Multiple Interfaces (Mif) J. Korhonen
Internet-Draft Nokia Siemens Networks
Intended status: Experimental T. Savolainen
Expires: March 4, 2013 Nokia
A. Ding, Ed.
University of Helsinki
August 31, 2012
Controlling Traffic Offloading Using Neighbor Discovery Protocol
draft-korhonen-mif-ra-offload-05.txt
Abstract
This specification defines an extension to IPv6 Neighbor Discovery
Protocol, which allows management of IPv4 traffic offloading for
multi-interface dual-stack capable hosts and moving IPv4 traffic away
from a specific interface.
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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 4, 2013.
Copyright Notice
Copyright (c) 2012 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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements and Terminology . . . . . . . . . . . . . . . . . 3
3. Problem Background . . . . . . . . . . . . . . . . . . . . . . 3
4. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Neighbor Discovery Offload Option . . . . . . . . . . . . 4
4.2. Lowering IPv4 Router Preference . . . . . . . . . . . . . 7
4.3. IPv4 Offloading to Default Gateway . . . . . . . . . . . . 7
4.4. IPv4 Offloading to Specific Routes . . . . . . . . . . . . 8
4.5. Offload Lifetime . . . . . . . . . . . . . . . . . . . . . 8
5. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 8
6. Host Behavior . . . . . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Normative References . . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . . 10
Appendix A. Address Selection Approach . . . . . . . . . . . . . 11
A.1. Modification to Default Address Selection . . . . . . . . 11
A.2. Address selection examples . . . . . . . . . . . . . . . . 11
A.2.1. Case 1: IPv6-only cellular and IPv4-only WLAN
accesses . . . . . . . . . . . . . . . . . . . . . . . 11
A.2.2. Case 2: WLAN access with multiple prefixes . . . . . . 12
A.2.3. Case 3: WLAN and cellular interface with
cellular's IPv4 not default route . . . . . . . . . . 12
A.2.4. Case 4: Dual-stack cellular access . . . . . . . . . . 12
A.2.5. Case 5: Dual-stack cellular and single stack WLAN . . 13
A.2.6. Case 6: Coexistence with RFC4191 . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
This specification defines an extension to Neighbor Discovery
Protocol [RFC4861], which allows management of IPv4 traffic
offloading for multi-interface dual-stack capable hosts and moving
IPv4 traffic away from a specific interface.
The described solution is intended to be used during transition
towards IPv6, during which time multi-interfaced hosts are often
likely to have network interfaces with IPv4-only capability. A
common scenario where coexistence of IPv4 and IPv6 network interfaces
is expected to occur is when a smartphone has IPv6-enabled cellular
connection and IPv4-only WLAN connection active at the same time.
2. Requirements and Terminology
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 [RFC2119].
3. Problem Background
Current Internet hosts generally prefer IPv6 addresses over IPv4
addresses when performing source and destination address selections,
as is recommended in [I-D.ietf-6man-rfc3484bis].
A multi-interfaced host may have IPv6 enabled on a more 'expensive'
interface and a 'cheaper' interface may have support only for IPv4.
In such a scenario it might be desirable for hosts to prefer IPv4 in
communication instead of IPv6.
The above mentioned scenario can become a problem, for example, when
a smartphone has simultaneously IPv6-enabled cellular connection
([RFC6459]) and IPv4-only WLAN connectivity active. When connecting
to dual-stack capable destinations it would oftentimes be generally
more efficient to use WLAN network interface. Furthermore, a
cellular network operator may want hosts to offload traffic away from
the cellular network whenever hosts have alternate network accesses
available.
Similar issues can arise also when a host has multiple interfaces
with IPv4 connectivity. The interface that provides better
performance at a lower price should oftentimes be used for the
communication, but it may not be clear for a host which one of the
available interfaces it should prefer.
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4. Solution
This document introduces a new Neighbor Discovery option that a
network can use to communicate router's willingness to act as a
default gateway for IPv4 traffic and IPv4 offloading information for
specific routes.
