Internet DRAFT - draft-hong-autoconf-multicast-ipv4
draft-hong-autoconf-multicast-ipv4
INTERNET DRAFT Yong-Geun Hong
Expires: January 2002 Jung-soo Park
Min-kyo In
Yong-jin Kim
ETRI
July 2001
Multicast Address Allocation using IPv4 Link-local Address
<draft-hong-autoconf-multicast-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
In this document, we describe a method by which a host
automatically allocates multicast addresses using IPv4 link local
address without any address allocation server. These multicast
addresses do not collide with other multicast addresses in a local
scope.
Table of Contents:
1. Introduction
2. IPv4 Multicast Address Allocation
2.1 The IPv4 Local Scope Multicast Address
2.2 Multicast Address Generation using IPv4 Link-local Address
3 Consideration of Variable Network
3.1 Intra-domain Network
3.2 Inter-domain Network
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3.3 Consideration for Joining to a Global Network
4. Limitations
References
1. Introduction
IPv4 addresses in the 169.254/16 ranges are used for link-local
communication. These are valuable in networking where no other
configuration and administration is available. We call this
networking Zero configuration networking. The zero configuration
network don't need any centralized administration. Networks where
zeroconf protocols apply can include (but are not limited to)
environments where no DHCP, MADCAP, or DNS servers are present.
There are two methods for allocating an IP multicast address.
Firstly, it can be allocated by using a multicast address
allocation server. Secondly, it can be allocated without the
server. The former allocates a hierarchical multicast address by
using a MAAs server, or MADCAP server to guarantee the global
uniqueness of the allocated address. The latter is a method where a
host chooses a multicast address by its own way in the well-known
multicast address range, and then checks the duplication of the
address. In this document, we deal with the latter case that
servers do not exist. While the latter method has the advantage of
no need to use any server, it can cause a significant address
resolution delay and increased traffic.
In this document, we will describe multicast address allocation
method without the delay and increased traffic within a local scope
network.
2. IPv4 Multicast Address Allocation
Typically, an IP address is used to identify a node within a
network. A port number is used to identify a data stream between
endpoints. Therefore, the host address and port number can be used
as an identifier that differentiates sessions in a specific area.
2.1 The IPv4 Local Scope Multicast Address
Originally the address space 239.255.0.0/16 was defined as being
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used in the IPv4 local scope multicast address, and that expanded
to the reserved ranges of 239.254.0.0/16 and 239.253.0.0/16. If the
demand of IPv4 local multicast scope is increased, the local
multicast scope will be further extended.
In this document, we consider two important issues. The first one
is keeping the status of IP multicast address allocation.
The second one is that the packet with a multicast address
specified in local scope should not forward to outside networks. So
we must define the routing policy at the border router such as
"Administratively Scoped IP Multicast"[1]. With this routing
policy, we can easily deal with the situations such as inter-domain
networking and joining to a global network.
2.2 Multicast Address Generation using IPv4 Link-local Address
In this document, a multicast address in the local scope is made
from the combination of IPv4 link-local address (169.254.x.x) and
multicast address prefix. The multicast address consists of two
upper octets of an IPv4 local scope multicast address and two lower
octets of a link-local address, as shown in figure 1.
Host IP Address
(link-local address) Port number
+-------------+ +------+
|169.254.c.d | | u.v |
+-------------+ +------+
| |
| |
V V
+------------------------------------------------------+
| +--------------+ (1) +---------+ (2) |
| | 239.255.c.d | | | |
| | 239.254.c.d | | (u.v) | |
| | 239.253.c.d | | | |
| +--------------+ +---------+ |
+------------------------------------------------------+
Multicast Address subspace port number
Figure 1: Extended multicast address subspace formation using IPv4
link-local address
To make a multicast address in local scope, two upper octets are
selected among [239.255/16, 239.254/16, 239.253/16] according to
the above definition and two lower octets are generated by the copy
the two lower octets of link-local address.
