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This chapter describes how to configure multicast services on the Catalyst 6000 and 6500 series switches.
This chapter consists of the following sections:
Multicasting uses a multicast address to send the same data stream to multiple recipients while using the least bandwidth. Without multicasting, multiple unicast-addressed copies of the data stream would have to be sent to individual recipients.
Multicasts flood like broadcasts unless multicast services are used. Multicast services can control the distribution of multicasts by determining which switch ports need to participate in multicasts.
Catalyst 6000 and 6500 series switches support the Internet Group Management Protocol (IGMP) snooping Layer 2 multicast service. IGMP (see RFC 1112) is a Layer 3 multicast service for routers that can determine which router ports need to participate in multicasts. IGMP snooping looks at Layer 3 IGMP data to determine which switch ports need to participate in multicasts.
A multicast service functions only with hosts that support the service. Hosts that do not support a multicast service generate uncontrolled multicasts.
These sections describe how to configure multicast services:
IGMP snooping allows Catalyst 6000 and 6500 series switches to examine IGMP packets and make forwarding decisions based on their content. These guidelines apply when you are configuring IGMP snooping on the Catalyst 6000 and 6500 series switches:
These sections describe how to configure IGMP on the Catalyst 6000 and 6500 series switches:
To enable IGMP snooping, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Enable IGMP snooping on the switch. | set igmp enable |
Step 2 Verify that IGMP snooping is enabled. | show igmp statistics [vlan_num] |
This example shows how to enable IGMP snooping and verify the configuration (shown by the arrow):
Console> (enable) set igmp enable IGMP Snooping is enabled. CGMP is disabled. Console> (enable) show igmp statistics
IGMP enabled IGMP statistics for vlan 1: Total valid pkts rcvd: 18951 Total invalid pkts recvd 0 General Queries recvd 377 Group Specific Queries recvd 0 MAC-Based General Queries recvd 0 Leaves recvd 14 Reports recvd 16741 Queries Xmitted 0 GS Queries Xmitted 16 Reports Xmitted 0 Leaves Xmitted 0 Failures to add GDA to EARL 0 Topology Notifications rcvd 10 IGMP packets dropped 0 Console> (enable)
When you enable IGMP snooping, the switch automatically learns to which ports a multicast router is connected.
To statically define multicast router ports, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Configure multicast router ports. | set multicast router mod_num/port_num |
Step 2 Verify the multicast router configuration. | show multicast router [mod_num/port_num] [vlan_id] |
Step 3 Verify the multicast router information that was learned dynamically through IGMP. | show multicast router igmp [mod_num/port_num] [vlan_id] |
This example shows how to define a multicast router port manually and verify the configuration (the asterisk [*] next to the multicast router on port 5/7 indicates that the entry was configured manually):
Console> (enable)set multicast router 5/7Port 5/7 added to multicast router port list.Console> (enable)show multicast router CGMP disabled IGMP enabled Port Vlan --------- ---------------- 1/1 1 2/1 2,99,255 5/7 * 99 Total Number of Entries = 3 '*' - Configured Console> (enable)
This example shows how to display only those multicast router ports that were learned dynamically through IGMP snooping:
Console> (enable) show multicast router igmp
CGMP disabled
IGMP enabled
Port Vlan
--------- ----------------
1/1 1
2/1 2,99,255
Total Number of Entries = 2
'*' - Configured
Console> (enable)
To check IGMP snooping statistics on the switch, perform this task:
| Task | Command |
|---|---|
Display IGMP snooping statistics. | show igmp statistics [vlan_id] |
This example shows how to display IGMP snooping statistics:
Console> (enable) show igmp statistics IGMP enabled IGMP statistics for vlan 1: Total valid pkts rcvd: 18951 Total invalid pkts recvd 0 General Queries recvd 377 Group Specific Queries recvd 0 MAC-Based General Queries recvd 0 Leaves recvd 14 Reports recvd 16741 Queries Xmitted 0 GS Queries Xmitted 16 Reports Xmitted 0 Leaves Xmitted 0 Failures to add GDA to EARL 0 Topology Notifications rcvd 10 IGMP packets dropped 0 Console> (enable)
To clear manually configured multicast router ports, perform one of these tasks in privileged mode:
| Task | Command |
|---|---|
| clear multicast router mod_num/port_num |
| clear multicast router all |
This example shows how to clear a manually configured multicast router port entry:
Console> (enable) clear multicast router 2/12 Port 2/12 cleared from multicast router port list. Console> (enable)
To disable IGMP snooping on the switch, perform this task in privileged mode:
| Task | Command |
|---|---|
Disable IGMP snooping on the switch. | set igmp disable |
This example shows how to disable IGMP snooping:
Console> (enable) set igmp disable IGMP feature for IP multicast disabled Console> (enable)
These sections describe how to use the multicast group commands on the Catalyst 6000 and 6500 series switches:
To display the multicast groups on the switch, perform this task:
| Task | Command |
|---|---|
Display multicast groups. | show multicast group [mac_addr] [vlan_id] |
This example shows how to display the multicast groups for VLAN 1:
Console> show multicast group 1 IGMP enabled VLAN Dest MAC/Route Des Destination Ports or VCs / [Protocol Type] ---- ------------------ ---------------------------------------------------- 1 01-00-5e-00-01-28* 3/1,12/9 1 01-00-5e-63-7f-6f* 3/1,12/5,12/9 Total Number of Entries = 2 Console>
To display the number of multicast groups on the switch, perform this task:
