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IETF RFC 6441
Last modified on Tuesday, November 29th, 2011
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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
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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
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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.
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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.
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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/
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RFC TOTAL SIZE: 8646 bytes
PUBLICATION DATE: Tuesday, November 29th, 2011
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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