Hello Guy
Your just not getting it.
The question is given the ip address of '74.125.127.208', how does one query
a DNS server (in this case DNS ip 8.8.8.8 = public Google DNS) to get the
reply 'bskyb-pop3-ssl.l.google.co' (which is the reply Wireshark gets), and
not the reply 'pz-in-f208.1e100.net', which is what nslookup gets back.
Regards
Richard
-----Original Message-----
From: wireshark-dev-bounces@xxxxxxxxxxxxx
[mailto:wireshark-dev-bounces@xxxxxxxxxxxxx] On Behalf Of Guy Harris
Sent: 07 January 2010 00:29
To: Developer support list for Wireshark
Subject: Re: [Wireshark-dev] How does Wireshark do name resolution?
On Jan 6, 2010, at 12:55 PM, Richard Brooks wrote:
> I think that Sky have more than one email server/mirror. Try doing an
> nslookup on '74.125.127.208', on my PC it came back as
> 'pz-inf208.1e100.net'.'
So there are at least two different A records out there in DNSland that
return 74.125.127.208.
Let's see:
$ host -a bskyb-pop3-ssl.l.google.com
Trying "bskyb-pop3-ssl.l.google.com"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 51975
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 4, ADDITIONAL: 4
;; QUESTION SECTION:
;bskyb-pop3-ssl.l.google.com. IN ANY
;; ANSWER SECTION:
bskyb-pop3-ssl.l.google.com. 211 IN A 74.125.127.208
;; AUTHORITY SECTION:
google.com. 31920 IN NS ns1.google.com.
google.com. 31920 IN NS ns3.google.com.
google.com. 31920 IN NS ns4.google.com.
google.com. 31920 IN NS ns2.google.com.
;; ADDITIONAL SECTION:
ns2.google.com. 341295 IN A 216.239.34.10
ns1.google.com. 36532 IN A 216.239.32.10
ns4.google.com. 150710 IN A 216.239.38.10
ns3.google.com. 70248 IN A 216.239.36.10
Received 197 bytes from XX.XX.XX.XX#53 in 23 ms
$ host -a pz-in-f208.1e100.net
Trying "pz-in-f208.1e100.net"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 34359
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 13, ADDITIONAL: 13
;; QUESTION SECTION:
;pz-in-f208.1e100.net. IN ANY
;; ANSWER SECTION:
pz-in-f208.1e100.net. 86351 IN A 74.125.127.208
;; AUTHORITY SECTION:
net. 17825 IN NS E.GTLD-SERVERS.net.
net. 17825 IN NS H.GTLD-SERVERS.net.
net. 17825 IN NS D.GTLD-SERVERS.net.
net. 17825 IN NS J.GTLD-SERVERS.net.
net. 17825 IN NS F.GTLD-SERVERS.net.
net. 17825 IN NS G.GTLD-SERVERS.net.
net. 17825 IN NS I.GTLD-SERVERS.net.
net. 17825 IN NS A.GTLD-SERVERS.net.
net. 17825 IN NS C.GTLD-SERVERS.net.
net. 17825 IN NS K.GTLD-SERVERS.net.
net. 17825 IN NS B.GTLD-SERVERS.net.
net. 17825 IN NS M.GTLD-SERVERS.net.
net. 17825 IN NS L.GTLD-SERVERS.net.
;; ADDITIONAL SECTION:
B.GTLD-SERVERS.net. 75602 IN A 192.33.14.30
B.GTLD-SERVERS.net. 75602 IN AAAA 2001:503:231d::2:30
F.GTLD-SERVERS.net. 85234 IN A 192.35.51.30
J.GTLD-SERVERS.net. 78545 IN A 192.48.79.30
H.GTLD-SERVERS.net. 79639 IN A 192.54.112.30
L.GTLD-SERVERS.net. 150475 IN A 192.41.162.30
I.GTLD-SERVERS.net. 155091 IN A 192.43.172.30
A.GTLD-SERVERS.net. 57911 IN A 192.5.6.30
A.GTLD-SERVERS.net. 57911 IN AAAA 2001:503:a83e::2:30
D.GTLD-SERVERS.net. 55140 IN A 192.31.80.30
K.GTLD-SERVERS.net. 109507 IN A 192.52.178.30
M.GTLD-SERVERS.net. 41034 IN A 192.55.83.30
C.GTLD-SERVERS.net. 75746 IN A 192.26.92.30
Received 507 bytes from XX.XX.XX.XX#53 in 2 ms
Both of those came from an internal server caching the results. And for the
reverse lookup:
$ host -a 74.125.127.208
Trying "208.127.125.74.in-addr.arpa"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 55402
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 4, ADDITIONAL: 4
;; QUESTION SECTION:
;208.127.125.74.in-addr.arpa. IN PTR
;; ANSWER SECTION:
208.127.125.74.in-addr.arpa. 86210 IN PTR pz-in-f208.1e100.net.
;; AUTHORITY SECTION:
125.74.in-addr.arpa. 44346 IN NS NS4.GOOGLE.COM.
125.74.in-addr.arpa. 44346 IN NS NS1.GOOGLE.COM.
125.74.in-addr.arpa. 44346 IN NS NS3.GOOGLE.COM.
125.74.in-addr.arpa. 44346 IN NS NS2.GOOGLE.COM.
;; ADDITIONAL SECTION:
NS1.GOOGLE.COM. 36446 IN A 216.239.32.10
NS3.GOOGLE.COM. 70162 IN A 216.239.36.10
NS4.GOOGLE.COM. 150624 IN A 216.239.38.10
NS2.GOOGLE.COM. 341209 IN A 216.239.34.10
Received 225 bytes from XX.XX.XX.XX#53 in 7 ms
Again, from the internal server.
Perhaps if some other server is queried, a different PTR record will come
back for 208.127.125.74.in-addr.arpa. It would be interesting to see the
DNS traffic issued when you do an nslookup on 74.125.127.208 and when
Wireshark resolves 74.125.127.208.
The problem is that the difference might just reflect configuration
differences in the resolvers, or quirks of the current implementations of
those resolvers, or something else not guaranteed to be an invariant
characteristic of whatever resolver Wireshark happens to be using (which is
a function of how it was built - it might just be using the native OS's
resolver, rather than any of the asynchronous resolvers it can be configured
to use).
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