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M3SR Series 4100
5.3.3.11
Editing the Multicast Routing Table
Multicast Routing Basics
In a multicast-enabled environment, the radio can act as a multicast router in order to forward
multicast IP (internet protocol) packets from the source towards the destination. The radio is
not intended for sending or receiving multicast packets itself. The multicast (MC) routing ta-
ble allows a static definition of the forwarding rules for multicast packets. Dynamic population
of the table with the help of a multicast routing protocol like IGMP (internet group manage-
ment protocol) is not supported.
The multicast routing table is completely independent of the unicast routing table.
Multicast IP packets are destined to a group of receivers (1 to n relationship), specified by
the group IP address.
According to RFC 1112 (request for commands), the multicast group IP address has a range
of 224.0.0.0 to 239.255.255.255.
RFC 3171 (Internet Assigned Numbers Authority (IANA) Guidelines for IPv4 Multicast Ad-
dress Assignments) lists the current assignment practice of multicast group addresses. The
block from 224.0.0.0 to 224.0.0.255 is reserved for multicast routing protocols. Like most
router implementations, the R&S radio does not route packets within this block. Therefore
the possible configuration range is limited to 224.0.1.0 to 239.255.255.255.
It is advised to follow the guidelines of RFC 3171 and to use only the block 239.0.0.0 to
239.255.255.255, which is defined as an administratively scoped block, i.e. for local usage.
A multicast routing table entry consists of the sender IP address, group IP address, routing
direction and the time-to-live (TTL) threshold.
The sender IP address defines the source / sender of multicast packets that shall be routed.
The group IP address defines the multicast group that wants to receive multicast data from
the multicast sender.
The routing direction specifies the incoming and outgoing IP interface of a route, i.e. ETH
(Ethernet) AIR defines the Ethernet IP interface as incoming and the air IP interface as
outgoing interface.
It is possible to configure more than one multicasting route with the same sender and group
IP but different routing directions, creating a 1-to-n relationship between incoming and out-
going interfaces, e.g. to configure direction AIR ETH and AIR PPP (point-to-point pro-
tocol). In this case, multicast packets coming from the air IP interface will be forwarded to the
Ethernet IP interface and to the PPP IP interface.
On the other side it makes no sense to configure two routes with the same sender and group
IP, but opposite directions, like AIR ETH and ETH AIR.
The AIR -> AIR routing direction is used only in multi-hop scenarios.
5.84
Editing the Multicast Routing Table
Operating Manual 6175.4760.02 – 01
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