Subject: LLMNR Issue 33: PTR via Unicast

From: Bernard Aboba <[email-masked]>
Date: Wed, 16 Apr 2003 10:19:17 -0700 (PDT)

Issue 33: PTR via Unicast
Submitter: Mika Liljeberg
Submitter email address: [email-masked]
Date first submitted: April 17, 2003
Reference:
<[email-masked]>
Document: LLMNR-16
Comment type: T
Priority: S
Section: 3
Rationale/Explanation of issue:

It occurs to me that it would be a whole lot simpler to do PTR
queries using unicast. The LLMNR resolver could use a TTL=1 when
sending the query. This way it would either get an immediate no-route
response from the local TCPIP stack, a direct response from the holder
of the address, or an ICMP time exceeded reply from the default router.
Either way, the resolver wouldn't have to do any checking on the
address. This approach has several benefits:

1) Immediate error response if there is no route for the address
2) Error response from default router if the address is off-link
3) LLMNR resolver does not need to do any checking on the address
4) Unicast is easier on the network

Note that conflict resolution for addresses is taken care by DAD, so
using unicast for PTR shouldn't make any difference there. Another
assumption is that the PTR query is already vulnerable to spoofing on
the local link, so, as long as we use TTL=1 for the query there should
be no perceivable additional risk.

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