RFC 922 (rfc922) - Page 1 of 12
Broadcasting Internet datagrams in the presence of subnets
Alternative Format: Original Text Document
Network Working Group Jeffrey Mogul
Request for Comments: 922 Computer Science Department
Stanford University
October 1984
BROADCASTING INTERNET DATAGRAMS IN THE PRESENCE OF SUBNETS
Status of this Memo
We propose simple rules for broadcasting Internet datagrams on local
networks that support broadcast, for addressing broadcasts, and for
how gateways should handle them.
This RFC suggests a proposed protocol for the ARPA-Internet
community, and requests discussion and suggestions for improvements.
Distribution of this memo is unlimited.
Acknowledgement
This proposal here is the result of discussion with several other
people, especially J. Noel Chiappa and Christopher A. Kent, both of
whom both pointed me at important references.
1. Introduction
The use of broadcasts, especially on high-speed local area networks,
is a good base for many applications. Since broadcasting is not
covered in the basic IP specification [12], there is no agreed-upon
way to do it, and so protocol designers have not made use of it. (The
issue has been touched upon before, e.g. [6], but has not been the
subject of a standard.)
We consider here only the case of unreliable, unsequenced, possibly
duplicated datagram broadcasts (for a discussion of TCP broadcasting,
see [10].) Even though unreliable and limited in length, datagram
broadcasts are quite useful [1].
We assume that the data link layer of the local network supports
efficient broadcasting. Most common local area networks do support
broadcast; for example, Ethernet [7, 5], ChaosNet [9], token ring
networks [2], etc.
We do not assume, however, that broadcasts are reliably delivered.
(One might consider providing a reliable datagram broadcast protocol
as a layer above IP.) It is quite expensive to guarantee delivery of
broadcasts; instead, what we assume is that a host will receive most
of the broadcasts that are sent. This is important to avoid
excessive use of broadcasts; since every host on the network devotes
at least some effort to every broadcast, they are costly.
Mogul