what to do after received multiple NS record?

[Matus UHLAR - fantomas]

On 20.05.09 06:53, MontyRee wrote:
> If client executes recursive query, client will receive some NS records
> like below.
>  
> $ dig www.example.com
> example.com.            172800  IN      NS      a.iana-servers.net.
> example.com.            172800  IN      NS      b.iana-servers.net.
> 
> if 
> a.iana-servers.net. is local network and fast
> b.iana-servers.net. is remote network and very slow, 
>  
> 1. then, client querys most to a.iana-servers.net or randomly?

the client may prefer server that is closer, but should remember other one,
if the first fails.
BIND does that afaik.

I'm not sure what order does it process unknown servers in, I guess it's
initially in the order responses were sent.

Since BIND has options to sort responses, it would be good to use that,
since the admin may know which server is topologically closer, although I'm
not sure if this is used here and for NS records.

> 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.

>    I can't find any icmp packets or related packets.

I think bind queries servers it does not have RTT's for to find it out, then
prefers servers with shorter RTT and ocasionaly checks others if anything
changed.

> 3. below is a cache_dump.db.
>    Anyone can explain what's the meaning of TTL and srtt?

TTL is the time an entry will be valid. srtt is the response time, used for
selection described above.

> ; J.ROOT-SERVERS.NET [v4 TTL 86393] [v4 success] [v6 unexpected]
> ;       192.58.128.30 [srtt 18] [flags 00000000] [ttl 1793]
> ; k.gtld-servers.net [v4 TTL 3] [v4 success] [v6 unexpected]
> ;       192.52.178.30 [srtt 9] [flags 00000000] [ttl 1793]
> 
> If any RFC or related documents, please let me know.

I'm not sure if any rfc requires 
-- 
Matus UHLAR - fantomas, uhlar at fantomas.sk ; http://www.fantomas.sk/
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