draft-ietf-ipv6-host-load-sharing-04.txt   rfc4311.txt 
IPv6 Working Group R. Hinden Network Working Group R. Hinden
INTERNET-DRAFT Nokia Request for Comments: 4311 Nokia
June 23, 2005 D. Thaler Updates: 2461 D. Thaler
Expires December 2005 Microsoft Category: Standards Track Microsoft
November 2005
IPv6 Host to Router Load Sharing
<draft-ietf-ipv6-host-load-sharing-04.txt>
Status of this Memo
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months and may be updated, replaced, or obsoleted by other
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improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice Copyright Notice
Draft IPv6 Host to Router Load Sharing June 2005 Copyright (C) The Internet Society (2005).
Copyright (C) The Internet Society (2005). All Rights Reserved.
Abstract Abstract
The original IPv6 conceptual sending algorithm does not do load- The original IPv6 conceptual sending algorithm does not do load
sharing among equivalent IPv6 routers, and suggests schemes which sharing among equivalent IPv6 routers, and suggests schemes that can
can be problematic in practice. This document updates the be problematic in practice. This document updates the conceptual
conceptual sending algorithm in RFC 2461 so that traffic to sending algorithm in RFC 2461 so that traffic to different
different destinations can be distributed among routers in an destinations can be distributed among routers in an efficient
efficient fashion. fashion.
1. Introduction 1. Introduction
In the conceptual sending algorithm in [ND] and in the optional In the conceptual sending algorithm in [ND] and in the optional
extension in [ROUTERSEL], a next hop is chosen when no destination extension in [ROUTERSEL], a next hop is chosen when no destination
cache entry exists for an off-link destination or when cache entry exists for an off-link destination or when communication
communication through an existing router is failing. Normally a through an existing router is failing. Normally, a router is
router is selected the first time traffic is sent to a specific selected the first time traffic is sent to a specific destination IP
destination IP address. Subsequent traffic to the same address. Subsequent traffic to the same destination address
destination address continues to use the same router unless there continues to use the same router unless there is some reason to
is some reason to change to a different router (e.g., a redirect change to a different router (e.g., a redirect message is received,
message is received, or the router is found to be unreachable). or the router is found to be unreachable).
In addition, as described in [ADDRSEL], the choice of next hop may In addition, as described in [ADDRSEL], the choice of next hop may
also affect the choice of source address, and hence indirectly also affect the choice of source address, and hence indirectly (and
(and to a lesser extent) may affect the router used for inbound to a lesser extent) may affect the router used for inbound traffic as
traffic as well. well.
In both the base sending algorithm and in the optional extension, In both the base sending algorithm and in the optional extension,
sometimes a host has a choice of multiple equivalent routers for a sometimes a host has a choice of multiple equivalent routers for a
destination. That is, all other factors are equal and a host must destination. That is, all other factors are equal and a host must
break a tie via some implementation-specific means. break a tie via some implementation-specific means.
It is often desirable when there is more than one equivalent It is often desirable when there is more than one equivalent router
router that hosts distribute their outgoing traffic among these that hosts distribute their outgoing traffic among these routers.
routers. This shares the load among multiple routers and provides This shares the load among multiple routers and provides better
better performance for the host's traffic. performance for the host's traffic.
On the other hand, load sharing can be undesirable in situations On the other hand, load sharing can be undesirable in situations
where sufficient capacity is available through a single router and where sufficient capacity is available through a single router and
the traffic patterns could be more predictable by using a single the traffic patterns could be more predictable by using a single
router; in particular, this helps to diagnose connectivity router; in particular, this helps to diagnose connectivity problems
problems beyond the first-hop routers. beyond the first-hop routers.
Draft IPv6 Host to Router Load Sharing June 2005
[ND] does not require any particular behavior in this respect. It [ND] does not require any particular behavior in this respect. It
specifies that an implementation may always choose the same router specifies that an implementation may always choose the same router
(e.g., the first in the list) or may cycle through the routers in (e.g., the first in the list) or may cycle through the routers in a
a round-robin manner. Both of these suggestions are problematic. round-robin manner. Both of these suggestions are problematic.
Clearly, always choosing the same router does not provide load Clearly, always choosing the same router does not provide load
sharing. Some problems with load sharing using naive tie-breaking sharing. Some problems with load sharing using naive tie-breaking
techniques such as round-robin and random are discussed in techniques such as round-robin and random are discussed in
[MULTIPATH]. While the destination cache provides some stability [MULTIPATH]. While the destination cache provides some stability
since the determination is not per-packet, cache evictions or since the determination is not per packet, cache evictions or
timeouts can still result in unstable or unpredictable paths over timeouts can still result in unstable or unpredictable paths over
time, lowering the performance and making it harder to diagnose time, lowering the performance and making it harder to diagnose
problems. Round-robin selection may also result in problems. Round-robin selection may also result in synchronization
synchronization issues among hosts, where in the worst case the issues among hosts, where in the worst case the load is concentrated
load is concentrated on one router at a time. on one router at a time.
In the remainder of this document, the key words "MUST", "MUST In the remainder of this document, the key words "MUST", "MUST NOT",
NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in [RFC2119]. described in [RFC2119].
2. Load Sharing 2. Load Sharing
When a host chooses from multiple equivalent routers, it SHOULD When a host chooses from multiple equivalent routers, it SHOULD
support choosing using some method which distributes load for support choosing using some method that distributes load for
different destinations among the equivalent routers rather than different destinations among the equivalent routers rather than
always choosing the same router (e.g., the first in the list). always choosing the same router (e.g., the first in the list). This
This memo takes no stance on whether the support for load sharing memo takes no stance on whether the support for load sharing should
should be turned on or off by default. Furthermore, a host that be turned on or off by default. Furthermore, a host that does
does attempt to distribute load among routers SHOULD use a hash- attempt to distribute load among routers SHOULD use a hash-based
based scheme which takes (at least) the destination IP address scheme that takes (at least) the destination IP address into account,
into account, such as those described in [MULTIPATH], for choosing such as those described in [MULTIPATH], for choosing a router to use.
a router to use.
