need some help to setup nslookup

[Denis Vlasenko]

On 7/27/07, Choi Jason <kbc_hyper at hotmail.com> wrote:
> Thank you
>
> Routing Table on my target is,
>
> # route
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref    Use
> Iface
> 192.168.5.0     *               255.255.255.0   U     0      0        0
> eth0
> 127.0.0.0       *               255.0.0.0       U     0      0        0 lo
> default         192.168.5.1     0.0.0.0         UG    0      0        0
> eth0
>
> and my /etc/hosts is as followings,
> # cat hosts
>
> 127.0.0.1       localhost
> 192.168.5.60    hyper3.site hyper3
> 209.131.36.158  www.yahoo.com
>
> and my /etc/resolv.conf is as followings
> search abc.net
> nameserver 4.2.2.1
>
> But I don't understand libc relate things, could you tell
> me more about this?
> Thanks in advance. :)

You can see how your target talks with DNS server, Example from my box:

# tcpdump -nlieth0 -s0 -vvv port 53 and host 172.26.128.68
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size
65535 bytes

My box asks DNS:
14:35:33.185908 IP (tos 0x0, ttl  64, id 56103, offset 0, flags [DF],
proto: UDP (17), length: 66) 172.28.3.151.33502 > 172.26.128.68.53:
[bad udp cksum 72c5!]  15029+ A? www.sdjhgfklsdjg.com. (38)

DNS answers:
14:35:33.186167 IP (tos 0x0, ttl  63, id 31911, offset 0, flags [DF],
proto: UDP (17), length: 139) 172.26.128.68.53 > 172.28.3.151.33502:
[udp sum ok]  15029 NXDomain q: A? www.sdjhgfklsdjg.com. 0/1/0 ns:
com. SOA a.gtld-servers.net. nstld.verisign-grs.com. 1185716104 1800
900 604800 900 (111)

If you see similar things, then the problem is not in your box's config.
DNS server just can't resolve names.
If you don't see answers at all, you talk to wrong/nonexistent DNS server.
If you don't see _questions_, you have routing/firewall problem on your box.
--
vda