Re: DNS lookup for a system on the same subnet

From: Jay (root_at_127.0.0.1)
Date: 01/12/05 

Date: Tue, 11 Jan 2005 21:46:34 -0600

Hi,

Thanks for the responses.

>From some reading I found the following _might_ be the problem: Reverse
DNS lookups (even for local addresses - 192.168.x.x) timing out with
the ISP's nameservers. This problem also comes up when I SSH into the
box via VPN - after giving the password, it takes a few seconds (<10)
to get to the prompt.

If I do a traceroute from the Linux box (192.168.2.253) to the Windows
system (192.168.2.254), it is painfully slow, eventhough it is only one
hop --

# traceroute 192.168.2.254
traceroute to 192.168.2.254 (192.168.2.254), 30 hops max, 38 byte
packets
<<-- 15 sec delay -->>
 1 192.168.2.254 (192.168.2.254) 0.160 ms 0.162 ms 0.093 ms

The packets I captured with tcpdump show that for the traceroute above,
it queries the two DNS servers at the ISP... after the first server
times-out, I see an ARP request "who has 192.168.2.254? Tell
192.168.2.253". Then for some reason, it queries the second DNS server,
and obviously that times-out as well.

When I rename the file /etc/resolv.conf - everything speeds up. The
apps on Tomcat are as fast as possible, and the traceroute to Windows
is also fast.

Also, when I add the windows box's IP to the /etc/hosts file, the
delays between the systems is gone.

However, I am not sure if either of these (renaming resolv.conf or
adding _all_ local systems to the hosts file) are the right way to fix
the problem or avoid future issues.

I read online some instructions on editing the named.conf file, but
would like to be sure if that is the way to go... I don't have this
file, though I do have a named.custom file. Any pointers?

Following are some of the files:

--- begin /etc/resolv.conf---
nameserver 205.171.3.65
nameserver 198.6.1.3
search
--- end /etc/resolv.conf---

--- begin /etc/hosts (real domain name replaced by xx) ---
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1 localhost.localdomain localhost
192.168.2.253 oakdev02.xx.com oakdev02
--- end /etc/hosts ---

--- begin /etc/named.custom ---
## named.custom - custom configuration for bind
#
# Any changes not currently supported by redhat-config-bind should be
# put in this file.
#

zone "." {
        type hint;
        file "named.ca";
};

options {
        directory "/var/named/";
};

--- end /etc/named.custom ---

Note that there is no file "named.ca" on the system, and there are no
files under the directory /var/named/ .

Thanks for all the help!
Jay

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