Section 29.1.3 – Westermo RedFox Series User Manual
Page 650
Westermo OS Management Guide
Version 4.17.0-0
❼ Enable IP forwarding
❼ Enable IP multicast forwarding
❼ Setup a multicast route
❼ Multicast data with a TTL > 1
The two enable flags simply control routing and multicast routing, respectively.
However, if IP forwarding is disabled toggling the multicast forwarding flag will
have no effect.
A static multicast route is made up of a group, an inbound interface, an optional
sender address and one or more outbound interfaces. There can be at most 128
multicast routes with at most eight (8) outbound interfaces per route.
The source, or sender address, is optional in WeOS but the underlying Linux ker-
nel still needs a source address to be able to route the traffic. The multicast
routing daemon in WeOS manages this by adding rules to the kernel on-demand
based on the “source-less” rules specified. For each new multicast stream, from a
given group and inbound interface, the routing daemon checks to see if a match-
ing mroute rule exists and then adds that source specific rule to the kernel. This
may cause some initial delays in activation of such rules.
29.1.3
IP multicast and IGMP Snooping
In LAN networks IGMP Snooping is often employed in switches to limit the distribu-
tion of IP multicast. Without subscribers to a certain multicast group, distribution
of a camera’s multicast stream is halted at the first switch. When IGMP Snooping
is disabled, the camera’s multicast stream is instead broadcast to all ports on the
switch, or all ports in the VLAN. For details, see
and
In currently available network equipment, as well as modern operating systems,
IGMP is a well established protocol that works well. There may however still
exist older networking equipment, e.g., Programmable Logic Controllers (PLCs),
that does not know how to join a multicast group using IGMP. For such devices to
receive multicast it is possible in WeOS to either disable IGMP Snooping per VLAN,
add a specific FDB MAC entry for the multicast group to open up additional ports
in the switch, or use the multicast router port feature to forward all multicast on
a given port.
650
➞ 2015 Westermo Teleindustri AB