class B delegation
Andris Kalnozols
andris at hpl.hp.com
Tue Dec 18 01:08:27 UTC 2001
> In article <9vla47$n2t at pub3.rc.vix.com>,
> Michael Kjorling <michael at kjorling.com> wrote:
> >Remember the alias law: a CNAME can not point to a CNAME.
>
> RFC 1034 seems to describe this as a good idea, but not quite a "law":
>
> Domain names in RRs which point at another name should always point at
> the primary name and not the alias. This avoids extra indirections in
> accessing information. For example, the address to name RR for the
> above host should be:
>
> 52.0.0.10.IN-ADDR.ARPA IN PTR C.ISI.EDU
>
> rather than pointing at USC-ISIC.ARPA. Of course, by the robustness
> principle, domain software should not fail when presented with CNAME
> chains or loops; CNAME chains should be followed and CNAME loops
> signalled as an error.
FWIW, here are BIND's observed limits of chasing the following CNAME chain:
$ORIGIN example.com.
cname-1 CNAME cname-2
cname-2 CNAME cname-3
...
cname-20 CNAME foo
foo CNAME 127.0.0.1
BIND 8 will chase 8 CNAMEs - if #8 points to a non-CNAME RR, you'll
get the answer. If #8 points to yet another CNAME, you'll get the
9 CNAMEs and the response code will be set to SERVFAIL.
BIND 9 will chase 16 CNAMEs - if #16 points to a non-CNAME RR, you'll
get the answer. If #16 points to yet another CNAME, you'll get the
17 CNAMEs with a NOERROR response code.
Andris
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