TCP IP Illustrated

the multicast address 224011 is for ntp the network

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ese well-known multicast addresses are listed in the latest Assigned Numbers RFC. Notice that it is the multicast address of the group that is permanent, not the membership of the group. For example, 224.0.0.1 means "all systems on this subnet," and 224.0.0.2 means "all routers on this subnet." The multicast address 224.0.1.1 is for NTP, the Network Time Protocol, 224.0.0.9 is for RIP-2 (Section 10.5), and 224.0.1.2 is for SGI's (Silicon Graphics) dogfight application. Converting Multicast Group Addresses to Ethernet Addresses The IANA owns an Ethernet address block, which in hexadecimal is 00:00:5e. This is the high-order 24 bits of the Ethernet address, meaning that this block includes addresses in the range 00:00:5e:00:00:00 through 00:00:5e:ff:ff:ff. The IANA allocates half of this block for multicast addresses. Given that the first byte of any Ethernet address must be 01 to specify a multicast address, this means the Ethernet addresses corresponding to IP multicasting are in the range 01:00:5e:00:00:00 through 01:00:5e:7f:ff:ff. Our notation here uses the Internet standard bit order, for a CSMA/CD or token bus network, as the bits appear in memory. This is what most programmers and system administrators deal with. The IEEE documentation uses the transmission order of the bits. The Assigned Numbers RFC gives additional details on the differences between these representations. file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/broadcas.htm (9 of 12) [12/09/2001 14.47.00] Chapter 12. Broadcasting and Multicasting This allocation allows for 23 bits in the Ethernet address to correspond to the IP multicast group ID. The mapping places the low-order 23 bits of the multicast group ID into these 23 bits of the Ethernet address. This is shown in Figure 12.3. Since the upper 5 bits of the multicast group ID are ignored in this mapping, it is not unique. Thirty-two different multicast group IDs map to each Ethernet address. For example, the multicast addresses 224.128.64.32 (hex e0.80.40.2...
View Full Document

Ask a homework question - tutors are online