Note that traffic for a given destination address will use the
same router as long as the Destination Cache Entry for the
destination address is not deleted. With a hash-based scheme,
traffic for a given destination address will use the same router
over time even if the Destination Cache Entry is deleted, as long
as the list of equivalent routers remains the same.
Draft IPv6 Host to Router Load Sharing June 2005 Note that traffic for a given destination address will use the same
router as long as the Destination Cache Entry for the destination
address is not deleted. With a hash-based scheme, traffic for a
given destination address will use the same router over time even if
the Destination Cache Entry is deleted, as long as the list of
equivalent routers remains the same.
3. Security Considerations 3. Security Considerations
As mentioned in [MULTIPATH], when next-hop selection is As mentioned in [MULTIPATH], when next-hop selection is predictable,
predictable, an application can synthesize traffic that will all an application can synthesize traffic that will all hash the same,
hash the same, making it possible to launch a denial-of-service making it possible to launch a denial-of-service attack against the
attack against the load sharing algorithm, and overload a load-sharing algorithm, and overload a particular router. This can
particular router. This can even be done by a remote application even be done by a remote application that can cause a host to respond
that can cause a host to respond to a given destination address. to a given destination address. A special case of this is when the
A special case of this is when the same (single) next-hop is same (single) next-hop is always selected, such as in the algorithm
always selected, such as in the algorithm allowed by [ND]. allowed by [ND]. Introducing hashing can make such an attack more
Introducing hashing can make such an attack more difficult; the difficult; the more unpredictable the hash is, the harder it becomes
more unpredictable the hash is, the harder it becomes to conduct a to conduct a denial-of-service attack against any single router.
denial-of-service attack against any single router.
However, a malicious local application can bypass the algorithm
for its own traffic by using mechanisms such as raw sockets, and
remote attackers can still overload the routers directly. Hence,
the mechanisms discussed herein have no significant incremental
impact on Internet infrastructure security.
4. IANA Considerations
This document has no actions for IANA.
5. Acknowledgments However, a malicious local application can bypass the algorithm for
its own traffic by using mechanisms such as raw sockets, and remote
attackers can still overload the routers directly. Hence, the
mechanisms discussed herein have no significant incremental impact on
Internet infrastructure security.
The authors of this document would like to thank Erik Nordmark, 4. Acknowledgements
Brian Haberman, Steve Deering, Aron Silverton, Christian Huitema,
and Pekka Savola.
6. Normative References The authors of this document would like to thank Erik Nordmark, Brian
Haberman, Steve Deering, Aron Silverton, Christian Huitema, and Pekka
Savola.
[ND] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery 5. Normative References
for IP Version 6 (IPv6)", RFC 2461, December 1998.
[RFC2119] [ND] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Bradner, S., "Key words for use in RFCs to Indicate Discovery for IP Version 6 (IPv6)", RFC 2461, December
Requirement Levels", RFC 2119, BCP0014, March 1997. 1998.
[ADDRSEL] [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Draves, R., "Default Address Selection for Internet Protocol Requirement Levels", BCP 14, RFC 2119, March 1997.
version 6 (IPv6)", RFC 3484, February 2003.
Draft IPv6 Host to Router Load Sharing June 2005 [ADDRSEL] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003.
[ROUTERSEL] [ROUTERSEL] Draves, R. and D. Thaler, "Default Router Preferences
Draves, R. and D. Thaler, "Default Router Preferences and and More-Specific Routes", RFC 4191, November 2005.
More-Specific Routes", Work in progress, draft-ietf-
ipv6-router-selection-07.txt, January 2005.
7. Informative References 6. Informative References
[MULTIPATH] [MULTIPATH] Thaler, D. and C. Hopps, "Multipath Issues in Unicast
Thaler, D. and C. Hopps, "Multipath Issues in Unicast and and Multicast Next-Hop Selection", RFC 2991, November
Multicast Next-Hop Selection", RFC 2991, November 2000. 2000.
8. Authors' Addresses Authors' Addresses
Robert Hinden Robert Hinden
Nokia Nokia
313 Fairchild Drive 313 Fairchild Drive
Mountain View, CA 94043 Mountain View, CA 94043
Phone: +1 650 625-2004 Phone: +1 650 625-2004
Email: bob.hinden@nokia.com EMail: bob.hinden@nokia.com
Dave Thaler Dave Thaler
Microsoft Corporation Microsoft Corporation
One Microsoft Way One Microsoft Way
Redmond, WA 98052 Redmond, WA 98052
Phone: +1 425 703 8835 Phone: +1 425 703 8835
EMail: dthaler@microsoft.com EMail: dthaler@microsoft.com
9. Full Copyright Statement Full Copyright Statement
Copyright (C) The Internet Society (2005). This document is Copyright (C) The Internet Society (2005).
subject to the rights, licenses and restrictions contained in BCP
78, and except as set forth therein, the authors retain all their
rights.
This document and the information contained herein are provided on This document is subject to the rights, licenses and restrictions
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE contained in BCP 78, and except as set forth therein, the authors
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND retain all their rights.
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EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT
THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR
ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
PARTICULAR PURPOSE.
Draft IPv6 Host to Router Load Sharing June 2005 This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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