Subject: Re: LLMNR Issue 34: Unicast over TCP only

From: Joshua Graessley <[email-masked]>
Date: Thu, 24 Apr 2003 09:45:38 -0700

If unicast TCP queries with a TTL of 1 are used, it seems quite likely 
that PTR queries using LLMNR that could have succeeded will fail in 
cases where more than one ip subnet is present on the local link. If my 
machine does not have a routing entry, it will send the packet to the 
router, which will presumably decrement the TTL and put the packet back 
on the same link. Since the TTL is set to 1 my packet would be dropped. 
If I sent the same query using multicast, the device on the same link 
would have a chance to respond.

This TTL=1 setting may get us in a bind of a response to an LLMNR query 
sets the TC bit and the source address of the response is on a 
different subnet.

I also think that for queries in certain domains, LLMNR should always 
be used. It makes sense to use LLMNR for queries with names ending in 
"254.169.in-addr.arpa." and "0.8.e.f.ip6.arpa.".

I oppose issue 33, 34 and 35.

-josh

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From: Mika Liljeberg <[email-masked]>
Date: 24 Apr 2003 21:40:01 +0300

Josh,

> would have a chance to respond.

This seems a bit far fetched. Do you have a real world example in mind?

Note that if we want to support something like this, we really have no
choice but try all PTR queries with LLMNR, since there is no way to tell
which destination addresses the default router might bounce back to the
local link.

> "254.169.in-addr.arpa." and "0.8.e.f.ip6.arpa.".

I think I agree, although I would reverse this and say that it does not
make sense to send these PTR queries to a DNS server, so that phase may
be skipped.

	MikaL

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From: Joshua Graessley <[email-masked]>
Date: Thu, 24 Apr 2003 16:57:50 -0700

> which destination addresses the default router might bounce back to the

At home, I have a network with a NAT and a few global IP addresses. 
Both subnets are on the same network. I would like to be able to use 
LLMNR to resolve the names of devices with global addresses from 
devices that have NAT addresses. There are a lot of problems with this 
setup and some tweaks to routing tables would make the TTL 1 rule work. 
My concern is that if the two devices can get information using 
multicast queries, but then fail if the TC bit is set because of the 
TTL requirement, it might be a little difficult to understand what's 
going on. Then again, resolving a name to a private address won't do 
much good without the proper routing configuration on the local 
machines.

So no, I can't think of a real world example.

-josh