| Task | Command |
|---|---|
Display the number of multicast groups. | show multicast group count [mac_addr] [vlan_id] |
This example shows how to display the number of multicast groups for VLAN 1:
Console> show multicast group count 1 GMRP disabled IGMP enabled Total Number of Entries = 2 Console> (enable)
To statically configure a multicast group, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Add one or more multicast MAC addresses to the CAM1 table. | set cam {static | permanent} multicast_mac mod_num/port_num [vlan] |
Step 2 Verify the multicast group configuration. | show multicast group [mac_addr] [vlan_id] |
Step 3 Verify the multicast group information that was learned dynamically through IGMP snooping. | show multicast group igmp [mac_addr] [vlan_id] |
Step 4 If desired, show the total number of multicast addresses (groups) in a VLAN. | show multicast group count [igmp] [vlan_id] |
| 1CAM=content addressable memory. |
This example shows how to define multicast groups manually and verify the configuration:
Console> (enable) set cam static 01-00-11-22-33-44 2/6-12 Static multicast entry added to CAM table. Console> (enable) set cam static 01-11-22-33-44-55 2/6-12 Static multicast entry added to CAM table. Console> (enable) set cam static 01-22-33-44-55-66 2/6-12 Static multicast entry added to CAM table. Console> (enable) set cam static 01-33-44-55-66-77 2/6-12 Static multicast entry added to CAM table. Console> (enable) show multicast group CGMP disabled IGMP enabled VLAN Dest MAC/Route Des Destination Ports or VCs / [Protocol Type] ---- ------------------ ---------------------------------------------------- 1 01-00-11-22-33-44* 2/6-12 1 01-11-22-33-44-55* 2/6-12 1 01-22-33-44-55-66* 2/6-12 1 01-33-44-55-66-77* 2/6-12 Total Number of Entries = 4 Console> (enable)
To disable manually configured multicast group entries, perform this task in privileged mode:
| Task | Command |
|---|---|
Clear a multicast group entry from the CAM table. | clear cam mac_addr [vlan] |
This example shows how to clear a multicast group entry from the CAM table:
Console> (enable) clear cam 01-11-22-33-44-55 1 CAM entry cleared. Console> (enable)
These sections describe how to use broadcast suppression on the Catalyst 6000 and 6500 series switches:
Broadcast suppression prevents switched ports on a LAN from being disrupted by a broadcast storm on one of the ports. A LAN broadcast storm occurs when broadcast or multicast packets flood the LAN, creating excessive traffic and degrading network performance. Errors in the protocol-stack implementation or in the network configuration can cause a broadcast storm.
Broadcast suppression uses filtering that measures broadcast activity on a LAN over a one-second time period and compares the measurement with a predefined threshold. If the threshold is reached, further broadcast activity is suppressed for the duration of a specified time period. Broadcast suppression is disabled by default.
Figure 12-1 shows the broadcast traffic patterns on a port over a given period of time. In this example, broadcast suppression occurs between time intervals T1 and T2 and between T4 and T5. During those time periods, the amount of broadcast traffic exceeded the configured threshold.
The broadcast suppression threshold numbers and the time interval combination make the broadcast suppression algorithm work with different levels of granularity. A higher threshold allows more broadcast packets to pass through.
Broadcast suppression on the Catalyst 6000 series and 6500 series switches is implemented in hardware. The suppression circuitry monitors packets passing from a port to the switching bus. Using the Individual/Group bit in the packet destination address, the broadcast suppression circuitry determines if the packet is a unicast or a broadcast. It keeps track of the current count of broadcasts within the one-second time interval, and when a threshold is reached, filters out subsequent broadcast packets.
Because hardware broadcast suppression uses a bandwidth-based method to measure broadcast activity, the most significant implementation factor is setting the percentage of total available bandwidth that can be used by broadcast traffic. A threshold value of 100 percent means that no limit is placed on broadcast traffic. Using the set port broadcast command, you can set up the broadcast suppression threshold value.
Because packets do not arrive at uniform intervals, the one-second time interval during which broadcast activity is measured can affect the behavior of broadcast suppression.
These sections describe how to configure broadcast suppression on the Catalyst 6000 series and 6500 series switches:
To enable broadcast suppression, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Specify the broadcast suppression threshold for one or more ports as a percentage of total bandwidth. | set port broadcast mod_num/port_num threshold% |
Step 2 Verify the broadcast suppression configuration. | show port broadcast [mod_num[/port_num]] |
This example shows how to enable bandwidth-based broadcast suppression and verify the configuration:
Console> (enable) set port broadcast 3/1 75% Port(s) 3/1-24 broadcast traffic limited to 75%. Console> (enable) show port broadcast 3 Port Broadcast-Limit Broadcast-Drop -------- --------------- -------------- 3/1-8 75 % - 3/9-16 75 % - 3/17-24 75 % - Console> (enable)
To disable broadcast suppression on one or more ports, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Disable broadcast suppression on one or more ports. | clear port broadcast mod_num/port_num |
This example shows how to disable broadcast suppression on one or more ports:
Console> (enable) clear port broadcast 3/1 Port 3/1-8 broadcast traffic unlimited. Console> (enable)
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