[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]
Versions: (draft-bagnulo-shim6-locator-pair-selection)
00 01 02 03 04
Network Working Group M. Bagnulo
Internet-Draft UC3M
Intended status: Informational October 23, 2008
Expires: April 26, 2009
Default Locator-pair selection algorithm for the SHIM6 protocol
draft-ietf-shim6-locator-pair-selection-04
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on April 26, 2009.
Abstract
In this note, we present a locator-pair selection mechanism for the
shim6 protocol. The presented mechanism provides an ordered list of
available locator-pairs that can be used for outgoing traffic.
Bagnulo Expires April 26, 2009 [Page 1]
Internet-Draft SHIM6 Locator-pair selection October 2008
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Preliminary considerations . . . . . . . . . . . . . . . . . . 4
2.1. Candidate Locator-pair set . . . . . . . . . . . . . . . . 4
2.2. Locator-pair States . . . . . . . . . . . . . . . . . . . 5
2.3. Locator preferences . . . . . . . . . . . . . . . . . . . 5
2.3.1. Remote locator preferences . . . . . . . . . . . . . . 5
2.3.2. Source locator preferences . . . . . . . . . . . . . . 6
2.4. Locator-pair selection table . . . . . . . . . . . . . . . 6
3. Default Locator-Pair Selection Algorithm . . . . . . . . . . . 7
4. Security considerations . . . . . . . . . . . . . . . . . . . 8
4.1. Privacy considerations . . . . . . . . . . . . . . . . . . 8
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 11
Bagnulo Expires April 26, 2009 [Page 2]
Internet-Draft SHIM6 Locator-pair selection October 2008
1. Introduction
Once that a shim6 context is established between two peers, they are
free to select the best locator pair to continue the communication.
In particular, when an outage is detected, they will need to select a
new locator pair to rehome the communication. Besides, policy or
other considerations may lead to change the locator pair used in the
communication even if no outage has occurred.
In this note, we present a locator-pair selection mechanism for the
shim6 protocol. The presented mechanism provides an ordered list of
available locator-pairs that can be used for outgoing traffic (note
that since unidirectional locator pairs are supported by the shim6
protocol, the locator pair used in the outgoing direction may not
affect the locator pair used by the peer to send incoming traffic).
The motivation for having a locator selection mechanism different
than RFC 3484 [RFC4291] is that RFC 3484 was designed to select
addresses that were both identifiers and locators, so, in some cases
the selection criteria differs from the one used when selecting
addresses that will used only as locators. In particular, when
addresses are to be used as identifiers and as locators, stable
addresses such as Home Addresses are preferred over more temporary
addresses as Care-Off Addresses. If an address is to be used only as
a locator, probably the stability property is not as important as
achieving a more direct path, making a Care-off Address more
attractive than a Home Address. Similar considerations can be made
with respect to private and public addresses. In addition, the
locator pair selection mechanism described in this document
incorporates into the selection mechanism shim-specific information,
such as available reachability information and local and remote
locator preferences obtained through the shim6 protocol. Finally,
the mechanism presented in this note is a locator pair selection
mechanism as opposed to separate source address and destination
address selection mechanisms as described in RFC 3484. We think that
such approach is more appropriate for the shim6 protocol, since
reachability seems to be a property of an address pair rather than a
property of a single address.
The presented mechanism takes into account general properties of the
available addresses, in particular the address family (v4 or v6),
address scope [RFC4291], mobility consideration (Home-Addresses and
Care-off Addresses) [RFC3775], status of the addresses (Preferred and
Deprecated addresses) [RFC2462], privacy considerations (Public and
Temporary addresses) [RFC3041]. In addition it also takes into
account shim6 specific information such as whether the addresses are
known to be locally operational (as defined in [faildet]), if locator
pairs are know to be unidirectionally operational [faildet], the
Bagnulo Expires April 26, 2009 [Page 3]
Internet-Draft SHIM6 Locator-pair selection October 2008
local and remote preferences for the different locators available in
the shim6 context.
