Configuring IGMP
Finding Feature
Information
Your software release
may not support all the features documented in this module. For the latest
caveats and feature information, see
Bug Search Tool and the
release notes for your platform and software release. To find information about
the features documented in this module, and to see a list of the releases in
which each feature is supported, see the feature information table.
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Prerequisites for
IGMP
-
Before performing
the tasks in this module, you should be familiar with the concepts explained in
the "IP Multicast Routing Technology Overview" module.
-
The tasks in this
module assume that IP multicast has been enabled and that the Protocol
Independent Multicast (PIM) interfaces have been configured using the tasks
described in the "Configuring
IP Multicast Routing” module.
Restrictions for
Configuring IGMP
The following are
the restrictions for configuring IGMP:
-
The
supports IGMP Versions 1, 2 , and 3.
 Note |
For IGMP
Version 3, only IGMP Version 3 BISS (Basic IGMPv3 Snooping Support) is
supported.
|
-
IGMP Version 3
uses new membership report messages that might not be correctly recognized by
older IGMP snooping
.
-
IGMPv3 can
operate with both ISM and SSM. In ISM, both exclude and include mode reports
are applicable. In SSM, only include mode reports are accepted by the last-hop
router. Exclude mode reports are ignored.
Information About IGMP
Role of the Internet Group Management Protocol
IGMP is used to dynamically register individual hosts in a multicast group on a particular LAN. Enabling PIM on an interface also enables IGMP. IGMP provides a means to automatically control and limit the flow of multicast traffic throughout your network with the use of special multicast queriers and hosts.
A querier is a network device, such as a router, that sends query messages to discover which network devices are members of a given multicast group.
A host is a receiver, including routers, that sends report messages (in response to query messages) to inform the querier of a host membership. Hosts use IGMP messages to join and leave multicast groups.
Hosts identify group memberships by sending IGMP messages to their local multicast device. Under IGMP, devices listen to IGMP messages and periodically send out queries to discover which groups are active or inactive on a particular subnet.
IGMP Multicast Addresses
IP multicast traffic uses group addresses, which are Class D IP addresses. The high-order four bits of a Class D address are 1110. Therefore, host group addresses can be in the range 224.0.0.0 to 239.255.255.255.
Multicast addresses in the range 224.0.0.0 to 224.0.0.255 are reserved for use by routing protocols and other network control traffic. The address 224.0.0.0 is guaranteed not to be assigned to any group.
IGMP packets are transmitted using IP multicast group addresses as follows:
IGMP general queries are destined to the address 224.0.0.1 (all systems on a subnet).
IGMP group-specific queries are destined to the group IP address for which the device is querying.
IGMP group membership reports are destined to the group IP address for which the device is reporting.
IGMPv2 leave-group messages are destined to the address 224.0.0.2 (all devices on a subnet).
IGMPv3 membership reports are destined to the address 224.0.0.22; all IGMPv3-capable multicast devices must listen to this address.
IGMP Versions
The
supports IGMP version 1, IGMP version
2, and IGMP version 3. These versions are interoperable on the
. For example, if IGMP snooping is
enabled and the querier's version is IGMPv2, and the
receives an IGMPv3 report from a host,
then the
can forward the IGMPv3 report to the
multicast router.
An IGMPv3
can receive messages from and forward
messages to a device running the Source Specific Multicast (SSM) feature.
IGMP Version 1
IGMP version 1 (IGMPv1) primarily uses a query-response model that enables the multicast router and multilayer to find which multicast groups are active (have one or more hosts interested in a multicast group) on the local subnet. IGMPv1 has other processes that enable a host to join and leave a multicast group. For more information, see RFC 1112.
IGMP Version 2
IGMPv2 extends IGMP functionality by providing such features as the IGMP leave process to reduce leave latency, group-specific queries, and an explicit maximum query response time. IGMPv2 also adds the capability for routers to elect the IGMP querier without depending on the multicast protocol to perform this task. For more information, see RFC 2236.
 Note |
IGMP version 2 is the default version for the .
|
IGMP Version
3
The
supports IGMP version 3.
