reserved addresses

All valid class a,b or c addresses are allowed...

rtr#conf t Enter configuration commands, one per line. End with CNTL/Z. rtr(config)#int lo99 rtr(config-if)#ip address 192.168.1.255 255.255.255.255 rtr(config-if)# rtr(config-if)#ip address 0.0.0.0 255.255.255.255 Not a valid host address - 0.0.0.0 rtr(config-if)# rtr(config-if)#ip address 1.0.0.0 255.255.255.255 rtr(config-if)# rtr(config-if)#ip address 1.0.0.255 255.255.255.255 rtr(config-if)# rtr(config-if)#ip address 1.255.255.255 255.255.255.255 rtr(config-if)# rtr(config-if)#ip address 0.0.0.1 255.255.255.255 Not a valid host address - 0.0.0.1 rtr(config-if)#ip address 255.0.0.1 255.255.255.255 Not a valid host address - 255.0.0.1 rtr(config-if)#

As long as they don't overlap with other interfaces..

rtr(config-if)#ip address 192.168.24.99 255.255.255.0 % 192.168.24.0 overlaps with Ethernet0 rtr(config-if)# rtr(config-if)#ip address 192.168.24.99 255.255.255.255 % 192.168.24.99 overlaps with Ethernet0 rtr(config-if)#

And as long as it is not the network or broadcast address for the mask chosen:

rtr(config-if)#ip address 10.0.0.255 255.255.255.0 Bad mask /24 for address 10.0.0.255 rtr(config-if)# rtr(config-if)#ip address 10.0.255.255 255.255.0.0 Bad mask /16 for address 10.0.255.255 rtr(config-if)# rtr(config-if)#ip address 10.0.255.254 255.255.0.0 rtr(config-if)# rtr(config-if)#ip address 10.0.0.0 255.255.0.0 Bad mask /16 for address 10.0.0.0 rtr(config-if)#

You can not confugure an IP address with all "1s" in the host portion of address. It's reserved for "broadcast" address, same way as all "0s" reserved for "network address". And even with the fact that you may be able to configure this address, you will be unable to do anything with it.

Good luck,

Mike

There are special rules for /31 and /32, especially in connection with point-to-point links.

Yes it is. All of our routers use a /32 for their loopback addresses.