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IETF RFC 6441



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Internet Engineering Task Force (IETF)                         L. Vegoda
Request for Comments: 6441                                         ICANN
BCP: 171                                                   November 2011
Category: Best Current Practice 
ISSN: 2070-1721


       Time to Remove Filters for Previously Unallocated IPv4 /8s

 Abstract

   It has been common for network administrators to filter IP traffic
   from and BGP prefixes of unallocated IPv4 address space.  Now that
   there are no longer any unallocated IPv4 /8s, this practise is more
   complicated, fragile, and expensive.  Network administrators are
   advised to remove filters based on the registration status of the
   address space.

   This document explains why any remaining packet and BGP prefix
   filters for unallocated IPv4 /8s should now be removed on border
   routers and documents those IPv4 unicast prefixes that should not be
   routed across the public Internet.

 Status of This Memo

   This memo documents an Internet Best Current Practice.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   BCPs is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/RFC 6441.

 Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must



Vegoda                    Best Current Practice              PAGE 1 top


RFC 6441 Remove /8 Filters November 2011 include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Traffic Filtering Options . . . . . . . . . . . . . . . . . . . 3 3.1. No Longer Filtering Based on Address Registration Status . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.2. Continuing to Filter Traffic from Unallocated IPv4 Space . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Prefixes That Should Not be Routed across the Internet . . . . 3 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 3 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 4 6.1. Normative References . . . . . . . . . . . . . . . . . . . 4 6.2. Informative References . . . . . . . . . . . . . . . . . . 4 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 5 1. Introduction It has been common for network administrators to filter IP traffic from and BGP prefixes of unallocated IPv4 address space. Now that there are no longer any unallocated IPv4 /8s, this practise is more complicated, fragile, and expensive. Network administrators are advised to remove filters based on the registration status of the address space. This document explains why any remaining packet and BGP prefix filters for unallocated IPv4 /8s should now be removed on border routers and documents those IPv4 unicast prefixes that should not be routed across the public Internet. 2. Terminology 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 BCP 14, RFC 2119 [RFC 2119]. Martians [RFC 1208] is a humorous term applied to packets that turn up unexpectedly on the wrong network because of bogus routing entries. It is also used as a name for a packet that has an altogether bogus (non-registered or ill-formed) Internet address. Bogons [RFC 3871] are packets sourced from addresses that have not yet been allocated Vegoda Best Current Practice PAGE 2 top

RFC 6441 Remove /8 Filters November 2011 by IANA or the Regional Internet Registries (RIRs), or addresses reserved for private or special use by RFCs [RFC 5735]. Bogons are referred to as "Dark IP" in some circles. 3. Traffic Filtering Options 3.1. No Longer Filtering Based on Address Registration Status Network administrators who implemented filters for unallocated IPv4 /8s did so in the knowledge that those /8s were not a legitimate source of traffic on the Internet and that there was a small number of bogon filters to implement. Now that there are no longer any unallocated unicast IPv4 /8s, there will be legitimate Internet traffic coming from all unicast /8s that are not reserved for special purposes in an RFC. Removing packet and prefix filters based on the registration status of the IPv4 address is a simple approach that will avoid blocking legitimate Internet traffic. Network operators SHOULD remove both ingress and egress packet filters as well as BGP prefix filters for previously unallocated IPv4 /8s. 3.2. Continuing to Filter Traffic from Unallocated IPv4 Space Some network administrators might want to continue filtering unallocated IPv4 addresses managed by the RIRs. This requires significantly more granular ingress filters and the highly dynamic nature of the RIRs' address pools means that filters need to be updated on a daily basis to avoid blocking legitimate incoming traffic. 4. Prefixes That Should Not be Routed across the Internet Network operators may deploy filters that block traffic destined for Martian prefixes. Currently, the Martian prefix table is defined by [RFC 5735] which reserves each Martian prefix for some specific, special use. If the Martian prefix table ever changes, that change will be documented in an RFC that either updates or obsoletes [RFC 5735]. 5. Security Considerations The cessation of filters based on unallocated IPv4 /8 allocations is an evolutionary step towards reasonable security filters. While these filters are no longer necessary, and in fact harmful, this does not obviate the need to continue other security solutions. These other solutions are as necessary today as they ever were. Vegoda Best Current Practice PAGE 3 top

RFC 6441 Remove /8 Filters November 2011 6. References 6.1. Normative References [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC 5735] Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses", BCP 153, RFC 5735, January 2010. 6.2. Informative References [RFC 1208] Jacobsen, O. and D. Lynch, "Glossary of networking terms", RFC 1208, March 1991. [RFC 3871] Jones, G., "Operational Security Requirements for Large Internet Service Provider (ISP) IP Network Infrastructure", RFC 3871, September 2004. Vegoda Best Current Practice PAGE 4 top

RFC 6441 Remove /8 Filters November 2011 Appendix A. Acknowledgments Thanks are owed to Kim Davies, Terry Manderson, Dave Piscitello, and Joe Abley for helpful advice on how to focus this document. Thanks also go to Andy Davidson, Philip Smith, and Rob Thomas for early reviews and suggestions for improvements to the text, and to Carlos Pignataro for his support and comments. Author's Address Leo Vegoda Internet Corporation for Assigned Names and Numbers 4676 Admiralty Way, Suite 330 Marina del Rey, CA 90292 United States of America Phone: +1-310-823-9358 EMail: leo.vegoda@icann.org URI: http://www.iana.org/ Vegoda Best Current Practice PAGE 5 top

RFC TOTAL SIZE: 8646 bytes PUBLICATION DATE: Tuesday, November 29th, 2011 LEGAL RIGHTS: The IETF Trust (see BCP 78)


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