An IGMPv3
supports Basic IGMPv3 Snooping Support
(BISS), which includes support for the snooping features on IGMPv1 and IGMPv2
switches and for IGMPv3 membership report messages. BISS constrains the
flooding of multicast traffic when your network includes IGMPv3 hosts. It
constrains traffic to approximately the same set of ports as the IGMP snooping
feature on IGMPv2 or IGMPv1 hosts.
An IGMPv3
can receive messages from and forward
messages to a device running the Source Specific Multicast (SSM) feature.
IGMPv3 Host Signalling
In IGMPv3, hosts signal membership to last hop routers of multicast groups. Hosts can signal group membership with filtering capabilities with respect to sources. A host can either signal that it wants to receive traffic from all sources sending to a group except for some specific sources (called exclude mode), or that it wants to receive traffic only from some specific sources sending to the group (called include mode).
IGMPv3 can operate with both Internet Standard Multicast (ISM) and Source Specific Multicast (SSM). In ISM, both exclude and include mode reports are applicable. In SSM, only include mode reports are accepted by the last-hop router. Exclude mode reports are ignored.
IGMP Versions
Differences
There are three
versions of IGMP, as defined by Request for Comments (RFC) documents of the
Internet Engineering Task Force (IETF). IGMPv2 improves over IGMPv1 by adding
the ability for a host to signal desire to leave a multicast group and IGMPv3
improves over IGMPv2 mainly by adding the ability to listen to multicast
originating from a set of source IP addresses only.
Table 1 IGMP Versions
IGMP Version
|
Description
|
IGMPv1
|
Provides the
basic query-response mechanism that allows the multicast device to determine
which multicast groups are active and other processes that enable hosts to join
and leave a multicast group. RFC 1112 defines the IGMPv1 host extensions for IP
multicasting.
|
IGMPv2
|
Extends IGMP,
allowing such capabilities as the IGMP leave process, group-specific queries,
and an explicit maximum response time field. IGMPv2 also adds the capability
for devices to elect the IGMP querier without dependence on the multicast
protocol to perform this task. RFC 2236 defines IGMPv2.
|
 Note |
By default,
enabling a PIM on an interface enables IGMPv2 on that device. IGMPv2 was
designed to be as backward compatible with IGMPv1 as possible. To accomplish
this backward compatibility, RFC 2236 defined special interoperability rules.
If your network contains legacy IGMPv1 hosts, you should be familiar with these
operability rules. For more information about IGMPv1 and IGMPv2
interoperability, see RFC 2236, Internet Group Management Protocol, Version 2 .
|
Devices That Run
IGMPv1
IGMPv1 devices send
IGMP queries to the “all-hosts” multicast address of 224.0.0.1 to solicit
multicast groups with active multicast receivers. The multicast receivers also
can send IGMP reports to the device to notify it that they are interested in
receiving a particular multicast stream. Hosts can send the report
asynchronously or in response to the IGMP queries sent by the device. If more
than one multicast receiver exists for the same multicast group, only one of
these hosts sends an IGMP report message; the other hosts suppress their report
messages.
In IGMPv1, there is
no election of an IGMP querier. If more than one device on the segment exists,
all the devices send periodic IGMP queries. IGMPv1 has no special mechanism by
which the hosts can leave the group. If the hosts are no longer interested in
receiving multicast packets for a particular group, they simply do not reply to
the IGMP query packets sent from the device. The device continues sending query
packets. If the device does not hear a response in three IGMP queries, the
group times out and the device stops sending multicast packets on the segment
for the group. If the host later wants to receive multicast packets after the
timeout period, the host simply sends a new IGMP join to the device, and the
device begins to forward the multicast packet again.
If there are
multiple devices on a LAN, a designated router (DR) must be elected to avoid
duplicating multicast traffic for connected hosts. PIM devices follow an
election process to select a DR. The PIM device with the highest IP address
becomes the DR.
The DR is
responsible for the following tasks:
-
Sending PIM
register and PIM Join and Prune messages toward the rendezvous point (RP) to
inform it about host group membership.
-
Sending IGMP
host-query messages.
-
Sending
host-query messages by default every 60 seconds in order to keep the IGMP
overhead on hosts and networks very low.
