Connectivity Guide
0/0 pim-assert messages sent/received
0/0 register messages sent/received
Multicast support on VLT
OS10 supports multicast in a VLT domain in active-standby mode.
In a VLT domain that is in active-standby mode, the designated router (DR) routes multicast trac (Layer 3) and the other peer VLT node
switches (Layer 2) incoming multicast trac over VLTi links.
In last hop router (LHR), the DR is responsible for triggering upstream PIM joins, but the trac from RP can reach any one of the VLT
peers. For example, if the trac reaches a peer VLT node that has not triggered the upstream join, it switches the incoming multicast
trac over VLTi links which will reach the originating LHR-DR node. The trac then gets routed at this node. The L3 routed trac gets
replicated over VLTi links for all the receiver VLANs. This trac is processed by non-DR LHR node and it forwards it to appropriate
receivers based on VLT L2 trac forwarding rules.
The behavior is the same with rst hop router (FHR) as well, where PIM registration is initiated by DR. The PIM join could be sent to the
DR or the non-DR FHR node. If the incoming multicast trac reaches the node which receives the PIM join, it routes the packet towards
the RP. If the incoming multicast trac reaches the peer VLT node that has not received the PIM join, it switches the packet over the VLTi
link to the other node, which will route the packet towards the RP.
The active-standby mechanism can potentially oversubscribe VLTi links, as multiple copies get replicated for the outgoing receiver VLANs.
Dell EMC recommends using only one PIM upstream VLAN towards the RP/source from FHR/LHR.
The following section provides a high-level description of trac ows for dierent use cases. The term, spanned VLAN used in the
following illustration refers to a VLAN that is congured on both the VLT nodes.
NOTE
: Dell EMC recommends that you align the designated router of all spanned VLANs, VLT VLANs and non-VLT VLANs, on to
a single VLT node.
Source on VLT VLAN—trac forwarded to DR
In the following illustration, the source is in VLT VLAN (VLAN 11) and trac is forwarded to the designated router (R2).
Multicast
673