Multicast addresses are out of the scope of the document.
2. Preliminary considerations
2.1. Candidate Locator-pair set
We define the local set of locally-operational locators (LOLs(local))
as the local locators that are included in the local locator set
(Ls(local) as defined in [shim]) and that are locally operational as
defined in [faildet]. Locally operational addresses are discovered
through local means that are outside of the scope of this document.
We define the set of the locally-operational locators of the peer
(LOLs(peer)) as the remote locators that are included in the peer
locator set (Ls(peer) as defined in [shim]) and that are locally
operational in the peer as defined in [faildet]. The peers' locally
operational locators are discovered through the Locator List Option
and the Locator Preferences Option (in particular the BROKEN flag)
defined in the shim protocol [shim].
The candidate locator-pair set is the set of locator pairs that can
be used to send packets in a shim context.
The candidate locator-pair set contains in all the possible locator
pairs formed with the first of them belonging to the local set of
locally-operational locators (LOLs(local)) and the second locator
belonging to the locally-operational locators of the peer
(LOLs(peer)).
This can be expressed as:
Cand_Loc_Pair_Set ={(x,y)/[x in LOLs(local) and y in LOLs(peer)}
Current shim6 protocol specification only supports IPv6 addresses as
locators. In case the shim6 protocol specification is updated and
IPv4 addresses are accepted as locators, the creation of the
Candidate Locator Pair Set must only accept locator pairs where both
source and destiantion address are of the same family. The result
would be the following formula:.
Cand_Loc_Pair_Set ={(x,y)/[family(x) = family(y)] AND [x in
LOLs(local) and y in LOLs(peer)]}
Question: should we allow locator pairs with all types of scope
Bagnulo Expires April 26, 2009 [Page 4]
Internet-Draft SHIM6 Locator-pair selection October 2008
combinations or should we restrict the type of scope combinations for
the inclusion in the cadidate set? If we don't allow all the
combinations, we can remove rule 1 aboput scopes
2.2. Locator-pair States
Locator pairs can be in the following state:
o Unidirectionally Operational state: As defined in [faildet], is
when packets send with the first locator as the source address and
the second locator as a destination address are known to reach the
destination. In the shim6 case, a locator pair is know to be
unidirectionally operational when there is fresh information about
packets reaching the peer, using the mechanisms defined in
[faildet] or thanks to recent ULP feedback. When the information
about reachability expires, the locator pair moves to Unknown
state.
o Non-Operational state: The locator pair is known to be non-
operational i.e. that packets containing the first locator as
source address and the second locator as destination address do
not reach the destination. In the shim6 case this can be known
because recent attempts to exchange packets have failed. When the
information about unreachability expires, the locator pair moves
to Unknown state.
o Unknown state: No recent reachability information is available for
this locator-pair.
2.3. Locator preferences
2.3.1. Remote locator preferences
Remote locator preferences can be obtained through the shim6 protocol
using the Locator Preference option. The preferences consist in a
Flag octet, a Priority octet and an optional Weight octet.
The weight field express the relative weight for locators with the
same priority, and as defined in [RFC2782] larger weights should be
given a proportionally higher probability of being selected. In
order to include this probability information in the locator-pair
selection algorithm, a new weight* information is generated from the
weight values as following:
We order each set of destination addresses with the same priority and
defined weight values using the following algorithm defined in
[RFC2782]:
Arrange all addresses (that have not been ordered yet) in any order,
except that all those with weight 0 are placed at the beginning of
Bagnulo Expires April 26, 2009 [Page 5]
Internet-Draft SHIM6 Locator-pair selection October 2008
the list.
