[Dnsmasq-discuss] IPv6 routes with length between 1 and 63

David Mandelberg david at mandelberg.org
Sat Oct 23 17:37:58 UTC 2021

So after looking into this more, I think an off-link prefix isn't the 
right way to do this. It looks like 
https://datatracker.ietf.org/doc/html/rfc4191 is the standard for doing 
what I want, but dnsmasq doesn't support it, and Linux's 
accept_ra_rt_info_max_plen sysctl defaults to not accepting it. I guess 
I'll configure static routes on the clients.

Op 22-10-2021 om 18:32 schreef David Mandelberg via Dnsmasq-discuss:
> Hi,
> I'm trying to configure interfaces where dnsmasq offers addresses 
> (DHCPv4, SLAAC, and DHCPv6), on-link prefixes (DHCPv4 and RA), and 
> routes via itself to off-link prefixes, but no default routes.
> For DHCPv4, I've got this (not yet tested):
> dhcp-option=tag:routesLocal,option:router
> dhcp-option=tag:routesLocal,option:classless-static-route,, 
> dhcp-range=set:routesLocal,10.X.Y.Z,10.U.V.W
> For DHCPv6/RA, I've got this:
> enable-ra
> ra-param=infra,0,0
> dhcp-range=tag:routesLocal,fdXX:XXXX:XXXX::,off-link,48
> dhcp-range=set:routesLocal,fdXX:XXXX:XXXX:YYYY::100,fdXX:XXXX:XXXX:YYYY::1ff,slaac 
> dhcp-range=set:routesLocal,::,constructor:infra,slaac
> And I'm getting this error from the off-link line:
> prefix length must be at least 64 at line 49 of /etc/dnsmasq.conf
> So my questions are: Is off-link the right way to advertise an IPv6 
> prefix that should be routed via the host dnsmasq is running on? If it 
> is, why is it restricted to length 64 or greater? I understand why 
> on-link prefixes shouldn't be too short, but doesn't this just affect 
> the routing table, which can handle shorter prefixes?
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