[radvd-devel-l] Advertise different router?

[Mark Smith]

Hi,

On Wed, 01 Jun 2011 10:09:33 +0200
Dyonisius Visser <visser at terena.org> wrote:

> Hi guys
> 
> I am in the process of setting up an IPv6 only network.
> I have a dedicated VLAN for this, and assigned a /64 to it.
> Our Cisco 3750 sends RAs on this network.
> 
> I have set-up a VM with Ecdysis to do nat64, and installed bind-9.8.0 to
> do dns64. Installed dibbler as well on this VM to do DHCPv6.
> 
> So far it seems to work great, Windows 7 and iOS can connect and
> everything (except Skype) works fine.
> 
> Now it would also like to have RFC5006 RDNSS being announced in the RAs.
> Unfortunately our Cisco does not support that.
> 
> So my idea was to run radvd on the VM, so that does the RAs, and stop
> doing it on the Cisco.
> 
> However radvd advertises the prefix but with itself as the router. This
> works, but now all traffic is going through the VM, which is not what I
> want, since we Cisco has native IPv6.
> 
> Maybe I'm asking a totally stupid question, but is it possible for radvd
> to advertise a prefix with a different router? In my case I would like
> radvd to announce the prefix with the Cisco as the router.
> 

You should be able to do that with a config as follows (presuming you
only want to use DHCPv6 for address assignment), although if you're
using DHCPv6, it is probably much better to achieve your RDNSS goal
using that, leaving RAs just for configuring basic network layer
parameters, with DHCPv6 being used for stateful address assignment and all other
service/application parameters e.g. RDNS addresses, SIP, NTP etc.


interface eth0 {

	AdvSendAdvert on;

	AdvManagedFlag on; # use DHCPv6 for address assignment

	AdvDefaultLifetime 0; # stops this router being a candidate default router

	prefix 2001:db8::/64 {

		AdvAutonomous off; # stops this prefix being used by SLAAC

	};
	
	RDNSS 2001:db8::1 2001:db8::2 {
	};


};


The Cisco will announce itself with a non-zero router lifetime,
which would make it the default router. Announcing the prefix in the
Cisco's RA is optional, although it might not be too bad to leave it
doing so with matching preferred and valid lifetimes to those in radvd.
Make sure you off the AdvAutonomous bit on that too if you do announce
the prefix.


Regards,
Mark.