North American Network Operators Group
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Re: v6 subnet size for DSL & leased line customers

  • From: Iljitsch van Beijnum
  • Date: Tue Dec 25 08:38:12 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, [email protected] 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 that.