Devices That Run
IGMPv2
IGMPv2 improves the
query messaging capabilities of IGMPv1.
The query and
membership report messages in IGMPv2 are identical to the IGMPv1 messages with
two exceptions:
-
IGMPv2 query
messages are broken into two categories: general queries (identical to IGMPv1
queries) and group-specific queries.
-
IGMPv1
membership reports and IGMPv2 membership reports have different IGMP type
codes.
IGMPv2 also
enhances IGMP by providing support for the following capabilities:
-
Querier
election process--Provides the capability for IGMPv2 devices to elect the IGMP
querier without having to rely on the multicast routing protocol to perform the
process.
-
Maximum
Response Time field--A new field in query messages permits the IGMP querier to
specify the maximum query-response time. This field permits the tuning of the
query-response process to control response burstiness and to fine-tune leave
latencies.
-
Group-Specific
Query messages--Permits the IGMP querier to perform the query operation on a
specific group instead of all groups.
-
Leave-Group
messages--Provides hosts with a method of notifying devices on the network that
they wish to leave the group.
Unlike IGMPv1, in
which the DR and the IGMP querier are typically the same device, in IGMPv2 the
two functions are decoupled. The DR and the IGMP querier are selected based on
different criteria and may be different devices on the same subnet. The DR is
the device with the highest IP address on the subnet, whereas the IGMP querier
is the device with the lowest IP address.
Query messages are
used to elect the IGMP querier as follows:
-
When IGMPv2
devices start, they each multicast a general query message to the all-systems
group address of 224.0.0.1 with their interface address in the source IP
address field of the message.
-
When an IGMPv2
device receives a general query message, the device compares the source IP
address in the message with its own interface address. The device with the
lowest IP address on the subnet is elected the IGMP querier.
-
All devices
(excluding the querier) start the query timer, which is reset whenever a
general query message is received from the IGMP querier. If the query timer
expires, it is assumed that the IGMP querier has gone down, and the election
process is performed again to elect a new IGMP querier.
By default, the
timer is two times the query interval.
IGMP Join and Leave Process
IGMP Join Process
When a host wants to join a multicast group, the host sends one or more unsolicited membership reports for the multicast group it wants to join. The IGMP join process is the same for IGMPv1 and IGMPv2 hosts.
In IGMPv3, the join process for hosts proceeds as follows:
When a hosts wants to join a group, it sends an IGMPv3 membership report to 224.0.0.22 with an empty EXCLUDE list.
When a host wants to join a specific channel, it sends an IGMPv3 membership report to 224.0.0.22 with the address of the specific source included in the INCLUDE list.
When a host wants to join a group excluding particular sources, it sends an IGMPv3 membership report to 224.0.0.22 excluding those sources in the EXCLUDE list.
 Note |
If some IGMPv3 hosts on a LAN wish to exclude a source and others wish to include the source, then the device will send traffic for the source on the LAN (that is, inclusion trumps exclusion in this situation).
|
IGMP Leave Process
The method that hosts use to leave a group varies depending on the version of IGMP in operation.
IGMPv1 Leave Process
There is no leave-group message in IGMPv1 to notify the devices on the subnet that a host no longer wants to receive the multicast traffic from a specific group. The host simply stops processing traffic for the multicast group and ceases responding to IGMP queries with IGMP membership reports for the group. As a result, the only way IGMPv1 devices know that there are no longer any active receivers for a particular multicast group on a subnet is when the devices stop receiving membership reports. To facilitate this process, IGMPv1 devices associate a countdown timer with an IGMP group on a subnet. When a membership report is received for the group on the subnet, the timer is reset. For IGMPv1 devices, this timeout interval is typically three times the query interval (3 minutes). This timeout interval means that the device may continue to forward multicast traffic onto the subnet for up to 3 minutes after all hosts have left the multicast group.
IGMPv2 Leave Process
IGMPv2 incorporates a leave-group message that provides the means for a host to indicate that it wishes to stop receiving multicast traffic for a specific group. When an IGMPv2 host leaves a multicast group, if it was the last host to respond to a query with a membership report for that group, it sends a leave-group message to the all-devices multicast group (224.0.0.2).
