes the ::1 for itself as you speculated).
It's all automatic and from an end user perspective, is almost identical to IPv4 DHCP.


OK, let's skip end user routers for a moment. Is there any interest in the ISP world to use router advertisement higher up the chain? I though that IPv6 aggregation was supposed to be a big selling point as it will greatly reduce the size of routing tables.

Will IPv6 be setup using statics only a la IPv4? Why not use RAs when possible?

Fort Lauderdale, FL
said by desweds :

Will IPv6 be setup using statics only a la IPv4? Why not use RAs when possible?

Depends on how you want your IPs to look. With RAs they are long and ugly.


Etobicoke, ON

1 recommendation

said by graysonf:

Depends on how you want your IPs to look. With RAs they are long and ugly.

How the IP addresses "look" is irrelevant.


Piscataway, NJ

3 recommendations

reply to cramer
Yes, most US based cable companies are deploying IPv6 dual stack with DHCPv6 prefix delegation. This means that you CPE router must support prefix delegation and it means that your cable provider is going to assign the prefix which you will use on your home lan.

Washington, DC

1 recommendation

reply to graysonf
said by graysonf:

Depends on how you want your IPs to look. With RAs they are long and ugly.

No. That's SLAAC not RA's. Router advertisements are still used (and required) for DHCPv6. They just use the managed flag.

Generally you have the following three flags:
Unmanaged - SLAAC
Assisted - SLAAC & DHCPv6
Managed - DHCPv6

There are actually a few more but most are not widely used. Check out rfc 5175

Stargate Universe fan

1 recommendation

reply to lestat99
sweetness....that's exactly what I was hoping. My (Linux) router can do DHCPv6, get a PD, then do things with that chunk of addresses (such as tweak radvd.conf and then restart it), and be on my merry way. Any other way has lots of potential problems, like having each LAN client do DHCPv6 and have the router act as a relay.

The need to run dual stack until the IPv6 transition is complete is a big limiting factor. Physically (or logically with VLANs), for v4, everything has to go through/be behind a single router with NAT. And if necessary, I can set up ND proxying for v6
English is a difficult enough language to interpret correctly when its rules are followed, let alone when a writer chooses not to follow those rules.

Jeopardy! replies and randomcaps REALLY suck!