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| Title | Size | Download |
|---|---|---|
| 02-IGMP Snooping Configuration | 276.64 KB |
Basic Concepts in IGMP Snooping
IGMP Snooping Configuration Task List
Configuring Basic Functions of IGMP Snooping
Configuring the Version of IGMP Snooping
Configuring IGMP Snooping Port Functions
Configuring Aging Timers for Dynamic Ports
Configuring Fast Leave Processing
Configuring IGMP Snooping Querier
Enabling IGMP Snooping Querier
Configuring IGMP Queries and Responses
Configuring Source IP Address of IGMP Queries
Configuring an IGMP Snooping Policy
Configuring a Multicast Group Filter
Configuring the Function of Dropping Unknown Multicast Data
Configuring IGMP Report Suppression
Configuring Maximum Multicast Groups that Can Be Joined on a Port
Configuring Multicast Group Replacement
Displaying and Maintaining IGMP Snooping
IGMP Snooping Configuration Examples
Troubleshooting IGMP Snooping Configuration
AP Fails in Layer 2 Multicast Forwarding
Configured Multicast Group Policy Fails to Take Effect
l Support of the H3C WA series WLAN access points (APs) for features may vary by AP model. For more information, see Feature Matrix.
l The display information varies by AP model and configuration.
l The term AP in this document refers to common APs, wireless bridges, and mesh APs.
l The term router in this document refers to both routers and routing-enabled APs.
l The models listed in this document are not applicable to all regions. Please consult your local sales office for the models applicable to your region.
This chapter includes these sections:
l IGMP Snooping Configuration Task List
l Displaying and Maintaining IGMP Snooping
l IGMP Snooping Configuration Examples
l Troubleshooting IGMP Snooping Configuration
IGMP Snooping Overview
Internet Group Management Protocol Snooping (IGMP snooping) is a multicast constraining mechanism that runs on Layer 2 devices to manage and control multicast groups.
Principle of IGMP Snooping
By analyzing received IGMP messages, a Layer 2 device running IGMP snooping establishes mappings between ports and multicast MAC addresses and forwards multicast data based on these mappings.
As shown in Figure 1-1, when IGMP snooping is not running on the switch, multicast packets are broadcast to all devices at Layer 2. When IGMP snooping is running on the switch, multicast packets for known multicast groups are multicast to the receivers, rather than broadcast to all hosts, at Layer 2.
Figure 1-1 Before and after IGMP snooping is enabled on the Layer 2 device
IGMP snooping forwards multicast data to only the receivers requiring it at Layer 2, and brings the following advantages:
l Reducing Layer 2 broadcast packets, thus saving network bandwidth.
l Enhancing the security of multicast traffic.
l Facilitating the implementation of per-host accounting.
Basic Concepts in IGMP Snooping
IGMP Snooping related ports
As shown in Figure 1-2, Router connects to the multicast source, IGMP snooping runs on Switch and AP, Host A and Host B are receiver hosts (namely, multicast group members).
Figure 1-2 IGMP snooping related ports
Ports involved in IGMP snooping, as shown in Figure 1-2, are described as follows:
l Router port: A router port is a port on an Ethernet switch or AP that leads the switch or AP towards the Layer 3 multicast device (DR or IGMP querier). In the figure, Ethernet 1/0 of Switch and Ethernet 1/0/1 of AP are router ports. The switch and AP register all their local router ports in their respective router port lists.
l Member port: A member port is a port on an Ethernet switch or AP that leads the switch or AP towards multicast group members. In the figure, Ethernet 1/1 of Switch and WLAN-BSS 1 and WLAN-BSS 2 of AP are member ports. The switch and AP register all their member ports in their respective IGMP snooping forwarding tables.
l Whenever mentioned in this document, a router port is a port on a switch or AP that leads the switch or AP to a Layer 3 multicast device, rather than a port on a router.
l Unless otherwise specified, router/member ports mentioned in this document include static and dynamic ports.
l An IGMP snooping–enabled switch or AP deems that all its ports on which IGMP general queries with the source IP address other than 0.0.0.0 or PIM hello messages are received to be dynamic router ports.
