INTERNET DRAFT Yong-Geun Hong
Expires: May 2002 Yong-Jin Kim
ETRI
Min-Tae Hwang
Changwon Nat'l Univ.
November 2001
Autoconfiguration of IPv4 Link-Local Addresses in Multilink Networks
<draft-hong-zeroconf-multilink-ipv4-00.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Abstract
This document describes a RPM(Router Proxy for Multilink) protocol
for proxy DAD(Duplication Address Detection) and proxy ARP(Address
Resolution Protocol)in multilink networks using IPv4 link-local
addresses. Herein we consider the multilink network dangled to a
single router as a single subnet, not as multiple subnets. Each
host generates an IPv4 link-local address automatically and checks
its duplication using DAD procedure. To check the address
duplication over all links the gateway router uses the proxy DAD
function. The router searches for link-local address lookup table
whether the desired address is already in use in the other links.
The router received an ARP request broadcasts messages as a proxy
DAD. During the proxy DAD function, the link-local address
lookup table is made. Also the router uses the proxy ARP function
to support the inter link communication. The proxy ARP in the
router replies to the request after looking up the lookup table
and broadcasts an ARP request packet only to the link that the
receiver host is located in for address resolution.
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Table of Contents:
1. Introduction
2. Example of Multilink Network
3. Operations of RPM(Router Proxy for Multilink) Protocol
3.1 Selecting an IPv4 Link-Local Address
3.2 Duplicate Address Detection over Multilink
3.3 Finding Router's Link-Local Address
3.4 Intra Link Communication
3.5 Inter Link Communication
4. Other Considerations
References
1. Introduction
It is possible for home networks to include multiple links. This
issue can arise, for example, in the case of a home network
supporting IEEE 802.11 wireless as well as IEEE 1394 and Ethernet.
In multilink small networks connected by a single router, it is
desirable for the people to be able to use IP application
software without the inconvenience of having to manually configure
static IP addresses or set up a DHCP server. Therefore the use of
zero configuration address is especially valuable in environments
where no other configuration mechanism is available.
In this document we describe a RPM(Router Proxy for Multilink)
protocol for proxy DAD and proxy ARP in multilink networks using
IPv4 link-local addresses.
Hosts in multilink network automatically configure their
interfaces with an IPv4 link-local addresses in the 169.254/16
range[1]. It will be desirable to consider the multilink networks
connected by a single router as a single subnet, not as multiple
subnets. Therefore we extend the normal DAD procedure[1] to prove
the uniqueness of their own link-local address to the whole links,
not confining to a single link. To check the address duplication
over all links the gateway router uses the proxy DAD function.
The router searches for link-local address lookup table whether
the desired address is already in use in the other links. The
router received an ARP request broadcasts messages as a proxy DAD.
During the proxy DAD function, the link-local address lookup table
is made. Also we describe the inter link communication using IPv4
link-local address with the help of a router's ARP proxy. The
proxy ARP in the router replies to the request after looking up the
lookup table and broadcasts an ARP request packet only to the link
that the receiver host is located in for address resolution.
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2. Example of Multilink Network
Figure 1 shows an example of multilink network model.
OUTSIDE : Multilink Host-A Host-B
: network | |
: +---+-----------+----- USB
: |
: +--------+ | Host-C Host-D
: | |---+ | |
------+ Router |==========+====+=====+=== Ethernet
: | |**** |
: +--------+ * Host-E
: *
: ****+***********+***** IEEE1394
: | |
: Host-F Host-G
:
Figure 1 Example of Multilink Network
Several home networking technologies, such as HomePNA(Home
Phoneline Networking Alliances), IEEE 802.11 wireless LAN, IrDA,
PLC(Powerline Communication), etc., are possible to be connected to
the router. The router helps the inter link communication.
3. Operations of RPM(Router Proxy for Multilink) Protocol
The RPM protocol uses some proxy functions in the router, such as
a proxy DAD to support the DAD procedure over multiple links and
a proxy ARP to support the inter link communication, in order to
emulate the multilink network as a single subnet to obey the
non-forwarding rule.
The non-forwarding rule means that hosts may assume that all
169.254/16 destination addresses are on-link and directly
reachable.
3.1 Selecting an IPv4 Link-Local Address
The selection, defense and delivery of IPv4 link-local address
within a link can be borrowed from the document[1].
When a host wishes to configure a link-local address, it selects an
address using a random (or pseudo-random) number generator with a
uniform distribution in the range from 169.254.1.0 to
169.254.254.255.