Compute the sum of the weights of those addresses, and with each
address associate the running sum in the selected order. Then choose
a uniform (pseudo)random number between 0 and the sum computed
(inclusive), and select the address whose running sum value is the
first in the selected order which is greater than or equal to the
(pseudo)random number selected. This address is the next one to be
included in the ordered list. Remove this address from the set of
the unordered addresses and apply the described algorithm to the
unordered address set to select the next target address. Continue
the ordering process until there are no unordered addresses.
The weight* (W*1, W*2,...,W*N) values for each of the addresses is
their final position in the resulting ordered list.
The procedure is repeated for each one of the sets containing
destination addresses with equal priority.
The Weight information is not used in the locator-pair selection
mechanism, but the Weight* information is.
2.3.2. Source locator preferences
With respect to the local locator preferences, this document assumes
that the host will have a mechanism to express Priority and Weight
information for local locators similar to the one defined in
[RFC2782].
The same procedure is used to assign Weight* values to the source
locators that have the same priority value.
Note that destination and source addresses are never included in the
same set, even if they have the same priority value.
The Weight information is not used in the locator-pair s election
mechanism, but the Weight* information is.
2.4. Locator-pair selection table
We define the Locator-pair selection table to express preferences
about which source address prefix to use when communicating with a
given destination address prefix. The table contains entries having
a source prefix and a destination prefix each. Given a locator pair,
it is then possible to find a match when both the source prefix is
contained in the source address and the destination prefix is
contained in the destination address.
Bagnulo Expires April 26, 2009 [Page 6]
Internet-Draft SHIM6 Locator-pair selection October 2008
3. Default Locator-Pair Selection Algorithm
The goal of the defualt locator-pair selection algorithm is to
produce an ordered list of locator pairs to be tried for rehoming an
ongoing communication. The ordered list can be produced with any
sorting algorithm. The set of rules described next are the
comparison criteria to be used in the locator-pair sorting algorithm.
This rules act must be processed in order and if a given rule selects
a locator pair over the other one, then the following rules don't
need to be processed and the selected locator pair is prefered.
We are comparing two locator pairs (src1,dst1) and (src2,dst2). Note
that in some cases the source or the destination addresses of the two
pairs may be equal.
Rule 1: Prefer appropriate scope: If scope(src1) >= scope(dst1) and
scope(src2) < scope(dst2), then prefer (src1,dst1).
Rule 2: Avoid Non-Operational pairs: If (src1,dst1) is in Non-
Operational state and (src2,dst2) is in Unidirectionally
Operational or in Unknown state, then prefer (src2,dst2).
Rule 3: Prefer Unidirectionally Operational state: If (src1,dst1) is
in Unknown state and (src2,dst2) is in Unidirectionally
Operational, then prefer (src2,dst2).
Rule 4: Prefer fresher reachability information: If (src1,dst1) and
(src2,dst2) are both in Unidirectionally Operational state,
then prefer the one with smallest age information i.e. the
one for which newer reachability information is available.
Rule 5: Prefer ULID-Pair: If (src1,dst1) is the ULID-pair of the
context, the prefer (src1,dst1)
Rule 6: Prefer matching scope: If scope(src1) = scope(dst1) and
scope(src2) < scope(dst2), then prefer (src1,dst1)
Rule 7: Prefer Locator-pair table match: If (dst1,src1) has a match
in the Locator-pair selection table and (src2,dst2) does not
have a match in the locator-pair selection table, then
prefer (dst1,src1).
Rule 8: Prefer Preferred addresses: If src1 address is a Preferred
address in the RFC2462 sense and src2 is a deprecated
address in the RFC2462 sense, then prefer (src1,dst1)
Bagnulo Expires April 26, 2009 [Page 7]
Internet-Draft SHIM6 Locator-pair selection October 2008
Rule 9: Prefer Local Priority: If src1 of (src1,dst1) has a lowest
Priority than src2 of (src2,dst2) then prefer (src1,dst1)
Rule 10: Prefer Local Weight*: If src1 of (src1,dst1) has a lowest
Weight* than src2 of (src2,dst2) then prefer (src1,dst1)
Rule 11: Prefer Local Care-off Addresses: If src1 is a Care-off
address [RFC3775] and src2 is a Home Address, the prefer
(src1,dst1). This only applies to Mobile IP [RFC3775].
