Path: utzoo!mnetor!uunet!husc6!rutgers!aramis.rutgers.edu!athos.rutgers.edu!hedrick From: hedrick@athos.rutgers.edu (Charles Hedrick) Newsgroups: comp.protocols.tcp-ip Subject: Re: Who uses directed broadcasts? Message-ID: Date: 21 Mar 88 08:40:21 GMT References: <8803191947.AA19431@east.Berkeley.EDU> Organization: Rutgers Univ., New Brunswick, N.J. Lines: 28 We use directed broadcasts for at least two purposes: 1) Our kinetics Appletalk gateways use them to keep track of each other or of some hosts that provide services for them. (I'm a bit vague, since I'm not an expert with Kinetics. I support the main IP gateways, and I know I had to get directed broadcasts working properly in order to satisfy our Mac guys.) 2) The cisco gateways that we use have a concept of helper address. If a net doesn't have any servers on it, you can get a gateway to forward all requests of a certain class (those that would normally be used for booting: TFTP, bootp, timed, and named) to a specified address. FOr reliability reasons, we don't to provide several servers, so we use a subnet with lots of servers, and use directed broadcast onto that subnet. I have also done some experiments with sending messges warning of gateway reboots etc. by doing rwall to a broadcast addresss for each of the subnets affected. It seems to work. In general, I'd say the directed broadcast mechanism is useful, and that gateways should implement it. Note that the way you know whether to absorb the packet yourself or forward it onto the subnet is by whether it arrived as a physical broadcast or not. If it did, then it has already been broadcast, and you should process it as a host. If it arrives as a non-broadcast, then the sender wants you to put it out on the subnet as a broadcast. This must be implemented properly, or disaster will ensue.