RFC 6441 BEST CURRENT PRACTICE IPV4 · ROUTING · FILTERING
Time to Remove Filters for Previously Unallocated IPv4 /8s
Stop blocking IPv4 address space that has now been fully allocated.
RFC EDITOR
Vegoda, L., "Time to Remove Filters for Previously Unallocated IPv4 /8s", BCP 171, RFC 6441, DOI 10.17487/RFC6441, November 2011, <https://www.rfc-editor.org/info/rfc6441>.
BIBTEX
@misc{rfc6441,
series = {Request for Comments},
number = 6441,
howpublished = {RFC 6441},
publisher = {RFC Editor},
doi = {10.17487/RFC6441},
url = {https://www.rfc-editor.org/info/rfc6441},
author = {L. Vegoda},
title = {{Time to Remove Filters for Previously Unallocated IPv4 /8s}},
pagetotal = 5,
year = 2011,
month = nov,
} RFC text
Contents
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/rfc6441.
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
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
[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 allocated
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 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
[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.
6. References
6.1. 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.
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/
AI ELI5
On this page
PROBLEMNetwork administrators have filtered traffic from unallocated IPv4 address blocks to block bogus sources, but all IPv4 /8 blocks have now been allocated, making the filters fragile and likely to block legitimate traffic.
MECHANISMRemove packet and BGP prefix filters that block traffic based on allocation status. Continue filtering only Martian prefixes reserved for special use by RFC 5735.
OPERATIONAL GUIDANCENetwork operators can simplify their border filters and avoid accidentally blocking valid traffic as address assignments change.
§1Why Filters Became Obsolete
For years, network administrators filtered traffic from and BGP prefixes of unallocated IPv4 address blocks. These bogon filters made sense when most of the address space was unallocated. However, all IPv4 /8 blocks are now allocated to regional registries. Continuing to filter based on allocation status is complex, fragile, and blocks legitimate traffic as assignments change daily.
When most addresses were unowned, filtering them was simple. Now that everything is owned, the filter just breaks things.
§2What to Remove and What to Keep
Network operators SHOULD remove both ingress and egress packet filters and BGP prefix filters for previously unallocated IPv4 /8s. The only filters worth keeping are for Martian prefixes—addresses reserved for special use by RFC 5735, such as loopback, private, and link-local ranges. These are defined in RFC 5735 and update processes ensure the list stays current.
Delete the filters for unallocated blocks. Keep only the ones for special addresses that are reserved forever, like your home Wi-Fi network.
§3Security and Maintenance Benefits
Removing obsolete filters simplifies network configuration and reduces operational costs. It also prevents accidental blocking of legitimate traffic from newly allocated address ranges. Network administrators maintaining old bogon filters face a fragile and expensive situation: they must update their filters daily as new address assignments happen, risking mistakes. Removing the filters based on allocation status while keeping filters for reserved special-use prefixes provides a cleaner, more maintainable approach.
Throwing away old filters is simpler and cheaper than trying to keep them up to date. And you will not accidentally block real customers.