IGMPv3 Leave Process
IGMPv3 enhances the leave process by introducing the capability for a host to stop receiving traffic from a particular group, source, or channel in IGMP by including or excluding sources, groups, or channels in IGMPv3 membership reports.
Default IGMP Configuration
This table displays the default IGMP configuration for the .
Table 2 Default IGMP ConfigurationFeature
|
Default Setting
|
Multilayer as a member of a multicast group
|
No group memberships are defined.
|
Access to multicast groups
|
All groups are allowed on an interface.
|
IGMP version
|
Version 2 on all interfaces.
|
IGMP host-query message interval
|
60 seconds on all interfaces.
|
IGMP query timeout
|
60 seconds on all interfaces.
|
IGMP maximum query response time
|
10 seconds on all interfaces.
|
Multilayer as a statically connected member
|
Disabled.
|
How to Configure IGMP
Configuring the
as a Member of a Group
You can configure the
as a member of a multicast group and discover multicast reachability in a
network. If all the multicast-capable routers and multilayer
that you administer are members of a multicast group, pinging that group causes
all of these devices to respond. The devices respond to ICMP echo-request
packets addressed to a group of which they are members. Another example is the
multicast trace-route tools provided in the software.
 Caution |
Performing this procedure
might impact the CPU performance because the CPU will receive all data traffic
for the group address.
|
This procedure is optional.
SUMMARY STEPS1.
enable
2.
configure
terminal
3.
interface
interface-id
4.
ip igmp
join-group
group-address
5.
end
6.
show ip igmp interface [interface-id]
7.
copy running-config
startup-config
DETAILED STEPS | Command or Action | Purpose |
---|
Step 1 |
enable
Example:
Switch> enable
|
Enables
privileged EXEC mode. Enter your password if prompted.
|
Step 2 | configure
terminal
Example:
Switch# configure terminal
|
Enters the global
configuration mode.
|
Step 3 | interface
interface-id
Example:
Switch(config)# interface
gigabitethernet 1/0/1
|
Specifies
the
interface on which you want to enable multicast routing, and
enters interface configuration mode.
|
Step 4 | ip igmp
join-group
group-address
Example:
Switch(config-if)# ip igmp
join-group 225.2.2.2
|
Configures the
to join a multicast group.
By default, no
group memberships are defined.
For
group-address, specify the multicast IP address in
dotted decimal notation.
|
Step 5 | end
Example:
Switch(config)# end
|
Returns to
privileged EXEC mode.
|
Step 6 | show ip igmp interface [interface-id]
Example:
Switch# show ip igmp interface
|
Verifies your
entries.
|
Step 7 | copy running-config
startup-config
Example:
Switch# copy running-config startup-config
|
(Optional) Saves your entries
in the configuration file.
|
Controlling Access
to IP Multicast Group
The switch sends
IGMP host-query messages to find which multicast groups have members on
attached local networks. The switch then forwards to these group members all
packets addressed to the multicast group. You can place a filter on each
interface to restrict the multicast groups that hosts on the subnet serviced by
the interface can join.
This procedure is
optional.
SUMMARY STEPS1.
enable
2.
configure
terminal
3.
interface
interface-id
4.
ip igmp access-group
access-list-number
5.
exit
6.
access-list
access-list-number {deny |
permit}
source
[source-wildcard]
7.
end
8.
show ip igmp interface [interface-id]
DETAILED STEPS | Command or Action | Purpose |
---|
Step 1 |
enable
Example:
Switch> enable
|
Enables
privileged EXEC mode. Enter your password if prompted.
|
Step 2 | configure
terminal
Example:
Switch# configure terminal
|
Enters the global
configuration mode.
|
Step 3 | interface
interface-id
Example:
Switch(config)# interface GigabitEthernet 1/0/12
|
Specifies the
interface to be configured, and enters interface configuration mode.
|
Step 4 | ip igmp access-group
access-list-number
Example:
Switch(config-if)# ip igmp access-group 10
|
Specifies the
multicast groups that hosts on the subnet serviced by an interface can join.
By default, all
groups are allowed on an interface.
For
access-list-number, specify an IP standard access
list number.
The range is 1
to 199.
