Internet DRAFT - draft-wen-ipv6-rsra-opt-pid
draft-wen-ipv6-rsra-opt-pid
IETF IPv6 Working Group Haibo Wen
Internet-Draft Alcatel Shanghai Bell
Expires: December 22, 2006 June 23, 2006
Port Identifier option for RS/RA messages in IPv6 access network
draft-wen-ipv6-rsra-opt-pid-01.txt
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Copyright (C) The Internet Society (2006).
Abstract
This document makes an extension to stateless address auto-
configuration (SAAC) mechanism by defining Port Identifier option for
RS/RA messages in IPv6 access network. This option can make SAAC
possible without upgrading access node and CPE to be layer 3 devices.
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Conventions used in this document
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 RFC 2119 [3].
Terminology
This document uses the terminology described in [1][2][3]. In
addition, some new terms are defined below:
Access node
Access node is the point to which the subscriber network physically
connects. In this document, Layer 3 access node is an access node
that works at layer 3, acts as a router with access management
functions in access network. Layer 2 access node is an access node
that works at layer 2 and can handle some special layer 3 packet.
Aggregation network
The part of the network stretching from from access node to the
Broadband Network Gateways(BNG, i.e., IP edge router).
BRAS
Broadband Remote Access Server is a broadband network gateway and
is the aggregation point for the subscriber traffic. It also
provides subscriber authentication, management and other functions
before forwarding IP traffic to and receiving it from the Internet.
Subscriber Network
a network which is owned by a subscriber, and attached to an access
node. In this network, all the terminals/hosts share same prefixes,
each can be trusted to behave correctly, so they are friendly to
each other. Subscriber network can also be called home network.
1. Introduction
Stateless Address Auto-Configuration [1] (SAAC) is a very important
feature for IPv6 technology. And SAAC has been proposed with the
following goals: (1) No manual configuration of individual machines
before connecting them to the network. (2)No DHCP server or router as
a prerequistie for the communication between a set of machines
attached to a single link. The machines can form their IPv6 addresses
by appending their 64-bit interface identifier to a well-known link-
local prefix. (3)No requirement of the presence of DHCP server for
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address configuration in a large site with multiple networks and
routers. (4) Facilitating the graceful renumbering of a site's
machines.
With the explosive growth of Internet and end user, Network Service
Providers (NAP) are considering evolving their network architecture
to support IPv6 technology. It's a trend that many terminals/hosts in
subscriber network will connect to Internet via CPE in the future,
thus the devices in subscriber network can form a subnet. Considering
simple management and maintenance, the policy of one prefix per
subscriber network, i.e., a /64 prefix will be assigned to each
subscriber network, will be deployed by NAP. And in current access
network, most of the CPEs in the subscriber networks are layer 2
devices, and the access nodes in aggregrate network are layer 2
devices, too. Because replacing CPE and access node to be layer 3
devices will require much more investment, it is a better way to make
current access network support SAAC without this kind of investment.
And this will help operators protect exiting investment.
This document contributes on how to implement SAAC with one prefix
per subscriber network in IPv6 access network without replacing
current CPE and access node with layer 3 devices. This is done by
defining a new option for Router Advertisment (RA) /Router
Solicitation (RS) messages.
2. Port Identifier option
2.1 Motivation
In the standard IPv6 stateless configuration, a router sends
periodical as well as solicited RA messages out its advertising
interfaces. The RA messages are encapsulated in ICMPv6 packets.
Within the RA messages, global IP prefixes are advertised to the
directly attached link. Thus all the terminals can obtain the IPv6
prefixes to form their global IPv6 addresses by appending their
interface identifier to the IPv6 prefixes.
When an interface of an IPv6 terminal becomes enabled, the terminal
which may be unwilling to wait for the next unsolicited RA message to
locate default routers or learn prefixes, will transimit RS message.
In IPv6 access network with layer 2 CPE and layer 2 access node, RA
messages will be advertised from BRAS/BNG to subscriber networks. For
RS/RA messages, each subscriber network and the BRAS's interface that
will advertise RA message must be formed into a logical LAN. If not,
the following problems occur: (1) Because the subscriber network
information (or subscriber line information) is terminated at the
access node, BRAS/BNG cannot identify the originating subscriber
network of any upstream RS message, then it doesn't know how to
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choose correct prefix to form an appropriate RA to respond. (2)
Access node couldn't know the exact destination subscriber network of
each downstream RA message, if the RA message is broadcasted to all
the subscriber networks connecting to the same access node, this may
lead to prefix spoofing.
