Ephemeral Source Ports

• UDP client applications typically request an ephemeral source port

• The operating system allocates the ports from a pool in round robin fashion

• • Typical range is 1024-4999 on most systems
  • Above 50000 on later Solaris versions

• The goal is to avoid using the same “socket” {srcIP, dstIP, IPproto, srcPort, dstPort} combination at the same time

• • Illegal and potentially harmful

• Some UDP applications will use their well-known server port as a client port

• • Used when there is only one client process per application
  • This is less common for TCP clients