Note
|
To disable
groups on an interface, use the no ip igmp
access-group interface configuration command.
|
|
Step 5 | exit
Example:
Switch(config-if)# exit
|
Returns to global
configuration mode.
|
Step 6 | access-list
access-list-number {deny |
permit}
source
[source-wildcard]
Example:
Switch(config)# access-list 10 permit
|
Creates a
standard access list.
-
For
access-list-number, specify the access list
created in Step 3.
-
The
deny keyword
denies access if the conditions are matched. The
permit keyword
permits access if the conditions are matched.
-
For
source, specify
the multicast group that hosts on the subnet can join.
-
(Optional)
For
source-wildcard, enter the wildcard bits in dotted
decimal notation to be applied to the source. Place ones in the bit positions
that you want to ignore.
Recall that the
access list is always terminated by an implicit deny statement for everything.
|
Step 7 | end
Example:
Switch(config-igmp-profile)# end
|
Returns to privileged EXEC
mode.
|
Step 8 | show ip igmp interface [interface-id]
Example:
Switch# show ip igmp interface
|
Verifies your
entries.
|
Changing the IGMP
Version
By default, the
switch uses IGMP Version 2, which provides features such as the IGMP query
timeout and the maximum query response time.
All systems on the
subnet must support the same version. The switch does not automatically detect
Version 1 systems and switch to Version 1. You can mix Version 1 and Version 2
hosts on the subnet because Version 2 routers or switches always work correctly
with IGMPv1 hosts.
Configure the switch
for Version 1 if your hosts do not support Version 2.
This procedure is
optional.
SUMMARY STEPS1.
enable
2.
configure
terminal
3.
interface
interface-id
4.
ip igmp version {1
|
2 |
3
}
5.
end
6.
show ip igmp interface [interface-id]
7.
copy running-config
startup-config
DETAILED STEPS | Command or Action | Purpose |
---|
Step 1 |
enable
Example:
Switch> enable
|
Enables
privileged EXEC mode. Enter your password if prompted.
|
Step 2 | configure
terminal
Example:
Switch# configure terminal
|
Enters the global
configuration mode.
|
Step 3 | interface
interface-id
Example:
Switch(config)# interface gigabitethernet 1/0/1
|
Specifies the interface to be
configured, and enters the interface configuration mode.
|
Step 4 | ip igmp version {1
|
2 |
3
}
Example:
Switch(config-if)# ip igmp version 2
| Specifies the
IGMP version that the switch uses.
Note
|
If you change
to Version 1, you cannot configure the ip igmp query-interval or the
ip igmp
query-max-response-time interface configuration commands.
|
To return to the
default setting, use the no ip igmp
version interface configuration command.
|
Step 5 | end
Example:
Switch(config)# end
|
Returns to
privileged EXEC mode.
|
Step 6 | show ip igmp interface [interface-id]
Example:
Switch# show ip igmp interface
|
Verifies your
entries.
|
Step 7 | copy running-config
startup-config
Example:
Switch# copy running-config startup-config
|
(Optional) Saves your entries
in the configuration file.
|
Modifying the IGMP Host-Query Message Interval
The
periodically sends IGMP host-query messages to discover which multicast groups
are present on attached networks. These messages are sent to the all-hosts
multicast group (224.0.0.1) with a time-to-live (TTL) of 1. The
sends host-query messages to refresh its knowledge of memberships present on
the network. If, after some number of queries, the software discovers that no
local hosts are members of a multicast group, the software stops forwarding
multicast packets to the local network from remote origins for that group and
sends a prune message upstream toward the source.
The
elects a PIM designated router (DR) for the LAN (subnet). The designated router
is responsible for sending IGMP host-query messages to all hosts on the LAN. In
sparse mode, the designated router also sends PIM register and PIM join
messages toward the RP router. With IGMPv2, the DR is the router or multilayer
with the highest IP address. With IGMPv1, the DR is elected according to the
multicast routing protocol that runs on the LAN.
This procedure is optional.
