Operational Issues Associated With Long IPv6 Extension Header Chains
draft-wkumari-long-headers-01
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Expired".
|
|
|---|---|---|---|
| Authors | Warren "Ace" Kumari , Joel Jaeggli , Ron Bonica | ||
| Last updated | 2013-07-03 | ||
| RFC stream | (None) | ||
| Formats | |||
| Additional resources | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-wkumari-long-headers-01
6MAN W. Kumari
Internet-Draft Google
Intended status: Best Current Practice J. Jaeggli
Expires: January 05, 2014 Zynga
R. Bonica
Juniper Networks
July 04, 2013
Operational Issues Associated With Long IPv6 Extension Header Chains
draft-wkumari-long-headers-01
Abstract
This document explains why IPv6 header chain length affects the cost
of ASIC-based packet forwarding. It also explains why some network
service providers discard packets with exceptionally long header
chains. Finally, it identifies a reasonable header chain length.
While a network service provider can enforce any filtering policy
that supports its security model, a network service provider should
not discard IPv6 packets based solely upon header chain length if the
header chain is not longer than the value specified herein.
Requirements Language
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 RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 05, 2014.
Copyright Notice
Kumari, et al. Expires January 05, 2014 [Page 1]
Internet-Draft long-v6-headers July 2013
Copyright (c) 2013 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. Termnology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Need to see upper-layer to filter . . . . . . . . . . . . . . 5
4. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. Normative References . . . . . . . . . . . . . . . . . . . . 7
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
In order to make a forwarding decision, the forwarding device may
require information from both the IPv6 header and an upper layer
header. When a software-based forwarder encounters an IPv6 datagram
that includes a long header chain, it parses the header chain,
acquires the required information and makes its forwarding decision.
Typically, software-based forwarders are not required to process a
large number of packets per second. Therefore, they can perform the
above mentioned procedure within their processing budget.
By contrast, ASIC-based forwarders are engineered to forward many
more packets per second. In order to fulfill this requirement, the
forwarder copies a fixed number of bytes from the beginning of the
packet to on-chip memory. The ASIC does this because it can access
on-chip memory much more quickly than it can access off-chip memory.
Once the beginning of the packet has been transferred to on-chip
memory, subsequent processing and forwarding decisions can be made
very quickly.
Kumari, et al. Expires January 05, 2014 [Page 2]
Internet-Draft long-v6-headers July 2013
The act of copying bytes from the beginning of a packet to on-chip
memory consumes both wall-time and processor cycles. Therefore, the
number of bytes copied to on-chip memory must be chosen wisely. If a
forwarder copies more bytes than it needs, it wastes resources,
significantly increasing cost and decreasing maximum performance. If
it copies too few bytes, it cannot parse the header chain and make a
correct forwarding decision.
As currently specified in [RFC2460], the IPv6 header chain can exceed
64 kilobytes. However, packets with header chains exceeding 128
bytes are rarely observed on the Internet. Therefore, most ASIC-
based forwarders copy a relatively small number of bytes from the
beginning of the packet into on-chip memory.
This document explains why IPv6 header chain length affects the cost
of ASIC-based packet forwarding. It also explains why some network
service providers discard packets with exceptionally long header
chains. Finally, it identifies a reasonable header chain length.
While a network service provider can enforce any filtering policy
that supports its security model, a network service provider SHOULD
NOT discard IPv6 packets based upon header chain length if the header
chain is not longer than the value specified herein.
1.1. Termnology
For the purposes of this document, the terms Extension Header, Header
Chain and Upper-layer Header are used as follows:
Extension Header :
Extension Headers are defined in Section 4 of [RFC2460].
Currently, six extension header types are defined. [RFC2460]
defines the hop-by-hop, routing, fragment and destination options
extension header types. [RFC4302] defines the authentication
header (AH) type and [RFC4303] defines the encapsulating security
payload (ESP) header type.
Header Chain :
The initial portion of an IPv6 datagram containing headers. The
first member of the header chain is always an IPv6 header. For a
subsequent header to qualify as a member of the header chain, it
must be referenced by the "Next Header" field of the previous
member of the header chain. The header chain can include IPv6
headers, IPv6 extension headers and an upper-layer header. If the
header chain includes two IPv6 headers, as is the case when IPv6
is tunneled over IPv6, the second IPv6 header terminates the
header chain. Any headers following the second IPv6 headers are
Kumari, et al. Expires January 05, 2014 [Page 3]
Internet-Draft long-v6-headers July 2013
not members of the header chain. Likewise, if the header chain
includes an ESP header, the ESP header terminates the header
chain. Only the first 8 bytes of the ESP header contribute to the
header chain length. Any headers following ESP header are not
members of the header chain.
Upper-layer Header :
In the general case, the upper-layer header is the first member of
the header chain that is neither an IPv6 header nor an IPv6
extension header. Typically, the upper-layer header represents a
transport protocol (e.g., TCP, UDP, SCTP). However, it can
represent a non-transport layer protocol. For example, when IPv4
is tunneled over IPv6, the upper-layer header is an IPv4 header.
If the header chain includes two IPv6 headers, as is the case when
IPv6 is tunneled over IPv6, the second IPv6 header is considered
to be the upper-layer header and terminates the header chain.
For the purposes of this document, when the upper-layer protocol
is ICMPv6, the first 32 bits of the ICMPv6 message (i.e., the
type, code fields and checksum fields) are considered to be the
ICMPv6 header.