Port Identifier (PID) option is defined in this document to solve the
problems above-mentioned. It is kind of DHCP relay agent option
(option 82) for Dynamic Host Configuration Protocol in IPv4. For the
upstream RS message, access node inserts the subscriber line
information (i.e., the Port Identifier of the user port on the access
node) into RS with PID option. In downstream RA message, BRAS/BNG
should arrange the PID option with the corresponding Prefix
Information in pair <PID option, Prefix Information option> (i.e.,
each RA contains a Port Identifier and the Prefix information that
has been assigned to the subscriber network that connects to the port
that is identified by Port identifier).
2.1 Port Identifier option
Port Identifier (PID) option contains a subscriber network identifier
, or the identifier of the port in relay agent (i.e., access node)
which connects the subscriber network. In additon, it contains the
relay agent ID which can be used by operator for network management
purpose and also it can be used to help the BNG or BRAS forwards the
RA to the correct relay agent efficiently.
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 | Reserved |I|Relay agent ID
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Relay agent ID ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Port Infomation ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields:
Type 8-bit identifier of the option type (TBD: IANA)
Option Name Type
Port Identifier option (TBD)
Length 8-bit unsigned integer. The length of the option
(including the type and length fields) is in units
of 8 octets. The value 0 is invalid. Nodes MUST
silently discard an ND packet that contains an
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option with length zero.
Reserved 7-bit reserved field. It is set 0.
I 1-bit field. If set to 1, it indicates Relay agent
ID field carrys IPv6 address as Relay agent ID.
Relay agent ID This field uniquely identifies an RS/RA relay agent
(i.e., an access node). When field I is set to 1,an
IPv6 address identifies the relay agent. Any layer
2/3 ID can be used by the service provider to
identify the access node in its network if needed.
Port Information
This field consists of a sequence of SubOpt/Length
/Value turples for each sub-option, encoded in the
following manner(which will be discussed in 2.1.1):
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
| SubOpt Type |SubOpt Data Len| Option Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
SubOpt Data Len is the length of the Option Data
field of this sub-option, in octets.
Description
This option is used in the network environment
when RS/RA is running in aggregationn network,
i.e., between subscriber network and BRAS/BNG; in
another word, access node is not a layer3 access
node and CPE is not a layer3 device either. This
option is used to indicate which subscriber network
sends the RS message or which subscriber network
this RA message will be sent to. In upstream
direction, access node is responsible for inserting
this option in the incoming RS messages, then
forwarding it to BNG (or BRAS). In downstream
direction, BRAS/BNG addes this option to the
corresponding RA, access nodes identify the option,
remove it and forward the RA to correct subscriber
network.
This option has no influence of the protocol stack
on hosts/terminals.
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2.1.1 Sub-Options
2.1.1.1 Pad sub-options
There are two pad sub-options which are used to insert to the Port
Information field area of Port Identifier option. Normally, Pad sub-
option appears in the end of Port Informaiton field to make sure that
the whole Port Identifier option to be in units of 8 octets.
Pad1 sub-option (alignment requirement: none)
+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+
NOTE! the format of the Pad1 option is a special case -- it does
not have length and value fields.
The Pad1 option is used to insert one octet of padding into the
Port Information field of Port Identifier option. If more than one
octet of padding is required, the PadN option, described next,
should be used, rather than multiple Pad1 options.
PadN option (alignment requirement: none)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
| 1 |SubOpt Data Len| Option Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
The PadN option is used to insert two or more octets. For N octets
of padding, the SubOpt Data Len field contains the value N-2, and
the Option Data consists of N-2 zero-valued octets.
2.1.1.2 Agent Circuit ID Sub-option
This sub-option may be added by access nodes (or Relay Agent) which
terminate switched or permanent circuits or port or logical port. It
encodes an agent-local identifier of the circuit (i.e., port
identifier) from which a RS message was received. It is intended for
use by access nodes/agents in relaying RA messages back to the proper
circuit/DSL-line/subscriber network.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SubOpt Type(2)|SubOpt Data Len| Circuit ID Info ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Fields:
SubOpt Type 8-bit identifier of the option type: 2.
SubOpt Data Len
8-bit unsigned integer. The length of Circuit
Information field is in octets. The value 0 is
invalid. Nodes MUST silently discard an ND packet
that contains an option with length zero.
Circuit ID Info.
This field is possible be the user port number of
access node, or cable data virtual circuit number,
or other local number which can be used to identify
the connection to subscriber network.
3. Scenarios for usage of new option for stateless auto-configuration in
IPv6 access network
3.1 No router in the subscriber network
Figure 1 illustrates a network architecture where there is no routed
gateway in the subscriber network. The terminals in the subscriber
network are connected to layer 2 access node located in NAP network
through bridged CPE. Terminals initiate RS message to access network,
and BRAS can advertise RA message to the subscriber network. The
Figure 2 shows the procedure of stateless auto-configuration in this
IPv6 access network.
