Configuring Basic IP Multicast Routing

• Prerequisites for Basic IP Multicast Routing, on page 1

• Restrictions for Basic IP Multicast Routing, on page 1

• Information About Basic IP Multicast Routing, on page 2

• How to Configure Basic IP Multicast Routing, on page 3

• Monitoring and Maintaining Basic IP Multicast Routing, on page 13

• Additional References for Basic IP Multicast Routing, on page 15

• Feature Information for Basic IP Multicast Routing, on page 15

Prerequisites for Basic IP Multicast Routing

The following are the prerequisites for configuring basic IP multicast routing:

• You must configure the PIM version and the PIM mode in order to perform IP multicast routing. The

switch populates its multicast routing table and forwards multicast packets it receives from its directly

connected LANs according to the mode setting. You can configure an interface to be in the PIM dense

mode, sparse mode, or sparse-dense mode.

• Enabling PIM on an interface also enables IGMP operation on that interface. (To participate in IP

multicasting, the multicast hosts, routers, and multilayer device must have IGMP operating. )

If you enable PIM on multiple interfaces, when most of these interfaces are not on the outgoing interface

list, and IGMP snooping is disabled, the outgoing interface might not be able to sustain line rate for

multicast traffic because of the extra replication.

Restrictions for Basic IP Multicast Routing

The following are the restrictions for IP multicast routing:

• Packets that have a multicast destination IP address and unicast MAC address are dropped.

• For some multicast groups, when more than 8K mroutes are installed in a system, the network may

experience higher traffic losses upon switchover of the HA system. This is due to flushing the old multicast

forwarding entries before the new entries are updated. As the number of routes increase, more time is

required for the entries to be updated in the MFIB. To reduce the traffic loss in this scenario, you should

increase the multicast route-flush timer (using the ip multicast redundancy routeflush maxtime

command) to a value exceeding the default (30 seconds).

Configuring Basic IP Multicast Routing

Information About Basic IP Multicast Routing

IP multicasting is an efficient way to use network resources, especially for bandwidth-intensive services such

as audio and video. IP multicast routing enables a host (source) to send packets to a group of hosts (receivers)

anywhere within the IP network by using a special form of IP address called the IP multicast group address.

The sending host inserts the multicast group address into the IP destination address field of the packet, and

IP multicast routers and multilayer devices forward incoming IP multicast packets out all interfaces that lead

to members of the multicast group. Any host, regardless of whether it is a member of a group, can send to a

group. However, only the members of a group receive the message.

Multicast Forwarding Information Base Overview

The device uses the Multicast Forwarding Information Base (MFIB) architecture and the Multicast Routing

Information Base (MRIB) for IP multicast.

The MFIB architecture provides both modularity and separation between the multicast control plane (Protocol

Independent Multicast [PIM] and Internet Group Management Protocol [IGMP]) and the multicast forwarding

plane (MFIB). This architecture is used in Cisco IOS IPv6 multicast implementations.

MFIB itself is a multicast routing protocol independent forwarding engine; that is, it does not depend on PIM

or any other multicast routing protocol. It is responsible for:

• Forwarding multicast packets

• Registering with the MRIB to learn the entry and interface flags set by the control plane

• Handling data-driven events that must be sent to the control plane

• Maintaining counts, rates, and bytes of received, dropped, and forwarded multicast packets

The MRIB is the communication channel between MRIB clients. Examples of MRIB clients are PIM, IGMP,

the multicast routing (mroute) table, and the MFIB.

Default IP Multicast Routing Configuration

This table displays the default IP multicast routing configuration.

Table 1: Default IP Multicast Routing Configuration

Default SettingFeature

Disabled on all interfaces.Multicast routing

Version 2.PIM version

No mode is defined.PIM mode

None configured.PIM stub routing

None configured.PIM RP address

Disabled.PIM domain border

Configuring Basic IP Multicast Routing

Information About Basic IP Multicast Routing

Default SettingFeature

None.PIM multicast boundary

Disabled.Candidate BSRs

Disabled.Candidate RPs

0 kb/s.Shortest-path tree threshold rate

30 seconds.PIM router query message interval

How to Configure Basic IP Multicast Routing

Configuring Basic IP Multicast Routing

By default, multicast routing is disabled, and there is no default mode setting.

This procedure is required.

Before you begin

You must configure the PIM version and the PIM mode. The switch populates its multicast routing table and

forwards multicast packets it receives from its directly connected LANs according to the mode setting.

