Viewing Multicast Forwarding Database Information
The Layer 2 Multicast Forwarding Database (MFDB) is used by the switch to make forwarding decisions
for packets that arrive with a multicast destination MAC address. By limiting multicasts to only certain
ports in the switch, traffic is prevented from going to parts of the network where that traffic is
unnecessary.
When a packet enters the switch, the destination MAC address is combined with the VLAN ID and a
search is performed in the Layer 2 Multicast Forwarding Database. If no match is found, the packet is
either flooded to all ports in the VLAN or discarded, depending on the switch configuration. If a match
is found, the packet is forwarded only to the ports that are members of that multicast group.
MFDB Table
Use the MFDB Table page to view the port membership information for all active multicast address
entries. The key for an entry consists of a VLAN ID and MAC address pair. Entries may contain data for
more than one protocol.
To access this page, click
Switching
>
Multicast Forwarding Database
>
Summary
in the navigation
menu.
Table 220: MFDB Summary Fields
Field
Description
MAC Address
The VLAN ID (the first two groups of hexadecimal digits) and multicast MAC
address (the last six groups of hexadecimal digits) that has been added to the
MFDB.
Component
The feature on the device that was responsible for adding the entry to the
multicast forwarding database, which is one of the following:
•
IGMP Snooping – A Layer 2 feature that allows the device to dynamically add
or remove ports from IPv4 multicast groups by listening to
leave requests.
•
MLD Snooping – A Layer 2 feature that allows the device to dynamically add
or remove ports from IPv6 multicast groups by listening to MLD join and
leave requests.
•
GMRP – Generic Address Resolution Protocol (GARP) Multicast Registration
Protocol, which helps help control the flooding of multicast traffic by keeping
track of group membership information.
•
Static Filtering – A static MAC filter that was manually added to the address
table by an administrator.
Type
The type of entry, which is one of the following:
•
Static – The entry has been manually added to the MFDB by an
administrator.
•
Dynamic – The entry has been added to the MFDB as a result of a learning
process or protocol.
Description
A text description of this multicast table entry.
Configuring Switching Information
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