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3.2 Duplicate Address Detection over Multilink
In order to probe the uniqueness of the selected address, the host
broadcasts an ARP request for the desired address. On a network
such as Ethernet that supports ARP, address collision detection is
done using ARP probe[1].
When the link-local address is already in use in the same link,
the reply message notifies the address confliction. Then the host
tries again to generate another link-local address.
To check address collision over all links, the router searches for
the link-local address lookup table whether the desired address is
already in use in the other links. The router received an ARP
request may broadcast messages to each attached link in the
multilink, except one from which the ARP request was just
received. So the router acts as a proxy DAD.
If the link-local address is already in use in the other link, the
router send a reply message to the originating host of the ARP
request. Then the originating host knows it and tries again to
generate another link-local address.
If not, the originating host may use the desired address. In this
case the router adds the link local address to the link-local
address lookup table in the appropriate entry. The router creates
and maintains the link-local address lookup table. Figure 2 shows
an example of link-local address lookup table.
+---------------+---------------+---------------+
| Link 1 | Link 2 | Link 3 |
+---------------+---------------+---------------+
| 169.254.1.11 | 169.254.3.234 | 169.254.2.123 |
+---------------+---------------+---------------+
| 169.254.2.151 | 169.254.9.8 | 169.254.1.5 |
+---------------+---------------+---------------+
| : | 169.254.2.111 | : |
+ +---------------+ +
| | : | |
+---------------+---------------+---------------+
Figure 2. Example of Link-Local Address Lookup Table
3.3 Finding Router's Link-Local Address
At a multilink network, the router has multiple interfaces and
each interface has a unique link-local address.
The host which wants to know the router's link-local address
generates a RS(Router Solicitation) message. And the router
sends a reply message to the originating host.
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Then the host gets the router's link-local address.
Also, a router may send RA(Router Advertisement) messages
periodically through each interface. The hosts received this RA
message know the router's link-local address.
3.4 Intra Link Communication
We don't describe this operation in this document. See [1].
3.5 Inter Link Communication
In the multilink network environment, the link layer address
used in one link is different from that of the other links, when
the implementation technologies(e.g. USB, IEEE 1394, Ethernet)
are different each other. Therefore the inter link
communication by using ARP broadcasting for address resolution
is not possible.
We describe the proxy ARP in the router to support the inter link
communication.
A host which wants to communicate with the hosts on the other links
broadcasts an ARP request on the same link. In this case the
proxy ARP in the router replies to the request after looking up the
lookup table when the receiver's link-local address is in the
table. Then the originating host knows the receiver's link layer
address, herein the router's link layer address, and sends a packet
to the router.
The router broadcasts an ARP request packet only to the link
that the receiver host is located in for address resolution. Then
the receiver replies its link layer address to the router and the
router sends the received packet to the receiver host.
Figure 3 shows a procedure of inter link communication.
Sender host Router Receiver host
| :: |
| ARP request :: |
|-------------------------->:: |
| Lookup Table |
| ARP reply :: ARP request |
|<--------------------------::------------------------->|
| :: ARP reply |
| IP packet send ::<-------------------------|
|-------------------------->:: ARP request(optional) |
| ::------------------------->|
| :: ARP reply(optional) |
| ::<-------------------------|
| :: IP packet send |
| ::------------------------->|
| Link 1 :: Link 2 |
Figure 3 Procedure of inter link communication
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4. Other Considerations
The router must dynamically update the link-local address lookup
table when a host is down or going up.
To consider a multilink network in IPv6, see [2].
The security condition between links is not concerned in this
document.
References
[1] Stuart Cheshire, "Dynamic Configuration of IPv4 Link-Local
Addresses", <draft-ietf-zeroconf-ipv4-linklocal-04.txt>, 2001.
[2] Dave Thaler, "Multi-link Subnets Support in IPv6", <draft-thaler-
-ipngwg-multilink-subnets-01.txt>, 2001.
Authors Addresses
Yong-Geun Hong, Yong-Jin Kim
ETRI PEC
161 Gajeong-Dong, Yuseong-Gu, Daejon 305-350, Korea
Tel : +82 42 860 6557
Fax : +82 42 861 5404
E-mail : {yghong, yjkim}@pec.etri.re.kr
Min-Tae Hwang
Changwon National University
9 Sarim-Dong, Changwon, 641-773, Korea
Tel : +82 55 279 7632
Fax : +82 55 279 7639
E-mail : mthwang@sarim.changwon.ac.kr
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