draft-ietf-shim6-locator-pair-selection-03.txt   draft-ietf-shim6-locator-pair-selection-04.txt 
Network Working Group M. Bagnulo Network Working Group M. Bagnulo
Internet-Draft UC3M Internet-Draft UC3M
Intended status: Informational February 22, 2008 Intended status: Informational October 23, 2008
Expires: August 25, 2008 Expires: April 26, 2009
Default Locator-pair selection algorithm for the SHIM6 protocol Default Locator-pair selection algorithm for the SHIM6 protocol
draft-ietf-shim6-locator-pair-selection-03 draft-ietf-shim6-locator-pair-selection-04
Status of this Memo Status of this Memo
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skipping to change at page 1, line 34 skipping to change at page 1, line 34
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Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract Abstract
In this note, we present a locator-pair selection mechanism for the In this note, we present a locator-pair selection mechanism for the
shim6 protocol. The presented mechanism provides an ordered list of shim6 protocol. The presented mechanism provides an ordered list of
available locator-pairs that can be used for outgoing traffic. available locator-pairs that can be used for outgoing traffic.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Preliminary considerations . . . . . . . . . . . . . . . . . . 4 2. Preliminary considerations . . . . . . . . . . . . . . . . . . 4
2.1. Candidate Locator-pair set . . . . . . . . . . . . . . . . 4 2.1. Candidate Locator-pair set . . . . . . . . . . . . . . . . 4
2.2. Locator-pair States . . . . . . . . . . . . . . . . . . . 5 2.2. Locator-pair States . . . . . . . . . . . . . . . . . . . 5
2.3. Locator preferences . . . . . . . . . . . . . . . . . . . 5 2.3. Locator preferences . . . . . . . . . . . . . . . . . . . 5
2.3.1. Remote locator preferences . . . . . . . . . . . . . . 5 2.3.1. Remote locator preferences . . . . . . . . . . . . . . 5
2.3.2. Source locator preferences . . . . . . . . . . . . . . 6 2.3.2. Source locator preferences . . . . . . . . . . . . . . 6
2.4. Locator-pair selection table . . . . . . . . . . . . . . . 6 2.4. Locator-pair selection table . . . . . . . . . . . . . . . 6
3. Default Locator-Pair Selection Algorithm . . . . . . . . . . . 6 3. Default Locator-Pair Selection Algorithm . . . . . . . . . . . 7
4. Security considerations . . . . . . . . . . . . . . . . . . . 8 4. Security considerations . . . . . . . . . . . . . . . . . . . 8
4.1. Privacy considerations . . . . . . . . . . . . . . . . . . 8 4.1. Privacy considerations . . . . . . . . . . . . . . . . . . 8
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 11 Intellectual Property and Copyright Statements . . . . . . . . . . 11
1. Introduction 1. Introduction
Once that a shim6 context is established between two peers, they are Once that a shim6 context is established between two peers, they are
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communication even if no outage has occurred. communication even if no outage has occurred.
In this note, we present a locator-pair selection mechanism for the In this note, we present a locator-pair selection mechanism for the
shim6 protocol. The presented mechanism provides an ordered list of shim6 protocol. The presented mechanism provides an ordered list of
available locator-pairs that can be used for outgoing traffic (note available locator-pairs that can be used for outgoing traffic (note
that since unidirectional locator pairs are supported by the shim6 that since unidirectional locator pairs are supported by the shim6
protocol, the locator pair used in the outgoing direction may not protocol, the locator pair used in the outgoing direction may not
affect the locator pair used by the peer to send incoming traffic). affect the locator pair used by the peer to send incoming traffic).
