Configuring Basic Multicast Routing - Cisco Catalyst 3750 Software Configuration Manual

Configuring IP Multicast Routing
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Configuring Basic Multicast Routing

You must enable IP multicast routing and configure the PIM version and the PIM mode. Then the
software can forward multicast packets, and the switch can populate its multicast routing table.
You can configure an interface to be in PIM dense mode, sparse mode, or sparse-dense mode. The switch
populates its multicast routing table and forwards multicast packets it receives from its directly
connected LANs according to the mode setting. You must enable PIM in one of these modes for an
interface to perform IP multicast routing. Enabling PIM on an interface also enables IGMP operation on
that interface.
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. 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.
By default, multicast routing is disabled, and there is no default mode setting. This procedure is required.
Beginning in privileged EXEC mode, follow these steps to enable IP multicasting, to configure a PIM
version, and to configure a PIM mode. This procedure is required.
Command
Step 1
configure terminal
Step 2
ip multicast-routing distributed
Step 3 interface interface-id
Catalyst 3750 Metro Switch Software Configuration Guide
31-10
If you have a network that includes non-Cisco routers, configure the Auto-RP mapping agent and
the BSR on a Cisco PIMv2 router or multilayer switch. Ensure that no PIMv1 device is on the path
between the BSR and a non-Cisco PIMv2 router.
If you have non-Cisco PIMv2 routers that need to interoperate with Cisco PIMv1 routers and
multilayer switches, both Auto-RP and a BSR are required. We recommend that a Cisco PIMv2
device be both the Auto-RP mapping agent and the BSR. For more information, see the
Auto-RP and a BSR" section on page
Purpose
Enter global configuration mode.
Enable IP multicast distributed switching.
Specify the Layer 3 interface on which you want to enable multicast
routing, and enter interface configuration mode.
The specified interface must be one of the following:
These interfaces must have IP addresses assigned to them. For more
information, see the
page
31-21.
• 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.
"Configuring Layer 3 Interfaces" section on
9-18.
Chapter 31 Configuring IP Multicast Routing
"Using
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