Aging timers for dynamic ports in IGMP Snooping and related messages and actions
Table 1-1 Aging timers for dynamic ports in IGMP snooping and related messages and actions
|
Timer |
Description |
Message before expiry |
Action after expiry |
|
Dynamic router port aging timer |
For each dynamic router port, the AP sets a timer initialized to the dynamic router port aging time. |
IGMP general query of which the source address is not 0.0.0.0 or PIM hello |
The AP removes this port from its router port list. |
|
Dynamic member port aging timer |
When a port dynamically joins a multicast group, the AP sets a timer for the port, which is initialized to the dynamic member port aging time. |
IGMP membership report |
The AP removes this port from the IGMP snooping forwarding table. |
The port aging mechanism of IGMP snooping works only for dynamic ports; a static port will never age out.
How IGMP Snooping Works
An AP running IGMP snooping performs different actions when it receives different IGMP messages, as follows:
The description about adding or deleting a port in this section is only for a dynamic port. Static ports can be added or deleted only through the corresponding configurations. For more information, see Configuring Static Ports.
When receiving a general query
The IGMP querier periodically sends IGMP general queries to all hosts and routers (224.0.0.1) on the local subnet to find out whether active multicast group members exist on the subnet.
Upon receiving an IGMP general query, the AP forwards it through all ports in the VLAN except the receiving port and performs the following to the receiving port:
l If the receiving port is a dynamic router port existing in its router port list, the AP resets the aging timer of this dynamic router port.
l If the receiving port is not a dynamic router port existing in its router port list, the AP adds it into its router port list and sets an aging timer for this dynamic router port.
When receiving a membership report
A host sends an IGMP report to the IGMP querier in the following circumstances:
l Upon receiving an IGMP query, a multicast group member host responds with an IGMP report.
l When intended to join a multicast group, a host sends an IGMP report to the IGMP querier to announce that it is interested in the multicast information addressed to that group.
Upon receiving an IGMP report, the AP forwards it through all the router ports in the VLAN, resolves the address of the reported multicast group, and performs the following:
l If no forwarding table entry exists for the reported group, the AP creates an entry, adds the port as a dynamic member port to the outgoing port list, and starts a member port aging timer for that port.
l If a forwarding table entry exists for the reported group, but the port is not included in the outgoing port list for that group, the AP adds the port as a dynamic member port to the outgoing port list, and starts an aging timer for that port.
l If a forwarding table entry exists for the reported group and the port is included in the outgoing port list, which means that this port is already a dynamic member port, the AP resets the aging timer for that port.
An AP does not forward an IGMP report through a non-router port. This is because if the AP forwards a report message through a member port, all the attached hosts listening to the reported multicast address will suppress their own reports upon receiving this report according to the IGMP report suppression mechanism on them, and this will prevent the AP from knowing whether the reported multicast group still has active members attached to that port.
When receiving a leave message
When an IGMPv1 host leaves a multicast group, the host does not send an IGMP leave message, so the AP cannot know immediately that the host has left the multicast group. However, as the host stops sending IGMP reports as soon as it leaves a multicast group, the AP deletes the forwarding entry for the dynamic member port corresponding to the host from the forwarding table when its aging timer expires.
When an IGMPv2 or IGMPv3 host leaves a multicast group, the host sends an IGMP leave message to the multicast router.
When the AP receives an IGMP leave message on a dynamic member port, it first checks whether a forwarding table entry for the group address in the message exists, and, if one exists, whether the outgoing port list contains the port.
l If the forwarding table entry does not exist or if the outgoing port list does not contain the port, the AP discards the IGMP leave message instead of forwarding it to any port.
l If the forwarding table entry exists and the outgoing port list contains the port, the AP forwards the leave message to all router ports in the native VLAN. Because the AP does not know whether any other hosts attached to the port are still listening to that group address, the AP does not immediately remove the port from the outgoing port list of the forwarding table entry for that group; instead, it resets the aging timer for the port.
Upon receiving the IGMP leave message from a host, the IGMP querier resolves the multicast group address in the message and sends an IGMP group-specific query to that multicast group through the port that received the leave message. Upon receiving the IGMP group-specific query, the AP forwards it through all its router ports in the VLAN and all member ports for that multicast group, and performs the following to the port on which it received the IGMP leave message:
l If any IGMP report in response to the group-specific query is received on the port (suppose it is a dynamic member port) before its aging timer expires, this means that some host attached to the port is receiving or expecting to receive multicast data for that multicast group. The AP resets the aging timer of the port.
l If no IGMP report in response to the group-specific query is received on the port before its aging timer expires, this means that no hosts attached to the port are still listening to that group address. The AP removes the port from the outgoing port list of the forwarding table entry for that multicast group when the aging timer expires.
