/etc/services, a service name can have multiple (transport protocol, port number) pairs. For example, The Linux Programming Interface says:
The /etc/services file consists of lines containing three columns, as shown in the following examples:
# Service name port/protocol [aliases] http 80/tcp # Hypertext Transfer Protocol http 80/udp ssh 22/tcp # Secure Shell ssh 22/udp telnet 23/tcp # Telnet telnet 23/udp smtp 25/tcp # Simple Mail Transfer Protocol smtp 25/udp
Which field(s) can be a key in the table?
The example shows a service name can correspond to more than one transport protocols.
Given a service name and a transport protocol, can they correspond to more than one port numbers? In other words, can a service listen at two ports in the same transport protocol?