Multiple Interfaces (Mif) J. Korhonen
Internet-Draft Nokia Siemens Networks
Intended status: Experimental T. Savolainen
Expires: May 3, 2012 Nokia
Y. Ding, Ed.
University of Helsinki
October 31, 2011
Controlling Traffic Offloading Using Neighbor Discovery Protocol
draft-korhonen-mif-ra-offload-03.txt
Abstract
This specification defines an extension to IPv6 Neighbor Discovery
Protocol, which allows management of IPv6 traffic offloading to IPv4
and moving IPv4 traffic away from a specific interface.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
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This Internet-Draft will expire on May 3, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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 . . . . . . . . . . . . . 5
4.3. IPv4 Offloading to Specific Routes . . . . . . . . . . . . 6
4.4. IPv4 Offloading to Default Gateway . . . . . . . . . . . . 7
4.5. Offload Lifetime . . . . . . . . . . . . . . . . . . . . . 7
5. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 7
6. Host Behavior . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . . 9
Appendix A. Address Selection Approach . . . . . . . . . . . . . 9
A.1. Modification to Default Address Selection . . . . . . . . 9
A.2. Address selection examples . . . . . . . . . . . . . . . . 10
A.2.1. Case 1: IPv6-only cellular and IPv4-only WLAN
accesses . . . . . . . . . . . . . . . . . . . . . . . 10
A.2.2. Case 2: WLAN access with multiple prefixes . . . . . . 10
A.2.3. Case 3: WLAN and cellular interface with
cellular's IPv4 not default route . . . . . . . . . . 11
A.2.4. Case 4: Dual-stack cellular access . . . . . . . . . . 11
A.2.5. Case 5: Dual-stack cellular and single stack WLAN . . 11
A.2.6. Case 6: Coexistence with RFC4191 . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
This specification defines an extension to Neighbor Discovery
Protocol [RFC4861], which allows management of IPv6 traffic
offloading to IPv4 and moving IPv4 traffic away from a specific
network connection.
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-rfc3484-revise].
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
([I-D.ietf-v6ops-3gpp-eps]) 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 cellular network whenever hosts have alternate
network accesses available.
Similar issue 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 the level of router's willingness to
act as a router for IPv4 traffic.
The new Neighbor Discovery option was chosen to support hosts without
DHCPv6 [RFC3315] support and also to work on networks not utilizing
DHCPv6.
The new Neighbor Discovery option can be used together with the Route
Information option defined in [RFC4191] to communicate offloading
information for specific routes.
The new Neighbor Discovery option shall 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. Router 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=2 |D| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Gateway |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Router Advertisement Offload Option
Type
TBD by IANA.
Length
MUST be set to 2.
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D (IPv4 Gateway Preference)
Indicates the willingness of the Dual-Stack capable router (who
originated the Router Advertisement) to serve as a gateway for the
IPv4 traffic. If 'D' is unset (0) then the router indicates no
specific to be or not to be 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
A 15-bit unused field. It MUST be initialized to zero by the
sender and MUST be ignored by the receiver.
Gateway
The address of the dual-stack router's IPv4 interface used as the
next-hop from hosts 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
option. If the router is IPv6 only, then this field MUST be set
to unspecified address (0.0.0.0) or the Neighbor Discovery Offload
option MUST be omitted in all Router Advertisements originated by
the router.
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 the value of Route
Lifetime contained in the Route Information option [RFC4191], if
present, in the same Router Advertisement.
Padding
The padding MUST be initialized to zero by the sender and MUST be
ignored by the receiver.
The behavior of 'IPv4 Gateway Preference' (see Section 4.2) is
discussed in more detail in the following sections. The usage of
'Gateway' for offloading is discussed in Section 4.3 and Section 4.4.
The Offload option is only used in Router Advertisement messages.
4.2. Lowering IPv4 Router Preference
The 'D' flag bit in the Offload option indicates the willingness of
Dual-Stack capable router originating the Router Advertisement to
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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 '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 routers.
