Westermo RedFox Series User Manual
Page 278
Westermo OS Management Guide
Version 4.17.0-0
Note
Switches ”learn” the location of (unicast) MAC address by inspecting the
”source” MAC address, while they ”forward” packets based on the ”destina-
tion” MAC address.
Unicast MAC addresses learnt automatically will stay in the MAC forwarding database
until they are aged out – the aging timeout defaults to 300 seconds. The aging
timeout is configurable, and aging can be disabled.
13.1.8.2
Managing Broadcast and Multicast MAC addresses
Packets transmitted to the broadcast MAC address (”ff:ff:ff:ff:ff:ff”) will be for-
warded onto all ports in the associated VLAN. Other group MAC addresses (here
referred to as multicast MAC addresses) are handled differently if IGMP Snooping
is enabled or not (see
for detailed information on IGMP Snooping):
❼ IGMP Snooping Disabled: With IGMP Snooping disabled on a VLAN, packets
sent to multicast MAC addresses will be handled in the same way as broad-
cast, i.e., such packets will be forwarded onto all ports in the associated
VLAN.
❼ IGMP Snooping Enabled: With IGMP Snooping enabled on a VLAN, packets
sent to multicast MAC addresses will be blocked on all ports by default, and
only forwarded onto ports (1) where the switch has learnt that there is a host
interested in receiving traffic to that multicast MAC address, or (2) which the
switch believes lead to a multicast router.
WeOS also allows an operator to manually specify where to forward multicast MAC
addresses, i.e., the operator can add static multicast MAC filters. This feature is
useful for several reasons:
❼ IGMP snooping and non-IP multicast: With IGMP snooping enabled, all MAC
multicast will be blocked, except those learnt via IGMP snooping. As IGMP
snooping only learns MAC multicast based on IP multicast, all other types of
MAC multicast will be blocked.
Adding static MAC filters enables the use of non-IP multicast on VLANs where
IGMP snooping is enabled.
❼ IGMP Snooping and IP multicast in the 224.0.0.X range: IP multicast in the
224.0.0.X range should be forwarded onto all ports in the VLAN irrespective
if any host has indicated interest in that multicast address via IGMP or not.
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