Protocols and Standards
IGMP snooping is documented in:
l RFC 4541: Considerations for Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) Snooping Switches
IGMP Snooping Configuration Task List
Complete these tasks to configure IGMP snooping:
|
Task |
Remarks |
|
|
Required |
||
|
Optional |
||
|
Optional |
||
|
Optional |
||
|
Optional |
||
|
Optional |
||
|
Optional |
||
|
Optional |
||
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Optional |
||
|
Optional |
||
|
Optional |
||
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Optional |
||
|
Configuring Maximum Multicast Groups that Can Be Joined on a Port |
Optional |
|
|
Optional |
||
l Configurations made in IGMP snooping view are effective for all VLANs, while configurations made in VLAN view are effective only for ports belonging to the current VLAN. For a given VLAN, a configuration made in IGMP snooping view is effective only if the same configuration is not made in VLAN view.
l Configurations made in IGMP snooping view are effective for all ports; configurations made in interface view are effective only for the current interface. For a given port, a configuration made in IGMP snooping view is effective only if the same configuration is not made in Ethernet interface view.
Configuring Basic Functions of IGMP Snooping
Configuration Prerequisites
Before configuring the basic functions of IGMP snooping, complete the following task:
l Configure the corresponding VLANs.
Before configuring the basic functions of IGMP snooping, prepare the following data:
l Version of IGMP snooping.
Enabling IGMP Snooping
Follow these steps to enable IGMP snooping:
|
To do... |
Use the command... |
Remarks |
|
Enter system view |
system-view |
— |
|
Enable IGMP snooping globally and enter IGMP snooping view |
igmp-snooping |
Required Disabled by default |
|
Return to system view |
quit |
— |
|
Enter VLAN view |
vlan vlan-id |
— |
|
Enable IGMP snooping in the VLAN |
igmp-snooping enable |
Required Disabled by default |
l IGMP snooping must be enabled globally before it can be enabled in a VLAN.
l When you enable IGMP snooping in a specified VLAN, this function takes effect for the ports in this VLAN only.
Configuring the Version of IGMP Snooping
By configuring an IGMP snooping version, you actually configure the version of IGMP messages that IGMP snooping can process.
l IGMP snooping version 2 can process IGMPv1 and IGMPv2 messages, but not IGMPv3 messages, which will be flooded in the VLAN.
l IGMP snooping version 3 can process IGMPv1, IGMPv2 and IGMPv3 messages.
Follow these steps to configure the version of IGMP snooping:
|
To do... |
Use the command... |
Remarks |
|
Enter system view |
system-view |
— |
|
Enter VLAN view |
vlan vlan-id |
— |
|
Configure the version of IGMP snooping |
igmp-snooping version version-number |
Optional Version 2 by default |
If you switch IGMP snooping from version 3 to version 2, the system will clear all IGMP snooping forwarding entries from dynamic joins, and will:
l Keep forwarding entries for version 3 static (*, G) joins;
l Clear forwarding entries from version 3 static (S, G) joins, which will be restored when IGMP snooping is switched back to version 3.
For more information about static joins, see Configuring Static Ports.
Configuring IGMP Snooping Port Functions
Configuration Prerequisites
Before configuring IGMP snooping port functions, enable IGMP snooping in the VLAN
Before configuring IGMP snooping port functions, prepare the following data:
l Aging time of dynamic router ports,
l Aging time of dynamic member ports, and
l Multicast group and multicast source addresses
Configuring Aging Timers for Dynamic Ports
If an AP receives no IGMP general queries or PIM hello messages on a dynamic router port, it removes the port from the router port list when the aging timer of the port expires.
If an AP receives no IGMP reports for a multicast group on a dynamic member port, it removes the port from the outgoing port list of the forwarding table entry for that multicast group when the aging timer of the port for that group expires.
If multicast group memberships change frequently, you can set a relatively small value for the dynamic member port aging timer, and vice versa.
