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This chapter describes how to configure Internet Group Management Protocol (IGMP) snooping and GARP Multicast Registration Protocol (GMRP) on the Catalyst 6000 family switches.
This chapter consists of these sections:
These sections describe how multicasting works on the Catalyst 6000 family switches:
Switches can use IGMP snooping or GMRP to dynamically configure switch ports so that IP multicast traffic is forwarded only to those ports associated with IP multicast hosts.
IGMP software components run on both the Cisco router and the switch. An IGMP-capable IP multicast router sees all IGMP packets and can inform the switch when specific hosts join or leave IP multicast groups.
When the IGMP-capable router receives an IGMP control packet, it creates an IGMP packet that contains the request type (either join or leave), the multicast group address, and the MAC address of the host. The router sends the packet to a well-known address to which all switches listen. When a switch receives the packet, the supervisor engine interprets the packet and modifies the forwarding table automatically.
You can statically configure multicast groups using the set cam static command. Multicast groups learned through IGMP snooping are dynamic. If you specify group membership for a multicast group address, your static setting supersedes any automatic manipulation by IGMP snooping. Multicast group membership lists can consist of both user-defined and IGMP snooping-learned settings.
If an IGMP snooping-learned port link is disabled for any reason, that port is removed from any multicast group memberships.
When a host wants to join an IP multicast group, it sends an IGMP join message specifying its MAC address and the IP multicast group it wants to join. The IGMP-capable router then builds an IGMP join message and multicasts the join message to the well-known address to which the switches listen.
Upon receipt of the join message, each switch searches its Enhanced Address Recognition Logic (EARL) table to determine if it contains the MAC address of the host asking to join the multicast group. If a switch finds the MAC address of the host in its EARL table associating the MAC address with a nontrunking port, the switch creates a multicast forwarding entry in the EARL forwarding table. The host associated with that port receives multicast traffic for that multicast group. In this way, the EARL automatically learns the MAC addresses and port numbers of the IP multicast hosts.
The IGMP-capable router sends periodic multicast group queries. If a host wants to remain in a multicast group, it responds to the query from the router. In this case, the router does nothing. If a host does not want to remain in the multicast group, it does not respond to the router query. If after a number of queries the router receives no reports from any host in a multicast group, the router sends an IGMP command to the switch, telling it to remove the multicast group from its forwarding tables.
GARP Multicast Registration Protocol (GMRP) is a Generic Attribute Registration Protocol (GARP) application that provides a constrained multicast flooding facility similar to IGMP snooping. GMRP and GARP are industry-standard protocols defined by the IEEE. For detailed protocol operational information, refer to IEEE 802.1p.
GMRP software components run on both the switch and on the host (Cisco is not a source for GMRP host software). On the host, GMRP is typically used with IGMP: the host GMRP software spawns Layer 2 GMRP versions of the host's Layer 3 IGMP control packets. The switch receives both the Layer 2 GMRP and the Layer 3 IGMP traffic from the host. The switch uses the received GMRP traffic to constrain multicasts at Layer 2 in the host's VLAN.
When a host wants to join an IP multicast group, it sends an IGMP join message, which spawns a GMRP join message.
Upon receipt of the GMRP join message, the switch adds the port through which the join message was received to the appropriate multicast group. The switch propagates the GMRP join message to all other hosts in the VLAN, one of which is typically the multicast source. When the source is multicasting to the group, the switch forwards the multicast only to the ports from which it received join messages for the group.
The switch sends periodic GMRP queries. If a host wants to remain in a multicast group, it responds to the query. In this case, the switch does nothing. If a host does not want to remain in the multicast group, it can either send a leave message or not respond to the periodic queries from the switch. If the switch receives a leave message or receives no response from the host for the duration of the leaveall timer, the switch removes the host from the multicast group.