The motivation for having a locator selection mechanism different The motivation for having a locator selection mechanism different
than RFC 3484 [3] is that RFC 3484 was designed to select addresses than RFC 3484 [RFC4291] is that RFC 3484 was designed to select
that were both identifiers and locators, so, in some cases the addresses that were both identifiers and locators, so, in some cases
selection criteria differs from the one used when selecting addresses the selection criteria differs from the one used when selecting
that will used only as locators. In particular, when addresses are addresses that will used only as locators. In particular, when
to be used as identifiers and as locators, stable addresses such as addresses are to be used as identifiers and as locators, stable
Home Addresses are preferred over more temporary addresses as Care- addresses such as Home Addresses are preferred over more temporary
Off Addresses. If an address is to be used only as a locator, addresses as Care-Off Addresses. If an address is to be used only as
probably the stability property is not as important as achieving a a locator, probably the stability property is not as important as
more direct path, making a Care-off Address more attractive than a achieving a more direct path, making a Care-off Address more
Home Address. Similar considerations can be made with respect to attractive than a Home Address. Similar considerations can be made
private and public addresses. In addition, the locator pair with respect to private and public addresses. In addition, the
selection mechanism described in this document incorporates into the locator pair selection mechanism described in this document
selection mechanism shim-specific information, such as available incorporates into the selection mechanism shim-specific information,
reachability information and local and remote locator preferences such as available reachability information and local and remote
obtained through the shim6 protocol. Finally, the mechanism locator preferences obtained through the shim6 protocol. Finally,
presented in this note is a locator pair selection mechanism as the mechanism presented in this note is a locator pair selection
opposed to separate source address and destination address selection mechanism as opposed to separate source address and destination
mechanisms as described in RFC 3484. We think that such approach is address selection mechanisms as described in RFC 3484. We think that
more appropriate for the shim6 protocol, since reachability seems to such approach is more appropriate for the shim6 protocol, since
be a property of an address pair rather than a property of a single reachability seems to be a property of an address pair rather than a
address. property of a single address.
The presented mechanism takes into account general properties of the The presented mechanism takes into account general properties of the
available addresses, in particular the address family (v4 or v6), available addresses, in particular the address family (v4 or v6),
address scope [3], mobility consideration (Home-Addresses and Care- address scope [RFC4291], mobility consideration (Home-Addresses and
off Addresses) [4], status of the addresses (Preferred and Deprecated Care-off Addresses) [RFC3775], status of the addresses (Preferred and
addresses) [5], privacy considerations (Public and Temporary Deprecated addresses) [RFC2462], privacy considerations (Public and
addresses) [6]. In addition it also takes into account shim6 Temporary addresses) [RFC3041]. In addition it also takes into
specific information such as whether the addresses are known to be account shim6 specific information such as whether the addresses are
locally operational (as defined in [2]), if locator pairs are know to known to be locally operational (as defined in [faildet]), if locator
be unidirectionally operational [2], the local and remote preferences pairs are know to be unidirectionally operational [faildet], the
for the different locators available in the shim6 context. local and remote preferences for the different locators available in
the shim6 context.
Multicast addresses are out of the scope of the document. Multicast addresses are out of the scope of the document.
2. Preliminary considerations 2. Preliminary considerations
2.1. Candidate Locator-pair set 2.1. Candidate Locator-pair set
We define the local set of locally-operational locators (LOLs(local)) We define the local set of locally-operational locators (LOLs(local))
as the local locators that are included in the local locator set as the local locators that are included in the local locator set
(Ls(local) as defined in [1]) and that are locally operational as (Ls(local) as defined in [shim]) and that are locally operational as
defined in [2]. Locally operational addresses are discovered through defined in [faildet]. Locally operational addresses are discovered
local means that are outside of the scope of this document. through local means that are outside of the scope of this document.
We define the set of the locally-operational locators of the peer We define the set of the locally-operational locators of the peer
(LOLs(peer)) as the remote locators that are included in the peer (LOLs(peer)) as the remote locators that are included in the peer
locator set (Ls(peer) as defined in [1]) and that are locally locator set (Ls(peer) as defined in [shim]) and that are locally
operational in the peer as defined in [2]. The peers' locally operational in the peer as defined in [faildet]. The peers' locally
operational locators are discovered through the Locator List Option operational locators are discovered through the Locator List Option
and the Locator Preferences Option (in particular the BROKEN flag) and the Locator Preferences Option (in particular the BROKEN flag)
defined in the shim protocol [1]. defined in the shim protocol [shim].
The candidate locator-pair set is the set of locator pairs that can The candidate locator-pair set is the set of locator pairs that can
be used to send packets in a shim context. be used to send packets in a shim context.
The candidate locator-pair set contains in all the possible locator The candidate locator-pair set contains in all the possible locator
pairs formed with the first of them belonging to the local set of pairs formed with the first of them belonging to the local set of
locally-operational locators (LOLs(local)) and the second locator locally-operational locators (LOLs(local)) and the second locator
belonging to the locally-operational locators of the peer belonging to the locally-operational locators of the peer
(LOLs(peer)). (LOLs(peer)).
