what to do after received multiple NS record?

[Mark Andrews]

In message <BLU149-W46E5DD6F8A7EAE4E31E5DC85580 at phx.gbl>, MontyRee writes:
> 
> So thanks for your kind answer.
>  
>  
> >> 2. if client received NS records(a.iana-servers.net and b.iana-servers.net)
> >> from root servers, how to check which DNS is fast or slow?
> >
> > only by sending queries and seeing reply.
> 
> But if I tested, I can't find any related packets.
> after flushing the all cache, I executed like below.
>  
> $ dig @127.0.0.1 www.example.com   (192.168.1.3 is dns client)
> 
> 19:23:49.711259 IP 192.168.1.3.12825> 192.54.112.30.domain:  58548 [1au] A? www.example.com. (44)
> 19:23:49.987665 IP 192.54.112.30.domain> 192.168.1.3.12825:  58548- 0/2/3 (124)
> 19:23:49.987903 IP 192.168.1.3.29328> 192.112.36.4.domain:  57596% [1au] A? a.iana-servers.net. (47)
> 19:23:49.987971 IP 192.168.1.3.29630> 192.112.36.4.domain:  57429% [1au] A? b.iana-servers.net. (47)
> 19:23:50.139827 IP 192.112.36.4.domain> 192.168.1.3.29328:  57596- 0/13/16 (532)
> 19:23:50.140108 IP 192.112.36.4.domain> 192.168.1.3.29630:  57429- 0/13/16 (532)
> 19:23:50.140265 IP 192.168.1.3.11208> 192.48.79.30.domain:  56734% [1au] A? a.iana-servers.net. (47)
> 19:23:50.140476 IP 192.168.1.3.64270> 192.48.79.30.domain:  19705% [1au] A? b.iana-servers.net. (47)
> 19:23:50.207358 IP 192.48.79.30.domain> 192.168.1.3.11208:  56734- 1/5/4 A 192.0.34.43 (212)
> 19:23:50.207365 IP 192.48.79.30.domain> 192.168.1.3.64270:  19705- 1/5/4 A 193.0.0.236 (214)
> 19:23:50.207703 IP 192.168.1.3.58817> 193.0.0.236.domain:  59823 [1au] A? www.example.com. (44)
> 19:23:50.482477 IP 193.0.0.236.domain> 192.168.1.3.58817:  59823*- 1/2/3 A 208.77.188.166 (140)
>  
>  
> as you see, two dns serves are 192.0.34.43 and 193.0.0.236. but dns client only 
> querys to 193.0.0.236 without any reply from 192.0.34.43.

	named works out the rtt as a side effect of ordinary queries.
	For zones that are queried often it will home in on the
	closest server (in network terms).  For zones that are
	queried once or twice the rtt processing doesn't provide
	any benefit.
  
> Thanks again.
>  
> bind-users mailing list
> bind-users at lists.isc.org
> https://lists.isc.org/mailman/listinfo/bind-users

-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews at isc.org