Configuring aging timers for dynamic ports globally
Follow these steps to configure aging timers for dynamic ports globally:
|
To do... |
Use the command... |
Remarks |
|
Enter system view |
system-view |
— |
|
Enter IGMP snooping view |
igmp-snooping |
— |
|
Configure dynamic router port aging time |
router-aging-time interval |
Optional 105 seconds by default |
|
Configure dynamic member port aging time |
host-aging-time interval |
Optional 260 seconds by default |
Configuring aging timers for dynamic ports in a VLAN
Follow these steps to configure aging timers for dynamic ports in a VLAN:
|
To do... |
Use the command... |
Remarks |
|
Enter system view |
system-view |
— |
|
Enter VLAN view |
vlan vlan-id |
— |
|
Configure dynamic router port aging time |
igmp-snooping router-aging-time interval |
Optional 105 seconds by default |
|
Configure dynamic member port aging time |
igmp-snooping host-aging-time interval |
Optional 260 seconds by default |
Configuring Static Ports
If all the hosts attached to a port are interested in the multicast data addressed to a particular multicast group or the multicast data that a particular multicast source sends to a particular group, you can configure static (*, G) or (S, G) joining on that port, namely configure the port as a group-specific or source-and-group-specific static member port.
You can configure a port of an AP to be a static router port, through which the AP can forward all the multicast traffic it received.
Follow these steps to configure a static port:
|
To do... |
Use the command... |
Remarks |
|
Enter system view |
system-view |
— |
|
Enter Ethernet interface |
interface interface-type interface-number |
— |
|
Configure the port as static member port |
igmp-snooping static-group group-address [ source-ip source-address ] vlan vlan-id |
Required No static member ports by default |
|
Configure the port as static router port |
igmp-snooping static-router-port vlan vlan-id |
Required No static router ports by default |
l A static member port does not respond to queries from the IGMP querier; when static (*, G) or (S, G) joining is enabled or disabled on a port, the port does not send an unsolicited IGMP report or an IGMP leave message.
l Static member ports and static router ports never age out. To remove such a port, you need to use the corresponding undo command.
l You cannot configure a WLAN-BSS port as a static member port or router port.
Configuring Simulated Joining
Generally, a host running IGMP responds to IGMP queries from the IGMP querier. If a host fails to respond due to some reasons, the multicast router may deem that no member of this multicast group exists on the network segment, and therefore will remove the corresponding forwarding path.
To avoid this situation from happening, you can enable simulated joining on a port of an AP, namely configure the port as a simulated member host for a multicast group. When receiving an IGMP query, the simulated host gives a response. Thus, the AP can continue receiving multicast data.
A simulated host acts like a real host, as follows:
l When a port is configured as a simulated member host, the AP sends an unsolicited IGMP report through that port.
l After a port is configured as a simulated member host, the AP responds to IGMP general queries by sending IGMP reports through that port.
l When the simulated joining function is disabled on a port, the AP sends an IGMP leave message through that port.
Follow these steps to configure simulated joining:
|
To do... |
Use the command... |
Remarks |
|
Enter system view |
system-view |
— |
|
Enter Ethernet interface |
interface interface-type interface-number |
— |
|
Configure simulated (*, G) or (S, G) joining |
igmp-snooping host-join group-address [ source-ip source-address ] vlan vlan-id |
Required Disabled by default |
l Each simulated host is equivalent to an independent host. For example, when receiving an IGMP query, the simulated host corresponding to each configuration responds respectively.
l Unlike a static member port, a port configured as a simulated member host will age out like a dynamic member port.
l You cannot configure a WLAN-BSS port as a simulated host.
Configuring Fast Leave Processing
In VLANs where only one host is attached to each port, fast leave processing helps improve bandwidth and resource usage.
Configuring fast leave processing globally
Follow these steps to configure fast leave processing globally:
|
To do... |
Use the command... |
Remarks |
|
Enter system view |
system-view |
— |
|
Enter IGMP snooping view |
igmp-snooping |
— |
|
Enable fast leave processing |
fast-leave [ vlan vlan-list ] |
Required Disabled by default |
Configuring fast leave processing on a port
Follow these steps to configure fast leave processing on a port:
|
To do... |
Use the command... |
Remarks |
|
Enter system view |
system-view |
— |
|
Enter Ethernet interface |
interface interface-type interface-number |
— |
|
Enable fast leave processing |
igmp-snooping fast-leave [ vlan vlan-list ] |
Required Disabled by default |
l If fast leave processing is enabled on a port to which more than one host is attached, when one host leaves a multicast group, the other hosts attached to the port and interested in the same multicast group will fail to receive multicast data for that group.
l You cannot configure fast leave processing on a WLAN-BSS port.
