Deployment Guide

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 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, the system does not clear the existing sessions. Entries are cleared after a timeout (you may
also clear entries using clear ip mroute).
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 system 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.
The default is 15000.
NOTE
: The IN-L3-McastFib CAM partition is used to store multicast routes and is a separate hardware limit that exists per port-
pipe. Any software-congured limit may supersede by this hardware space limitation. The opposite is also true, the CAM partition
might not be exhausted at the time the system-wide route limit the ip multicast-limit command sets is reached.
Preventing a Host from Joining a Group
You can prevent a host from joining a particular group by blocking specic IGMP reports. Create 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 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.
INTERFACE mode
ip igmp access-group access-list-name
Dell Networking OS Behavior: Do not enter the ip igmp access-group command before creating the access-list. If you do, after
entering your rst deny rule, the system clears multicast routing table and re-learns all groups, even those not covered by the rules in the
access-list, because there is an implicit deny all rule at the end of all access-lists. Therefore, conguring an IGMP join request lter in this
order might result in data loss. If you must enter the ip igmp access-group command before creating the access-list, prevent the
system from clearing the routing table by entering a permit any rule with high sequence number before you enter any other rules.
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Multicast Features