Handbook of Local Area Networks, 1998 Edition:Advanced LAN Interconnectivity Issues and Solutions
Click Here!
Search the site:
ITLibrary
ITKnowledge
EXPERT SEARCH
Programming Languages
Databases
Security
Web Services
Network Services
Middleware
Components
Operating Systems
User Interfaces
Groupware & Collaboration
Content Management
Productivity Applications
Hardware
Fun & Games
EarthWeb sites
Crossnodes
Datamation
Developer.com
DICE
EarthWeb.com
EarthWeb Direct
ERP Hub
Gamelan
GoCertify.com
HTMLGoodies
Intranet Journal
IT Knowledge
IT Library
JavaGoodies
JARS
JavaScripts.com
open source IT
RoadCoders
Y2K Info
Previous
Table of Contents
Next
Address Prefix Allocation
One of the goals of the IPv6 address format is to accommodate many different types of addresses. The beginning of an address contains a 3- to 10-bit format prefix defining the general address type; the remaining bits contain the actual host address, in a format specific to the indicated address type. Table 4-1-2 represents an address prefix allocation (from RFC 1884).
TABLE 4-1-2. ADDRESS PREFIX ALLOCATION (FROM RFC 1884)
Allocation
Prefix (Binary)
Fraction of Address Space
Reserved
0000 0000
1/256
Unassigned
0000 0001
1/256
Reserved for NSAP
Allocation
0000 001
1/128
Reserved for IPX
Allocation
0000 010
1/128
Unassigned
0000 011
1/128
Unassigned0000 1
1/32
Unassigned
0001
1/16
Unassigned
001
1/8
Provider-Based
Unicast Address
010
1/8
Unassigned
011
1/8
Reserved for
Geographic-Based
Unicast Addresses
100
1/8
Unassigned
101
1/8
Unassigned
110
1/8
Unassigned
1110
1/16
Unassigned
1111 0
1/32
Unassigned
1111 10
1/64
Unassigned
1111 110
1/128
Unassigned
1111 1110 0
1/512
Link Local Use
Addresses
1111 1110 10
1/1024
Site Local Use
Addresses
1111 1110 11
1/1024
Multicast Addresses
1111 1111
1/256
The Provider-Based Unicast Address
The provider-based unicast address is an IPv6 address that might be assigned by an Internet service provider (ISP) to a customer. Exhibit 4-1-2 shows a provider-based unicast address format. This type of address contains a number of subfields, including the following:
• Format prefix. This indicates the type of address as provider-based unicast. It is always 3 bits, coded “010.”
• Registry identifier. This identifies the Internet address registry from which the ISP obtains addresses.
• Provider identifier. This identifies the ISP. This field contains the address block assigned to the ISP by the address registry authority.
• Subscriber identifier. This identifies the ISP’s subscriber. This field contains the address assigned to this subscriber by the ISP. The provider ID and subscriber ID fields together are 56 bits in length.
• Intrasubscriber. This contains the portion of the address assigned and managed by the subscriber.
Exhibit 4-1-2. Provider-Based Unicast Address Format
IPv4-Compatible Addresses
Another particularly important address type is the one that indicates an IPv4 address. With more than 16 million hosts using 32-bit addresses, the public Internet must continue to accommodate IPv4 addresses even as it slowly migrates to IPv6 addressing,
IPv4 addresses are carried in a 128-bit IPv6 address that begins with 80 zeros (0:0:0:0:0). The next 16-bit block contains the compatibility bits, which indicate the way in which the host/router handles IPv4 and IPv6 addresses. If the device can handle either IPv4 or IPv6 addresses, the compatibility bits are all set to zero(0) and this is termed an “IPv4-compatible IPv6 address”; if the address represents an IPv4-only node, the compatibility bits are all set to one (0xFFFF) and the address is termed an “IPv4-mapped IPv6 address.” The final 32 bits contain a 32-bit IPv4 address in dotted decimal form.
Multicast Addresses
IPv6 multicast addresses provide an identifier for a group of nodes. A node may belong to any number of multicast groups. Multicast addresses may not be used as a source address in IPv6 packets or appear in any routing.
All multicast addresses, as shown in Exhibit 4-1-3, begin with 8 ones (0xFF). The next 4 bits are a set of flag bits (flgs); the 3 high-order bits are set to zero; and the fourth bit (T-bit) indicates a permanently assigned (“well-known”) multicast address (T=0) or a nonpermanently assigned (“transient”) multicast address (T=1). The next 4 bits indicate the scope of the address, or the part of the network for which this multicast address is relevant; options include node-local (0x1), link-local (0x2), site-local (0x5), organization-local (0x8), or global (0xE).
Exhibit 4-1-3. Multicast Address Format
The remaining 112 bits are the group identifier, which identifies the multicast group, either permanent or transient, within the given scope. The interpretation of a permanently assigned multicast address is independent of the scope value. For example, if the World Wide Web (WWW) server group is assigned a permanent multicast address with a group identifier of 0x77, then:
• FF01:0:0:0:0:0:0:77 would refer to all WWW servers on the same node as the sender.
• FF02:0:0:0:0:0:0:77 would refer to all WWW servers on the same link as the sender.
• FF05:0:0:0:0:0:0:77 would refer to all WWW servers at the same site as the sender.
• FF0E:0:0:0:0:0:0:77 would refer to all WWW servers in the Internet.
Finally, a number of well-known multicast addresses are predefined, including:
• Reserved multicast addresses. These are reserved and are never assigned to any multicast group. These addresses have the form FF0x:0:0:0:0:0:0:0, where x is any hexadecimal digit.
• All nodes’ addresses. These identify the group of all IPv6 nodes within the given scope. These addresses are of the form FF0t:0:0:0:0:0:0:1, where t =1 (node-local) or 2 (link-local).
• All routers’ addresses. These identify the group of all IPv6 routers within the given scope. These addresses are of the form FF0t: 0:0:0:0:0:0:2, where t =1 (node-local) or 2 (link-local).
• The dynamic host configuration protocol (DHCP) server/relay-agent address. This identifies the group of all IPv6 DHCP servers and relay agents with the link-local scope; this address is FF02:0:0:0:0:0:0:C.
Previous
Table of Contents
Next
Use of this site is subject certain Terms & Conditions.
Copyright (c) 1996-1999 EarthWeb, Inc.. All rights reserved. Reproduction in whole or in part in any form or medium without express written permission of EarthWeb is prohibited.
Please read our privacy policy for details.
Wyszukiwarka
Podobne podstrony:
13 (374)378,6,artykulBY Barejsza J , Ab atrybucyi i datawanni dzwiuch maniet Aleksinskaha skarbu, Bankauski wiesnik, nr [371 374371 374373 374374 Premia pieniężna w księgach rachunkowych01 (378)378 379378 38109 (378)372 378więcej podobnych podstron