S R A / S F X 2 1 0 0 S E R I E S S A T E L L I T E R E C E I V E R
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Multicast Routing
The Multicast Routing submenu maintains the multicasting routing table associated with the
receiver. Each receiver can support up to 200 multicast routes. The multicast routing
function is responsible for managing multicast packets that are traveling through the
receiver (host), from external interface to external interface. It is not responsible for
managing multicast packets that are delivered to an application running on the receiver, but
the two functions are inter-related.
Multicast packets are routed through the host according to a multicast routing table that is
maintained by the Linux kernel. Initially, this table is empty and incoming multicast packets
are routed according to a default route.
Multicast Routing follows a number of rules, as described in the list below. Many rules are
best described by examples. Many of these rules are more important in the SFX series
receiver, where a number of local applications may be consuming multicast packets (e.g.
streaming media decoder).
1. IP packets can originate from any of the available network interfaces and are
processed by the receiver in accordance with the data flow in Figure 4-9.
2. Up to 200 routes may be entered in the Multicast Routing Table, and order doesn’t
matter, assuming that routes don’t overlap.
3. For assigned routes, IGMP is supported.
4. Should the multicast routing function be terminated for any reason, all multicast
routes are automatically erased by the Linux kernel.
5. If a multicast packet is received, whose source IP Address matches the IP Address
of one of the receiver's network interfaces, that packet is discarded regardless of
the current multicast routing rules. This happens because the receiver assumes it
is involved in a multicast loop. For a normal device, this behaviour does not pose a
problem, but in a satellite environment, care must be taken to ensure that the IP
address of a multicast source at the head end does not match the IP address of
any receiver interface.
6. Local Application Rule 1: A multicast route is not required in order for a local
application program running on the receiver to receive multicast packets.
However, a static route is needed so that the program can properly set up a
receiving socket (e.g. XD in the SFX). For example, if a program needs to receive
multicast data on 224.1.1.1 from the sat0 interface, the following static route must
be entered (see
Static Routing
section of this manual):
Interface: sat0
Gateway: 0.0.0.0
Destination: 224.1.1.1
Netmask: 255.255.255.255
or the more general route could be entered:
Interface: sat0
