Administrator Guide

Dell EMC Networking OS does not support multicast routing in the following VLT scenarios:
• In a VLT enabled PIM router, multicast routing is not supported when there are multiple PIM spanned paths to reach source or RP.
The workaround is to configure only one PIM spanned path to reach any PIM router in the aggregation or spine.
• If a source is connected to a non-spanned interface of the VLT peer nodes and the RP is reachable on a spanned interface from both
the VLT nodes, there is a possibility to receive duplicate traffic on the source. To avoid this, you should configure the source to be
reachable on a spanned interface.
First Packet Forwarding for Lossless Multicast
All initial multicast packets are forwarded to receivers to achieve lossless multicast.
When the Dell Networking system is the RP, and has receivers for a group G, it forwards all initial multicast packets for the group based on
the (*,G) entry rather than discarding them until the (S,G) entry is created, making Dell Networking systems suitable for applications
sensitive to multicast packet loss.
NOTE: When a source begins sending traffic, the Source DR forwards the initial packets to the RP as encapsulated
registered packets. These packets are forwarded via the soft path at a maximum rate of 70 packets/second. Incoming
packets beyond this rate are dropped.
Multicast Policies
The Dell Networking OS supports multicast features for IPv4. IPv6 multicast is not supported.
• IPv4 Multicast Policies
IPv4 Multicast Policies
The following sections describe IPv4 multicast policies.
• Limiting the Number of Multicast Routes
• Preventing a Host from Joining a Group
• Rate Limiting IGMP Join Requests
• Preventing a PIM Router from Forming an Adjacency
• Preventing a Source from Registering with the RP
• Preventing a PIM Router from Processing a Join
Limiting the Number of Multicast Routes
When the total number of multicast routes on a system limit is reached, Dell Networking OS does not process any IGMP or multicast
listener discovery protocol (MLD) joins to PIM — though it still processes leave messages — until the number of entries decreases below
95% of the limit.
When the limit falls below 95% after hitting the maximum, the system begins relearning route entries through IGMP, MLD, and MSDP.
• If the limit is increased after it is reached, join subsequent join requests are accepted. In this case, increase the limit by at least 10% for
IGMP and MLD to resume.
• If the limit is decreased after it is reached, Dell Networking OS does not clear the existing sessions. Entries are cleared after a timeout
(you may also clear entries using clear ip mroute).
NOTE:
Dell Networking OS waits at least 30 seconds between stopping and starting IGMP join processing. You may
experience this delay when manipulating the limit after it is reached.
When the multicast route limit is reached, Dell Networking OS displays the following:
3w1d13h: %RPM0-P:RP2 %PIM-3-PIM_TIB_LIMIT: PIM TIB limit reached. No new routes will
be learnt until TIB level falls below low watermark.
3w1d13h: %RPM0-P:RP2 %PIM-3-PIM_TIB_LIMIT: PIM TIB below low watermark. Route learning
will begin.
To limit the number of multicast routes, use the following command.
• Limit the total number of multicast routes on the system.
CONFIGURATION mode
Multicast Features
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