One document matched: draft-jeon-ipv6-ndp-ieee802.16-01.txt
Differences from draft-jeon-ipv6-ndp-ieee802.16-00.txt
Network Working Group H. Jeon
Internet-Draft J. Jee
Expires: September 7, 2006 ETRI
March 6, 2006
IPv6 NDP for Common Prefix Allocation in IEEE 802.16
draft-jeon-ipv6-ndp-ieee802.16-01.txt
Status of this Memo
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This Internet-Draft will expire on September 7, 2006.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
IPv6 Neighbor Discovery Protocol [RFC 2461] assumes that the
underlying link layer support native multicast while IEEE 802.16 is a
point-to-multipoint network without bi-directional native multicast
support. Such a discordance between IPv6 Neighbor Discovery Protocol
and IEEE 802.16 network results in the on-link and multicast issues.
This document defines a mechanism, IPv6 NDP Relay and Multicast
Emulation, to solve these issues.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. IPv6 Neighbor Discovery Issues over IEEE 802.16 . . . . . . . 5
4.1. On-Link Issue . . . . . . . . . . . . . . . . . . . . . . 5
4.2. Multicast Issue . . . . . . . . . . . . . . . . . . . . . 5
4.3. IEEE 802.16 Convergence Sublayer . . . . . . . . . . . . . 5
5. IPv6 Neighbor Discovery Support over IEEE 802.16 . . . . . . . 6
5.1. IP Convergence Sublayer . . . . . . . . . . . . . . . . . 6
5.1.1. IPv6 NDP Relay . . . . . . . . . . . . . . . . . . . . 6
5.1.2. Multicast Emulation . . . . . . . . . . . . . . . . . 7
5.2. Ethernet Convergence Sublayer . . . . . . . . . . . . . . 9
5.2.1. IPv6 NDP Relay . . . . . . . . . . . . . . . . . . . . 9
5.2.2. Multicast Emulation . . . . . . . . . . . . . . . . . 10
6. Consideration for alternative approaches . . . . . . . . . . . 10
6.1. Proxy Neighbor Advertisements . . . . . . . . . . . . . . 10
6.2. Proxy DAD . . . . . . . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . . . 14
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1. Introduction
IEEE 802.16 [IEEE 802.16][IEEE 802.16e] is a connection-oriented
broadband wireless access(BWA) technology. Down-stream in IEEE
802.16 is a point-to-multipoint connection and thus it is possible to
broadcast messages toward SS (Subscriber Station) from BS (Base
Station). However, up-stream is connected as point-to-point type.
Therefore, SS is not capable of multicasting as well broadcasting.
IPv6 Neighbor Discovery Protocol (IPv6 NDP) [RFC 2461] aims to solve
problems due to the interaction between nodes attached on the same
link. It is designed without dependence on a specific link layer
technology, but assumes that the link layer technology support a
native multicasting. As mentioned above, IEEE 802.16 supports
multicast and broadcast in down-stream. However, the original aim of
the multicast and broadcast is to transmit IEEE 802.16 MAC management
messages for bandwidth allocation, not IP data. Thus, IPv6 Neighbor
Discovery message on IEEE 802.16 cannot be delivered to neighboring
hosts by means of multicast.
IPv6 NDP messages have link-local scoped address as IP destination
address. It means those messages have to be delivered toward on-link
any hosts. However, when all SSs under same BS are configured with
common IPv6 network prefix, IEEE 802.16 disagrees with IPv6 Neighbor
Discovery on the definition of on-link host. This is because IPv6
NDP determines the on-link host with assigned prefixs while up-stream
in IEEE 802.16 is a point-to-point connection. IEEE 802.16 does not
allow direct communication among SSs even though each SS knows that
other SSs are neighboring ones at the IP level. Eventually, this
discrepancy results in limitation of transmission coverage of IPv6
NDP messages with link-local scoped address.
Following the 3GPP model for IPv6 NDP [RFC 3314], Access Router (AR)
may assign distinct subnet to each SSs. In the case, IPv6 NDP can be
deployed without any modification and some operations in IPv6 NDP
such as Address Resolution and Neighbor Unreachability Detection may
be unnecessary. However, such a unique prefix allocation disallows
network renumbering with prefix and cannot simplify network
management.
IPv6 over NBMA networks [RFC 2491] presents a general architecture
for IPv6 over Non-Broadcast Multiple Access (NBMA) network.
Specifically, [RFC 2491] focuses on an NBMA network with SVC mode
which utilizes dynamically managed point to point and point to
multipoint call between both communication hosts. On the other hand,
IEEE 802.16 is employed as access network technology in most cases
and thus does not provide communication between end hosts.