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Question: should we allow locator pairs with all types of scope Question: should we allow locator pairs with all types of scope
combinations or should we restrict the type of scope combinations for combinations or should we restrict the type of scope combinations for
the inclusion in the cadidate set? If we don't allow all the the inclusion in the cadidate set? If we don't allow all the
combinations, we can remove rule 1 aboput scopes combinations, we can remove rule 1 aboput scopes
2.2. Locator-pair States 2.2. Locator-pair States
Locator pairs can be in the following state: Locator pairs can be in the following state:
o Unidirectionally Operational state: As defined in [2], is when o Unidirectionally Operational state: As defined in [faildet], is
packets send with the first locator as the source address and the when packets send with the first locator as the source address and
second locator as a destination address are known to reach the the second locator as a destination address are known to reach the
destination. In the shim6 case, a locator pair is know to be destination. In the shim6 case, a locator pair is know to be
unidirectionally operational when there is fresh information about unidirectionally operational when there is fresh information about
packets reaching the peer, using the mechanisms defined in [2] or packets reaching the peer, using the mechanisms defined in
thanks to recent ULP feedback. When the information about [faildet] or thanks to recent ULP feedback. When the information
reachability expires, the locator pair moves to Unknown state. about reachability expires, the locator pair moves to Unknown
state.
o Non-Operational state: The locator pair is known to be non- o Non-Operational state: The locator pair is known to be non-
operational i.e. that packets containing the first locator as operational i.e. that packets containing the first locator as
source address and the second locator as destination address do source address and the second locator as destination address do
not reach the destination. In the shim6 case this can be known not reach the destination. In the shim6 case this can be known
because recent attempts to exchange packets have failed. When the because recent attempts to exchange packets have failed. When the
information about unreachability expires, the locator pair moves information about unreachability expires, the locator pair moves
to Unknown state. to Unknown state.
o Unknown state: No recent reachability information is available for o Unknown state: No recent reachability information is available for
this locator-pair. this locator-pair.
2.3. Locator preferences 2.3. Locator preferences
2.3.1. Remote locator preferences 2.3.1. Remote locator preferences
Remote locator preferences can be obtained through the shim6 protocol Remote locator preferences can be obtained through the shim6 protocol
using the Locator Preference option. The preferences consist in a using the Locator Preference option. The preferences consist in a
Flag octet, a Priority octet and an optional Weight octet. Flag octet, a Priority octet and an optional Weight octet.
The weight field express the relative weight for locators with the The weight field express the relative weight for locators with the
same priority, and as defined in [7] larger weights should be given a same priority, and as defined in [RFC2782] larger weights should be
proportionally higher probability of being selected. In order to given a proportionally higher probability of being selected. In
include this probability information in the locator-pair selection order to include this probability information in the locator-pair
algorithm, a new weight* information is generated from the weight selection algorithm, a new weight* information is generated from the
values as following: weight values as following:
We order each set of destination addresses with the same priority and We order each set of destination addresses with the same priority and
defined weight values using the following algorithm defined in [7]: defined weight values using the following algorithm defined in
[RFC2782]:
Arrange all addresses (that have not been ordered yet) in any order, 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 except that all those with weight 0 are placed at the beginning of
the list. the list.
Compute the sum of the weights of those addresses, and with each Compute the sum of the weights of those addresses, and with each
address associate the running sum in the selected order. Then choose address associate the running sum in the selected order. Then choose
a uniform (pseudo)random number between 0 and the sum computed a uniform (pseudo)random number between 0 and the sum computed
(inclusive), and select the address whose running sum value is the (inclusive), and select the address whose running sum value is the
first in the selected order which is greater than or equal to the first in the selected order which is greater than or equal to the
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The procedure is repeated for each one of the sets containing The procedure is repeated for each one of the sets containing
destination addresses with equal priority. destination addresses with equal priority.
The Weight information is not used in the locator-pair selection The Weight information is not used in the locator-pair selection
mechanism, but the Weight* information is. mechanism, but the Weight* information is.
2.3.2. Source locator preferences 2.3.2. Source locator preferences
With respect to the local locator preferences, this document assumes With respect to the local locator preferences, this document assumes
that the host will have a mechanism to express Priority and Weight that the host will have a mechanism to express Priority and Weight
information for local locators similar to the one defined in [7]. information for local locators similar to the one defined in
[RFC2782].
