Dell PowerSwitch S4820T 9.50.1 Configuration Guide for the S4820T System - Page 628

• 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. 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, Dell Networking OS 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 Dell Networking OS 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 239.0.0.1 and 239.0.0.2, a multicast routing table entry is created only for group 239.0.0.1. VLAN 300 has 628 Multicast Features