Routing Table Entries and Sizes

Routing tables contain a list of IP addresses. Each IP address identifies a remote router (or other network gateway) that the local router is configured to recognize. For each IP address, the routing table additionally stores a network mask and other data that specifies the destination IP address ranges that remote device will accept.

Home network routers utilize a very small routing table because they simply forward all outbound traffic to the Internet Service Provider (ISP) gateway which takes care of all other routing steps. Home router tables typically contain ten or fewer entries. By comparison, the largest routers at the core of the Internet backbone must maintain the full Internet routing table that exceeds 100,000 entries and growing as the Internet expands.

Two hypothetical, partial routing table entries are shown below:

IP Address: 172.48.11.181 - Network Mask: 255.255.255.255

IP Address: 192.168.1.1 - Network Mask: 255.255.255.0

In this example, the first entry represents the route to the ISP's primary DNS server. Requests made from the home network to any destination on the Internet will be sent to the IP address 172.48.11.181 for forwarding. The second entry represents the route between any computers within the home network, where the home router has IP address 192.168.1.1.