The same procedure is used to assign Weight* values to the source The same procedure is used to assign Weight* values to the source
locators that have the same priority value. locators that have the same priority value.
Note that destination and source addresses are never included in the Note that destination and source addresses are never included in the
same set, even if they have the same priority value. same set, even if they have the same priority value.
The Weight information is not used in the locator-pair s election The Weight information is not used in the locator-pair s election
mechanism, but the Weight* information is. mechanism, but the Weight* information is.
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scope(src2) < scope(dst2), then prefer (src1,dst1) scope(src2) < scope(dst2), then prefer (src1,dst1)
Rule 7: Prefer Locator-pair table match: If (dst1,src1) has a match Rule 7: Prefer Locator-pair table match: If (dst1,src1) has a match
in the Locator-pair selection table and (src2,dst2) does not in the Locator-pair selection table and (src2,dst2) does not
have a match in the locator-pair selection table, then have a match in the locator-pair selection table, then
prefer (dst1,src1). prefer (dst1,src1).
Rule 8: Prefer Preferred addresses: If src1 address is a Preferred 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 and src2 is a deprecated
address in the RFC2462 sense, then prefer (src1,dst1) address in the RFC2462 sense, then prefer (src1,dst1)
Rule 9: Prefer Local Priority: If src1 of (src1,dst1) has a lowest Rule 9: Prefer Local Priority: If src1 of (src1,dst1) has a lowest
Priority than src2 of (src2,dst2) then prefer (src1,dst1) Priority than src2 of (src2,dst2) then prefer (src1,dst1)
Rule 10: Prefer Local Weight*: If src1 of (src1,dst1) has a lowest Rule 10: Prefer Local Weight*: If src1 of (src1,dst1) has a lowest
Weight* than src2 of (src2,dst2) then prefer (src1,dst1) Weight* than src2 of (src2,dst2) then prefer (src1,dst1)
Rule 11: Prefer Local Care-off Addresses: If src1 is a Care-off Rule 11: Prefer Local Care-off Addresses: If src1 is a Care-off
address [4] and src2 is a Home Address, the prefer address [RFC3775] and src2 is a Home Address, the prefer
(src1,dst1). This only applies to Mobile IP [4]. (src1,dst1). This only applies to Mobile IP [RFC3775].
Rule 12: Prefer Remote Priority: If dst1 of (src1,dst1) has a lowest Rule 12: Prefer Remote Priority: If dst1 of (src1,dst1) has a lowest
Priority than dst2 of (src2,dst2) then prefer (src1,dst1) Priority than dst2 of (src2,dst2) then prefer (src1,dst1)
Rule 13: Prefer Remote Weight*: If dst1 of (src1,dst1) has a lowest Rule 13: Prefer Remote Weight*: If dst1 of (src1,dst1) has a lowest
Weight* than dst2 of (src2,dst2) then prefer (src1,dst1) Weight* than dst2 of (src2,dst2) then prefer (src1,dst1)
Rule 14: Prefer Remote Care-off Addresses: If dst1 is a Care-off Rule 14: Prefer Remote Care-off Addresses: If dst1 is a Care-off
address (Temporary flag set in the Locator preferences address (Temporary flag set in the Locator preferences
options defined in [1]) and dst2 is not a Care-off address, options defined in [shim]) and dst2 is not a Care-off
the prefer (src1,dst1). This only applies to Mobile IP [4]. address, the prefer (src1,dst1). This only applies to
Mobile IP [RFC3775].
Other rules that may be worth taking into account are: Other rules that may be worth taking into account are:
o Prefer native transport o Prefer native transport
o Prefer smaller scope o Prefer smaller scope
o Prefer most dissimilar locator pair to the currently used o Prefer most dissimilar locator pair to the currently used
o Prefer locator pair contained in incoming packet o Prefer locator pair contained in incoming packet
o Longest prefix match o Longest prefix match
o Should we eliminate the site and link local addresses from the o Should we eliminate the site and link local addresses from the
accpetable locator set? accpetable locator set?
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Note that according to the shim6 protocol specification, locators are Note that according to the shim6 protocol specification, locators are
included in the Ls(peer) only after HBA/CGA verification has been included in the Ls(peer) only after HBA/CGA verification has been
successful. This eliminates the possibility of using locators that successful. This eliminates the possibility of using locators that
do not belong to the peer. Besides, it should be noted that before do not belong to the peer. Besides, it should be noted that before
using a given locator pair to actually send data packets, a using a given locator pair to actually send data packets, a
reachability test is performed in order to prevent flooding attacks. reachability test is performed in order to prevent flooding attacks.
