v6 subnet size for DSL & leased line customers

Iljitsch van Beijnum iljitsch at muada.com
Tue Dec 25 13:30:20 UTC 2007

On 25 dec 2007, at 6:43, Kevin Loch wrote:

>> With router advertisements present you don't need VRRP because you  
>> have dead neighbor detection.

> And that helps the hosts on the same l2 segment that need different
> gateways how?  Or hosts with access to multiple l2 segments with
> different gateways?

In my opinion, having hosts with different default gateways on the  
same LAN is not the most desirable way to build a network. If you have  
hosts with multiple interfaces and you want to set routes on those  
host for stuff that's reachable through a router on the interface  
that's not talking to the default router, then I agree VRRP would be  
useful. But again, I would probably try to avoid a setup like that.  
(Not saying that I'm dead set against the availability of VRRP for  
IPv6, though.)

On 25 dec 2007, at 11:24, sthaug at nethelp.no wrote:

>> since for reasons passing understanding, DHCP6 specifically won't do
>> gateway assignment.

> For those of us with lots of IPv4 customers dependent on DHCP, it  
> would
> be good to know more detail about this point. What is the problem, and
> are there plans to do anything about it in DHCPv6?

It looks like many people working on DHCP for IPv6 favor a model where  
there is a separation of tasks between RAs and DHCPv6. So one does one  
thing, the other does something else. No overlap. Now I don't  
subscribe to that philosophy, because I want my hosts to learn their  
DNS servers from RAs (and finally we have RFC 5006!) but in this case  
I agree: there is no good way to make sure that what a DHCP server  
says is actually working, while a router advertising its own presence  
obviously does that.

Address configuration and everything associated with it is the place  
where IPv4 and IPv6 are really different, so don't try to copy  
existing stuff in this area to IPv6 blindly, more often than not  
that's not the most optimal approach.

There are actually some people asking for default gateways in DHCPv6.  
If this happens, it should be such that a DHCPv6 server can tell you  
which of the available gateways to prefer, but nothing stronger than  

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