Specifications

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Cisco MWR 2941 Mobile Wireless Edge Router Software Configuration Guide, Release 12.2(33)MRB
OL-21227-02
Chapter 1 Cisco MWR 2941 Router Overview
Features
IP Multicast Address Scoping
The multicast address range is subdivided to provide predictable behavior for various address ranges and
for address reuse within smaller domains. Table 1 is a summary of the multicast address ranges. A brief
summary description of each range follows.
Table 1 Multicast Address Range Assignments
Reserved Link-Local Addresses
The IANA has reserved the range 224.0.0.0 to 224.0.0.255 for use by network protocols on a local
network segment. Packets with an address in this range are local in scope and are not forwarded by IP
routers. Packets with link local destination addresses are typically sent with a time-to-live (TTL) value
of 1 and are not forwarded by a router.
Within this range, reserved link-local addresses provide network protocol functions for which they are
reserved. Network protocols use these addresses for automatic router discovery and to communicate
important routing information. For example, Open Shortest Path First (OSPF) uses the IP addresses
224.0.0.5 and 224.0.0.6 to exchange link-state information.
IANA assigns single multicast address requests for network protocols or network applications out of the
224.0.1.xxx address range. Multicast routers forward these multicast addresses.
Globally Scoped Addresses
Addresses in the range 224.0.1.0 to 238.255.255.255 are called globally scoped addresses. These
addresses are used to send multicast data between organizations across the Internet. Some of these
addresses have been reserved by IANA for use by multicast applications. For example, the IP address
224.0.1.1 is reserved for Network Time Protocol (NTP).
Source Specific Multicast Addresses
Addresses in the range 232.0.0.0/8 are reserved for Source Specific Multicast (SSM) by IANA. In
Cisco IOS software, you can use the ip pim ssm command to configure SSM for arbitrary IP multicast
addresses also. SSM is an extension of Protocol Independent Multicast (PIM) that allows for an efficient
data delivery mechanism in one-to-many communications. SSM is described in the “IP Multicast
Delivery Modes” section on page 1-22.
Name Range Description
Reserved Link-Local Addresses 224.0.0.0 to 224.0.0.255 Reserved for use by network protocols on a local network
segment.
Globally Scoped Addresses 224.0.1.0 to
238.255.255.255
Reserved to send multicast data between organizations and
across the Internet.
Source Specific Multicast 232.0.0.0 to
232.255.255.255
Reserved for use with the SSM datagram delivery model
where data is forwarded only to receivers that have
explicitly joined the group.
GLOP Addresses 233.0.0.0 to
233.255.255.255
Reserved for statically defined addresses by organizations
that already have an assigned autonomous system (AS)
domain number.
Limited Scope Address 239.0.0.0 to
239.255.255.255
Reserved as administratively or limited scope addresses for
use in private multicast domains.