Flooding; Mld Querier - IBM RackSwitch G8000 Application Manual

Flooding

MLD Querier

242
RackSwitch G8000: Application Guide
When flood option is disabled, the unknown multicast traffic is discarded if no
Mrouters are learned on the switch. You can set the flooding behavior by configuring
the flood and cpu options. You can optimize the flooding to ensure that unknown
IP multicast (IPMC) data packets are not dropped during the learning phase.
The flooding options include:
• flood: Enable hardware flooding in VLAN for the unregistered IPMC; This
option is enabled by default.
• cpu: Enable sending unregistered IPMC to the Mrouter ports. However, during
the learning period, there will be some packet loss. The cpu option is enabled by
default. You must ensure that the flood and optflood options are disabled.
• optflood: Enable optimized flooding to allow sending the unregistered IPMC to
the Mrouter ports without having any packet loss during the learning period; This
option is disabled by default; When optflood is enabled, the flood and cpu
settings are ignored.
The flooding parameters must be configured per VLAN. Enter the following
command to set the flood or cpu option:
RS G8000(config)# vlan <vlan number>
RS G8000(config-vlan)# [no] flood
RS G8000(config-vlan)# [no] cpu
RS G8000(config-vlan)# [no] optflood
An Mrouter acts as a Querier and periodically (at short query intervals) sends query
messages in the subnet. If there are multiple Mrouters in the subnet, only one can
be the Querier. All Mrouters on the subnet listen to the messages sent by the
multicast address listeners, and maintain the same multicast listening information
state.
All MLDv2 queries are sent with the FE80::/64 link-local source address prefix.
Querier Election
Only one Mrouter can be the Querier per subnet. All other Mrouters will be
non-Queriers. MLD versions 1 and 2 elect the Mrouter with the numerically lowest
IPv6 address as the Querier.
If the switch is configured as an Mrouter on a subnet, it also acts as a Querier by
default and sends multiple general queries. If the switch receives a general query
from another Querier with a numerically lower IPv6 address, it sets the other querier
present timer to the other querier present timeout, and changes its state to
non-Querier. When the other querier present timer expires, it regains the Querier
state and starts sending general queries.
Note: When MLD Querier is enabled on a VLAN, the switch performs the role of an
MLD Querier only if it meets the MLD Querier election criteria.