Configuring IGMP Snooping Querier
Configuration Prerequisites
Before configuring IGMP snooping querier, complete the following task:
l Enable IGMP snooping in the VLAN.
Before configuring IGMP snooping querier, prepare the following data:
l IGMP general query interval,
l IGMP last-member query interval,
l Maximum response time to IGMP general queries,
l Source address of IGMP general queries, and
l Source address of IGMP group-specific queries.
Enabling IGMP Snooping Querier
Follow these steps to enable IGMP snooping querier:
|
To do... |
Use the command... |
Remarks |
|
Enter system view |
system-view |
— |
|
Enter VLAN view |
vlan vlan-id |
— |
|
Enable IGMP snooping querier |
igmp-snooping querier |
Required Disabled by default |
It is meaningless to configure an IGMP snooping querier in a multicast network running IGMP. Although an IGMP snooping querier does not take part in IGMP querier elections, it may affect IGMP querier elections because it sends IGMP general queries with a low source IP address.
Configuring IGMP Queries and Responses
You can tune the IGMP general query interval based on actual condition of the network.
Upon receiving an IGMP query (general query or group-specific query), a host starts a timer for each multicast group it has joined. This timer is initialized to a random value in the range of 0 to the maximum response time (the host obtains the value of the maximum response time from the Max Response Time field in the IGMP query it received). When the timer value comes down to 0, the host sends an IGMP report to the corresponding multicast group.
An appropriate setting of the maximum response time for IGMP queries allows hosts to respond to queries quickly and avoids bursts of IGMP traffic on the network caused by reports simultaneously sent by a large number of hosts when the corresponding timers expire simultaneously.
l For IGMP general queries, you can configure the maximum response time to fill their Max Response time field.
l For IGMP group-specific queries, you can configure the IGMP last-member query interval to fill their Max Response time field. Namely, for IGMP group-specific queries, the maximum response time equals to the IGMP last-member query interval.
Configuring IGMP queries and responses globally
Follow these steps to configure IGMP queries and responses globally:
|
To do... |
Use the command... |
Remarks |
|
Enter system view |
system-view |
— |
|
Enter IGMP snooping view |
igmp-snooping |
— |
|
Configure the maximum response time to IGMP general queries |
max-response-time interval |
Optional 10 seconds by default |
|
Configure the IGMP last-member query interval |
last-member-query-interval interval |
Optional 1 second by default |
Configuring IGMP queries and responses in a VLAN
Follow these steps to configure IGMP queries and responses in a VLAN:
|
To do... |
Use the command... |
Remarks |
|
Enter system view |
system-view |
— |
|
Enter VLAN view |
vlan vlan-id |
— |
|
Configure IGMP general query interval |
igmp-snooping query-interval interval |
Optional 60 seconds by default |
|
Configure the maximum response time to IGMP general queries |
igmp-snooping max-response-time interval |
Optional 10 seconds by default |
|
Configure the IGMP last-member query interval |
igmp-snooping last-member-query-interval interval |
Optional 1 second by default |
In the configuration, make sure that the IGMP general query interval is larger than the maximum response time for IGMP general queries. Otherwise, multicast group members may be deleted by mistake.
Configuring Source IP Address of IGMP Queries
Upon receiving an IGMP query whose source IP address is 0.0.0.0 on a port, an AP will not set that port as a dynamic router port. This may prevent multicast forwarding entries from being correctly created at the data link layer and cause multicast traffic forwarding failure in the end. When a Layer 2 device acts as an IGMP snooping querier, to avoid the aforesaid problem, you are commended to configure a non-all-zero IP address as the source IP address of IGMP queries.
Follow these steps to configure source IP address of IGMP queries:
|
To do... |
Use the command... |
Remarks |
|
Enter system view |
system-view |
— |
|
Enter VLAN view |
vlan vlan-id |
— |
|
Configure the source address of IGMP general queries |
igmp-snooping general-query source-ip { ip-address | current-interface } |
Optional 0.0.0.0 by default |
|
Configure the source IP address of IGMP group-specific queries |
igmp-snooping special-query source-ip { ip-address | current-interface } |
Optional 0.0.0.0 by default |
The source address of IGMP query messages may affect IGMP querier selection within the segment.
