On Wed, 2018-12-19 at 14:54 +0000, Naslund, Steve wrote:
I am wondering how a netmask could be not contiguous when the network portion of the address must be contiguous. I suppose a bit mask could certainly be anything you want but a netmask specifically identifies the network portion of an address.
Before CIDR, subnets allowed further subdividing Classful addresses and the mask bits after the network part could be non-contiguous. For a class A network the first 8 bits covered the classful network, but the remaining subnet bits did not have to be contiguous. Most network admins made the subnet part contiguous, but allowing non-contiguous subnet masks simplified the actual implementation. There was no need to check if the bits were contiguous in the code. Also subnet masks had to be the exactly the same on all devices. You could not have variable length masks. A common practice if you could get a Class B network (16 bit network part) was to use a 24 bit mask to divide the network into 254 subnetworks which was adequate for most purposes at the time. -- Smoot Carl-Mitchell System/Network Architect voice: +1 480 922-7313 cell: +1 602 421-9005 smoot@tic.com