routing table

Definition of routing table in The Network Encyclopedia.

What is a Routing Table?

An internal table that a computer or router uses to determine which router interface to send packets to, based on their destination network addresses.

Microsoft Windows platforms automatically build their own routing tables, which are used to determine whether to forward specific packets to:

  • The local network segment
  • A near-side router interface
  • The default gateway for the segment

To view the internal TCP/IP routing table on a computer running Windows 2000, Windows NT, Windows 98, or Windows 95, type route print at the command prompt.

A typical routing table looks like the following:

Active Routes:
Network Address Netmask Gateway Address Interface Metric
127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
172.16.8.0 255.255.255.0 172.16.8.50 172.16.8.50 1
172.16.8.50 255.255.255.255 127.0.0.1 127.0.0.1 1
172.16.255.255 255.255.255.255 172.16.8.50 172.16.8.50 1
224.0.0.0 224.0.0.0 172.16.8.50 172.16.8.50 1
255.255.255.255 255.255.255.255 172.16.8.50 172.16.8.50 1

This computer has a single network interface card (NIC) with the address 172.16.8.50. The columns of this table are as follows:

  • Network Address:
    A destination network address on the network

     

  • Netmask:
    The portion of the network address that must match in order for that route to be used

     

  • Gateway Address:
    Where the packet needs to be forwarded (a local NIC or a local router interface)

     

  • Interface:
    The address of the NIC through which the packet should be sent

     

  • Metric:
    The number of hops to the destination network

     

NOTE

In Microsoft Exchange Server, the routing table is the internal table that defines how messages can be routed to other sites in the Exchange organization and to foreign mail systems through installed connectors and gateways. This routing table is generally known as the Gateway Address Routing Table (GWART).