Users Guide

Multicast Policies
The Dell Networking OS supports multicast features for IPv4.
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, the Dell Networking OS does not process Internet group
management protocol (IGMP) or multicast listener discovery protocol (MLD) joins to protocol-independent multicast (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 multicast
source discovery protocol (MSDP).
• If you increase the limit after it is reached, subsequent join requests are accepted. In this case, increase the limit by at least 10% for
IGMP and MLD to resume.
• If you decrease the limit after it is reached, the Dell Networking OS does not clear the existing sessions. Entries are cleared after a
timeout (you may also clear entries using the clear ip mroute command).
NOTE:
The 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, the following displays:
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 is from 1 to 16000.
The default is 4000.
NOTE:
The IN-L3-McastFib CAM partition stores multicast routes and is a separate hardware limit that exists per port-
pipe. Any software-configured limit may supersede this hardware space limitation. The opposite is also true, the CAM
partition might not be exhausted at the time the system-wide route limit is reached using the ip multicast-limit
command.
Preventing a Host from Joining a Group
You can prevent a host from joining a particular group by blocking specific IGMP reports using an extended access list containing the
permissible source-group pairs.
NOTE:
For rules in IGMP access lists, source is the multicast source, not the source of the IGMP packet. For IGMPv2,
use the keyword any for source (as shown in the following example) because the IGMPv2 hosts do not know in advance
who the source is for the group in which they are interested.
To apply the access list, use the following command.
• Apply the access list.
Multicast Features
503