Path: utzoo!utgpu!water!watmath!clyde!bellcore!faline!thumper!karn From: karn@thumper.bellcore.com (Phil R. Karn) Newsgroups: comp.protocols.tcp-ip Subject: Re: default broadcast address Summary: link vs IP broadcast addresses Message-ID: <1224@thumper.bellcore.com> Date: 12 Jul 88 21:03:48 GMT References: <8807120110.AA15188@acetes.dec.com> Organization: Bell Communications Research, Inc Lines: 19 The "correct" IP address to use in broadcast packets seems to have become a perennial issue. So once again I'll point out that, in my opinion, hosts should treat any packet as a broadcast if it comes in with the LINK level broadcast address (e.g., all 1's on Ethernet). The IP destination address field in such packets should be completely IGNORED. An "out of band" indication of whether a given packet is a broadcast or not should be passed up along with the packet to the IP layer, and from there to the various transport protocols. (Certain protocols, e.g. TCP, have good reason to refuse to respond to broadcast packets). This is the only way I know to keep gateways from forwarding broadcasts from hosts with the "incorrect" IP broadcast address. When you think about it, much of an IP header (including the destination address field) is meaningless in the context of a broadcast packet anyway since broadcasts are not supposed to pass through gateways. Phil