Zeroconfig and Multicast DNS

[Pat Lashley]

> > I think that I'd reverse the default on that. There should normally be
> > no harm in having an LLA address, as long as we've got the non-LLA
> > preference stuff working correctly. It is quite likely that the LLA
> > address would never actually be used; but so what?
> >
>
> I've been thinking about that too, but I'm still not sure. The RFC
> says that you shouldn't add a LLA address to an interface that
> already is configured with a routeable address.

I think that you're referring to the first paragraph of section 1.9. That 
section appears to assume that some sort of ARP-based routing will be used by 
all parties to allow hosts with IP addresses in different (sub)nets to directly 
communicate if they are on the same segment.

That section then goes on to specify when both a routable and an IPv4 
Link-Local address MAY be assigned. Sub-paragraph 2 indicates that if a 
routable address is available on the interface, we MUST stop -advertising- the 
IPv4 Link-Local address (i.e., remove it from the mDNS records); but may keep 
(and defend) the address and accept new connections on it.

Note that this only applies to IPv4. It doesn't say that we can't continue to 
advertise an IPv6 Link-Local address. (Which makes sense; since the point of 
the restriction is to reduce problems caused by dynamically changing IP 
addresses; and that won't happen with IPv6 Link-Local.)

> Configuring LLA via rc.conf should probably be done like DHCP, by
> using a magic word in the ifconfig_ifX-line.
>
> We could have two words, one called LLA that would run in the "forced"
> mode and another LLA2 (I can't come up a good name) which would run
> in the RFC compliant way.

The problem with that is that we want to support the use of both on the same 
link. So we'd either need to allow more than one keyword, or have 'DHCP', 
'LLA', 'LLA+DHCP', etc. Neither of those is very attractive. I think it would 
be cleaner to have something like:

        ipv4-link-local-always="bge* fxp1"
        ipv4-link-local-fallback="fxp0"



-Pat