SUMMARY STEPS1.
enable
2.
configure
terminal
3.
interface
interface-id
4.
ip igmp
query-interval
seconds
5.
end
6.
show ip igmp interface [interface-id]
7.
copy running-config
startup-config
DETAILED STEPS | Command or Action | Purpose |
---|
Step 1 |
enable
Example:
Switch> enable
|
Enables
privileged EXEC mode. Enter your password if prompted.
|
Step 2 | configure
terminal
Example:
Switch# configure terminal
|
Enters the global
configuration mode.
|
Step 3 | interface
interface-id
Example:
Switch(config)# interface
gigabitethernet 1/0/1
|
Specifies the
interface on
which you want to enable multicast routing, and enters interface configuration
mode.
|
Step 4 | ip igmp
query-interval
seconds
Example:
Switch(config-if)# ip igmp
query-interval 75
|
Configures the
frequency at which the designated router sends IGMP host-query messages.
By default, the
designated router sends IGMP host-query messages every 60 seconds to keep the
IGMP overhead very low on hosts and networks.
|
Step 5 | end
Example:
Switch(config)# end
|
Returns to
privileged EXEC mode.
|
Step 6 | show ip igmp interface [interface-id]
Example:
Switch# show ip igmp interface
|
Verifies your
entries.
|
Step 7 | copy running-config
startup-config
Example:
Switch# copy running-config startup-config
|
(Optional) Saves your entries
in the configuration file.
|
Changing the IGMP Query Timeout for IGMPv2
If you are using IGMPv2, you
can specify the period of time before the
takes over as the querier for the interface. By default, the
waits twice the query interval period controlled by the
ip igmp query-interval interface configuration
command. After that time, if the
has received no queries, it becomes the querier.
This procedure is optional.
SUMMARY STEPS1.
enable
2.
configure
terminal
3.
interface
interface-id
4.
ip igmp
querier-timeout
seconds
5.
end
6.
show ip igmp interface [interface-id]
7.
copy running-config
startup-config
DETAILED STEPS | Command or Action | Purpose |
---|
Step 1 |
enable
Example:
Switch> enable
|
Enables
privileged EXEC mode. Enter your password if prompted.
|
Step 2 | configure
terminal
Example:
Switch# configure terminal
|
Enters the global
configuration mode.
|
Step 3 | interface
interface-id
Example:
Switch(config)# interface
gigabitethernet 1/0/1
|
Specifies the
interface on which you want to enable multicast routing, and
enters interface configuration mode.
|
Step 4 | ip igmp
querier-timeout
seconds
Example:
Switch(config-if)# ip igmp
querier-timeout 120
|
Specifies the
IGMP query timeout.
The default is 60
seconds (twice the query interval). The range is 60 to 300.
|
Step 5 | end
Example:
Switch(config)# end
|
Returns to
privileged EXEC mode.
|
Step 6 | show ip igmp interface [interface-id]
Example:
Switch# show ip igmp interface
|
Verifies your
entries.
|
Step 7 | copy running-config
startup-config
Example:
Switch# copy running-config startup-config
|
(Optional) Saves your entries
in the configuration file.
|
Changing the Maximum Query Response Time for IGMPv2
If you are using IGMPv2, you can change the
maximum query response time advertised in IGMP queries. The maximum query
response time enables the
to quickly detect that there are no more directly connected group members on a
LAN. Decreasing the value enables the
to prune groups faster.
This procedure is optional.
SUMMARY STEPS1.
enable
2.
configure
terminal
3.
interface
interface-id
4.
ip igmp
query-max-response-time
seconds
5.
end
6.
show ip igmp interface [interface-id]
7.
copy running-config
startup-config
DETAILED STEPS | Command or Action | Purpose |
---|
Step 1 |
enable
Example:
Switch> enable
|
Enables
privileged EXEC mode. Enter your password if prompted.
|
Step 2 | configure
terminal
Example:
Switch# configure terminal
|
Enters the global
configuration mode.
|
Step 3 | interface
interface-id
Example:
Switch(config)# interface
gigabitethernet 1/0/1
|
Specifies the
interface on
which you want to enable multicast routing, and enters interface configuration
mode.
|
Step 4 | ip igmp
query-max-response-time
seconds
Example:
Switch(config-if)# ip igmp
query-max-response-time 15
|
Changes the
maximum query response time advertised in IGMP queries.
