Whether it is a Windows PC, router, switches, Linux machine or network enable device, it is recommended to stop unnecessary services that are run by default. Every running, but unused, service on your system is an unnecessary security vulnerability. Users may not even be aware that many of these services are running. Each additional service running on it may be a possible avenue for a network cracker to penetrate the system.
It is important to know the security implication of any network service before enabling it in. For example, if the telnet service is activated, a telnet client running on another device on the network can easily establish a telnet session to the system; it needs only the address of the system and the port or socket number of the network service running on the system. The rule of thumb for TCP and UDP ports is: Turn off any services or listeners that you do not need for your application to function. One way to check the list of ports running on your system is to go to one of the many web sites that can run a remote scan of your system and tell you how secure the system.
