Information Technology Reference
In-Depth Information
IP Multicast Protocols
This section reviews the multicast protocols that are of interest in the CCIE written test.
Multicast Review
With multicast, packets are sent to a multicast group, which is identified with an IP multicast
address. Multicast supports the transmission of IP packets from one source to multiple hosts.
Packets with unicast addresses are sent to one device and broadcast addresses are sent to all
hosts; packets with multicast addresses are sent to a group of hosts.
Multicast Addresses
You use class D addresses from the IPv4 protocol for multicast addressing.
Routing protocols (RIPv2, IS-IS, EIGRP and OSPF) use multicast addresses to speak to their
neighbors. For example, OSPF routers use 224.0.0.6 to speak to the designated router (DR) in
a multiaccess network. Class D multicast addresses range from 224.0.0.0 to 239.255.255.255.
Multicast addresses in the range of 224.0.0.1 to 224.255.255.255 are reserved for network
protocols on a multiaccess link. Table 10-5 contains some well-known addresses.
Multicast Addresses
Table 10-5
Multicast Address
Description
224.0.0.1
All hosts or all systems on this subnet
224.0.0.2
All multicast routers
224.0.0.4
DVMRP routers
224.0.0.5
All OSPF routers
224.0.0.6
All OSPF DR routers
224.0.0.9
RIPv2 routers
224.0.0.10
EIGRP routers
224.0.0.13
All PIM routers
224.0.0.39
Route Processor (RP)-Announce
224.0.0.40
RP-Discovery
Administrative Scoped Multicast Addresses
Per RFC 2365, multicast addresses 239.000.000.000-239.255.255.255 are reserved for
administratively scoped functions. This RFC defines administrative group addresses for IPv4
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