draft-ietf-ipv6-host-load-sharing-02.txt   draft-ietf-ipv6-host-load-sharing-03.txt 
IPv6 Working Group R. Hinden IPv6 Working Group R. Hinden
INTERNET-DRAFT Nokia INTERNET-DRAFT Nokia
May 4, 2004 D. Thaler October 18, 2004 D. Thaler
Expires November 2004 Microsoft Expires April 2005 Microsoft
IPv6 Host to Router Load Sharing IPv6 Host to Router Load Sharing
<draft-ietf-ipv6-host-load-sharing-02.txt> <draft-ietf-ipv6-host-load-sharing-03.txt>
Status of this Memo Status of this Memo
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all provisions of Section 10 of RFC2026. patent or other IPR claims of which I am aware have been
disclosed, or will be disclosed, and any of which I become aware
will be disclosed, in accordance with RFC 3668.
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved. Draft IPv6 Host to Router Load Sharing October 2004
Draft IPv6 Host to Router Load Sharing May 2004 Copyright (C) The Internet Society (2004). 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 which
can be problematic in practice. This document updates the can be problematic in practice. This document updates the
conceptual sending algorithm so that traffic to different conceptual sending algorithm so that traffic to different
destinations can be distributed among routers in an efficient destinations can be distributed among routers in an efficient
fashion. fashion.
skipping to change at page 2, line 28 skipping to change at page 2, line 30
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 through an existing router is failing. Normally a communication through an existing router is failing. Normally a
router is selected the first time traffic is sent to a specific router is selected the first time traffic is sent to a specific
destination IP address. Subsequent traffic to the same destination IP address. Subsequent traffic to the same
destination address continues to use the same router unless there destination address continues to use the same router unless there
is some reason to change to a different router (e.g., a redirect is some reason to change to a different router (e.g., a redirect
message is received, or the router is found to be unreachable). message is received, or the router is found to be unreachable).
In both the base algorithm and in the optional extension, In addition, as described in [ADDRSEL], the choice of next hop may
also affect the choice of source address, and hence indirectly
(and to a lesser extent) may affect the router used for inbound
traffic as well.
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 typically desirable when there is more than one equivalent It is typically desirable when there is more than one equivalent
router that hosts distribute their outgoing traffic among these router that hosts distribute their outgoing traffic among these
routers. This shares the load among multiple routers and provides routers. This shares the load among multiple routers and provides
better performance for the host's traffic. better performance for the host's traffic.
On the other hand, load sharing can be undesirable in situations
where sufficient capacity is available through a single router and
the traffic patterns could be more predictable by using a single
router; in particular, this helps to diagnose connectivity
problems beyond the first-hop routers.
Draft IPv6 Host to Router Load Sharing October 2004
[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 round-robin manner. Both of these suggestions are problematic. a 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
Draft IPv6 Host to Router Load Sharing May 2004
synchronization issues among hosts, where in the worst case the synchronization issues among hosts, where in the worst case the
load is concentrated on one router at a time. load is concentrated 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", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", 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 which 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).
Furthermore, a host that does attempt to distribute load among This memo takes no stance on whether the support for load sharing
routers SHOULD use a hash-based scheme, such as those described in should be turned on or off by default. Furthermore, a host that
[MULTIPATH], which takes the destination IP address into account. does attempt to distribute load among routers SHOULD use a hash-
based scheme which takes the destination IP address into account,
such as those described in [MULTIPATH], for choosing a router to
use.
Note that traffic for a given destination address will use the Note that traffic for a given destination address will use the
same router as long as the Destination Cache Entry for the same router as long as the Destination Cache Entry for the
destination address is not deleted. With a hash-based scheme, destination address is not deleted. With a hash-based scheme,
traffic for a given destination address will use the same router traffic for a given destination address will use the same router
over time even if the Destination Cache Entry is deleted, as long over time even if the Destination Cache Entry is deleted, as long
as the list of equivalent routers remains the same. as the list of equivalent routers remains the same.
3. Acknowledgments Draft IPv6 Host to Router Load Sharing October 2004
The authors of this document would like to thank Erik Nordmark,
Brian Haberman, Steve Deering, Aron Silverton, and Christian
Huitema.