Therefore, IEEE 802.16 cannot be referred to as NBMA network stated
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in [RFC 2491].
This document presents a mechanism which can allocate a common
network prefix to all SS under the same IPv6 link. Through the
mechanism, the standard IPv6 NDP can be applied to IEEE 802.16
networks without modifying conventional host-side operation.
2. Requirements
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. Terminology
Description of following some terms is taken directly from [IEEE
802.16] and [IEEE 802.16e].
BS (Base Station) : A generalized equipment set providing
connectivity, management, and control of the subscriber station.
SS (Subscriber Station) : A generalized equipment set providing
connectivity between subscriber equipment and a base station.
CS (Service-specific Convergence Sublayer) : Sublayer in IEEE 802.16
MAC layer which classifier external network data and associates them
to the proper MAC service flow identifier and connection identifier.
CID (Connection Identifier) : A 16 bit value that identifies a
connection to equivalent peers in the MAC of the base station and
subscriber station.
DSA (Dynamic Service Addition) : The set of messages and protocols
that allow the base station and subscriber station to add the
characteristics of a service flow.
MBS (Multicast and Broadcast Services) : Globally defined service
flow that carries broadcast or multicast information towards a
plurality of SS.
MBS-CID (Multicast and Broadcast Services Connection ID) : Traffic
CID for MBS.
CCID (Common Connection Identifier) : CID shared by all SSs and BS
for the purpose of transmitting IPv6 Neighbor Discovery messages.
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4. IPv6 Neighbor Discovery Issues over IEEE 802.16
This section summarizes issues when IPv6 Neighbor Discovery is
employed over IEEE 802.16 under the condition all SSs are assigned
with common prefix address.
4.1. On-Link Issue
The assignment of a common prefix to all SSs under a specific AR
means locating them "on-link" in terms of IP packet transfer. From
[I-D.ietf-ipv6-2461bis], IP node determines destinations are on-link
by performing a longest prefix match against the prefix list.
Therefore, SSs sharing common prefix can be said to on-link IP nodes.
IPv6 NDP is a protocol to solve problems due to the interaction
between on-link nodes and requires direct communication between them.
By the way, IEEE 802.16 is a connection-oriented network. Even
though all data in IEEE 802.16 can be broadcasted to air shared to
all SSs, only SS associated with the CID included in the data can
receive the data. The connection of IEEE 802.16 always ends at the
BS. There is no support from 802.16 MAC/PHY for the direct
communication among SSs [I-D.jee-16ng-ps-goals] which results in the
problem of locating SSs on-link in terms of IP packet transfer.
4.2. Multicast Issue
IPv6 Neighbor Discovery messages excepting Redirect are destined for
link-local scoped multicast address such as all-router multicast
address, all-node multicast address, and solicited-node multicast
address.
However, there is no dedicated CIDs for multicasting IPv6 packet in
IEEE 802.16. Thus, any available traffic CID value needs to be
allocated for multicasting IPv6 packet.
4.3. IEEE 802.16 Convergence Sublayer
IEEE 802.16 defines two types of Convergence Sublayer (CS), IP CS and
Ethernet CS.
When IP CS is applied, BS and AR may need to be tightly coupled by
physically or logically by tunneling mechanism like GRE Tunneling
(Figure 1 and 2). Therefore, IP packets which are destined for on-
link IP nodes needs to be first transfered toward AR. Special
consideration is required on the AR in treating IPv6 NDP messages
which have different destination forms like link-local unicast, link-
local all-nodes multicast, link-local all-routers multicast and
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solicited node multicast address.
+------+
| AR |
+-------+ +------+
| AR/BS | // || \\
+-------+ // || \\ <= tunnel
// || \\
BS1 BS2 BS3
Figure 1 Figure 2
In case of Ethernet CS, IEEE 802.16 deployment architecture can be
configured as shown in Figure 3. Assuming Ethernet link between BS
and AR, we can consider similar bridging function on BS to one on
WLAN access point. Additional bridging function on BS is to
interpret the Ethernet header of packets received from SS and
transmit the packets toward expected next node. In Figure 3, such an
next node can be another BS, another SS, or AR.
+-----+
| AR |
+--+--+
|
-----+-----
/ / | \ \
/ | | | \
BS1 BS2 BS3 BS4 BS5
Figure 3
5. IPv6 Neighbor Discovery Support over IEEE 802.16
Following subsections provide a mechanism to handle the mentioned
respective issues. The mechanism may require explicit cooperation
with IEEE 802.16 technology or enhanced bridge function on BS. The
mechanism will be described by case of CS type.
