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Internet Engineering Task Force (IETF) N. Hilliard
Request for Comments: 6666 INEX
Category: Informational D. Freedman
ISSN: 2070-1721 Claranet
August 2012
A Discard Prefix for IPv6
Abstract
Remote triggered black hole filtering describes a method of
mitigating the effects of denial-of-service attacks by selectively
discarding traffic based on source or destination address. Remote
triggered black hole routing describes a method of selectively re-
routing traffic into a sinkhole router (for further analysis) based
on destination address. This document updates the "IPv6 Special
Purpose Address Registry" by explaining why a unique IPv6 prefix
should be formally assigned by IANA for the purpose of facilitating
IPv6 remote triggered black hole filtering and routing.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
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). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see 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/rfc6666.
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RFC 6666 IPv6 Discard Prefix August 2012
Copyright Notice
Copyright (c) 2012 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
1.1. Notational Conventions .....................................3
2. A Discard Prefix for IPv6 .......................................3
3. Operational Implications ........................................4
4. IANA Considerations .............................................4
5. Security Considerations .........................................4
6. References ......................................................5
6.1. Normative References .......................................5
6.2. Informative References .....................................5
1. Introduction
Remote Triggered Black Hole (RTBH) filtering describes a class of
methods of blocking IP traffic either from a specific source
([RFC5635]) or to a specific destination ([RFC3882]) on a network.
RTBH routing describes a class of methods of re-routing IP traffic
destined to the attacked/targeted host to a special path (tunnel)
where a sniffer could capture the traffic for analysis. Both of
these methods operate by setting the next-hop address of an IP packet
with a specified source or destination address to be a unicast prefix
that is connected locally or remotely to a router's discard, null, or
tunnel interface. Typically, reachability information for this
prefix is propagated throughout an autonomous system using a dynamic
routing protocol such as BGP ([RFC3882]). By deploying RTBH systems
across a network, traffic to or from specific destinations may be
selectively black-holed or re-routed to a sinkhole device in a manner
that is efficient, scalable, and straightforward to implement.
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On some networks, operators configure RTBH installations using
[RFC1918] address space or the address blocks reserved for
documentation in [RFC5737]. This approach is inadequate because RTBH
configurations are not documentation, but rather operationally
important features of many public-facing production networks.
Furthermore, [RFC3849] specifies that the IPv6 documentation prefix
should be filtered in both local and public contexts. On this basis,
it is suggested that both private network address blocks and the
documentation prefixes described in [RFC5737] are inappropriate for
RTBH configurations and that a dedicated IPv6 prefix should be
assigned instead.
This document updates the "IPv6 Special Purpose Address Registry"
[IANA-IPV6REG].
1.1. Notational Conventions
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 [RFC2119].
2. A Discard Prefix for IPv6
For the purposes of implementing an IPv6 RTBH configuration, a
unicast address block is required. There are currently no IPv6
unicast address blocks that are specifically nominated for the
purposes of implementing such RTBH systems.
While it could be argued that there are other addresses and address
prefixes that could be used for this purpose (e.g., documentation
prefixes, private address space), or that an operator could assign an
address block from their own address space for this purpose, there is
currently no operational clarity on what address block would be
appropriate or inappropriate to use for this purpose. By assigning a
globally unique discard prefix for IPv6, the IETF will introduce good
practice for the implementation of IPv6 RTBH configurations and will
facilitate operational clarity by allowing operators to implement
consistent and deterministic inter-domain prefix and traffic
filtering policies for black-holed traffic.
As [RFC3882] and [RFC5635] describe situations where more than one
discard address may be used for implementing multiple RTBH scenarios,
a single address is not sufficient to cover all likely RTBH
situations. Consequently, an address block is required.
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RFC 6666 IPv6 Discard Prefix August 2012
3. Operational Implications
This assignment MAY be carried in a dynamic routing protocol within
an autonomous system. The assignment SHOULD NOT be announced to or
accepted from third-party autonomous systems, and IPv6 traffic with a
destination address within this prefix SHOULD NOT be forwarded to or
accepted from third-party autonomous systems. If the prefix or a
subnet of the prefix is inadvertently announced to or accepted from a
third-party autonomous system, this may cause excessive volumes of
traffic to pass unintentionally between the two networks, which would
aggravate the effect of a denial-of-service attack.
On networks that implement IPv6 remote triggered black holes, some or
all of this network block MAY be configured with a next-hop
destination of a discard or null interface on any or all IPv6 routers
within the autonomous system.
4. IANA Considerations
Per this document, IANA has recorded the allocation of the IPv6
address prefix 0100::/64 as a Discard-Only Prefix in the "Internet
Protocol Version 6 Address Space" and added the prefix to the "IANA
IPv6 Special Purpose Address Registry" [IANA-IPV6REG]. No end party
has been assigned to this prefix. The prefix has been allocated from
::/3.
5. Security Considerations
As the prefix specified in this document ought not normally be
transmitted or accepted over inter-domain BGP sessions for the
reasons described in Section 3, it is usually appropriate to include
this prefix in inter-domain BGP prefix filters [RFC3704] or otherwise
ensure the prefix is neither transmitted to nor accepted from a
third-party autonomous system.
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6. References
6.1. Normative References
[IANA-IPV6REG]
Internet Assigned Numbers Authority, "IPv6 Special Purpose
Address Registry", 2012, <http://www.iana.org/assignments/
iana-ipv6-special-registry>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3882] Turk, D., "Configuring BGP to Block Denial-of-Service
Attacks", RFC 3882, September 2004.
[RFC5635] Kumari, W. and D. McPherson, "Remote Triggered Black Hole
Filtering with Unicast Reverse Path Forwarding (uRPF)",
RFC 5635, August 2009.
6.2. Informative References
[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
and E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
Networks", BCP 84, RFC 3704, March 2004.
[RFC3849] Huston, G., Lord, A., and P. Smith, "IPv6 Address Prefix
Reserved for Documentation", RFC 3849, July 2004.
[RFC5737] Arkko, J., Cotton, M., and L. Vegoda, "IPv4 Address Blocks
Reserved for Documentation", RFC 5737, January 2010.
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Authors' Addresses
Nick Hilliard
INEX
4027 Kingswood Road
Dublin 24
IE
EMail: nick@inex.ie
David Freedman
Claranet
21 Southampton Row, Holborn
London WC1B 5HA
UK
EMail: david.freedman@uk.clara.net
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