In populating the multicast routing table, dense-mode interfaces are always added to the table. Sparse-mode

interfaces are added to the table only when periodic join messages are received from downstream devices or

when there is a directly connected member on the interface. When forwarding from a LAN, sparse-mode

operation occurs if there is an RP known for the group. If so, the packets are encapsulated and sent toward

the RP. When no RP is known, the packet is flooded in a dense-mode fashion. The multicast source address

must be on the directly connected incoming interface (that is part of the same subnet) of the first-hop router

for both PIM dense mode and PIM any-source multicast mode. If the multicast traffic from a specific source

is sufficient, the receiver’s first-hop router might send join messages toward the source to build a source-based

distribution tree.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface interface-id

4. ip pim {dense-mode | sparse-mode | sparse-dense-mode}

5. end

6. show running-config

7. copy running-config startup-config

DETAILED STEPS

PurposeCommand or Action

Enables privileged EXEC mode.enable

Step 1

Configuring Basic IP Multicast Routing

How to Configure Basic IP Multicast Routing

PurposeCommand or Action

Example:

Enter your password, if prompted.

Device> enable

Enters global configuration mode.configure terminal

Example:

Step 2

Device# configure terminal

Specifies the Layer 3 interface on which you want to enable

multicast routing, and enters interface configuration mode.

interface interface-id

Example:

Step 3

The specified interface must be one of the following:

Device(config)# interface

• A routed port—A physical port that has been

configured as a Layer 3 port by entering the no

gigabitethernet 1/0/1

switchport interface configuration command. You

will also need to enable IP PIM sparse-dense-mode on

the interface, and join the interface as a statically

connected member to an IGMP static group.

• An SVI—A VLAN interface created by using the

interface vlan vlan-id global configuration command.

You will also need to enable IP PIM

sparse-dense-mode on the VLAN, join the VLAN as

a statically connected member to an IGMP static group,

and then enable IGMP snooping on the VLAN, the

IGMP static group, and physical interface.

These interfaces must have IP addresses assigned to them.

Enables a PIM mode on the interface.ip pim {dense-mode | sparse-mode | sparse-dense-mode}

Step 4

Example:

By default, no mode is configured.

Device(config-if)# ip pim

The keywords have these meanings:

sparse-dense-mode

• dense-mode—Enables dense mode of operation.

• sparse-mode—Enables sparse mode of operation. If

you configure sparse mode, you must also configure

an RP.

• sparse-dense-mode—Causes the interface to be

treated in the mode in which the group belongs.

Sparse-dense mode is the recommended setting.

To disable PIM on an interface, use the no ip

pim interface configuration command.

Note

Configuring Basic IP Multicast Routing

PurposeCommand or Action

Returns to privileged EXEC mode.end

Example:

Step 5

Device(config-if)# end

Verifies your entries.show running-config

Example:

Step 6

Device# show running-config

(Optional) Saves your entries in the configuration file.copy running-config startup-config

Example:

Step 7

Device# copy running-config startup-config

Configuring IP Multicast Forwarding

You can use the following procedure to configure IPv4 Multicast Forwarding Information Base (MFIB)

interrupt-level IP multicast forwarding of incoming packets or outgoing packets on the device.

After you have enabled IP multicast routing by using the ip multicast-routing command, IPv4 multicast

forwarding is enabled. Because IPv4 multicast forwarding is enabled by default, you can use the no form of

the ip mfib command to disable IPv4 multicast forwarding.

Note

SUMMARY STEPS

1. enable

2. configure terminal

3. ip mfib

4. exit

5. show running-config

6. copy running-config startup-config

DETAILED STEPS

PurposeCommand or Action

Enables privileged EXEC mode.enable

Step 1

Example:

Enter your password, if prompted.

Device> enable

Configuring Basic IP Multicast Routing

Configuring IP Multicast Forwarding

PurposeCommand or Action

Enters global configuration mode.configure terminal

Example:

Step 2

Device# configure terminal

Enables IP multicast forwarding.ip mfib

Example:

Step 3

Device(config)# ip mfib

Returns to privileged EXEC mode.exit

Example:

Step 4

Device(config)# exit

Verifies your entries.show running-config

Example:

Step 5

Device# show running-config

(Optional) Saves your entries in the configuration file.copy running-config startup-config

Example:

Step 6

Device# copy running-config

startup-config

Configuring a Static Multicast Route (mroute)

You can use the following procedure to configure static mroutes. Static mroutes are similar to unicast static

routes but differ in the following ways:

• Static mroutes are used to calculate RPF information, not to forward traffic.

