Users Guide

VLT multicast routing
OS10 supports multicast routing in a VLT domain for IPv4 networks. This feature provides resiliency to multicast-routed trac when a VLT
peer node or the VLTi link goes down.
Multicast routing table synchronization
Multicast routing protocols do not exchange multicast routes between peer VLT nodes. Each VLT node runs the PIM protocol independent
of the peer VLT node. Hence, the PIM states do not synchronize between the nodes. However, OS10 synchronizes the multicast routing
table with routes that the PIM learns on each of the nodes between the peer VLT nodes. Multicast routing table synchronization:
• Avoids unoptimized forwarding over VLTi links. Table synchronization allows the incoming trac sent to the wrong peer to be routed
locally within the device.
• Provides trac resiliency in the event of a VLT node failure. The trac is forwarded until the PIM protocol reconverges and builds a new
tree.
IGMP message synchronization
VLT nodes use the VLTi link to synchronize IGMP messages across their peers. Any IGMP join message that is received on one of the VLT
nodes synchronizes with the peer node. Therefore, the IGMP tables are identical in a VLT domain.
Egress mask
When multicast trac from the source arrives at one of the VLT peer nodes, it is sent to the downstream receivers using local routing or
switching and over the VLTi link. The port block at the VLTi link of the peer node drops the multicast trac. This port block, also known as
the egress mask, avoids duplicate trac forwarding on the VLT port channel by both VLT nodes. However, if the receiver is connected to
the peer node, the system forwards the multicast trac to the receiver.
Spanned VLAN
Any VLAN congured on both the VLT peer nodes is known as a spanned VLAN. The VLT interconnect (VLTi) port is automatically added
as a member of the spanned VLAN. Any adjacent router connected to at least one VLT node on a spanned VLAN subnet is directly
reachable from both the VLT peer nodes at the L3 level.
• Spanned VLAN L3 interface: If you enable PIM on each of the spanned VLAN L3 interfaces on both VLT nodes, the interface is a
spanned VLAN L3 interface.
– Spanned VLT VLAN L3 interface: Includes all spanned L3 VLANs that have at least one VLT port that is congured as a port
channel member.
– Spanned non-VLT VLAN L3 interface: Includes all spanned VLANs that do not have VLT ports congured as port channel members.
• Nonspanned L3 interface: All point-to-point interfaces or L3 VLANs that do not have VLT ports congured as port channel members.
For more information, see Deployment considerations.
Multicast
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