The new Neighbor Discovery option was chosen to support hosts without
DHCPv6 [RFC3315] and DHCPv4 Classless Static Route Option [RFC3442]
support and also to work on networks not utilizing DHCPv6 and DHCPv4.
The Neighbor Discovery option proposed in this document SHOULD be
phased out when IPv4 usage diminishes.
4.1. Neighbor Discovery Offload Option
This specification defines a new Neighbor Discovery [RFC4861] option
called Offload (Type TBD) to be used in Router Advertisements. The
option is illustrated in Figure 1 and Figure 2. Routers and hosts
implementing this specification MUST understand the Offload option.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |D| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Gateway |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GW Lifetime | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Specific Route Information ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 1: Router Advertisement Offload Option
Type
TBD by IANA.
Length
8-bit unsigned integer. The length of the option (including the
Type and Length fields) is in units of 8 octets. The Length field
depends on the optional Specific Route Information. If there is
no Specific Route Information, the Length MUST be 2.
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D (IPv4 Gateway Preference)
Indicates the willingness of the Dual-Stack capable router (which
originated the Router Advertisement) to serve as a gateway for the
IPv4 traffic. If 'D' is unset (0) then the router indicates no
preference as to whether it is willing to serve as a gateway for
IPv4 traffic. If 'D' is set (1) then the router explicitly
indicates it is not willing to serve as a gateway for IPv4 traffic
if there are other usable gateways present in the same or other
available interfaces.
Reserved
Unused field. It MUST be initialized to zero by the sender and
MUST be ignored by the receiver.
IPv4 Gateway
The address of a dual-stack router's IPv4 interface which is used
as the next-hop from the host's point of view for sending and
receiving IPv4 traffic on this link. The IPv4 address MUST belong
to the same interface that originated the Router Advertisement
containing this Offload option.
GW Lifetime
16-bit unsigned integer. The Lifetime in seconds limits the
validity of state changes caused by this new option. The value of
Lifetime in this option SHOULD be smaller than or equal to the
value of Router Lifetime contained in the header of the same
Router Advertisement[RFC4191].
Specific Route Information
Optional information for IPv4 offloading to specific routes. The
format is illustrated in Figure 2. An Offload option can contain
multiple specific route entries.
Each Specific Route Information entry is in the length of 8 octets,
containing Route Lifetime, Route Preference, Prefix Length, and IPv4
Prefix. Multiple Specific Route entries can be contained within the
same Offload option.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Lifetime |Prf| Resvd | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Prefix 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Lifetime |Prf| Resvd | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Prefix 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| More Specific Routes ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Figure 2: Specific Route Information
Route Lifetime
16-bit unsigned integer. The length of time in seconds (relative
to the time the packet is sent) that the IPv4 prefix is valid for
route determination. The value of Route Lifetime SHOULD be
smaller than or equal to the value of GW Lifetime contained in the
same Offload option.
Prf (Route Preference)
2-bit signed integer. The preference values are encoded as
follows: 01 for High; 00 for Medium (default); 11 for Low; and 10
for Reserved which MUST NOT be sent. The Route Preference
indicates whether to prefer the router associated with this prefix
over others, when multiple identical prefixes for different
routers have been received.
Resvd (Reserved)
6-bit unused field. It MUST be initialized to zero by the sender
and MUST be ignored by the receiver.
Prefix Length
8-bit unsigned integer. The number of leading bits in the IPv4
Prefix field that are valid. The value ranges from 0 to 32.
IPv4 Prefix
The IPv4 Prefix field contains an IPv4 address. The Prefix Length
field contains the number of valid leading bits in the prefix.
The bits in the prefix after the prefix length (if any) are
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reserved and MUST be initialized to zero by the sender and ignored
by the receiver.
If the router is IPv6 only, the Neighbor Discovery Offload option
MUST be omitted in all Router Advertisements originated by the
router.
To avoid misconfiguration of offloading operation, a single Router
Advertisement MUST contain only one Offload option.