4.1. Privacy considerations 4.1. Privacy considerations
Including or not RFC3041 [6] addresses in the Locator set available Including or not RFC3041 [RFC3041] addresses in the Locator set
for a shim6 context may have privacy implications. This is so available for a shim6 context may have privacy implications. This is
because of two reaosns: First, the inclusion of RFC 3041 addresses in so because of two reaosns: First, the inclusion of RFC 3041 addresses
the locator set discloses the RFC3041 addresses of the host to the in the locator set discloses the RFC3041 addresses of the host to the
peer. Second, the locator sets of both peers are exchanged in clear peer. Second, the locator sets of both peers are exchanged in clear
text during the shim6 context establishment and/or in the subsequent text during the shim6 context establishment and/or in the subsequent
UPDATE messages. This means that an attacker located along the path UPDATE messages. This means that an attacker located along the path
that can observe such packets can discover that all the addresses that can observe such packets can discover that all the addresses
included in the locator set belong to the same host, beating the included in the locator set belong to the same host, beating the
purpose of RFC3041 private addresses. So, when forming the locator purpose of RFC3041 private addresses. So, when forming the locator
set of a shim6 context the host must take into account these privacy set of a shim6 context the host must take into account these privacy
considerations in order to decide whether to include RFC3041 considerations in order to decide whether to include RFC3041
addresses in the locator set of a shim6 context. addresses in the locator set of a shim6 context.
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probability in the locator-pair selection process was suggested by probability in the locator-pair selection process was suggested by
Albert Banchs. Albert Banchs.
Marcelo Bagnulo worked on this document while visiting Ericsson Marcelo Bagnulo worked on this document while visiting Ericsson
Research laboratory Nomadiclab. Research laboratory Nomadiclab.
Iljitsch van Beijnum provided a detailed review of this document. Iljitsch van Beijnum provided a detailed review of this document.
6. References 6. References
[1] Nordmark, E. and M. Bagnulo, "Level 3 multihoming shim [shim] Nordmark, E. and M. Bagnulo, "Level 3 multihoming shim
protocol", draft-ietf-shim6-proto-04 (work in progress), protocol", draft-ietf-shim6-proto-04 (work in progress),
March 2006. March 2006.
[2] Arkko, J. and I. Beijnum, "Failure Detection and Locator Pair [faildet] Arkko, J. and I. Beijnum, "Failure Detection and Locator
Exploration Protocol for IPv6 Multihoming", Pair Exploration Protocol for IPv6 Multihoming",
draft-ietf-shim6-failure-detection-03 (work in progress), draft-ietf-shim6-failure-detection-03 (work in progress),
December 2005. December 2005.
[3] Hinden, R. and S. Deering, "IP Version 6 Addressing [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006. Architecture", RFC 4291, February 2006.
[4] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in [RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
IPv6", RFC 3775, June 2004. in IPv6", RFC 3775, June 2004.
[5] Thomson, S. and T. Narten, "IPv6 Stateless Address [RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998. Autoconfiguration", RFC 2462, December 1998.
[6] Narten, T. and R. Draves, "Privacy Extensions for Stateless [RFC3041] Narten, T. and R. Draves, "Privacy Extensions for
Address Autoconfiguration in IPv6", RFC 3041, January 2001. Stateless Address Autoconfiguration in IPv6", RFC 3041,
January 2001.
[7] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782, specifying the location of services (DNS SRV)", RFC 2782,
February 2000. February 2000.
[8] Draves, R., "Default Address Selection for Internet Protocol [RFC3484] Draves, R., "Default Address Selection for Internet
version 6 (IPv6)", RFC 3484, February 2003. Protocol version 6 (IPv6)", RFC 3484, February 2003.
Author's Address Author's Address
Marcelo Bagnulo Marcelo Bagnulo
Universidad Carlos III de Madrid Universidad Carlos III de Madrid
Av. Universidad 30 Av. Universidad 30
Leganes, Madrid 28911 Leganes, Madrid 28911
SPAIN SPAIN
Phone: 34 91 6248814 Phone: 34 91 6248814
skipping to change at page 11, line 44 skipping to change at line 443
attempt made to obtain a general license or permission for the use of attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
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