• Static mroutes cannot be redistributed.

Static mroutes are strictly local to the device on which they are defined. Because Protocol Independent Multicast

(PIM) does not have its own routing protocol, there is no mechanism to distribute static mroutes throughout

the network. Consequently, the administration of static mroutes tends to be more complicated than the

administration of unicast static routes.

When static mroutes are configured, they are stored on the device in a separate table referred to as the static

mroute table. When configured, the ip mroute command enters a static mroute into the static mroute table

for the source address or source address range specified for the source-address and mask arguments. Sources

that match the source address or that fall in the source address range specified for the source-address argument

will RPF to either the interface associated with the IP address specified for the rpf-address argument or the

Configuring Basic IP Multicast Routing

Configuring a Static Multicast Route (mroute)

local interface on the device specified for the interface-type and interface-number arguments. If an IP address

is specified for the rpf-address argument, a recursive lookup is done from the unicast routing table on this

address to find the directly connected neighbor.

If there are multiple static mroutes configured, the device performs a longest-match lookup of the mroute

table. When the mroute with the longest match (of the source-address) is found, the search terminates and the

information in the matching static mroute is used. The order in which the static mroutes are configured is not

important.

The administrative distance of an mroute may be specified for the optional distance argument. If a value is

not specified for the distance argument, the distance of the mroute defaults to zero. If the static mroute has

the same distance as another RPF source, the static mroute will take precedence. There are only two exceptions

to this rule: directly connected routes and the default unicast route.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip mroute [vrf vrf-name] source-address mask { fallback-lookup {global | vrf vrf-name }[ protocol ]

{rpf-address | interface-type interface-number}} [distance]

4. exit

5. show running-config

6. copy running-config startup-config

DETAILED STEPS

PurposeCommand or Action

Enables privileged EXEC mode.enable

Step 1

Example:

Enter your password, if prompted.

Device> enable

Enters global configuration mode.configure terminal

Example:

Step 2

Device# configure terminal

The source IP address 10.1.1.1 is configured to be reachable

through the interface associated with IP address 10.2.2.2.

ip mroute [vrf vrf-name] source-address mask {

fallback-lookup {global | vrf vrf-name }[ protocol ]

{rpf-address | interface-type interface-number}} [distance]

Step 3

Example:

Device(configure)# ip mroute 10.1.1.1

255.255.255.255 10.2.2.2

Returns to privileged EXEC mode.exit

Example:

Step 4

Configuring Basic IP Multicast Routing

Configuring a Static Multicast Route (mroute)

PurposeCommand or Action

Device(config)# exit

(Optional) Verifies your entries.show running-config

Example:

Step 5

Device# show running-config

(Optional) Saves your entries in the configuration file.copy running-config startup-config

Example:

Step 6

Device# copy running-config

startup-config

Configuring Optional IP Multicast Routing Features

Defining the IP Multicast Boundary

You define a multicast boundary to prevent Auto-RP messages from entering the PIM domain. You create

an access list to deny packets destined for 224.0.1.39 and 224.0.1.40, which carry Auto-RP information.

This procedure is optional.

SUMMARY STEPS

1. enable

2. configure terminal

3. access-list access-list-number deny source [source-wildcard]

4. interface interface-id

5. ip multicast boundary access-list-number

6. end

7. show running-config

8. copy running-config startup-config

DETAILED STEPS

PurposeCommand or Action

Enables privileged EXEC mode.enable

Step 1

Example:

• Enter your password if prompted.

Device> enable

Configuring Basic IP Multicast Routing

Configuring Optional IP Multicast Routing Features

PurposeCommand or Action

Enters global configuration mode.configure terminal

Example:

Step 2

Device# configure terminal

Creates a standard access list, repeating the command as

many times as necessary.

access-list access-list-number deny source

[source-wildcard]

Step 3

Example:

• For access-list-number, the range is 1 to 99.

Device(config)#

access-list 12 deny 224.0.1.39

• The deny keyword denies access if the conditions are

matched.

access-list 12 deny 224.0.1.40

• For source, enter multicast addresses 224.0.1.39 and

224.0.1.40, which carry Auto-RP information.

• (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.

The access list is always terminated by an implicit deny

statement for everything.