Rule 12: Prefer Remote Priority: If dst1 of (src1,dst1) has a lowest
Priority than dst2 of (src2,dst2) then prefer (src1,dst1)
Rule 13: Prefer Remote Weight*: If dst1 of (src1,dst1) has a lowest
Weight* than dst2 of (src2,dst2) then prefer (src1,dst1)
Rule 14: Prefer Remote Care-off Addresses: If dst1 is a Care-off
address (Temporary flag set in the Locator preferences
options defined in [shim]) and dst2 is not a Care-off
address, the prefer (src1,dst1). This only applies to
Mobile IP [RFC3775].
Other rules that may be worth taking into account are:
o Prefer native transport
o Prefer smaller scope
o Prefer most dissimilar locator pair to the currently used
o Prefer locator pair contained in incoming packet
o Longest prefix match
o Should we eliminate the site and link local addresses from the
accpetable locator set?
4. Security considerations
Note that according to the shim6 protocol specification, locators are
included in the Ls(peer) only after HBA/CGA verification has been
successful. This eliminates the possibility of using locators that
do not belong to the peer. Besides, it should be noted that before
using a given locator pair to actually send data packets, a
reachability test is performed in order to prevent flooding attacks.
4.1. Privacy considerations
Including or not RFC3041 [RFC3041] addresses in the Locator set
available for a shim6 context may have privacy implications. This is
so because of two reaosns: First, the inclusion of RFC 3041 addresses
in the locator set discloses the RFC3041 addresses of the host to the
Bagnulo Expires April 26, 2009 [Page 8]
Internet-Draft SHIM6 Locator-pair selection October 2008
peer. Second, the locator sets of both peers are exchanged in clear
text during the shim6 context establishment and/or in the subsequent
UPDATE messages. This means that an attacker located along the path
that can observe such packets can discover that all the addresses
included in the locator set belong to the same host, beating the
purpose of RFC3041 private addresses. So, when forming the locator
set of a shim6 context the host must take into account these privacy
considerations in order to decide whether to include RFC3041
addresses in the locator set of a shim6 context.
5. Acknowledgements
The idea of pre-assigning Weight* values for introducing the Weight
probability in the locator-pair selection process was suggested by
Albert Banchs.
Marcelo Bagnulo worked on this document while visiting Ericsson
Research laboratory Nomadiclab.
Iljitsch van Beijnum provided a detailed review of this document.
6. References
[shim] Nordmark, E. and M. Bagnulo, "Level 3 multihoming shim
protocol", draft-ietf-shim6-proto-04 (work in progress),
March 2006.
[faildet] Arkko, J. and I. Beijnum, "Failure Detection and Locator
Pair Exploration Protocol for IPv6 Multihoming",
draft-ietf-shim6-failure-detection-03 (work in progress),
December 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.
[RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[RFC3041] Narten, T. and R. Draves, "Privacy Extensions for
Stateless Address Autoconfiguration in IPv6", RFC 3041,
January 2001.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
Bagnulo Expires April 26, 2009 [Page 9]
Internet-Draft SHIM6 Locator-pair selection October 2008
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003.
Author's Address
Marcelo Bagnulo
Universidad Carlos III de Madrid
Av. Universidad 30
Leganes, Madrid 28911
SPAIN
Phone: 34 91 6248814
Email: marcelo@it.uc3m.es
URI: http://www.it.uc3m.es
Bagnulo Expires April 26, 2009 [Page 10]
Internet-Draft SHIM6 Locator-pair selection October 2008
Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is 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 an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, 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.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Bagnulo Expires April 26, 2009 [Page 11]
Html markup produced by rfcmarkup 1.129b, available from
https://tools.ietf.org/tools/rfcmarkup/