The default is 10
seconds. The range is 1 to 25.
|
Step 5 | end
Example:
Switch(config)# end
|
Returns to
privileged EXEC mode.
|
Step 6 | show ip igmp interface [interface-id]
Example:
Switch# show ip igmp interface
|
Verifies your
entries.
|
Step 7 | copy running-config
startup-config
Example:
Switch# copy running-config startup-config
|
(Optional) Saves your entries
in the configuration file.
|
Configuring the
as a Statically Connected Member
At various times, either
there is not a group member on a network segment or a host that cannot report
its group membership by using IGMP. However, you may want multicast traffic to
be sent to that network segment. The following commands are used to pull
multicast traffic down to a network segment:
-
ip igmp
join-group—The
accepts the multicast packets in addition to forwarding them. Accepting the
multicast packets prevents the
from fast switching.
-
ip igmp
static-group—The
does not accept the packets itself, but only forwards them. This method enables
fast switching. The outgoing interface appears in the IGMP cache, but the
itself is not a member, as evidenced by lack of an L (local) flag in the
multicast route entry.
This procedure is optional.
SUMMARY STEPS1.
enable
2.
configure
terminal
3.
interface
interface-id
4.
ip igmp
static-group
group-address
5.
end
6.
show ip igmp interface [interface-id]
7.
copy running-config
startup-config
DETAILED STEPS | Command or Action | Purpose |
---|
Step 1 |
enable
Example:
Switch> enable
|
Enables
privileged EXEC mode. Enter your password if prompted.
|
Step 2 | configure
terminal
Example:
Switch# configure terminal
|
Enters the global
configuration mode.
|
Step 3 | interface
interface-id
Example:
Switch(config)# interface
gigabitethernet 1/0/1
|
Specifies the
interface on
which you want to enable multicast routing, and enters interface configuration
mode.
|
Step 4 | ip igmp
static-group
group-address
Example:
Switch(config-if)# ip igmp static-group 239.100.100.101
|
Configures
the
as a statically connected member of a group.
By default, this
feature is disabled.
|
Step 5 | end
Example:
Switch(config)# end
|
Returns to
privileged EXEC mode.
|
Step 6 | show ip igmp interface [interface-id]
Example:
Switch# show ip igmp interface
gigabitethernet 1/0/1
|
Verifies your
entries.
|
Step 7 | copy running-config
startup-config
Example:
Switch# copy running-config startup-config
|
(Optional) Saves your entries
in the configuration file.
|
Monitoring
IGMP
You can display specific
statistics, such as the contents of IP routing tables, caches, and databases.
 Note |
This release does not support
per-route statistics.
|
You can display information
to learn resource usage and solve network problems. You can also display
information about node reachability and discover the routing path that packets
of your device are taking through the network.
You can use any
of the privileged EXEC commands in the following table to display various
routing statistics.
Table 3 Commands for Displaying
System and Network Statistics
Command
|
Purpose
|
show ip igmp groups
[type-number |
detail
]
|
Displays the multicast groups
that are directly connected to the
and that were learned through IGMP.
|
show ip igmp interface
[type number]
|
Displays multicast-related
information about an interface.
|
show ip igmp profile
[
profile_number]
|
Displays
IGMP profile information.
|
show ip igmp
ssm-mapping [
hostname/IP address ]
|
Displays
IGMP SSM mapping information.
|
show ip igmp
static-group {class-map [
interface [
type ] ]
|
Displays
static group information.
|
show ip igmp vrf
|
Displays
the selected VPN routing/forwarding instance by name.
|
Configuration Examples for IGMP
Example: Configuring the as a Member of a Multicast Group
This example shows how to enable the to join multicast group 255.2.2.2:
Switch(config)# interface gigabitethernet1/0/1
Switch(config-if)# ip igmp join-group 255.2.2.2
Switch(config-if)#
Example: Controlling Access to IP Multicast Groups
This example shows how to configure hosts attached to a port as able to join only group 255.2.2.2:
Switch(config)# access-list 1 255.2.2.2 0.0.0.0
Switch(config-if)# interface gigabitethernet1/0/1
Switch(config-if)# ip igmp access-group 1