Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!seismo!rutgers!ucla-cs!zen!ucbcad!ames!hc!hi!kurt From: kurt@hi.UUCP (Kurt Zeilenga) Newsgroups: comp.dcom.lans,comp.protocols.tcp-ip Subject: Multiple netmasks Message-ID: <12107@hi.UUCP> Date: Tue, 28-Jul-87 12:36:54 EDT Article-I.D.: hi.12107 Posted: Tue Jul 28 12:36:54 1987 Date-Received: Wed, 29-Jul-87 07:25:24 EDT Reply-To: kurt@hi.UUCP (Kurt Zeilenga) Organization: U. of New Mexico, Albuquerque Lines: 45 Xref: mnetor comp.dcom.lans:692 comp.protocols.tcp-ip:735 Keywords: 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..."