Section 18.1.2 – Westermo RedFox Series User Manual
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Westermo OS Management Guide
Version 4.17.0-0
queries.
Multicast router timeout: When a multicast router, or a switch acting as IGMP
querier, goes down, the lack of IGMP Query messages will cause a reelection
to establish a new IGMP querier. This timeout can be configured via the CLI
”multicast-router-timeout” setting. Default: 300 sec.
When a multicast receiver attached to a switch port leaves a multicast group (i.e.,
stops subscribing to an IP multicast address or is simply disconnected from the
port), the IGMP snooping leave latency (the time until the switch stops forwarding
the associated multicast data) is within 2-3 times the configured Query Interval.
18.1.2
Multicast Router Ports
When IGMP snooping is enabled, the switch will learn on which ports there are
interested receivers of a certain multicast group. It accomplishes this by listening
to IGMP Report messages sent by all subscribers. Thus, the switch only forwards
multicast on ports leading to members of each specific multicast group.
The switch also forwards all multicast traffic, both subscribed (known) and un-
known, on ports leading to multicast routers. The following ports are considered
as multicast router ports:
❼ Ports configured as multicast router ports
❼ Ports where IGMP Queries are received, usually queries are sent by multicast
routers, but also by IGMP snooping aware switches like WeOS
❼ FRNT Ring Coupling ports and Multi-link Dual-Homing ports: To provide fast
fail-over of multicast traffic, FRNT Ring Coupling and Multi-link Dual-Homing
uplinks (see
) are added to the list of multicast router ports. This
is both done at the Ring Coupling nodes and Dual-Homing nodes, as well as
on switches on the remote side of the uplink
FRNT ring ports are no longer considered multicast router ports. The Fast Re-
connect feature of FRNT is instead handled per multicast group: if a multicast
receiver is located on a ring port, the other ring port is automatically added to
the ATU MAC filter
. In case of ring breakage this practice ensures an extremely
low reconfiguration time for multicast over FRNT.
4
An exception is when connecting a Dual-Homing uplink to a non-FRNT switch, the fail-over of
multicast traffic will instead occur on the next reception of an IGMP Report (if IGMP snooping is
enabled). See also
5
This can be seen using the CLI command ”show fdb”
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