Supporting Connected Routes to Subnet Zero

Supporting Connected Routes to Subnet Zero

IOS allows the network engineer to tell a router to either allow addresses on the zero subnet or not. The motivation have to does with some older IP routing protocols so did not support the use of the zero subnet. Basically, with the IP subnet-zero command configured, IOS allows the zero subnet with no restrictions. With the no IP subnet-zero command configured, the router rejects any IP address command This uses an ad Dress/mask combination for the zero subnet. For many of the more recent iOS versions, iOS allows the use of the zero subnet.

Note The error message does not mention the zero subnet, instead simply stating "Bad mask."

Note that the no IP subnet-zero command affects the local router's IP address commands, as well as the L ocal router ' s IP route commands (which define static routes). However, it does not affect the local router ' s routes as learned with a routing protocol. For example, R1 could is configured with no IP Subnet-zero, but still learn a route for a zero subnet using a routing prot Ocol.