Reference Guide

• Multicast is not supported on secondary IP addresses.
• Egress L3 ACL is not applied to multicast data traffic if you enable multicast routing.
First Packet Forwarding for Lossless Multicast
Beginning with FTOS version version 8.3.1.0, all initial multicast packets are forwarded to receivers to achieve lossless
multicast.
In previous versions, when the Dell Networking system is an RP, all initial packets are dropped until PIM creates an
(S,G) entry. When the system is an RP and a Source DR, these initial packet drops represent a loss of native data, and
when the system is an RP only, the initial packets drops represent a loss of register packets.
Both scenarios might be unacceptable depending on the multicast application. Beginning with the FTOS versions noted
here, 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
FTOS offers parallel multicast features for IPv4 and IPv6.
• IPv4 Multicast Policies
• IPv6 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, FTOS 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, FTOS does not clear the existing sessions. Entries are cleared after a
timeout (you may also clear entries using clear ip mroute).
NOTE: FTOS 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.
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