Specifies the interface to be configured, and enters interface

configuration mode.

interface interface-id

Example:

Step 4

The specified interface must be one of the following:

Device(config)# interface gigabitethernet 1/0/1

• A routed port—A physical port that has been

configured as a Layer 3 port by entering the no

switchport interface configuration command.

• An SVI—A VLAN interface created by using the

interface vlan vlan-id global configuration command.

These interfaces must have IP addresses assigned to them.

Configures the boundary, specifying the access list you

created in Step 2.

ip multicast boundary access-list-number

Example:

Step 5

Device(config-if)# ip multicast boundary 12

Returns to privileged EXEC mode.end

Example:

Step 6

Device(config)# end

Configuring Basic IP Multicast Routing

Defining the IP Multicast Boundary

PurposeCommand or Action

Verifies your entries.show running-config

Example:

Step 7

Device# show running-config

(Optional) Saves your entries in the configuration file.copy running-config startup-config

Example:

Step 8

Device# copy running-config startup-config

Configuring sdr Listener Support

Enabling sdr Listener Support

By default, the device does not listen to session directory advertisements.

This procedure is optional.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface interface-id

4. ip sap listen

5. end

6. show running-config

7. copy running-config startup-config

DETAILED STEPS

PurposeCommand or Action

Enables privileged EXEC mode.enable

Step 1

Example:

Enter your password, if prompted.

Device> enable

Enters global configuration mode.configure terminal

Example:

Step 2

Device# configure terminal

Specifies the interface to be enabled for sdr, and enters

interface configuration mode.

interface interface-id

Example:

Step 3

Configuring Basic IP Multicast Routing

Configuring sdr Listener Support

PurposeCommand or Action

The specified interface must be one of the following:

Device(config)# interface

• A routed port—A physical port that has been

configured as a Layer 3 port by entering the no

gigabitethernet 1/0/1

switchport interface configuration command. You

will also need to enable IP PIM sparse-dense-mode on

the interface, and join the interface as a statically

connected member to an IGMP static group. For a

configuration example, see Example: Interface

Configuration as a Routed Port

• An SVI—A VLAN interface created by using the

interface vlan vlan-id global configuration command.

You will also need to enable IP PIM

sparse-dense-mode on the VLAN, join the VLAN as

a statically connected member to an IGMP static group,

and then enable IGMP snooping on the VLAN, the

IGMP static group, and physical interface. For a

configuration example, see Example: Interface

Configuration as an SVI

These interfaces must have IP addresses assigned to them.

Enables the device software to listen to session directory

announcements.

ip sap listen

Example:

Step 4

Device(config-if)# ip sap listen

Returns to privileged EXEC mode.end

Example:

Step 5

Device(config-if)# end

Verifies your entries.show running-config

Example:

Step 6

Device# show running-config

(Optional) Saves your entries in the configuration file.copy running-config startup-config

Example:

Step 7

Device# copy running-config

startup-config

Configuring Basic IP Multicast Routing

Enabling sdr Listener Support

Limiting How Long an sdr Cache Entry Exists

By default, entries are never deleted from the sdr cache. You can limit how long the entry remains active so

that if a source stops advertising SAP information, old advertisements are not unnecessarily kept.

This procedure is optional.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip sap cache-timeout minutes

4. end

5. show running-config

6. show ip sap

7. copy running-config startup-config

DETAILED STEPS

PurposeCommand or Action

Enables privileged EXEC mode.enable

Step 1

Example:

Enter your password, if prompted.

Device> enable

Enters global configuration mode.configure terminal

Example:

Step 2

Device# configure terminal

Limits how long a Session Announcement Protocol (SAP)

cache entry stays active in the cache.

ip sap cache-timeout minutes

Example:

Step 3

By default, entries are never deleted from the cache.

Device(config)# ip sap cache-timeout 30

For minutes, the range is 1 to 1440 minutes (24 hours).

Returns to privileged EXEC mode.end

Example:

Step 4

Device(config)# end

Verifies your entries.show running-config

Example:

Step 5

Device# show running-config

Configuring Basic IP Multicast Routing

Limiting How Long an sdr Cache Entry Exists

PurposeCommand or Action

Displays the SAP cache.show ip sap

Example:

Step 6

Device# show ip sap

(Optional) Saves your entries in the configuration file.copy running-config startup-config

Example:

Step 7

Device# copy running-config

startup-config

Monitoring and Maintaining Basic IP Multicast Routing

Clearing Caches, Tables, and Databases

You can remove all contents of a particular cache, table, or database. Clearing a cache, table, or database

might be necessary when the contents of the particular structure are or suspected to be invalid.

