Connectivity Guide

The behavior is the same with first 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 traffic reaches the node which receives the PIM join, it
routes the packet towards the RP. If the incoming multicast traffic 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 traffic flows for different use cases. The term, spanned VLAN used in
the following illustration refers to a VLAN that is configured 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—traffic forwarded to DR
In the following illustration, the source is in VLT VLAN (VLAN 11) and traffic is forwarded to the designated router (R2).
Traffic flow:
1. R4: Traffic from source is switched to VLT LAG, through VLAN 11, and arrives at R2 which is the designated router (DR).
2. R2:
a. The (S, G) entry is created.
b. Traffic is routed to VLAN 12, VLAN 13, and VLAN 14 for receivers R12, R13, and R14.
c. Traffic is routed to ICL through VLAN 13, and switched to ICL through VLAN 11.
3. R1: Traffic floods on VLAN 13.
Multicast
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