Allied Telesis SB251-13 - Manual (Page 16)

16 Patch Release Note
Patch SB251-13 for Software Release 2.5.1
C613-10361-00 REV M
MLD snooping on the switch uses the last 4 bytes of the IPv6 address to
distinguish multicast addresses. It is therefore unable to distinguish different
multicast addresses that end with the same 4 bytes. Creating an entry for a
multicast group will have the effect of creating an entry for all groups with
addresses that end with the same 4 bytes as that group’s address. For example,
traffic for the groups:
ffxx xxxx xxxx xxxx xxxx xxxx 1234 5678 and
ffyy yyyy yyyy yyyy yyyy yyyy 1234 5678
will be forwarded out the same set of ports, irrespective of the values of x and
y. Therefore, if MLD snooping is used, no two groups within the multicast
domain should be given an address that ends in the same 4 bytes.
Similarly, all addresses beginning with ff02 and ending with any of:
0000:0001, 0000:0002, 0000:0004, 0000:0005, 0000:0006,
0000:0009, 0000:000d, 0000:000f or 0000:0012
will be flooded out all ports in the VLAN, because MLD snooping cannot
distinguish them from IPv6 special addresses. These addresses should be
avoided if MLD snooping is used.
MLD snooping is enabled by default. To disable it, use the command:
DISABLE MLDSNOOPING
Note that IPv6 multicast packets will flood the VLAN when MLD snooping is
disabled. Disabling MLD snooping may be useful on Rapier i Series Switches if
filters are used extensively, because MLD snooping uses a Layer 3 filter. When
MLD snooping is disabled, this filter becomes available. See “Hardware Packet
Filters” in the Switching chapter of the Software Reference for information
about filters.
To enable MLD snooping, use the command:
ENABLE MLDSNOOPING
MLD snooping can only be enabled if a free filter entry is available.
To display debugging information, use the command:
ENABLE MLDSNOOPING DEBUG
This command displays the ports that are currently receiving MLD packets and
the ports that are being added or taken off the switch’s multicast group
membership registration.
To disable debugging, use the command:
DISABLE MLDSNOOPING DEBUG
To display information about MLD snooping, use the command:
SHOW MLDSNOOPING [COUNTER]
Example output from the SHOW MLDSNOOPING command is described in
Figure 1 on page 17 and Table 1 on page 18. Example output from the SHOW
MLDSNOOPING COUNTER command is described in Figure 2 on page 18
and Table 2 on page 18.