You can use any of the privileged EXEC commands in the following table to clear IP multicast caches, tables,

and databases.

Table 2: Commands for Clearing Caches, Tables, and Databases

PurposeCommand

Deletes entries from the IGMP cache.clear ip igmp group {group [ hostname | IP address]

| vrf name group [ hostname | IP address] }

Deletes entries from the IP multicast routing table.clear ip mroute { * | [hostname | IP address] | vrf

name group [ hostname | IP address] }

Deletes the Session Directory Protocol Version 2

cache or an sdr cache entry.

clear ip sap [group-address | “session-name”]

Displaying System and Network Statistics

You can display specific statistics, such as the contents of IP routing tables, caches, and databases.

This release does not support per-route statistics.

Note

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.

Configuring Basic IP Multicast Routing

Monitoring and Maintaining Basic IP Multicast Routing

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

PurposeCommand

Sends an ICMP Echo Request to a multicast group

address.

ping [group-name | group-address]

Displays the multicast groups that are directly

connected to the device and that were learned through

IGMP.

show ip igmp groups

[group-name|group-address|type-number]

Displays multicast-related information about an

interface.

show ip igmp interface [type number]

Displays the contents of the IP multicast routing table.show ip mroute [group-name | group-address]

[source] [ count | interface | proxy | pruned |

summary | verbose]

Displays information about interfaces configured for

PIM. This command is available in all software

images.

show ip pim interface [type number] [count | detail

| df | stats ]

Lists the PIM neighbors discovered by the device.

This command is available in all software images.

show ip pim neighbor [type number]

Displays the RP routers associated with a sparse-mode

multicast group. This command is available in all

software images.

show ip pim rp [group-name | group-address]

Displays how the device is doing Reverse-Path

Forwarding (that is, from the unicast routing table,

DVMRP routing table, or static mroutes).

Command parameters include:

• Host name or IP address—IP name or group

address.

• Select—Group-based VRF select information.

• vrf—Selects VPN Routing/Forwarding instance.

show ip rpf {source-address | name}

Displays the Session Announcement Protocol (SAP)

Version 2 cache.

Command parameters include:

• A.B.C.D—IP group address.

• WORD—Session name (in double quotes).

• detail—Session details.

show ip sap [group | “session-name” | detail]

Configuring Basic IP Multicast Routing

Displaying System and Network Statistics

Configuration Examples for IP Multicast Routing

Example: Configuring an IP Multicast Boundary

This example shows how to set up a boundary for all administratively-scoped addresses:

Device(config)# access-list 1 deny 239.0.0.0 0.255.255.255

Device(config)# access-list 1 permit 224.0.0.0 15.255.255.255

Device(config)# interface gigabitethernet1/0/1

Device(config-if)# ip multicast boundary 1

Example: Responding to mrinfo Requests

The software answers mrinfo requests sent by mrouted systems and Cisco routers and multilayer devices. The

software returns information about neighbors through DVMRP tunnels and all the routed interfaces. This

information includes the metric (always set to 1), the configured TTL threshold, the status of the interface,

and various flags. You can also use the mrinfo privileged EXEC command to query the router or device itself,

as in this example:

Device# mrinfo

171.69.214.27 (mm1-7kd.cisco.com) [version cisco 11.1] [flags: PMS]:

171.69.214.27 -> 171.69.214.26 (mm1-r7kb.cisco.com) [1/0/pim/querier]

171.69.214.27 -> 171.69.214.25 (mm1-45a.cisco.com) [1/0/pim/querier]

171.69.214.33 -> 171.69.214.34 (mm1-45c.cisco.com) [1/0/pim]

171.69.214.137 -> 0.0.0.0 [1/0/pim/querier/down/leaf]

171.69.214.203 -> 0.0.0.0 [1/0/pim/querier/down/leaf]

171.69.214.18 -> 171.69.214.20 (mm1-45e.cisco.com) [1/0/pim]

171.69.214.18 -> 171.69.214.19 (mm1-45c.cisco.com) [1/0/pim]

171.69.214.18 -> 171.69.214.17 (mm1-45a.cisco.com) [1/0/pim]

Additional References for Basic IP Multicast Routing