Configuring an IGMP Snooping Policy
Configuration Prerequisites
Before configuring an IGMP snooping policy, enable IGMP snooping in the VLAN
Before configuring an IGMP snooping policy, prepare the following data:
l ACL rule for multicast group filtering
l The maximum number of multicast groups that can pass the ports
Configuring a Multicast Group Filter
On an IGMP snooping–enabled AP, the configuration of a multicast group allows the service provider to define restrictions on multicast programs available to different users.
In an actual application, when a user requests a multicast program, the user’s host initiates an IGMP report. Upon receiving this report message, the AP checks the report against the configured ACL rule. If the port on which the report was received can join this multicast group, the AP adds an entry for this port in the IGMP snooping forwarding table; otherwise the AP drops this report message. Any multicast data that has failed the ACL check will not be sent to this port. In this way, the service provider can control the VOD programs provided for multicast users.
Configuring a multicast group filter globally
Follow these steps to configure a multicast group filter globally:
|
To do... |
Use the command... |
Remarks |
|
Enter system view |
system-view |
— |
|
Enter IGMP snooping view |
igmp-snooping |
— |
|
Configure a multicast group filter |
group-policy acl-number [ vlan vlan-list ] |
Required No group filter is configured by default. |
Configuring a multicast group filter on a port
Follow these steps to configure a multicast group filter on a port:
|
To do... |
Use the command... |
Remarks |
|
Enter system view |
system-view |
— |
|
Enter Ethernet interface |
interface interface-type interface-number |
— |
|
Configure a multicast group filter |
igmp-snooping group-policy acl-number [ vlan vlan-list ] |
Required No filter is configured by default. |
Configuring the Function of Dropping Unknown Multicast Data
Unknown multicast data refers to multicast data for which no entries exist in the IGMP snooping forwarding table. When an AP receives such multicast traffic:
l With the function of dropping unknown multicast data enabled, the AP drops all the unknown multicast data received.
l With the function of dropping unknown multicast data disabled, the AP floods unknown multicast data in the VLAN which the unknown multicast data belongs to.
Configuring globally the function of dropping unknown multicast data
Follow these steps to configure globally the function of dropping unknown multicast data:
|
To do... |
Use the command... |
Remarks |
|
Enter system view |
system-view |
— |
|
Enter IGMP snooping view |
igmp-snooping |
— |
|
Enable the function of dropping unknown multicast data |
drop-unknown |
Required Disabled by default |
Configuring the function of dropping unknown multicast data in a VLAN
Follow these steps to configure the function of dropping unknown multicast data in a VLAN:
|
To do... |
Use the command... |
Remarks |
|
Enter system view |
system-view |
— |
|
Enter VLAN view |
vlan vlan-id |
— |
|
Enable the function of dropping unknown multicast data |
igmp-snooping drop-unknown |
Required Disabled by default |
l For APs that support both drop-unknown and igmp-snooping drop-unknown commands at the same time, the configuration made in IGMP snooping view and the configuration made in VLAN view are mutually exclusive. Namely, after this function is enabled in IGMP snooping view, it cannot be enabled or disabled in VLAN view, and vice versa.
l When enabled to drop unknown IPv4 multicast data, the AP is automatically enabled to drop unknown IPv6 multicast data.
l When enabled to drop unknown multicast data, the AP still forwards unknown multicast data to other router ports in the VLAN.
Configuring IGMP Report Suppression
When a Layer 2 device receives an IGMP report from a multicast group member, the AP forwards the message to the Layer 3 device directly connected with it. Thus, when multiple members of a multicast group are attached to the Layer 2 device, the Layer 3 device directly connected with it will receive duplicate IGMP reports from these members.
With the IGMP report suppression function enabled, within each query cycle, the Layer 2 device forwards only the first IGMP report per multicast group to the Layer 3 device and will not forward the subsequent IGMP reports from the same multicast group to the Layer 3 device. This helps reduce the number of packets being transmitted over the network.
