Broadcasting Internet datagrams in the presence of subnets (RFC0922)
Original Publication Date: 1984-Oct-01
Included in the Prior Art Database: 2000-Oct-06
Internet Society Requests For Comment (RFCs)
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 , 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. , but has not been the subject of a standard.)
Network Working Group Jeffrey Mogul
Request for Comments: 922 Computer Science Department
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.
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.
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 , 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. , 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 .) Even though unreliable and limited in length, datagram
broadcasts are quite useful .
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 , token ring
networks , 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.
RFC 922 October 1984
Broadcasting Internet Datagrams in the Presence of Subnets
When a datagram is broadcast, it imposes a cost on every host that
hears it. Therefore, broadcasting should not be used
indiscriminately, but rather only when it is the best solution to a
Because broadcasting depends on the specific data link layer in use
on a local network, we must discuss it with reference to both
physical networks and logical networks.
The terms we will use in referring to physical networks are, from the
point of view of the host sending or forwarding a broadcast:
Local Hardware Network
The physical link to which the host is attached...