The upper-layer payload is not part of the upper-layer header and
therefore, is not part of the IPv6 header chain. For example, if
the upper-layer protocol is TCP, the TCP payload is not part of
the TCP header or the IPv6 header chain.
2. Background
When IPv6 was first conceived, forwarding was largely performed in
software running on general-purpose processors. Due to the required
performance, parsing a long header chain was not an issue.
In the years between the conception of IPv6 and publication of this
documentation, the Internet evolved as follows:
o Throughput requirements increased dramatically, requiring the
deployment of ASIC-based forwarders in both core and edge networks
o New network types emerged, including very large enterprises,
social networks, data centers and "clouds". Like core networks,
these network require very high throughput. Like edge networks,
these networks require "high-touch" edge services, which require
the forwarder to access the entire header chain
Kumari, et al. Expires January 05, 2014 [Page 4]
Internet-Draft long-v6-headers July 2013
o Requirements for "high-touch" service, which require the forwarder
to access the entire header chain, increased in networks of all
kinds
During those years, IPv4 [RFC0791] was the most commonly deployed
protocol on the Internet. ASIC-based forwarders could meet the
requirements of the evolving Internet because ASICs could predict the
number of bytes that needed to be copied into on-chip memory in order
to make a forwarding decision.
Today, as IPv6 is being deployed, ASIC-forwarders cannot safely
predict the size of the header chain. This leads to complexity and
vulnerability in handling extension headers. For this reason, many
network operators filter all IPv6 packets containing extension
headers.
3. Need to see upper-layer to filter
There is a school of thought that ISPs, content-providers and
enterprises should not be performing any sort of filtering in the
network and that the filtering is more appropriately performed at the
end hosts. Unfortunately this solution, while clean and elegant,
simply doesn't work in the real world. Filtering unknown traffic at
the edge (and / or in the core) of the network is needed for a number
of reasons, some of which are discussed below.
o ISPs (and cloud providers) are routinely called upon to filter DoS
traffic aimed at their customers (for example to block multi-Gbps
DNS reflection attacks aimed at web servers, etc). At Large Edge
Sites this is often a large part of the "service" provided by the
network team.
o IPv6 stacks are still relatively immature and operators still have
concerns that stack or kernel vulnerabilities may still surface.
If this turns out to be the case, a means to protect the end nodes
is needed.
o In many enterprises the end systems are not sufficiently hardened
to be exposed on the public Internet. Even if there were no
remotely exploitable operating system vulnerabilities there is
significant risk that an employee may install vulnerable software,
accidentally share confidential files or folders publicly or start
offering (unauthorized) services.
Kumari, et al. Expires January 05, 2014 [Page 5]
Internet-Draft long-v6-headers July 2013
o Content providers (and similar) need to be able to filter traffic
and only allow "expected" traffic into their networks. This is
needed both for DoS protection, but also to ensure that
development systems, databases, test systems, etc are not
accidentally exposed.
o While it would be nice if all employees, system and database
administrators could be trusted to always ensure that only the
"correct" services were listening on ports, that all software was
always fully patches (and contained no vulnerabilities), that
confidential data was only shared with internal addressed and that
all credentials were strong and regularly changed, this simply
does not reflect reality.
All of these lead to the requirement that operators be able to filter
at Layer 3 and Layer 4, at line rate, in the network. Obviously, to
be able to filter at layers 3 and 4, the router needs to be able to
see the layer 3 and 4 information. Unfortunately, if the size of
extension header chain varies between 0 and 64 kilobytes, extension
headers cannot be processed efficiently in ASICs.
Because many implementation do not process IPv6 extension headers
well, many operators filter all IPv6 packets that include them.
4. Recommendations
An ISP SHOULD NOT discard IPv6 packets based solely upon header chain
length if the header chain contains 128 bytes or fewer. However, it
is common practice ISPs to filter IPv6 packets with long extension
header chains. This document offers no recommendation regarding the
maximum extension header chain length that an ISP should forward.
See Section 1.1 for a formal definition of the header chain.
5. IANA Considerations
This document makes no requests of the IANA
6. Security Considerations
There are potential implications to the filtering or acceptances of
packets which cannot be processed according to the configuration of
the network operator. It is clear from the vantage point of the
authors that implementors and operators should be aware of
implications of relying on extension header chains or apply policies
that must necessarily discard packets which contain them.
Kumari, et al. Expires January 05, 2014 [Page 6]
Internet-Draft long-v6-headers July 2013
7. Acknowledgements
The authors wish to thank Paul Hoffman, KK and Fernando Gont.
8. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September
1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302, December
2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
4303, December 2005.
Appendix A. Changes / Author Notes.
[RFC Editor: Please remove this section before publication ]
Template to -00
o Initial submission.
-00 to -01
o Added maximum header chain recommendation.
o Rewrite the forwarding description.
Authors' Addresses
Warren Kumari
Google
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Email: warren@kumari.net
Kumari, et al. Expires January 05, 2014 [Page 7]
Internet-Draft long-v6-headers July 2013
Joel Jaeggli
Zynga
675 East Middlefield
Mountain View, CA
USA
Email: jjaeggli@zynga.com
Ronald P Bonica
Juniper Networks
2251 Corporate Park Drive
Herndon, VA
USA
Email: rbonica@juniper.net
Kumari, et al. Expires January 05, 2014 [Page 8]