How do I reserve ports for my application?

To ensure the kernel won't give out 49000 and 49001 to clients as you wish to use them for your servers on linux.

sysctl -w net.ipv4.ip_local_reserved_ports = 49000, 49001

drop it in /etc/sysctl.conf, and then run sysctl -p.

Note that this is untested.

References

• Documentation / networking / ip-sysctl.txt

Technically, there's no such thing as a "reserved port".

In TCP/UDP, the only way to "reserve" a port is to actually bind() a socket to it. A bound port will not be used by other applications; an unused port is, well, unused so other applications are free to use it.

If you are writing server software, then you can bind your sockets to specific ports as early as you want in the application code. Make the port numbers configurable, or at least clearly state them in the documentation, so that a systems administrator can quickly identify clashes and move conflicting applications to separate servers.

Actually, the above answer is not entirely accurate. The sysctls net.inet.ip.portrange.first and net.inet.ip.portrange.last specify the range of ports the OS can allocate for random ports. You would want to make sure that the range of reserved ports for your application does not fall within these variables.

Take a look in the FreeBSD Handbook, section: 12.14. Tuning Kernel Limits. But the same basic premise should apply to Linux as well.