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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)
      9  TCP/IP Internet Layer (OSI Network Layer) Protocols
           9  Internet Protocol (IP/IPv4, IPng/IPv6) and IP-Related Protocols (IP NAT, IPSec, Mobile IP)
                9  Internet Protocol Version 4 (IP, IPv4)
                     9  IP Addressing
                          9  IP "Classful" (Conventional) Addressing

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IP Reserved, Loopback and Private Addresses
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IP Multicast Addressing
(Page 2 of 2)

Well-Known Multicast Addresses

The first block of 256 addresses is used to define special, well-known multicast address blocks. These do not represent arbitrary groups of devices and cannot be assigned in that manner. Instead, they have special meaning that allows a source to send a message to a predefined group. Table 49 shows some of the “well-known” multicast addresses:

Table 49: Well-Known IP Multicast Addresses

Range Start Address


Reserved; not used

All devices on the subnet

All routers on the subnet


All routers using DVMRP

All routers using OSPF

Designated routers using OSPF

Designated routers using RIP-2

Mobile agents (for Mobile IP)

DHCP Server / Relay Agent

Note: There are some other predefined groups that also refer to routers using particular routing protocols; I didn't bother listing them all as the table would get quite large.

Delivery of IP multicast traffic is more complex than unicast traffic due to the existence of multiple recipients. Instead of the normal resolution method through the ARP protocol used for unicast datagrams, a special mapping is performed between the IP multicast group and a hardware multicast group.

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Version 3.0 - Version Date: September 20, 2005

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