Configuration manual

• 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-configured 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 specific 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 first 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, configuring an IGMP join request filter 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.
In the following example, virtual local area network (VLAN) 400 is configured with an access list to permit
only IGMP reports for group 239.0.0.1. Though Receiver 2 sends a membership report for groups
584
Multicast Features