Supporting Connected Routes to Subnet Zero
IOS allows the network engineer to tell a router to either allow addresses in
the zero subnet or not. The motivation has to do with some older IP routing
protocols that 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 that uses
an address/mask combination for the zero subnet. For many of the more recent IOS
versions, IOS allows the use of the zero subnet.
Note that 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 local
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 be configured with no ip subnet-zero, but still
learn a route for a zero subnet using a routing protocol.
Supporting Connected Routes to Subnet Zero,布布扣,bubuko.com