Until now, the number of available multicast address is 3, and if
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the local multicast scope is extended, the number of available
multicast addresses is also increased. Keeping the status of
address allocation has some advantages, e.g., when a multicast
address is needed, it can choose unique one without any bothersome
jobs.
And we can use two octets port number of link-local address to
identify a multicast session address. The link-local address that
is used for multicast address is unique in local scope by the
mechanism of address collision detection [2]. So the generated
multicast address is also unique in the local scope. We don't have
to worry about the collision of the multicast address to other
hosts. Within a host, it solves the collision of multicast address
by keeping the status of address allocatioion.
For example, let us assume a host has an IP address of
169.254.190.121, and it can choose individual multicast addresses
of 239.255.190.121, 239.254.190.121 and 239.253.190.121. Also, it
can choose two octets-port numbers to identify the endpoint of the
session. These three multicast address spaces with port numbers are
unique in the local scope.
3 Consideration of Variable Network
3.1 Intra-domain Network
All nodes in an Intra-domain network must perform DAD (Duplicate
Address Detection) procedure. Throughout the DAD procedure, a host
can guarantee the uniqueness of the address in the local scope.
For example in figure 2. The hosts A, B and C receive packets that
have the multicast address 'a', and hosts C, D and E receive
packets of the multicast address 'e'. Host C can receive packets of
multicast address 'a' and 'e' concurrently. In the case, there is
no collision of multicast addresses and host C is not confused.
A B C D E
| | | | |
| | | | |
|(a) |(a) |(a,e) |(e) |(e)
------+-----------+----------+---------+--------+---
Network Address 169.254.x.x
Figure 2: Intra-domain Network
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3.2 Inter-domain Network
The IPv4 local scope multicast address can only be used in a local
area and cannot be forwarded to external networks by the routing
policy at the boarder router. If two isolated domains meet together
and form an inter-domain network, the packet should not be
delivered to neighbor domain. So, even though two multicast
addresses generated at each domain are the same, that causes no
problem because of the limited delivery. The inter-domain issue is
out of scope.
3.3 Consideration for Joining to a Global Network
The multicast address, which is allocated by the proposed scheme,
would be recommended to use in the isolated network. But it is
possible for the isolated network to join to a global network with
connection to a public network. At that time the proposed scheme
don't have any problems because the multicast address, which has a
local scope, is not allowed to be forwarded to the external network
through the border router.
4. Limitations
In this paper, we only deal with link-local range. Thus, global
range is out of scope of this document. To provide multicast
services through the Internet, MAAs and MADCAP servers can be used.
References
[1] D. Meyer. "Administratively Scoped IP Multicast", [RFC 2365], Jul.
1998.
[2] Stuart Cheshire, Apple Computer, Bernard Aboba and Mircrosoft,
"draft-ietf-zeroconf-IPv4-linklocal-03.txt", Mar. 2001
Authors Addresses
Yung-geun Hong
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ETRI PEC
161 Kajong-Dong, Yusong-Gu, Taejon 305-600, Korea
Tel : +82 42 860 6557
Fax : +82 42 861 5404
E-mail : yghong@etri.re.kr
Jung-soo Park
ETRI PEC
161 Kajong-Dong, Yusong-Gu, Taejon 305-600, Korea
Tel : +82 42 860 6514
Fax : +82 42 861 5404
E-mail : pjs@etri.re.kr
Min-kyo In
ETRI PEC
161 Kajong-Dong, Yusong-Gu, Taejon 305-600, Korea
Tel : +82 42 860 6489
Fax : +82 42 861 5404
E-mail : mkin@etri.re.kr
Yong-Jin Kim
ETRI PEC
161 Kajong-Dong, Yusong-Gu, Taejon 305-600, Korea
Tel : +82 42 860 6564
Fax : +82 42 861 5404
E-mail : kimyj@etri.re.kr
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