4. Security Considerations 3. Security Considerations
As mentioned in [MULTIPATH], when next-hop selection is As mentioned in [MULTIPATH], when next-hop selection is
predictable, an application can synthesize traffic that will all predictable, an application can synthesize traffic that will all
hash the same, making it possible to launch a denial-of-service hash the same, making it possible to launch a denial-of-service
attack against the load sharing algorithm, and overload a attack against the load sharing algorithm, and overload a
particular router. This can even be done by a remote application particular router. This can even be done by a remote application
that can cause a host to respond to a given destination address. that can cause a host to respond to a given destination address.
A special case of this is when the same (single) next-hop is A special case of this is when the same (single) next-hop is
always selected, such as in the algorithm allowed by [ND]. always selected, such as in the algorithm allowed by [ND].
Introducing hashing can make such an attack more difficult; the Introducing hashing can make such an attack more difficult; the
Draft IPv6 Host to Router Load Sharing May 2004
more unpredictable the hash is, the harder it becomes to conduct a more unpredictable the hash is, the harder it becomes to conduct a
denial-of-service attack against any single router. denial-of-service attack against any single router.
5. Normative References 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
The authors of this document would like to thank Erik Nordmark,
Brian Haberman, Steve Deering, Aron Silverton, Christian Huitema,
and Pekka Savola.
6. Normative References
[ND] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery [ND] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC 2461, December 1998. for IP Version 6 (IPv6)", RFC 2461, December 1998.
[RFC2119] [RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP0014, March 1997. Requirement Levels", RFC 2119, BCP0014, March 1997.
6. Informative References [ADDRSEL]
Draves, R., "Default Address Selection for Internet Protocol
version 6 (IPv6)", RFC 3484, February 2003.
Draft IPv6 Host to Router Load Sharing October 2004
7. Informative References
[MULTIPATH] [MULTIPATH]
Thaler, D. and C. Hopps, "Multipath Issues in Unicast and Thaler, D. and C. Hopps, "Multipath Issues in Unicast and
Multicast Next-Hop Selection", RFC 2991, November 2000. Multicast Next-Hop Selection", RFC 2991, November 2000.
[ROUTERSEL] [ROUTERSEL]
Draves, R. and D. Thaler, "Default Router Preferences and Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", Work in progress, draft-ietf- More-Specific Routes", Work in progress, draft-ietf-
ipv6-router-selection-03.txt, December 2003. ipv6-router-selection-03.txt, December 2003.
7. Authors' Addresses 8. 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
Draft IPv6 Host to Router Load Sharing May 2004
8. Revision History
(This section to be removed before publication as an RFC)
Changes from draft-ietf-ipv6-load-sharing-01.txt:
o Changed load sharing from a MUST to a SHOULD.
o Added standard IETF intellectual property notice.
Changes from draft-ietf-ipv6-router-selection-02.txt:
o Split load sharing back into its own document.
o Made hash-based, rather than random, the rule.
9. Full Copyright Statement 9. Full Copyright Statement
Copyright (C) The Internet Society (2004). All Rights Reserved. Copyright (C) The Internet Society (2004). This document is
subject to the rights, licenses and restrictions contained in BCP
This document and translations of it may be copied and furnished 78, and except as set forth therein, the authors retain all their
to others, and derivative works that comment on or otherwise rights.
explain it or assist in its implmentation may be prepared, copied,
published and distributed, in whole or in part, without
restriction of any kind, provided that the above copyright notice
and this paragraph are included on all such copies and derivative
works. However, this document itself may not be modified in any
way, such as by removing the copyright notice or references to the
Internet Society or other Internet organizations, except as needed
for the purpose of developing Internet standards in which case the
procedures for copyrights defined in the Internet Standards
process must be followed, or as required to translate it into
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The limited permissions granted above are perpetual and will not
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This document and the information contained herein is provided on This document and the information contained herein are provided on
an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
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THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 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 May 2004 Draft IPv6 Host to Router Load Sharing October 2004
10. Intellectual Property 10. Intellectual Property
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed Intellectual Property Rights or other rights that might be claimed
to pertain to the implementation or use of the technology to pertain to the implementation or use of the technology
described in this document or the extent to which any license described in this document or the extent to which any license
under such rights might or might not be available; nor does it under such rights might or might not be available; nor does it
represent that it has made any independent effort to identify any represent that it has made any independent effort to identify any
such rights. Information on the procedures with respect to rights such rights. Information on the procedures with respect to rights
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