Tnsping responses very slowly

The Oracle database 10g is running on Oracle Enterprise Linux 5. When I tried to connect to it through Oracle Net service or just tnsping it, it responses very slowly!

[oracle@gchen-pc admin]$ tnsping DB11R2

TNS Ping Utility for Linux: Version 11.2.0.1.0

Copyright (c) 1997, 2009, Oracle.  All rights reserved.

Used parameter files:
Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = gchen-pc.localdomain)(PORT = 1521))) (CONNECT_DATA = (SERVICE_NAME = DB11R2)))
OK <strong>(6030 msec)</strong>

However if I tnsping it using a physical IP, it then responses right away.

[oracle@gchen-pc admin]$ tnsping db11r2

TNS Ping Utility for Linux: Version 11.2.0.1.0

Copyright (c) 1997, 2009, Oracle.  All rights reserved.

Used parameter files:

Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = <strong>192.168.56.10</strong>)(PORT = 1521))) (CONNECT_DATA = (SERVICE_NAME = DB11R2)))
<strong>OK (0 msec)</strong>

So the slow connection must be caused by a poor DNS Resolution, rather than a slow network connection.

Check out the DNS server setting, I realized that recently I worked in a customer network, thus DNS server is still pointing to customer’s DNS server address which is not valid now.

The hostname resolution can also be performed by /etc/hosts as

192.168.56.10 gchen-pc.localdomain gchen-pc

The order in which Linux searches to resolve hostname is configured in files/etc/nsswitch.conf and /etc/host.conf

In file /etc/nsswitch.conf, look for

</pre>
<code>hosts:          files dns mdns4</code>
<pre>

In file /etc/host.conf, look for

</pre>
<code>order hosts,bind</code>
<pre>

where ‘hosts’ refers to /etc/hosts file and ‘bind’ refers DNS resolution.

Check the nsswitch.conf and host.conf man pages for details.

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