The behavior of 'IPv4 Gateway Preference' is discussed in more detail
in the following sections (see Section 4.2). The usage of 'IPv4
Gateway' for offloading is discussed in Section 4.4 and Section 4.3.
The Offload option is used only in Router Advertisements.
4.2. Lowering IPv4 Router Preference
The 'D' flag bit in the Offload option indicates the willingness of a
Dual-Stack capable router originating the Router Advertisement to
serve as a gateway for IPv4 traffic. If 'D' is set (1), the router
indicates that it SHOULD NOT be used as a gateway for IPv4 traffic,
if other gateways are present in the same or other available
interfaces. If 'D' is unset (0), the router does not indicate any
preference of being or not being a gateway for IPv4 traffic. When
'D' is unset (0), the decision of temporarily modifying the routing
status is left for hosts that receive the Offload option (see
Section 4.3 and Section 4.4). The 'IPv4 Gateway' field in the
Offload option contains the IPv4 address of the Dual-Stack interface
that originated the Router Advertisement. The address serves as the
identification of the next-hop IPv4 router.
4.3. IPv4 Offloading to Default Gateway
If there is no Specific Route Information in the Offload option, the
default gateway for IPv4 offloading can be added, updated, or deleted
depending on the 'D' flag, GW Lifetime, and existing routing status
on the hosts. When 'D' is set (1), the existing default gateway
matching to the advertised one SHOULD be removed if there are other
usable gateways present in the same or other available interfaces.
When 'D' is unset (0) and there is no default gateway present for the
receiving interface, the advertised IPv4 Gateway with valid lifetime
can be added. If the advertised gateway matches to the existing one
on the host, depending on the advertised lifetime, the existing
lifetime of default gateway shall be updated to the advertised GW
Lifetime in Offload option or deleted if the GW Lifetime is set to 0.
If there is a default gateway existing on the receiving interface,
which does not match the advertised gateway, the advertised one
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SHOULD be ignored.
4.4. IPv4 Offloading to Specific Routes
To enable IPv4 traffic offloading to specific routes, Specific Route
Information MUST be included in the same Offload option. A host
receiving such Router Advertisement needs to maintain status
including the IPv4 Gateway, IPv4 Prefix, Prefix Length, Route
Preference, and Route Lifetime. The Route Preference in the Offload
option indicates whether to prefer the IPv4 router associated with
this prefix over others. The Route Lifetime in the Offload option
determines how long the temporarily added specific route will be
valid.
When 'D' flag is unset (0) in the Offload option, the advertised
Specific Route Information shall be added by hosts if there is no
duplicated IPv4 prefix matching to the advertised IPv4 prefix and the
advertised Route Lifetime in Offload option is valid. If there is a
matching prefix, such specific route will be updated or deleted
according to the status of Route Lifetime and Route Preference. The
Route Lifetime in Offload option determines whether the route will be
deleted or updated depending on the existing routing status of the
hosts. If the advertised Route Lifetime is set to 0, any matched
IPv4 prefix and corresponding gateway MUST be removed. If Lifetime
is valid, the Route Preference further determines whether the IPv4
Gateway for the existing prefix, if matched, will be substituted to
the advertised one, or the lifetime for existing route will be
updated.
When 'D' flag is set (1) in the Offload option, any existing specific
routes with the next-hop router matching to the advertised IPv4
Gateway MUST be removed.
4.5. Offload Lifetime
The GW Lifetime in the Offload option determines the valid period of
temporary routing changes including IPv4 Gateway and offloading IPv4
traffic to specific routes. If a host receives a new Router
Advertisement without the Offload option, it MUST remove all existing
offload state information related to the router sending the Router
Advertisement.
5. Router Behavior
A router configuration SHOULD allow the network administrator to add
and configure this option into Router Advertisement messages. The
configuration can be selectively enabled (the Offload option is
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included in the Router Advertisement) or disabled (the Offload option
is not included in the Router Advertisement).
