Zeroconfig and Multicast DNS

[Pat Lashley]

> I treat LLA and mDNS as separate things. They can be used individually
> or together. I see LLA as a way of configuring an IP-address while
> mDNS is a way of resolving DNS-like hostnames.

Don't forget service discovery. That's an important part of zeroconf, 
implemented via mDNS.

> Howevery, your statement above brings up a question, do you assume
> that a system configured with lla should be able to communicate
> with a system configured via dhcp?

Yes, of course. The question is basically the same as whether hosts on the same 
link but different IP (sub)net ranges should be able to communicate with each 
other. The answer is that either both hosts must implement ARP/RARP 
functionality, or that there be at least one additional host with addresses in 
both ranges that is willing to act as a router.

> I would assume no, per standard IP/routing rules as they would be
> in different subnets and would require a router to tell them
> about each other which somehow violates the link local scope of
> the 169.254/16 address space.

No, it does not violate the link local scope as long as the router performs NAT 
to translate the 169.254/16 address into something else.

And I don't think that the RFC forbids non-LLA hosts on the same link from 
knowing about link local addresses or communicating directly with hosts that 
only have LLAs. The important thing is that the link local addresses not be 
visible outside the link.

(Which means that we may need some special purpose code in routed to prevent it 
from advertising 169.254/16 routes.)

> Yes, discovering a NAT-router via SD is certainly possible, but I'm not
> sure if this should be in the lla-daemon or in a separate program.

I would expect it to be handled like any other service - it is a function of 
mDNS-SD, not LLA; and it is up to the service consumer to do the discovery.  In 
this case, the consumer would be some script/utility/daemon to update the 
system's routing table.



-Pat