These sections describe how to configure IGMP snooping:
Table 34-1 shows the default IGMP snooping configuration.
| Feature | Default Value |
|---|---|
IGMP snooping | Disabled |
Multicast routers | None configured |
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:
Console> (enable) set igmp enable IGMP Snooping is enabled. 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 display the dynamically learned multicast router information, perform this task in privileged mode:
| Task | Command |
|---|---|
| show multicast router [mod_num/port_num] [vlan_id] |
| show multicast router igmp [mod_num/port_num] [vlan_id] |
This example shows how to display information on all multicast router ports (the asterisk [*] next to the multicast router on port 5/7 indicates that the entry was configured manually):
Console> (enable) show multicast router
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:
Console> (enable) show multicast router igmp
IGMP enabled
Port Vlan
--------- ----------------
1/1 1
2/1 2,99,255
Total Number of Entries = 2
'*' - Configured
Console> (enable)
To display information about multicast groups, perform this task in privileged mode:
| Task | Command |
|---|---|
| show multicast group [mac_addr] [vlan_id] |
| show multicast group igmp [mac_addr] [vlan_id] |
| show multicast group count [vlan_id] |
| show multicast group count igmp [vlan_id] |
This example shows how to display information about all multicast groups on the switch:
Console> (enable) show multicast group 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 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 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 configure the GARP Multicast Registration Protocol (GMRP):
GMRP requires supervisor engine software release 5.2 or later.
Table 34-2 shows the default GMRP configuration.
| Feature | Default Value |
|---|---|
GMRP enable state | Disabled |
GMRP per-port enable state | Disabled |
GMRP forward all | Disabled on all ports |
GMRP registration | Normal on all ports |
GARP/GMRP timers |
|
To enable GMRP globally, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Enable GMRP on the switch. | set gmrp enable |
Step 2 Verify the configuration. | show gmrp configuration |
This example shows how to enable GMRP and verify the configuration:
Console> (enable) set gmrp enable GMRP enabled. Console> (enable) show gmrp configuration Global GMRP Configuration: GMRP Feature is currently enabled on this switch. GMRP Timers (milliseconds): Join = 200 Leave = 600 LeaveAll = 10000 Port based GMRP Configuration: Port GMRP Status Registration ForwardAll -------------------------------------------- ----------- ------------ ---------- 1/1-2,3/1,6/1-48,7/1-24 Enabled Normal Disabled Console> (enable)
To enable GMRP on individual switch ports, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Enable GMRP on an individual switch port. | set port gmrp enable mod_num/port_num |
Step 2 Verify the configuration. | show gmrp configuration |
This example shows how to enable GMRP on port 6/12 and verify the configuration:
Console> (enable) set port gmrp enable 6/12 GMRP enabled on port 6/12. Console> (enable) show gmrp configuration Global GMRP Configuration: GMRP Feature is currently enabled on this switch. GMRP Timers (milliseconds): Join = 200 Leave = 600 LeaveAll = 10000 Port based GMRP Configuration: Port GMRP Status Registration ForwardAll -------------------------------------------- ----------- ------------ ---------- 1/1-2,3/1,6/1-9,6/12,6/15-48,7/1-24 Enabled Normal Disabled 6/10-11,6/13-14 Disabled Normal Disabled Console> (enable)
To disable GMRP on individual switch ports, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Disable GMRP on individual switch ports. | set port gmrp disable mod_num/port_num |
Step 2 Verify the configuration. | show gmrp configuration |
This example shows how to disable GMRP on ports 6/10-14 and verify the configuration:
Console> (enable) set port gmrp disable 6/10-14 GMRP disabled on ports 6/10-14. Console> (enable) show gmrp configuration Global GMRP Configuration: GMRP Feature is currently enabled on this switch. GMRP Timers (milliseconds): Join = 200 Leave = 600 LeaveAll = 10000 Port based GMRP Configuration: Port GMRP Status Registration ForwardAll -------------------------------------------- ----------- ------------ ---------- 1/1-2,3/1,6/1-9,6/15-48,7/1-24 Enabled Normal Disabled 6/10-14 Disabled Normal Disabled Console> (enable)
When you enable the GMRP forward-all option on a port, a copy of all multicast traffic registered on the switch is forwarded to that port. Enable the forward-all option on any port connected to a router that needs to receive any multicasts (routers do not support GMRP and so cannot send GMRP join messages). The forward-all option can also be used to forward all registered multicast traffic to a port with a network analyzer or probe attached.
