Multiple netmasks


Kurt Zeilenga (hi!kurt@hc.dspo.gov)
28 Jul 87 16:36:54 GMT


At present, if you want to break up a network into
different size subnets there is really no way of doing it.
Hence, I would like to (re)start a discussion on ways of
implementing multiple masks for said purpose.

How does the system know wether a given address is an A, B,
or C Class address? It looks at magic bits that are
hardcoded! It would be really nice to be able to
softcode some bits. Hence, every network could have a
subnetmask. The subnetmask is used to mask out n bits of
the IP address. Those n bits are then used to lookup what
netmask to use.

Consider Host A:
/etc/ifconfig ie0 0xXXXXf001 subnetmask 0x0000c000 up
/etc/ifconfig ie1 0xXXXX0081 subnetmask 0x0000c000 up

and Host B:
/etc/ifconfig ie0 0xXXXXf002 subnetmask 0x0000c000 up
/etc/ifconfig ie1 0xXXXX8101 subnetmask 0x0000c000 up

and in /etc/subnets (or wherever) there are three fields.
Network, Subnet, Mask. This so that if you have a
gateway between to different networks each doing subnetmasking.

0xXXXX0000 0x0000c000 0xfffff000
0xXXXX0000 0x00008000 0xffffff00
0xXXXX0000 0x00004000 0xffffff80
0xXXXX0000 0x00000000 0xffffffc0

Okay, say host A gets a packet off of ie1. The packet
is for IP address 0xXXXX8102. We mask the address with
the subnetmask and get 0x00008000, lookup the netmask and
get 0xffffff00. Using it we figure out that we need to
send this to host 2 on network 0xXXXX8100. We look in the
routing table and see that we ahve a rout to 0xXXXX8100 via
0xXXXXf002, we send the packet off.....

Of course there are problems with this idea, but it's a
start. Any comments?

--
	Kurt Zeilenga	 (zeilenga@hc.dspo.gov)		I want my talk.flame!

"Remember, Mommie, I'm off to get a commie..."



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