5.1. IP Convergence Sublayer
5.1.1. IPv6 NDP Relay
By aforementioned "On-Link" issue, IEEE 802.16 does not support
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direct communication between on-link SSs. Moreover, AR in IP CS case
is always a next-hop neighbor even when SS sends data to on-link SSs
and thus all data have to be sent to AR as mentioned in the section
4.3. As a result, the AR discards IPv6 NDP messages addressed link-
local all-node multicast and solicited node multicast address because
the messages do not intend for the AR. Therefore, it is necessary to
relay the restricted messages.
Multicast Relaying Part (MRP) serves as packets relayer and is
located in AR. MRP over AR intercepts packets destined for the
multicast addresses and then prepares packet relaying while passing
those to upper layer. Intercepting rule of MRP is different
according to the case when IEEE 802.16 CS supports IPv6 over Ethernet
or native IPv6. In case of IP CS, MRP holds packets, which begin
with FF02 in IPv6 address. Note that the MRP does not intercept
packets addressed FF02::2. This is due to the assumption the AR
serves as default router and there is no other router in the subnet.
Table 1 shows IP multicast address types used in IPv6 NDP.
+--------------------------------+--------------------------+
| Type | IP Address Type |
+--------------------------------+--------------------------+
| Link-local all-nodes | FF02::1 |
| multicast address | |
+--------------------------------+--------------------------+
| Link-local all-routers | FF02::2 |
| multicast address | |
+--------------------------------+--------------------------+
| Solicited-node | FF02::1:FFxx:x |
| multicast address | |
+--------------------------------+--------------------------+
xx:x is last 24 bits of a unicast IPv6 address.
Table 1
When BS and AR are coupled as shown in Figure 1, AR should forward
unicast packets destined for on-link host. In the case, the packets
must be transmitted again via the incoming interface and AR has to
transmit Redirect message to sender whenever communication between
on-link SSs occurs. This problem can be issue in implementation of
AR and MRP can treat the problem.
5.1.2. Multicast Emulation
This section describes how to transmit the packets with link-local
scoped multicast address into IEEE 802.16 network. We suggest
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following two different approaches for the purpose of multicast
emulation.
5.1.2.1. Multicast Emulation using Common CID
IEEE 802.16 enables multicast transmission in down-stream. However,
it is difficult to create and maintain CIDs for multicast because
there can be manifold multicast sessions. Therefore, this document
defines Common CID (CCID) for transmitting multicast data.
There is one unique CCID in BS and it is shared by all SSs served by
the BS. All SSs can receive data transmitted via the CCID and IPv6
module in SSs see whether the multicast data are destined to
themselves or not.
Current IEEE 802.16 does not specify CID which can be shared by all
SSs and used for IP data. Following describes how to make CCID with
existing MBS-CID.
[IEEE 802.16e] proposes Multicast and Broadcast Service (MBS), which
presents media service to SSs using multicast or broadcast. Under
MBS architecture, each SS selects MBS contents and then configures a
corresponding CID by the DSA procedure. Such a CID for MBS is
referred to as MBS-CID. MBS-CID is one of transport CIDs and is
shared by all SSs requesting same media content.
CCID can be seen as a special type of MBS-CID. CCID is allocated to
BS and all SSs served by the BS utilizing a general DSA procedure in
MBS for transmitting link-local multicast data. For the assigning
the CCID, we assume that service flow for link-local multicast is
globally defined and the service flow is known to BS and all SSs.
Once initialization between BS and SS is completed, they perform DSA
procedure for creating the link-local multicast service flow. The
detailed process creating new service flow and updating CS for
mapping of the service flow to CCID is outside scope of this
document.
BS transmits IPv6 Neighbor Discovery messages relayed by MRP towards
all SSs via the CCID.
5.1.2.2. Multicast Emulation using Replicated Unicast
The transmission using CCID allows IPv6 Neighbor Discovery messages
to be delivered only once per transmission. However, it requires a
new CID for multicast. This section shows how to transmit IPv6
Neighbor Discovery messages with existing unicast CID.
IPv6 Neighbor Discovery message can be delivered by repeated unicast
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transmissions towards SSs involved in the multicast address of the
IPv6 Neighbor Discovery message.
IPv6 Neighbor Discovery messages with link-local all node multicast
address should be sent to all SSs and thus they can be transmitted by
replicated unicasts via all established CIDs on BS.
In this context, IPv6 Neighbor Discovery messages with solicited-node
multicast address should be transmitted by replicated unicasts via
CIDs of corresponding SSs. Thus, it is required to identify CIDs for
solicited-node multicast addresses.
