TNS-12542: TNS:address already in use Linux Error: 98

Problem Description
After changing listener entry while you start the oracle listener it fails with error TNS-12542 like below.

[grid@DC-DB-01 ~]$ lsnrctl start listener2

LSNRCTL for Linux: Version 11.2.0.1.0 - Production on 19-SEP-2010 11:41:48

Copyright (c) 1991, 2009, Oracle.  All rights reserved.

Starting /u01/app/11.2.0/grid/bin/tnslsnr: please wait...

TNSLSNR for Linux: Version 11.2.0.1.0 - Production
System parameter file is /u01/app/11.2.0/grid/network/admin/listener.ora
Log messages written to /u01/app/11.2.0/grid/log/diag/tnslsnr/DC-DB-01/listener2/alert/log.xml
Listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=LISTENER2)))
Listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=DC-DB-01)(PORT=1522)))
Error listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=DC-DB-01-vip)(PORT=1522)))
TNS-12542: TNS:address already in use
TNS-12560: TNS:protocol adapter error
TNS-00512: Address already in use
Linux Error: 98: Address already in use

Listener failed to start. See the error message(s) above...

The XML log file shows following message.

<msg time='2010-09-19T11:42:38.026+06:00' org_id='oracle' comp_id='tnslsnr'
 type='UNKNOWN' level='16' host_id='DC-DB-01'
 host_addr='192.168.100.101'>
<txt>Error listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=DC-DB-01-vip)(PORT=1522)))
</txt>
</msg>
<msg time='2010-09-19T11:42:38.026+06:00' org_id='oracle' comp_id='tnslsnr'
 type='UNKNOWN' level='16' host_id='DC-DB-01'
 host_addr='192.168.100.101'>
<txt>TNS-12542: TNS:address already in use
TNS-12560: TNS:protocol adapter error
TNS-00512: Address already in use
Linux Error: 98: Address already in use
</txt>
</msg>
<msg time='2010-09-19T11:42:38.027+06:00' org_id='oracle' comp_id='tnslsnr'
 type='UNKNOWN' level='16' host_id='DC-DB-01'
 host_addr='192.168.100.101'>
<txt>No longer listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=LISTENER2)))
</txt>
</msg>
<msg time='2010-09-19T11:42:38.027+06:00' org_id='oracle' comp_id='tnslsnr'
 type='UNKNOWN' level='16' host_id='DC-DB-01'
 host_addr='192.168.100.101'>
<txt>No longer listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=DC-DB-01)(PORT=1522)))
</txt>
</msg>

Here goes listener.ora file contents.

LISTENER2 =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = IPC)(KEY = LISTENER2))
      (ADDRESS = (PROTOCOL = TCP)(HOST =DC-DB-01)(PORT = 1522))
      (ADDRESS = (PROTOCOL = TCP)(HOST =DC-DB-01-vip)(PORT = 1522))      
    )
  ) 

Cause of the Problem
The "TNS-00512: Address already in use" is occurred as there is duplicate port used in same listener2 entry. It is not possible to start a listener using duplicate TCP port or IPC KEY values in a single listener.ora file configuration.

Solution of the Problem
The solution is edit the listener entry so that there does exist duplicate listener TCP port or IPC key. You can either change the port or IPC key or remove the duplicate entry. So either of the following two entries are valid.

LISTENER2 =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = IPC)(KEY = LISTENER2))
      (ADDRESS = (PROTOCOL = TCP)(HOST =DC-DB-01)(PORT = 1522))
  
    )
  ) 

or,

LISTENER2 =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = IPC)(KEY = LISTENER2))
      (ADDRESS = (PROTOCOL = TCP)(HOST =DC-DB-01)(PORT = 1522))
      (ADDRESS = (PROTOCOL = TCP)(HOST =DC-DB-01-vip)(PORT = 1523))      
    )
  )