____________________
/ \
| ISP core network |
\__________ _________/
|
+-------+-------+
| BRAS | \
+-------+-------+ \
__________|___________ \
/ \ |
| aggregation network | |
\__________ ___________/ |
| |
+-------+-------+ |
| layer 2 | | access
| access node | | network
+-------+-------+ |
/ | /
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/ |
+------+------+ |DSL to subscriber /
| subscriber | |premises /
| network 2 | |
+------+------+ | \
+------+------+ \
| CPE | \
| (bridge) | \
+------+------+ |
| | Subscriber
+------------+--------------+ | network
| | | |
+-----+----+ +----+-----+ +-----+----+ /
| terminal | | terminal | | terminal | /
+----------+ +----------+ +----------+ /
Figure 1: network architecture for IPv6 access
The procedure consists of the following steps:
Step (a) : IPv6 terminal/Host sends RS (Router Solicitation) message
to get RA message.
Step (b) : Layer 2 access node inserts PID option to the incoming RS
message, and forward this RS to the BRAS/BNG.
Step (c) : BRAS/BNG forms the appropriate RA message according to the
Port ID in RS message, and then advertise it. The RA
message will containing the appropriate PID option and
Prefix Information option. The Port ID option is copied
from the corresponding RS message.
Step (d) : Access node receives the RA message, removes the PID
option from RA message, and then forward it to the
corresponding subscriber network. Then the terminal can
obtain the prefix from the RA message.
+---------+ +-----------+ +------------------+
|User IPv6| | layer2 | |ISP's edge router |
| terminal| |access node| | or BNG |
+---------+ +-----------+ +------------------+
| | |
(a)|------RS message------>| |
| |
(b)|--------RS with PID option-------->|
(c)|<-------RA with PID and Prefix-----|
| Information option |
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| |
(d)|<--RA with Prefix --|
| Information option |
Figure 2. Procedure of stateless auto-configuration for scenario 1
In this procedure, access node and BRAS/BNG are reponsible for
inserting/removing/identifying the Port Identifier option. It only
request access node and BRAS/BNG to implement this functionality.
There is no any requirement on terminals/hosts.
3.2 Co-existence for different subscriber networks
subscriber neteworks access network
___________/\________________ ___________/\_______________
/ \ / \
+--------+ +---------+ +--+------+ +--------------+
| host1 |----| router1 |--------| L2 AN |----| BRAS/router |
+--------+ +---------+ +---+-----+ +--------------+
+-----+ |
| |
+--------+ +---------+ |
| host2 |-------| L2 CPE | |
+--------+ +---------+ |
+-----------+
+--------+ |
| host3 |--+ +-----+---+
+--------+ +-----| L2 CPE |
+---------+
+------+/
| host |
+------+
Figure 3. the coexitence of different subscriber networks
Figure 3 shows the coexistence of different subscriber networks are
connected to access network: there are three subscriber networks, one
subscriber network has a router (i.e., router1) as its home gateway,
the other two subscriber networks have L2 CPE (i.e., layer2 CPE) as
their home gateway. L2 AN is Layer2 access node. The policy of one
prefix per subscriber network is still adopted.
There are two cases for SAAC:
(1) the subscriber network with router as its home gateway:
Router1 will get its IPv6 prefix via DHCPv6 Prefix Delegation from
BRAS/router, then SAAC will be carried out within this subscriber
network. No RS message will be sent to the access network by this
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subscriber network. RS/RA is running only within this subscriber
network.
(2) the subscriber network without router in itself:
RS will be sent to the access network, and L2 AN will insert the
corresponding PID option and then forward to BRAS/router, a RA with
PID option and Prefix Information option will be advertised to the
corresponding L2 AN, then this AN removes the PID option and forwards
the RA to the correct subscriber network.
4. Acknowledgements
The author would like to thank Songwei Ma, David Watkinson, Stefaan
De Cnodder, Jan Van den Abeele, Sven Ooghe, and the other members in
R&I wired access group in Alcatel Shanghai Bell for their comments
and help, and aslo thank the experts in IPv6 working group.
5. References
5.1 Normative References
[1] S. Thomson, and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC2462, December 1998.
[2] S. Deering, and R. Hiden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC2460, December 1998.
[3] S. Bradner, "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
Authors' Addresses
Haibo Wen
Alcatel Shanghai Bell Co., Ltd.
388#, NingQiao Road, Pudong Jinqiao
Shanghai 201206 P.R. China
Phone: +86 (21) 5854-1240, ext.: 9273
Email: Haibo.WEN@alcatel-sbell.com.cn
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