6. Host Behavior
A multi-interface capable host SHOULD monitor the presence of the
Offload option in Router Advertisements received. When an Offload
option is received, the IPv4 Gateway Preference and offloading status
for this router shall be temporarily updated as described in 4.2 and
4.3. Depending on the presence of Specific Route Information in the
same Offload option, the status of offloading IPv4 traffic to
specific routes shall be temporarily updated as described in 4.4.
Hosts SHOULD refer to both GW Lifetime and Route Lifetime (if
present) in the Offload option to determine the valid time of routing
changes caused by the Router Advertisement received.
If the host receives a Router Advertisement without the Offload
option and there is an existing state created by an earlier received
Offload option, then the host MUST remove all IPv4 gateway
preferences and offloading modifications from the previous Router
Advertisement. The removals concern only prefixes configured from
the router where the router advertisement was received.
7. Security Considerations
The Offload option allows malicious hosts and routers to affect a
victim host's next hop and default address selection if spoofing of
Router Advertisements are possible on the access link. This is a
well-known and understood security threat [RFC3756] and can be
mitigated using, for example, Secure Neighbor Discovery [RFC3971].
The security of utilizing the Offload option is at the equal level to
solution in [RFC4191].
8. IANA Considerations
This specification defines a new Neighbor Discovery option described
in Section 4.1.
9. Acknowledgements
Authors would like to thank Konstantinos Pentikousis for valuable
suggestions.
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10. References
10.1. Normative References
[I-D.ietf-6man-rfc3484bis]
Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol version 6
(IPv6)", draft-ietf-6man-rfc3484bis-06 (work in progress),
June 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3442] Lemon, T., Cheshire, S., and B. Volz, "The Classless
Static Route Option for Dynamic Host Configuration
Protocol (DHCP) version 4", RFC 3442, December 2002.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
10.2. Informative References
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3756] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor
Discovery (ND) Trust Models and Threats", RFC 3756,
May 2004.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, November 2005.
[RFC6459] Korhonen, J., Soininen, J., Patil, B., Savolainen, T.,
Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation
Partnership Project (3GPP) Evolved Packet System (EPS)",
RFC 6459, January 2012.
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Appendix A. Address Selection Approach
A.1. Modification to Default Address Selection
The 'lower-than-IPv4 Preference' affects the Source Address Selection
Rule 3. The notation Lower(SA) returns true if the address SA was
configured from the prefixes advertised by a 'lower-than-IPv4
Preference' router. Lower(SA) returns false is the address SA was
configured from prefixes advertised by other than 'lower-than-IPv4
Preference' router. The notation Default(D) returns false if the
address D has more specific routes (i.e. other than the default
route). Default(D) returns true if the address D points only to a
default route. The modified Rule 3 would be as follows:
Rule 3: Avoid deprecated addresses.
The addresses SA and SB have the same scope. If Lower(SA) == true
and Default(D) == true, then mark SA temporarily as "deprecated".
If Lower(SB) == true and Default(D) == true, then mark SB
temporarily as "deprecated". If one of the two source addresses
is "preferred" and one of them is "deprecated" (in the [RFC4862]
sense), then prefer the one that is "preferred."
Similar modification also concerns the Destination Address Selection
Rule 3 when checking whether a candidate source address for a given
destination is deprecated.
A.2. Address selection examples
Link-local addresses are omitted in all following examples. The
assumption is that possible destinations have a global scope and all
IPv6 enabled interfaces have at least one global scope IPv6 address.
Therefore, the default address selection would always output global
scope addresses over link-local addresses.
A.2.1. Case 1: IPv6-only cellular and IPv4-only WLAN accesses
A host has obtained global IPv6 address, 2001:db8::2, on a cellular
interface and with it has received Neighbor Discovery option with
'lower-than-IPv4' preference. The host also has global IPv4 address,
192.0.2.2, on a WLAN interface.
When connecting to a dual-stack enabled destination, both 2001:db8::2
and 192.0.2.2 are considered as source addresses candidates. IPv4
address is selected, because 2001:db8::2 is considered deprecated.
Hence host uses WLAN for communication.
When connecting to IPv6-only destination, 2001:db8::2 is selected and
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cellular network used, as there are no other IPv6 addresses
available.