Section 6.3.1.1 in [IEEE 802.16] states that a 48-bit universal MAC
address of SS is used during the initial ranging process to identify
connections to SS. Solicited-node multicast address of SS can be
derived by the MAC address. As a result, BS can be aware of the
solicited-node multicast addresses with the known MAC address of each
SS and match the derived addresses with each CIDs.
5.2. Ethernet Convergence Sublayer
5.2.1. IPv6 NDP Relay
In Ethernet CS type, MRP is located in BS.
The MRP on BS intercepts packets destined for the multicast addresses
from Ethernet CS. The intercepted packets are relayed again toward
other SSs served by the same BS while being passed to a bridge
operation on the BS.
The MRP intercepts packets, which begin with "33-33" in Ethernet
address excepting packets addressed routers ("33-33-00-00-00-02").
Table 2 shows Ethernet address corresponding to the multicast address
types used in IPv6 NDP.
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+--------------------------------+--------------------------+
| Type | Ethernet Addr. Type |
+--------------------------------+--------------------------+
| Link-local all-nodes | 33-33-00-00-00-01 |
| multicast address | |
+--------------------------------+--------------------------+
| Link-local all-routers | 33-33-00-00-00-02 |
| multicast address | |
+--------------------------------+--------------------------+
| Solicited-node | 33-33-FF-xx-xx-xx |
| multicast address | |
+--------------------------------+--------------------------+
xx-xx-xx is last 24 bits of a unicast IPv6 address.
Table 2
5.2.2. Multicast Emulation
Same as IP CS case.
6. Consideration for alternative approaches
There are a few ways to solve the IP "On-Link" issues over IEEE
802.16 network without depending on the Multicast Relaying Part (MRP)
proposed in this I-D.
6.1. Proxy Neighbor Advertisements
Through proxy neighbor advertisement, an AR in 802.16 network can
accept NS packets on behalf of SS. However, as noted from [I-D.ietf-
ipv6-2461bis], this mechanism is not intended as a general mechanism
to handle IP nodes, thus it needs more investigation in moving
forward based on this scheme.
6.2. Proxy DAD
Proxy DAD can be implemented to AR or BS to guarantee the uniqueness
of autoconfigured address which is based on the 48-bit MAC address.
However, as noted from [RFC 3314], this proxy DAD function would
increase the complexity and the amount of state to be kept in the AR.
Also, the AR would need to determine when the temporary addresses are
no longer in use, which would be difficult.
7. Security Considerations
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IEEE 802.16e architecture supports a number of mandatory
authorization mechanisms such as EAP-TTLS, EAP-SIM and EAP-AKA.
[RFC 3971] specifies security mechanisms for NDP and defines securing
NDP messages.
Basically, our approach of using "MRP" enables SSs to exchange IPv6
NDP messages directly without depending on any proxy function at the
AR or BS. Therefore, it has advantage in securing NDP messages by
the mechanism specified from [RFC 3971].
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
8.2. Informative References
[I-D.ietf-ipv6-2461bis]
Narten, T., "Neighbor Discovery for IP version 6 (IPv6)",
draft-ietf-ipv6-2461bis-05 (work in progress),
October 2005.
[I-D.jee-16ng-ps-goals]
Jee, J., "IP over 802.16 Problem Statements and Goals",
draft-jee-16ng-ps-goals-00 (work in progress),
February 2006.
[IEEE802.16]
IEEE Std 802.16-2004, "IEEE Standard for Local and
metropolitan area networks, Part 16: Air Interface for
Fixed Broadband Wireless Access Systems", October 2004.
[IEEE802.16e]
IEEE P802.16e/D10, "Draft IEEE Standard for Local and
metropolitan area networks, Amendment for Physical and
Medium Access Control Layers for Combined Fixed and
Mobile Operation in Licensed Bands", Auguest 2005.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461,
December 1998.
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[RFC2491] Armitage, G., Schulter, P., Jork, M., and G. Harter, "IPv6
over Non-Broadcast Multiple Access (NBMA) networks",
RFC 2491, January 1999.
[RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast
Listener Discovery (MLD) for IPv6", RFC 2710,
October 1999.
[RFC3314] Wasserman, M., "Recommendations for IPv6 in Third
Generation Partnership Project (3GPP) Standards",
RFC 3314, September 2002.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
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Authors' Addresses
Hongseok Jeon
Electronics Telecommunications Research Institute
161 Gajeong-dong, Yuseong-gu
Daejeon, 305-350
KOREA
Phone: +82-42-860-3892
Email: jeonhs@etri.re.kr
Junghoon Jee
Electronics Telecommunications Research Institute
161 Gajeong-dong, Yuseong-gu
Daejeon, 305-350
KOREA
Phone: +82-42-860-5126
Email: jhjee@etri.re.kr
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