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● 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
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. 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.
IPv4 Multicast Policies
The following sections describe IPv4 multicast policies.
● Limiting the Number of Multicast Routes
● Preventing a Host from Joining a Group
● 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
ip multicast-limit
The range if from 1 to 50000.
Multicast Features
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