Specifications

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Cisco MWR 2941 Mobile Wireless Edge Router Software Configuration Guide, Release 12.2(33)MRB
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Chapter 1 Cisco MWR 2941 Router Overview
Features
GLOP Addresses
GLOP addressing (as proposed by RFC 2770, GLOP Addressing in 233/8) proposes that the 233.0.0.0/8
range be reserved for statically defined addresses by organizations that already have an AS number
reserved. This practice is called GLOP addressing. The AS number of the domain is embedded into the
second and third octets of the 233.0.0.0/8 address range. For example, AS 62010 is written in
hexadecimal format as F23A. Separating the two octets F2 and 3A results in 242 and 58 in decimal
format. These values result in a subnet of 233.242.58.0/24 that would be globally reserved for AS 62010
to use.
Limited Scope Addresses
The range 239.0.0.0 to 239.255.255.255 is reserved as administratively or limited scoped addresses for
use in private multicast domains. These addresses are constrained to a local group or organization.
Companies, universities, and other organizations can use limited scope addresses to have local multicast
applications that will not be forwarded outside their domain. Routers typically are configured with filters
to prevent multicast traffic in this address range from flowing outside an autonomous system (AS) or
any user-defined domain. Within an AS or domain, the limited scope address range can be further
subdivided so that local multicast boundaries can be defined.
Note Network administrators may use multicast addresses in this range, inside a domain, without conflicting
with others elsewhere in the Internet.
Layer 2 Multicast Addresses
Historically, network interface cards (NICs) on a LAN segment could receive only packets destined for
their burned-in MAC address or the broadcast MAC address. In IP multicast, several hosts need to be
able to receive a single data stream with a common destination MAC address. Some means had to be
devised so that multiple hosts could receive the same packet and still be able to differentiate between
several multicast groups. One method to accomplish this is to map IP multicast Class D addresses
directly to a MAC address. Using this method, NICs can receive packets destined to many different
MAC address.
Cisco Group Management Protocol (CGMP) is used on routers connected to Catalyst switches to
perform tasks similar to those performed by IGMP. CGMP is necessary for those Catalyst switches that
cannot distinguish between IP multicast data packets and IGMP report messages, both of which are
addressed to the same group address at the MAC level.
IP Multicast Delivery Modes
IP multicast delivery modes differ only for the receiver hosts, not for the source hosts. A source host
sends IP multicast packets with its own IP address as the IP source address of the packet and a group
address as the IP destination address of the packet.
Any Source Multicast
For the Any Source Multicast (ASM) delivery mode, an IP multicast receiver host can use any version
of IGMP to join a multicast group. This group is notated as G in the routing table state notation. By
joining this group, the receiver host is indicating that it wants to receive IP multicast traffic sent by any
source to group G. The network will deliver IP multicast packets from any source host with the
destination address G to all receiver hosts in the network that have joined group G.