source address

Definition of source address in The Network Encyclopedia.

What is Source Address?

The address from which a frame or packet of data originates on a network. The source address identifies the sending host to the receiving host and is used by the receiving host as a destination address for a response packet (such as an acknowledgment). Bridges also use the source address in building their internal routing tables of media access control (MAC) addresses for determining which packets should be forwarded to other network segments.

The source address refers to one of the following:

  • The physical address, such as the MAC address of an Ethernet frame
  • The logical address, such as the IP address of an Internet Protocol (IP) packet

Source addresses always identify the specific host that transmitted the packet or frame onto the network. This is in contrast to destination addresses, which sometimes direct packets to all hosts or to a specific group of hosts on the network.


You can see the source address of a packet or frame by using a network sniffer such as Network Monitor, a tool included with Microsoft Systems Management Server (SMS). Network Monitor displays source addresses in both ASCII and hexadecimal form.

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