INTERNET-DRAFT                                                  D. Senie
Category: Informational                           Amaranth Networks Inc.
Updates: RFC 1812                                           January 1999
Expires in six months

        Changing the Default for Directed Broadcasts in Routers

Status of this Memo

   This document is an Internet-Draft. Internet-Drafts are working
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Copyright Notice

   Copyright (C) The Internet Society (1999). All Rights Reserved.

1. Introduction

   Router Requirements [1] specifies that routers must receive directed
   broadcasts, though it may contain configuration settings to disable
   this feature. While directed broadcasts have uses, their use on the
   Internet backbone appears to be comprised entirely of malicious
   attacks on other networks.

   Changing the required default for routers would help ensure new
   routers connected to the Internet do not add to the problems already

2. Discussion

   Damaging denial of service attacks led to the writing of [3] 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.

Senie                                                           [Page 1]

Internet-Draft    Default Change for Directed Broadcast     October 1998

   A recent trend in Smurf Attacks [2] 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.

3. Recommendation

   Router Requirements [1] is updated as follows. Routers MUST NOT
   process packets which are addressed to directed broadcast addresses.
   Routers MAY provide a configuration option to enable the processing
   of directed broadcasts for those situations and applications where
   this is required.

   Network service providers and corporate network operators are urged
   to ensure their networks are not susceptible to directed broadcast
   packets originating outside their networks.

4. Security Considerations

   The goal of this document is to reduce the efficacy of certain types
   of denial of service attacks.

5. References

   [1] F. Baker, "Requirements for IP Version 4 Routers", RFC1812, June

   [2] See the pages by Craig Huegen at:

   [3] P. Ferguson, D. Senie, "Ingress Filtering", RFC 2267, January

6. Author's Address

   Daniel Senie
   Amaranth Networks Inc.
   324 Still River Road
   Bolton, MA 01740

   Phone: (978) 779-6813


Senie                                                           [Page 2]