A.2.2. Case 2: WLAN access with multiple prefixes
A host has obtained two global IPv6 addresses, one of which was from
a router indicating 'lower-than-IPv4' preference. For example, 2001:
db8:1::2 from router with 'lower-than-IPv4' preference and
2001:db8:2::3 from router without any special preferences.
When connecting to IPv6-only destination, both addresses are
considered as source address candidates. Source address selection
chooses 2001:db8:2::3 as 2001:db8:1::2 is considered deprecated
(Lower(2001:db8::2) == true and Default(D) == true).
A.2.3. Case 3: WLAN and cellular interface with cellular's IPv4 not
default route
A host has obtained IPv6 address, 2001:db8::2, and IPv4 address,
192.0.2.2, from cellular network. The network has indicated 'lower-
than-IPv4' preference for IPv6 and 'not your default router' for
IPv4. The host also has dual-stack WLAN access with 2001:db8:1::3
and 192.0.2.30 addresses.
When connecting to IPv4-only destination, host selects 192.0.2.30 as
source address because default gateway on the interface of 192.0.2.2
address is 'not default gateway'. WLAN is used for communication.
When connecting to IPv6-only destination, host selects 2001:db8:1::3
from WLAN interface as the 2001:db8::2 is considered deprecated
(Lower(2001:db8::2) == true and Default(D) == true). WLAN is used
for communication.
When connecting to dual-stack destination, host selects from the four
candidate addresses 2001:db8:1::3, as IPv6 is preferred in general
and as that address is not deprecated. WLAN is used for
communication.
A.2.4. Case 4: Dual-stack cellular access
A host has obtained IPv6 address, 2001:db8::2, and IPv4 address,
192.0.2.2, from cellular network. The network has indicated 'lower-
than-IPv4' preference.
When connecting to a dual-stack enabled destination, both addresses
are considered as candidate source addresses. IPv4 address is
chosen, because IPv6 address is considered deprecated.
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A.2.5. Case 5: Dual-stack cellular and single stack WLAN
A host has obtained IPv6 address, 2001:db8::2, and IPv4 address,
192.0.2.2, from cellular network. The network has indicated 'lower-
than-IPv4' preference for IPv6 and 'not your default router' for
IPv4. The host also has WLAN access with 192.0.2.30 address.
When connecting to dual-stack destination, all three addresses are
considered as source address candidates. The IPv4 address from WLAN,
192.0.2.30, is selected as the IPv6 address, 2001:db8::2, is
considered deprecated and as the IPv4 default route points to WLAN.
Hence WLAN is used for communication.
A.2.6. Case 6: Coexistence with RFC4191
A host has obtained IPv6 address, 2001:db8:1::2/64 from cellular
network. The network has indicated 'lower-than-IPv4' preference for
IPv6 and a more specific route to 2001:db8:2::/48. The host also has
IPv6 WLAN access with 2001:db8:3::3/64 address.
When connecting to 2001:db8:2::1 the host selects 2001:db8:1::2 from
cellular interface as a source address, because Lower(2001:db8:1::2)
== true and Default(2001:db8:2::1) == false and hence the
2001:db8:1::2 is not considered as deprecated address even though
'lower-than-IPv4' preference was advertised.
When connecting to 2001:db8:4::1 the host selects 2001:db8:3::3 from
WLAN interface as a source address, because Lower(2001:db8:2::1) ==
true and Default(2001:db8:3::3) == true) and hence 2001:db8:2::1 is
considered as deprecated address.
Authors' Addresses
Jouni Korhonen
Nokia Siemens Networks
Linnoitustie 6
FI-02600 Espoo
Finland
Email: jouni.nospam@gmail.com
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Teemu Savolainen
Nokia
Hermiankatu 12 D
FI-33720 Tampere
Finland
Email: teemu.savolainen@nokia.com
Aaron Yi Ding (editor)
University of Helsinki
P.O. Box 68
FI-00014 University of Helsinki
Finland
Email: yding@cs.helsinki.fi
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