To forward a copy of all GMRP multicast packets registered on the switch to a port, perform this task in privileged mode:
| Task | Command |
|---|---|
Enable the GMRP forward-all option on a switch port. | set gmrp fwdall enable mod_num/port_num |
This example shows how to enable the GMRP forward-all option on port 1/1:
Console> (enable) set gmrp fwdall enable 1/1 GMRP Forward All groups option enabled on port 1/1. Console> (enable)
To disable the GMRP forward-all option on a port, perform this task in privileged mode:
| Task | Command |
|---|---|
Disable the GMRP forward-all option on a port. | set gmrp fwdall disable mod_num/port_num |
This example shows how to disable the GMRP forward-all option on port 1/1:
Console> (enable) set gmrp fwdall disable 1/1 GMRP Forward All groups option disabled on port 1/1. Console> (enable)
These sections describe how to configure GMRP registration modes on switch ports:
Configuring a port in normal registration mode allows dynamic GMRP multicast registration and deregistration on the port. Normal mode is the default on all switch ports.
To configure GMRP normal registration on a port, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Configure normal registration on a port. | set gmrp registration normal mod_num/port_num |
Step 2 Verify the configuration. | show gmrp configuration |
This example shows how to configure normal registration on port 2/10:
Console> (enable) set gmrp registration normal 2/10 GMRP Registration is set normal on port 2/10. Console> (enable)
When you configure a port in fixed registration mode, all the multicast groups currently registered on all ports are registered on the port, but the port ignores any subsequent registrations or deregistrations on other ports. A port in fixed registration mode continues to register multicast groups that are specific to the port. You must return the port to normal registration mode to deregister multicast groups on the port.
To configure GMRP fixed registration on a port, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Configure fixed registration on a port. | set gmrp registration fixed mod_num/port_num |
Step 2 Verify the configuration. | show gmrp configuration |
This example shows how to configure fixed registration on port 2/10 and verify the configuration:
Console> (enable) set gmrp registration fixed 2/10
GMRP Registration is set fixed on port 2/10.
Console> (enable) show gmrp configuration
Global GMRP Configuration:
GMRP Feature is currently enabled on this switch.
GMRP Timers (milliseconds):
Join = 200
Leave = 600
LeaveAll = 10000
Port based GMRP Configuration:
GMRP-Status Registration ForwardAll Port(s)
----------- ------------ ---------- --------------------------------------------
Enabled Normal Disabled 1/1-4
2/1-9,2/11-48
3/1-24
5/1
Enabled Fixed Disabled 2/10
Console> (enable)
Configuring a port in forbidden registration mode deregisters all GMRP multicasts and prevents any further GMRP multicast registration on the port.
To configure GMRP forbidden registration on a port, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Configure forbidden registration on a port. | set gmrp registration forbidden mod_num/port_num |
Step 2 Verify the configuration. | show gmrp configuration |
This example shows how to configure forbidden registration on port 2/10 and verify the configuration:
Console> (enable) set gmrp registration forbidden 2/10
GMRP Registration is set forbidden on port 2/10.
Console> (enable) show gmrp configuration
Global GMRP Configuration:
GMRP Feature is currently enabled on this switch.
GMRP Timers (milliseconds):
Join = 200
Leave = 600
LeaveAll = 10000
Port based GMRP Configuration:
GMRP-Status Registration ForwardAll Port(s)
----------- ------------ ---------- --------------------------------------------
Enabled Normal Disabled 1/1-4
2/1-9,2/11-48
3/1-24
5/1
Enabled Forbidden Disabled 2/10
Console> (enable)
You can modify the default GARP timer values on the switch.
