Enabling communications between database partition servers (Linux and UNIX)

This task describes how to enable communication between the database partition servers that participate in your partitioned database system. Communication between database partition servers is handled by the Fast Communications Manager (FCM). To enable FCM, a port or port range must be reserved in the /etc/services file on each computer in your partitioned database system.

Before you begin

You must have a user ID with root user authority.

You must perform this task on all computers that participate in the instance.

About this task

The number of ports to reserve for FCM is equal to the maximum number of database partitions hosted, or potentially hosted, by any computer in the instance.

In the following example, the db2nodes.cfg file contains these entries:

0 server1 0  
1 server1 1  
2 server2 0  
3 server2 1  
4 server2 2  
5 server3 0  
6 server3 1  
7 server3 2  
8 server3 3

Assume that the FCM ports are numbered starting at 60000. In this situation:

server1 uses two ports (60000, 60001) for its two database partitions
server2 uses three ports (60000, 60001, 60002) for its three database partitions
server3 uses four ports (60000, 60001, 60002, 60003) for its four database partitions

All computers must reserve 60000, 60001, 60002, and 60003, since this is the largest port range required by any computer in the instance.

If you use a high availability solution such as Tivoli® System Automation or IBM® PowerHA® SystemMirror® for AIX® to fail over database partitions from one computer to another, you must account for potential port requirements. For example, if a computer normally hosts four database partitions, but another computer's two database partitions could potentially fail over to it, six ports must be planned for that computer.

When you create an instance, a port range is reserved on the primary computer. The primary computer is also known as the instance-owning computer. However, if the port range originally added to the /etc/services file is not sufficient for your needs, you will need to extend the range of reserved ports by manually adding additional entries.

Procedure

To enable communications between servers in a partitioned database environment using /etc/services:

Log on to the primary computer (instance owning computer) as a user with root authority.
Create an instance.
View the default port range that has been reserved in the /etc/services file.
In addition to the base configuration, the FCM ports should appear similar to the following, depending on the version of Db2®. For version 11.5.5 and older:
```
   db2c_db2inst1         50000/tcp
   #Add FCM port information 
   DB2_db2inst1          60000/tcp
   DB2_db2inst1_1        60001/tcp
   DB2_db2inst1_2        60002/tcp
   DB2_db2inst1_END      60003/tcp
```
By default on version 11.5.5 and older, the first port (50000) is reserved for connection requests, and the first available four ports above 60000 are reserved for FCM communication.
For version 11.5.6 and newer:
```
db2c_db2inst1         25000/tcp
   #Add FCM port information 
   DB2_db2inst1          20000/tcp
   DB2_db2inst1_1        20001/tcp
   DB2_db2inst1_2        20002/tcp
   DB2_db2inst1_END      20003/tcp
```
By default on version 11.5.6 and newer, the first port (25000) is reserved for connection requests, and the first available four ports above 20000 are reserved for FCM communication.
One port is for the instance-owning database partition server and three ports are for logical database partition servers that you might choose to add to the computer after installation is complete.
The port range must include a start and an END entry. Intermediate entries are optional. Explicitly including intermediate values can be useful for preventing other applications from using these ports, but these entries are not verified by the database manager.
Db2 port entries use the following format:
```
   DB2_instance_name_suffix  port_number/tcp  # comment
```
where:
- instance_name is the name of the partitioned instance.
- suffix is not used for the first FCM port. Intermediate entries are those between the lowest and highest port. If you include the intermediate entries between the first and ending FCM port, the suffix consists of an integer that you increment by one for each additional port. For example, the second port is numbered 1, and third is numbered 2, and so on to ensure uniqueness. The word END must be used as the suffix for the last entry.
- port_number is the port number that you reserve for database partition server communications.
- comment is an optional comment describing an entry.
Ensure that there are sufficient ports reserved for FCM communication.
If the range of reserved ports is insufficient, add new entries to the file.
Ensure that none of the ports that are reserved for FCM communication is the same as the port used for the svcename - TCP/IP service name configuration parameter.
For more information about defining ports in the /etc/services file, see Technote - Reference #: 1386030 .
Log on as a root user to each computer participating in the instance and add identical entries to the /etc/services file.