Overview
The mrouted Routing Daemon
In this figure, the mrouted router R1 receives a multicast packet from node M. Because R1 is configured as one end of a tunnel, R1 encapsulates the IP multicast packet in a standard unicast IP packet addressed to the mrouted router R2. The packet, now treated as a normal IP packet, is sent through the intervening nonmulticast network to R2. R2 receives the packet and removes the outer IP header, thereby restoring the original multicast packet. R2 then forwards the multicast packet through its network interface to node N.
| IP Multicast Addresses | ||||||
| An IP Internet address can be either a | ||||||
| host on the Internet is assigned a unique IP address. There are four | ||||||
| classes of IP addresses: Class A, Class B, Class C, and Class D. Class D | ||||||
| IP addresses are identified as IP multicast addresses. Class A, Class B, | ||||||
| and Class C IP addresses are composed of two parts: a network ID | ||||||
| (netid) and a host ID (hostid). Class D IP addresses are structured | ||||||
| differently, as shown in Figure | ||||||
Figure | Class D IP Multicast Address Format | ||||||
| 0 1 2 3 4 | 31 | |||||
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| 1 | 1 | 1 | 0 |
| Multicast Group Address |
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The first 4 bits (0 through 3) identify the address as a multicast address. Bits 4 through 31 identify the multicast group. Multicast addresses are in the range 224.0.0.0 through 239.255.255.255. Addresses 224.0.0.0 through 224.0.0.255 are reserved, and address 224.0.0.1 is permanently assigned to the all hosts group. The all hosts group is used to reach all the hosts on a local network that participate in IP multicasting. The addresses of other permanent multicast groups are published in RFC 1060 (Assigned Numbers, March 1990).
You can use IP multicast addresses only as destination addresses, and they must never appear in the source address field of a datagram. Internet Control Message Protocol (ICMP) error messages are not generated for multicast datagrams.
Because IP Internet addressing is a software manifestation of the underlying physical network, you must map IP addresses to physical addresses that the hardware comprising the network understands.
Chapter 1 | 19 |