When setting the timer values, the value for leave must be equal to or greater than three times the join value (leave >= join * 3). The value for leaveall must be greater than the value for leave (leaveall > leave). The more registered attributes on the switch, the greater you should configure the difference between the leave value and the join value.
For better performance on switches with many registered multicast groups, increase the timer values to the order of seconds.
If you attempt to set a timer value that does not adhere to these rules, an error is returned. For example, if you set the leave timer to 600 ms and you attempt to configure the join timer to 350 ms, an error is returned. Set the leave timer to at least 1050 ms and then set the join timer to 350 ms.
 | Caution Set the same GARP timer values on all Layer 2-connected devices. If the GARP timers are set differently on the Layer 2-connected devices, GARP applications (for example, GMRP and GVRP) do not operate successfully. |
To adjust the GARP timer values, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Set the GARP timer values. | set garp timer {join | leave | leaveall} timer_value |
Step 2 Verify the configuration. | show garp timer |
This example shows how to set GARP timers and verify the configuration:
Console> (enable) set garp timer leaveall 12000 GMRP/GARP leaveAll timer value is set to 12000 milliseconds. Console> (enable) set garp timer leave 650 GMRP/GARP leave timer value is set to 650 milliseconds. Console> (enable) set garp timer join 300 GMRP/GARP join timer value is set to 300 milliseconds. Console> (enable) show garp timer Timer Timer Value (milliseconds) -------- -------------------------- Join 300 Leave 650 LeaveAll 12000 Console> (enable)
To display GMRP statistics on the switch, perform this task:
| Task | Command |
Display GMRP statistics. | show gmrp statistics [vlan_id] |
This example shows how to display GMRP statistics for VLAN 23:
Console> show gmrp statistics 23 GMRP Statistics for vlan <23>: Total valid GMRP Packets Received:500 Join Empties:200 Join INs:250 Leaves:10 Leave Alls:35 Empties:5 Fwd Alls:0 Fwd Unregistered:0 Total valid GMRP Packets Transmitted:600 Join Empties:200 Join INs:150 Leaves:45 Leave Alls:200 Empties:5 Fwd Alls:0 Fwd Unregistered:0 Total valid GMRP Packets Received:0 Total GMRP packets dropped:0 Total GMRP Registrations Failed:0 Console>
To clear all GMRP statistics on the switch, perform this task in privileged mode:
| Task | Command |
Clear GMRP statistics. | clear gmrp statistics {vlan_id | all} |
This example shows how to clear the GMRP statistics for all VLANs:
Console> (enable) clear gmrp statistics all Console> (enable)
To disable GMRP globally on the switch, perform this task in privileged mode:
| Task | Command |
|---|---|
Disable GMRP globally on the switch. | set gmrp disable |
This example shows how to disable GMRP globally on the switch:
Console> (enable) set gmrp disable GMRP disabled. Console> (enable)
These sections describe how to manually specify multicast router ports and configure multicast group entries:
When you enable IGMP snooping the switch automatically learns to which ports a multicast router is connected. However, if desired, you can manually specify multicast router ports.
To define multicast router ports manually, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Manually specify a multicast router port. | set multicast router mod_num/port_num |
Step 2 Verify the configuration. | show multicast router [mod_num/port_num] [vlan_id] |
This example shows how to specify a multicast router port manually and verify the configuration (the asterisk [*] next to the multicast router on port 3/1 indicates that the entry was configured manually):
Console> (enable)set multicast router 3/1Port 3/1 added to multicast router port list.Console> (enable)show multicast router IGMP disabled Port Vlan --------- ---------------- 2/1 99 2/2 255 3/1 * 1 7/9 2,99 Total Number of Entries = 4 '*' - Configured Console> (enable)
To configure a multicast group manually, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Add one or more multicast MAC addresses to the CAM 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] |
This example shows how to define multicast groups manually and verify the configuration (the asterisks indicate the entry was manually configured):
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 IGMP disabled 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 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 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)
Posted: Wed Dec 29 07:28:36 PST 1999
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