cname chain limit

[rams]

Hi ,

 

What is the cname chains limit ?

 

Thanks & Regards,

Ramesh

[Torsten]

Am Fri, 9 Jul 2010 15:08:20 +0530
schrieb rams <bram...@gmail.com>:

I've managed to get 17 cnames into a chain returned by dig. named-checkzone wouldn't mind additional cnames though. In my example zone I've put 100 cnames into a chain without any complains.

[toto@daddelkiste conf]# dig @127.0.0.1 cname-1.test a

; <<>> DiG 9.6.2-P2-RedHat-9.6.2-5.P2.fc12 <<>> @127.0.0.1 cname-1.test a
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 59028
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 17, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;cname-1.test. IN A

;; ANSWER SECTION:
cname-1.test. 43200 IN CNAME cname-2.test.
cname-2.test. 43200 IN CNAME cname-3.test.
cname-3.test. 43200 IN CNAME cname-4.test.
cname-4.test. 43200 IN CNAME cname-5.test.
cname-5.test. 43200 IN CNAME cname-6.test.
cname-6.test. 43200 IN CNAME cname-7.test.
cname-7.test. 43200 IN CNAME cname-8.test.
cname-8.test. 43200 IN CNAME cname-9.test.
cname-9.test. 43200 IN CNAME cname-10.test.
cname-10.test. 43200 IN CNAME cname-11.test.
cname-11.test. 43200 IN CNAME cname-12.test.
cname-12.test. 43200 IN CNAME cname-13.test.
cname-13.test. 43200 IN CNAME cname-14.test.
cname-14.test. 43200 IN CNAME cname-15.test.
cname-15.test. 43200 IN CNAME cname-16.test.
cname-16.test. 43200 IN CNAME cname-17.test.
cname-17.test. 43200 IN CNAME cname-18.test.

;; Query time: 0 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Fri Jul 9 12:55:50 2010
;; MSG SIZE rcvd: 413

Ciao
Torsten

[Matus UHLAR - fantomas]

On 09.07.10 15:08, rams wrote:
> What is the cname chains limit ?

the logical limit is 1. The technical limit usually depends on how big
packet can your (stub) resolver accept.
--
Matus UHLAR - fantomas, uh...@fantomas.sk ; http://www.fantomas.sk/
Warning: I wish NOT to receive e-mail advertising to this address.
Varovanie: na tuto adresu chcem NEDOSTAVAT akukolvek reklamnu postu.
I wonder how much deeper the ocean would be without sponges.

[Evan Hunt]

On Fri, Jul 09, 2010 at 03:08:20PM +0530, rams wrote:
> What is the cname chains limit ?

BIND will chase CNAME targets up to 16 times, then stop. It's a
loop-prevention method: if you have a.example.com pointing to
b.example.com which points back to a.example.com, BIND will try
16 times to find a useful target, then give up.

This has the side effect of cutting off a legitimate CNAME chain
at 17 records, but such a chain is pretty unlikely to occur in
nature.

--
Evan Hunt -- ea...@isc.org
Internet Systems Consortium, Inc.