Changing the Default for Directed Broadcasts in Routers (RFC2644)
Original Publication Date: 1999-Aug-01
Included in the Prior Art Database: 2000-Sep-13
Internet Society Requests For Comment (RFCs)
Router Requirements  specifies that routers must receive and forward directed broadcasts. It also specifies that routers MUST have an option to disable this feature, and that this option MUST default to permit the receiving and forwarding of directed broadcasts. While directed broadcasts have uses, their use on the Internet backbone appears to be comprised entirely of malicious attacks on other networks.
Network Working Group D. Senie
Request for Comments: 2644 Amaranth Networks Inc.
Updates: 1812 August 1999
Category: Best Current Practice
Changing the Default for Directed Broadcasts in Routers
Status of this Memo
This document specifies an Internet Best Current Practices for the
Internet Community, and requests discussion and suggestions for
improvements. Distribution of this memo is unlimited.
Copyright (C) The Internet Society (1999). All Rights Reserved.
Router Requirements  specifies that routers must receive and
forward directed broadcasts. It also specifies that routers MUST have
an option to disable this feature, and that this option MUST default
to permit the receiving and forwarding of directed broadcasts. While
directed broadcasts have uses, their use on the Internet backbone
appears to be comprised entirely of malicious attacks on other
Changing the required default for routers would help ensure new
routers connected to the Internet do not add to the problems already
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.
Damaging denial of service attacks led to the writing of  on
Ingress Filtering. Many network providers and corporate networks have
endorsed the use of these methods to ensure their networks are not
the source of such attacks.
A recent trend in Smurf Attacks  is to target networks which
permit directed broadcasts from outside their networks. By permitting
directed broadcasts, these systems become "Smurf Amplifiers."
While the continued implementation of ingress filters remains the
best way to limit these attacks, restricting directed broadcasts
should also receive priority.
Network service providers and corporate network operators are urged
to ensure their networks are not susceptible to directed broadcast
packets originating outside their networks.
Mobile IP  had provisions for using directed broadcasts in a
mobile node's use of dynamic agent discovery. While some
implementations support this feature, it is unclear whether it is
useful. Other methods of achieving the same result are documented in
. It may be worthwhile to consider removing the language on using
directed broadcasts as Mobile IP progresses on the standards track.
Router Requirements  is updated as follows:
Section 126.96.36.199 (d) is replaced with:
Directed Broadcast - a broadcast directed to the specified network
prefix. It MUST NOT be used as a source address. A router MAY
originate Network Directed Broadcast packets. A router MAY have a
configuration option to allow...