Follow these steps to configure IGMP report suppression:
|
To do... |
Use the command... |
Remarks |
|
Enter system view |
system-view |
— |
|
Enter IGMP snooping view |
igmp-snooping |
— |
|
Enable IGMP report suppression |
report-aggregation |
Optional Enabled by default |
Configuring Maximum Multicast Groups that Can Be Joined on a Port
By configuring the maximum number of multicast groups that can be joined on a port, you can limit the number of multicast programs on-demand available to users, thus to regulate traffic on the port.
Follow these steps to configure the maximum number of multicast groups allowed on a port:
|
To do... |
Use the command... |
Remarks |
|
Enter system view |
system-view |
— |
|
Enter Ethernet interface |
interface interface-type interface-number |
— |
|
Configure the maximum number of multicast groups allowed on the port |
igmp-snooping group-limit limit [ vlan vlan-list ] |
Optional 16 by default |
l When the number of multicast groups a port has joined reaches the maximum number configured, the system deletes all the forwarding entries persistent to that port from the IGMP snooping forwarding table, and the hosts on this port need to join the multicast groups again.
l If you have configured static or simulated joins on a port, however, when the number of multicast groups on the port exceeds the configured threshold, the system deletes all the forwarding entries persistent to that port from the IGMP snooping forwarding table and applies the static or simulated joins again, until the number of multicast groups joined by the port comes back within the configured threshold.
Configuring Multicast Group Replacement
For some special reasons, the number of multicast groups that can be joined on the current AP or port may exceed the number configured for the AP or the port. In addition, in some specific applications, a multicast group newly joined on the AP needs to replace an existing multicast group automatically. A typical example is “channel switching”, namely, by joining a new multicast group, a user automatically switches from the current multicast group to the new one.
To address such situations, you can enable the multicast group replacement function on the AP or certain ports. When the number of multicast groups joined on the AP or a port has joined reaches the limit:
l If the multicast group replacement feature is enabled, the newly joined multicast group automatically replaces an existing multicast group with the lowest address.
l If the multicast group replacement feature is not enabled, new IGMP reports will be automatically discarded.
Configuring multicast group replacement globally
Follow these steps to configure multicast group replacement globally:
|
To do... |
Use the command... |
Remarks |
|
Enter system view |
system-view |
— |
|
Enter IGMP snooping view |
igmp-snooping |
— |
|
Enable multicast group replacement |
overflow-replace [ vlan vlan-list ] |
Required Disabled by default |
Configuring multicast group replacement on a port
Follow these steps to configure multicast group replacement on a port:
|
To do... |
Use the command... |
Remarks |
|
Enter system view |
system-view |
— |
|
Enter Ethernet interface |
interface interface-type interface-number |
Required Use either approach |
|
port-group { manual port-group-name | aggregation agg-id } |
||
|
Enable multicast group replacement |
igmp-snooping overflow-replace [ vlan vlan-list ] |
Required Disabled by default |
Be sure to configure the maximum number of multicast groups allowed on a port (see Configuring Maximum Multicast Groups that Can Be Joined on a Port) before enabling multicast group replacement. Otherwise, the multicast group replacement functionality will not take effect.
Displaying and Maintaining IGMP Snooping
|
To do... |
Use the command... |
Remarks |
|
View IGMP snooping multicast group information |
display igmp-snooping group [ vlan vlan-id ] [ verbose ] |
Available in any view |
|
View the statistics information of IGMP messages learned by IGMP snooping |
display igmp-snooping statistics |
Available in any view |
|
Clear IGMP snooping multicast group information |
reset igmp-snooping group { group-address | all } [ vlan vlan-id ] |
Available in user view |
|
Clear the statistics information of all kinds of IGMP messages learned by IGMP snooping |
reset igmp-snooping statistics |
Available in user view |
l The reset igmp-snooping group command works only on an IGMP snooping–enabled VLAN.
l The reset igmp-snooping group command cannot clear the IGMP snooping multicast group information for static joins.
IGMP Snooping Configuration Examples
Configuring Group Policy
Network requirements
l As shown in Figure 1-3, Router connects to the multicast source through Ethernet 1/2 and to AP through Ethernet 1/1.
l IGMPv2 is required on Router, IGMP snooping version 2 is required on AP, and Router will act as the IGMP querier on the subnet.
l It is required that the receiver, Client A, attached to AP can receive multicast traffic addressed to multicast group 224.1.1.1 only.
Network diagram
Figure 1-3 Network diagram for group policy configuration
Configuration procedure
1) Configure IP addresses
Configure an IP address and subnet mask for each interface as per Figure 1-3. The detailed configuration steps are omitted.