4.3. IPv4 Offloading to Specific Routes
To enable offloading of IPv4 traffic to specific routes, both Offload
option and Route Information option [RFC4191] MUST present in the
same Router Advertisement. A host receiving such Router
Advertisement need to maintain a set of status including specific
route, Router Preference, and Lifetime. A specific route consists of
an IPv4 gateway from the Offload option and an IPv4 prefix from the
Route Information option. The Prefix field in the Route Information
option SHOULD follow the IPv4-mapped IPv6 address format defined in
[RFC4291]. The Prefix Length in the Route Information option is used
to indicate the IPv4 prefix length. The Router Preference in the
Route Information option indicates whether to prefer the IPv4 router
associated with this prefix over others. The Lifetime in the Offload
option determines how long the temporarily added specific route will
be valid. The Lifetime field in Route Information option SHOULD be
ignored.
When 'D' flag is unset (0) in the Offload option, the advertised
specific route shall be added by hosts if there is no duplicated
prefix matching to the advertised prefix and the advertised 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
Lifetime and Router Preference. The 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 Lifetime
is set to 0, any matched prefix and the corresponding route MUST be
removed. If Lifetime is valid, the Router Preference further
determines whether the gateway of the existing route, 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 gateway
SHOULD be removed.
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To avoid misconfiguration of offloading operation, only one Offload
option is allowed in a single Router Advertisement.
4.4. IPv4 Offloading to Default Gateway
If there is no Route Information options containing IPv4-mapped IPv6
addresses in the same Router Advertisement, the default gateway for
offloading can be added, updated, or deleted depending on the 'D'
flag, 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 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 default
gateway shall be updated to the advertised lifetime in Offload option
or deleted if the lifetime is set 0. If there is a default gateway
existing on the receiving interface, which does not match to the
advertised gateway, the advertised one SHOULD be ignored.
4.5. Offload Lifetime
The lifetime in the Offload option determines the valid period of
temporary routing changes including IPv4 gateway preferences and
offloading of IPv4 traffic to specific routes and default gateway.
If the router sends a new Router Advertisement without the Offload
option before the router lifetime expires, it is an indication to the
receiving hosts that any existing Offload option caused state/
information MUST be removed.
5. Router Behavior
A router configuration SHOULD allow network administrator to add and
configure this option into Router Advertisement messages. The
configuration can be selectively enabled (the Offload option is
included in the Router Advertisement) or disabled (the Offload option
is not included in the Router Advertisement). For specific route
offloading, the prefix(es) advertised in the Route Information option
SHOULD follow IPv4 mapped IPv6 address (e.g. ::ffff:1.2.3.4) as
described in 4.3.
6. Host Behavior
A multi-interface capable host SHOULD monitor presence of Offload
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option in received Router Advertisement messages. When the Offload
option is received, the IPv4 gateway preferences and offloading to
default gateway shall temporarily be updated as described in 4.2 and
4.4. Depending on the presence of Route Information in the same
Router Advertisement, the offloading to specific IPv4 routes shall
temporarily be updated as described in 4.3. Hosts SHOULD uses the
lifetime value in the Offload option to determine the valid time of
all 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 concerns the prefixes configured from
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. References
9.1. Normative References
[I-D.ietf-6man-rfc3484-revise]
Matsumoto, A., Kato, J., Fujisaki, T., and T. Chown,
"Update to RFC 3484 Default Address Selection for IPv6",
draft-ietf-6man-rfc3484-revise-04 (work in progress),
July 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
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"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.
9.2. Informative References
[I-D.ietf-v6ops-3gpp-eps]
Korhonen, J., Soininen, J., Patil, B., Savolainen, T.,
Bajko, G., and K. Iisakkila, "IPv6 in 3GPP Evolved Packet
System", draft-ietf-v6ops-3gpp-eps-08 (work in progress),
September 2011.
[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.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
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:
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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
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).
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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.
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.
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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
Teemu Savolainen
Nokia
Hermiankatu 12 D
FI-33720 Tampere
Finland
Email: teemu.savolainen@nokia.com
Yi Ding (editor)
University of Helsinki
P.O. Box 68
FI-00014 University of Helsinki
Finland
Email: yi.ding@cs.helsinki.fi
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