[dns-operations] pathtest.isc.org and truncation (Was: EDNS issue

[Stephane Bortzmeyer]

On Fri, Feb 25, 2011 at 04:59:03PM -0600,
 Michael Graff <mgraff at isc.org> wrote 
 a message of 34 lines which said:

> Sort of like "dig 1024.pathtest.isc.org txt +bufsize=4096" ?  :)
> 
> Replace 1024 with anything you like from 1 through 4095.

Nice tool, I was not aware of it.

It seems there is a *minimum* size of 1091 bytes. After that, the
answer is not sent:

% dig +ignore @ord.sns-pb.isc.org  1024.pathtest.isc.org txt +bufsize=1090 

; <<>> DiG 9.7.1 <<>> +ignore @ord.sns-pb.isc.org 1024.pathtest.isc.org txt +bufsize=1090
; (2 servers found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 64484
;; flags: qr aa tc rd; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;1024.pathtest.isc.org.         IN      TXT

;; Query time: 99 msec
;; SERVER: 199.6.0.30#53(199.6.0.30)
;; WHEN: Mon Feb 28 09:07:43 2011
;; MSG SIZE  rcvd: 50

% dig +ignore @ord.sns-pb.isc.org  1024.pathtest.isc.org txt +bufsize=1091

; <<>> DiG 9.7.1 <<>> +ignore @ord.sns-pb.isc.org 1024.pathtest.isc.org txt +bufsize=1091
; (2 servers found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 8693
;; flags: qr aa tc rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;1024.pathtest.isc.org.         IN      TXT

;; ANSWER SECTION:
1024.pathtest.isc.org.  0       IN      TXT     "\218\139...

The TC is set if the bufsize < 1152 bytes, which is strange.