Alcatel-Lucent omnistack 6124 User Manual
Multicast Filtering
4-5
Multicast Filtering
Multicasting sends data to a group of nodes instead of a single destination. The
simplest way to implement multicasting is to broadcast data to all nodes on the
network. However, such an approach wastes a lot of bandwidth if the target group is
small compared to overall the broadcast domain.
simplest way to implement multicasting is to broadcast data to all nodes on the
network. However, such an approach wastes a lot of bandwidth if the target group is
small compared to overall the broadcast domain.
Since applications such as video conferencing and data sharing are more widely
used today, efficient multicasting has become vital. A common approach is to use a
group registration protocol that lets nodes join or leave multicast groups. A switch or
router can then easily determine which ports contain group members and send data
out to those ports only. This procedure is called multicast filtering.
used today, efficient multicasting has become vital. A common approach is to use a
group registration protocol that lets nodes join or leave multicast groups. A switch or
router can then easily determine which ports contain group members and send data
out to those ports only. This procedure is called multicast filtering.
The purpose of multicast filtering is to optimize a switched network’s performance,
so multicast packets will only be forwarded to those ports containing multicast group
hosts or multicast routers/switches instead of flooding to all ports in the subnet
(VLAN). This OmniStack
so multicast packets will only be forwarded to those ports containing multicast group
hosts or multicast routers/switches instead of flooding to all ports in the subnet
(VLAN). This OmniStack
®
model supports multicast filtering by passively monitoring
IGMP Query and Report messages.
IGMP Snooping
A Layer 2 switch can passively snoop on IGMP Query and Report packets
transferred between IP Multicast Routers/Switches and IP Multicast host groups to
learn the IP Multicast group members. It simply monitors the IGMP packets passing
through it, picks out the group registration information, and configures multicast
filters accordingly. IGMP Snooping generates no additional network traffic, allowing
you to significantly reduce the multicast traffic passing through your switch.
transferred between IP Multicast Routers/Switches and IP Multicast host groups to
learn the IP Multicast group members. It simply monitors the IGMP packets passing
through it, picks out the group registration information, and configures multicast
filters accordingly. IGMP Snooping generates no additional network traffic, allowing
you to significantly reduce the multicast traffic passing through your switch.
IGMP Protocol
The Internet Group Management Protocol (IGMP) runs between hosts and their
immediately neighboring multicast router/switch. IGMP is a multicast host
registration protocol that allows any host to inform its local router that it wants to
receive transmissions addressed to a specific multicast group.
immediately neighboring multicast router/switch. IGMP is a multicast host
registration protocol that allows any host to inform its local router that it wants to
receive transmissions addressed to a specific multicast group.
A router, or multicast-enabled switch, can periodically ask their hosts is they want to
receive multicast traffic. If there is more than one router/switch on the LAN
performing IP multicasting, one of these devices is elected “querier” and assumes
the responsibility of querying the LAN for group members.
receive multicast traffic. If there is more than one router/switch on the LAN
performing IP multicasting, one of these devices is elected “querier” and assumes
the responsibility of querying the LAN for group members.
Based on the group membership information learned from IGMP, a router/switch can
determine which (if any) multicast traffic needs to be forwarded to each of its ports.
At Layer 3, multicast routers use this information, along with a multicast routing
protocol such as DVMRP, to support IP multicasting across the Internet.
determine which (if any) multicast traffic needs to be forwarded to each of its ports.
At Layer 3, multicast routers use this information, along with a multicast routing
protocol such as DVMRP, to support IP multicasting across the Internet.
Note that IGMP neither alters nor routes any IP multicast packets. A multicast router/
switch must be used to deliver IP multicast packets across different subnetworks.
switch must be used to deliver IP multicast packets across different subnetworks.