Subject: [Dime] Diameter Peer Discovery - A/AAAA vs. SRV

From: Stefan Winter <[email-masked]>
Date: Tue, 21 Oct 2008 08:19:31 +0200

Hello,

3588 and -bis define a peer lookup mechanism that first looks for NAPTR
records for a realm, and if that fails use an underscore construct in
conjunction with A and AAAA records:

"If no NAPTR records are found, the requester queries for those

       address records for the destination address,
       '_diameter._sctp'.realm or '_diameter._tcp'.realm.  Address
       records include A RR's, AAAA RR's or other similar records,
       chosen according to the requester's network protocol
       capabilities."

When looking into the same issue for RadSec, I received some (IMHO justified) off-list opposition. It appears to be seen as a very bad practice by a lot of DNS people to use underscore constructs in A or AAAA records.

The question had been raised why the lookup mechanism does not use SRV records as fallback after NAPTR - these were specifically designed for service discovery with underscores. The SRV RR RFC is also older than 3588, so the option to use it existed back then.

I wonder if there is a reason and/or actual deployed experience with this bit of the Diameter spec, and whether it is maybe about time to introduce SRV record lookups in 3588bis (and RadSec).

Greetings,

Stefan Winter

-- 
Stefan WINTER
Ingenieur de Recherche
Fondation RESTENA - Réseau Téléinformatique de l'Education Nationale et de la Recherche
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