Re: AS information available via DNS

[Havard Eidnes <]

> 	As one of the actions from the  last RIPE meeting we have been thinking
> about a nice way to have an automatic update procedure based on DNS. As a
> trial for this an auto-script has been been produced that loads current
> AS derived data into zonefiles under the domain aut-num.ripe.net. This
> has two very nice features straight away. It allows you to see a list of
> networks associated with an AS. For example...
> 
> [mature-tony-1480] host -lt txt as1104.aut-num.ripe.net
> AS1104.aut-num.ripe.net TXT     192.16.185.0
> AS1104.aut-num.ripe.net TXT     192.16.186.0
> AS1104.aut-num.ripe.net TXT     192.16.194.0
> AS1104.aut-num.ripe.net TXT     192.16.195.0
> AS1104.aut-num.ripe.net TXT     192.16.199.0
> AS1104.aut-num.ripe.net TXT     192.87.45.0

I've only one comment (I think): for large ASes there will be a lot of text
stored for a single label.  If you should try using DNS/UDP to query for
TXT for this label, default maximum DNS response packet size (512 bytes?)
will likely overflow.  If the resolver library in use followed the Host
Requirements it should notice a truncated response, and retry with TCP, but
who has a resolver library which correctly implements this?  I'm not sure
the resolver library in BIND does this right...  Witness the attached
output of "dig" and note the "tc" flag.  You could use A records instead, I
guess, and save some space in the DNS response packets, but this just
postpons the problem a short while.  I see you already did that (see
below), but I still get a truncated response to the as224.aut-num.ripe.net
query, so there you go...

However, if all you are interested in doing is zone transfers, then TCP is
already in use anyway, so maybe this is not of such a great concern.  I
should however point out that storing massive amounts of information on a
single label is fairly "unconventional use" of the DNS (?), which may
stress-test some pieces of code in new ways...

I'm not sure of what a solution to this problem should be, however, or
whether we just ignore the problem.


- Havard
skarv% dig @mature.ripe.net. as224.aut-num.ripe.net. any

; <<>> DiG 2.0 <<>> @mature.ripe.net. as224.aut-num.ripe.net. any
;; truncated answer
;; response truncated
;; ->>HEADER<<- opcode: QUERY , status: NOERROR, id: 11
;; flags: qr aa tc rd ra ; Ques: 1, Ans: 58, Auth: 0, Addit: 0
;; QUESTIONS:
;;      as224.aut-num.ripe.net, type = ANY, class = IN

;; ANSWERS:
as224.aut-num.ripe.net. 14400   NS      mature.ripe.net.
as224.aut-num.ripe.net. 14400   SOA     mature.ripe.net.  hostmaster.ripe.net. (
                        93051001        ;serial
                        14400   ;refresh
                        1800    ;retry
                        14400   ;expire
                        14400 ) ;minim

as224.aut-num.ripe.net. 14400   A       32.0.0.0
as224.aut-num.ripe.net. 14400   A       128.39.0.0
as224.aut-num.ripe.net. 14400   A       129.177.0.0
as224.aut-num.ripe.net. 14400   A       129.240.0.0
as224.aut-num.ripe.net. 14400   A       129.241.0.0
as224.aut-num.ripe.net. 14400   A       129.242.0.0
as224.aut-num.ripe.net. 14400   A       132.150.0.0
as224.aut-num.ripe.net. 14400   A       134.47.0.0
as224.aut-num.ripe.net. 14400   A       136.164.0.0
as224.aut-num.ripe.net. 14400   A       139.105.0.0
as224.aut-num.ripe.net. 14400   A       139.111.0.0
as224.aut-num.ripe.net. 14400   A       139.120.0.0
as224.aut-num.ripe.net. 14400   A       144.164.0.0
as224.aut-num.ripe.net. 14400   A       146.172.0.0
as224.aut-num.ripe.net. 14400   A       152.94.0.0
as224.aut-num.ripe.net. 14400   A       155.73.0.0
as224.aut-num.ripe.net. 14400   A       156.116.0.0
as224.aut-num.ripe.net. 14400   A       157.249.0.0
as224.aut-num.ripe.net. 14400   A       158.36.0.0
as224.aut-num.ripe.net. 14400   A       158.37.0.0
as224.aut-num.ripe.net. 14400   A       158.38.0.0
as224.aut-num.ripe.net. 14400   A       158.39.0.0
as224.aut-num.ripe.net. 14400   A       161.4.0.0
as224.aut-num.ripe.net. 14400   A       192.5.46.0
;; Sent 2 pkts, answer found in time: 305 msec
;; FROM: skarv to SERVER: mature.ripe.net.  192.87.45.6
;; WHEN: Mon May 10 23:32:43 1993
;; MSG SIZE  sent: 40  rcvd: 1012

skarv%