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Internet Engineering Task Force (IETF)                         L. VegodaRequest for Comments: 6441                                         ICANNBCP: 171                                                   November 2011Category: Best Current PracticeISSN: 2070-1721Time to Remove Filters for Previously Unallocated IPv4 /8sAbstract   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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6441.Copyright Notice   Copyright (c) 2011 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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 mustVegoda                    Best Current Practice                 [Page 1]

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 Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .22.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . .23.  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 . . . . . . . . . . . . . . . . . . . . . . . . . . .34.  Prefixes That Should Not be Routed across the Internet  . . . .35.  Security Considerations . . . . . . . . . . . . . . . . . . . .36.  References  . . . . . . . . . . . . . . . . . . . . . . . . . .46.1.  Normative References  . . . . . . . . . . . . . . . . . . .46.2.  Informative References  . . . . . . . . . . . . . . . . . .4Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . . .51.  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 inBCP 14,RFC 2119   [RFC2119].   Martians [RFC1208] 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 [RFC3871]   are packets sourced from addresses that have not yet been allocatedVegoda                    Best Current Practice                 [Page 2]

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 [RFC5735].  Bogons are   referred to as "Dark IP" in some circles.3.  Traffic Filtering Options3.1.  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   [RFC5735] 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   [RFC5735].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]

RFC 6441                    Remove /8 Filters              November 20116.  References6.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC5735]  Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses",BCP 153,RFC 5735, January 2010.6.2.  Informative References   [RFC1208]  Jacobsen, O. and D. Lynch, "Glossary of networking terms",RFC 1208, March 1991.   [RFC3871]  Jones, G., "Operational Security Requirements for Large              Internet Service Provider (ISP) IP Network              Infrastructure",RFC 3871, September 2004.Vegoda                    Best Current Practice                 [Page 4]

RFC 6441                    Remove /8 Filters              November 2011Appendix 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]