2) Configure Router
# Enable IP multicast routing, enable PIM-DM on each interface, and enable IGMP on Ethernet 1/1.
<Router> system-view
[Router] multicast routing-enable
[Router] interface ethernet 1/1
[Router-Ethernet1/1] igmp enable
[Router-Ethernet1/1] pim dm
[Router-Ethernet1/1] quit
[Router] interface ethernet 1/2
[Router-Ethernet1/2] pim dm
[Router-Ethernet1/2] quit
3) Configure AP
# Enable IGMP snooping globally.
<AP> system-view
[AP] igmp-snooping
[AP-igmp-snooping] quit
# Create VLAN 100, assign Ethernet 1/0/1 and WLAN-BSS 1 to this VLAN, and enable IGMP snooping and the function of dropping unknown multicast traffic in the VLAN.
[AP] vlan 100
[AP-vlan100] port GigabitEthernet 1/0/1
[AP-vlan100] port WLAN-BSS1
[AP-vlan100] igmp-snooping enable
[AP-vlan100] igmp-snooping drop-unknown
[AP-vlan100] quit
# Configure a multicast group filter so that the hosts in VLAN 100 can join only the multicast group 224.1.1.1.
[AP] acl number 2001
[AP-acl-basic-2001] rule permit source 224.1.1.1 0
[AP-acl-basic-2001] quit
[AP] igmp-snooping
[AP-igmp-snooping] group-policy 2001 vlan 100
[AP-igmp-snooping] quit
4) Verify the configuration
# View the detailed IGMP snooping multicast groups information in VLAN 100 on AP.
[AP] display igmp-snooping group vlan 100 verbose
Total 1 IP Group(s).
Total 1 IP Source(s).
Total 1 MAC Group(s).
Port flags: D-Dynamic port, S-Static port, C-Copy port
Subvlan flags: R-Real VLAN, C-Copy VLAN
Vlan(id):1.
Total 1 IP Group(s).
Total 1 IP Source(s).
Total 1 MAC Group(s).
Router port(s):total 1 port.
GigabitEthernet1/0/1 (D) ( 00:01:31 )
IP group(s):the following ip group(s) match to one mac group.
IP group address:224.1.1.1
(0.0.0.0, 224.1.1.1):
Attribute: Host Port
Host port(s):total 2 port.
WLAN-BSS1 (D) ( 00:04:07 )
WLAN-BSS2 (D) ( 00:04:07 )
MAC group(s):
MAC group address:0100-5e01-0101
Host port(s):total 2 port.
WLAN-BSS1
WLAN-BSS2
As shown above, WLAN-BSS 1 of AP has joined multicast group 224.1.1.1.
Troubleshooting IGMP Snooping Configuration
AP Fails in Layer 2 Multicast Forwarding
Symptom
An AP fails to implement Layer 2 multicast forwarding.
Analysis
IGMP snooping is not enabled.
Solution
1) Enter the display current-configuration command to view the running status of IGMP snooping.
2) If IGMP snooping is not enabled, use the igmp-snooping command to enable IGMP snooping globally, and then use igmp-snooping enable command to enable IGMP snooping in VLAN view.
3) If IGMP snooping is disabled only for the corresponding VLAN, just use the igmp-snooping enable command in VLAN view to enable IGMP snooping in the corresponding VLAN.
Configured Multicast Group Policy Fails to Take Effect
Symptom
Although a multicast group policy has been configured to allow hosts to join specific multicast groups, the hosts can still receive multicast data addressed to other multicast groups.
Analysis
l The ACL rule is incorrectly configured.
l The multicast group policy is not correctly applied.
l The function of dropping unknown multicast data is not enabled, so unknown multicast data is flooded.
Solution
1) Use the display acl command to check the configured ACL rule. Make sure that the ACL rule conforms to the multicast group policy to be implemented.
2) Use the display this command in IGMP snooping view or in the corresponding interface view to check whether the correct multicast group policy has been applied. If not, use the group-policy or igmp-snooping group-policy command to apply the correct multicast group policy.
3) Use the display current-configuration command to check whether the function of dropping unknown multicast data is enabled. If not, use the drop-unknown or igmp-snooping drop-unknown command to enable the function of dropping unknown multicast data.
