TCP/IP Illustrated - Chapter 2 - IPv4 Multicast

224.0.2.0-224.0.255.255

Ad hoc block I

224.3.0.0-224.4.255.255

Ad hoc block II

233.252.0.0-233.255.255.255

Ad hoc block III (233.252.0.0/24 is reserved for documentation

239.0.0.0 - 239.255.255.255

Administrative scope

What space has been reserved to support multicast addressing?

Class D space - 224.0.0.0/4

233.0.0.0/8

GLOP

Who establishes which sections of the IPv4 multicast addressing space are reserved?

IANA or the IETF

224.0.1.0/24

Internetwork control; forwarded normally

224.0.0.0/24

Local network control; not forwarded

224.0.1.1

NTP - Network Time Protocol multicast group. Resides within the Internetwork control group

224.1.0.0/16

Reserved

225.0.0.0-231.255.255.255

Reserved

224.5.0.0-224.255.255.255

Reserved - for specific application protocols or organizations

235.0.0.0 - 238.255.255.255

Reserved for IP4MA

224.2.0.0/16

SDP/SAP

232.0.0.0/8

SSM (Source-specific multicast)

What is SAP?

Session Announcement protocol

What is SDP?

Session Description Protocol

234.0.0.0/8

Unicast-prefix-based IPv4 multicast addresses

What is UBM?

Unicast-prefix-based multicast addressing

The SDP/SAP block

contains addresses used by applications such as the SDR, or that otherwise don't fit in either the local or internetwork control blocks. Globally routed and used by apps requiring small blocks of address (<=/24)

224.0.0.1

the all hosts group. Resides within the Local network control block

The SSM block

used by applications employing SSM in combination with their own unicast source IP address in forming SSM channels

List 3 advantages of UBM

§ Don't have the 16-bit restriction for AS numbers used by GLOP addressing § Allocated as a consequence of already-existing unicast address space allocations § Allocated at a finer granularity than GLOP addresses, which correspond to AS number allocations (vs. hosts or specific networks)

Explain UBM

• The most recent of the IPv4 multicast address allocation mechanisms. Associates a number of multicast addresses with an IPv4 unicast address prefix. ○ Based on a similar structure developed earlier for IPv6 ○ Range is 234.0.0.0/8 ○ A unicast address with a /24 or shorter prefix may make use of UBM addresses ○ Allocations with fewer addresses (longer prefixes) must use some other mechanism ○ Are a concatenation of the 234/8 prefix, the allocated unicast prefix, and the multicast group ID

The GLOP block

• addresses derived are based on the AS (autonomous system) of the host, on which the application allocating the address (MC) resides ○ AS - autonomous system - numbers used by Internet-wide routing protocols among ISPs in order to aggregate routes, and apply routing policies. Each AS has a unique AS number. § Originally these were 16 bits, but have been extended since to be 32 bits. ○ GLOP addresses are generated by placing a 16-bit AS number in the second and third bytes of the IPv4 multicast address, leaving room for 1 byte to represent the possible multicast addresses ○ NOTE: this means the 32bit extensions cannot be used

Describe the administratively scoped address block

• can be used to limit the distribution of multicast traffic to a particular collection of routers and hosts. ○ The multicast equivalent of private unicast IP addresses ○ Should not be used for distributing multicast into the Internet ○ Most are blocked at enterprise boundaries

The Ad hoc block I

• was created originally to hold addresses that did not fall into either the local or internetwork control blocks. ○ Most allocations in this range are for commercial services ○ Some of these allocations do not, and may never, require global address allocations § These allocations may one day be returned in favor of GLOP addressing