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'2') (Obsoleted by RFC 2827) -- Possible downref: Non-RFC (?) normative reference: ref. '3' ** Obsolete normative reference: RFC 2002 (ref. '4') (Obsoleted by RFC 3220) -- Possible downref: Non-RFC (?) normative reference: ref. '5' Summary: 10 errors (**), 0 flaws (~~), 6 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 INTERNET-DRAFT D. Senie 2 Category: BCP Amaranth Networks Inc. 3 Updates: RFC 1812 February 1999 4 Expires in six months 6 Changing the Default for Directed Broadcasts in Routers 8 Status of this Memo 10 This document is an Internet-Draft and is in full conformance with 11 all provisions of Section 10 of RFC2026. 13 Internet-Drafts are working documents of the Internet Engineering 14 Task Force (IETF), its areas, and its working groups. Note that other 15 groups may also distribute working documents as Internet-Drafts. 17 Internet-Drafts are draft documents valid for a maximum of six months 18 and may be updated, replaced, or obsoleted by other documents at any 19 time. It is inappropriate to use Internet-Drafts as reference 20 material or to cite them other than as "work in progress." 22 To view the list Internet-Draft Shadow Directories, see 23 http://www.ietf.org/shadow.html. 25 Copyright Notice 27 Copyright (C) The Internet Society (1999). All Rights Reserved. 29 1. Introduction 31 Router Requirements [1] specifies that routers must receive and 32 forward directed broadcasts. It also specifies that routers MUST have 33 an option to disable this feature, and that this option MUST default 34 to permit the receiving and forwarding of directed broadcasts. While 35 directed broadcasts have uses, their use on the Internet backbone 36 appears to be comprised entirely of malicious attacks on other 37 networks. 39 Changing the required default for routers would help ensure new 40 routers connected to the Internet do not add to the problems already 41 present. 43 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 44 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 45 document are to be interpreted as described in RFC 2119. 47 2. Discussion 48 Damaging denial of service attacks led to the writing of [2] on 49 Ingress Filtering. Many network providers and corporate networks have 50 endorsed the use of these methods to ensure their networks are not 51 the source of such attacks. 53 A recent trend in Smurf Attacks [3] is to target networks which 54 permit directed broadcasts from outside their networks. By permitting 55 directed broadcasts, these systems become "Smurf Amplifiers." 57 While the continued implementation of ingress filters remains the 58 best way to limit these attacks, restricting directed broadcasts 59 should also receive priority. 61 Network service providers and corporate network operators are urged 62 to ensure their networks are not susceptible to directed broadcast 63 packets originating outside their networks. 65 Mobile IP [4] had provisions for using directed broadcasts in a 66 mobile node's use of dynamic agent discovery. While some 67 implementations support this feature, it is unclear whether it is 68 useful. Other methods of achieving the same result are documented in 69 [5]. It may be worthwhile to consider removing the language on using 70 directed broadcasts as Mobile IP progresses on the standards track. 72 3. Recommendation 74 Router Requirements [1] is updated as follows: 76 Section 4.2.2.11 (d) is replaced with: 78 (d) { , -1 } 80 Directed Broadcast - a broadcast directed to the specified network 81 prefix. It MUST NOT be used as a source address. A router MAY 82 originate Network Directed Broadcast packets. A router MUST NOT 83 receive Network Directed Broadcast packets; however a router MAY 84 have a configuration option to allow reception of these packets. 85 Such an option MUST default to blocking reception. 87 Section 5.3.5.2, second paragraph replaced with: 89 A router MAY have an option to enable receiving network-prefix- 90 directed broadcasts on an interface and MAY have an option to 91 enable forwarding network-prefix-directed broadcasts. These 92 options MUST default to blocking receipt and blocking forwarding 93 of network-prefix-directed broadcasts. 95 4. Security Considerations 96 The goal of this document is to reduce the efficacy of certain types 97 of denial of service attacks. 99 5. References 101 [1] F. Baker, "Requirements for IP Version 4 Routers", RFC1812, June 102 1995. 104 [2] P. Ferguson, D. Senie, "Ingress Filtering", RFC 2267, January 105 1998. 107 [3] See the pages by Craig Huegen at: 108 http://www.quadrunner.com/~chuegen/smurf.txt. 110 [4] C. Perkins, "IP Mobility Support", RFC 2002, October 1996. 112 [5] P. Calhoun, C. Perkins, "Mobile IP Dynamic Home Address 113 Allocation Extensions", , 114 Work in progress, November 1998. 116 6. Acknowledgements 118 The author would like to thank Brandon Ross of Mindspring and Gabriel 119 Montenegro of Sun for their input. 121 6. Author's Address 123 Daniel Senie 124 Amaranth Networks Inc. 125 324 Still River Road 126 Bolton, MA 01740 128 Phone: (978) 779-6813 130 EMail: dts@senie.com