Cisco Cisco IOS Software Release 15.0(1)SY
Revised: January 12, 2015,
Configuring Multicast Distributed Switching
This module describes the required and optional tasks for configuring Multicast Distributed Switching (MDS).
Finding Feature Information
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this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this
module.
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Information About Multicast Distributed Switching
Advantages of Multicast Distributed Switching
Prior to MDS, IP multicast traffic was always switched at the Route Processor (RP) in the Route Switch Processor (RSP)-based
platforms.
platforms.
Switching multicast traffic at the RP had the following disadvantages:
• The load on the RP increased. This affected important route updates and calculations (for Border Gateway Protocol (BGP),
among others) and could stall the router if the multicast load was substantial.
• The net multicast performance was limited to what a single RP could switch.
MDS solves these problems by performing distributed switching of multicast packets received at the line cards (Versatile Interface
Processors [VIPs] in the case of RSP, and line cards in the case of Cisco 12000 series router). The line card is the interface card that
houses the VIPs (in the case of RSP) and the line card (in the case of Cisco 12000 series router). MDS is accomplished using a
forwarding data structure called a Multicast Forwarding Information Base (MFIB), which is a subset of the routing table. A copy of
MFIB runs on each line card and is always kept up to date with the MFIB table of the RP.
Processors [VIPs] in the case of RSP, and line cards in the case of Cisco 12000 series router). The line card is the interface card that
houses the VIPs (in the case of RSP) and the line card (in the case of Cisco 12000 series router). MDS is accomplished using a
forwarding data structure called a Multicast Forwarding Information Base (MFIB), which is a subset of the routing table. A copy of
MFIB runs on each line card and is always kept up to date with the MFIB table of the RP.
MDS can work in conjunction with Cisco Express Forwarding or unicast distributed fast switching (DFS).
Starting with Cisco IOS Release 11.2GS, IP multicast traffic can be distributed switched on RSP-based platforms with VIPs. MDS
is the only multicast switching method on the Cisco 12000 series router starting with Cisco IOS Release 11.2(11)GS.
is the only multicast switching method on the Cisco 12000 series router starting with Cisco IOS Release 11.2(11)GS.
Multicast Distributed Switching Is Disabled by Default
On the Cisco 7500 series router, the default is IP multicast fast switching. MDS is an option that is available and is disabled by default.
On the Cisco 12000 series routers, MDS is also disabled by default. To switch multicast packets on the Cisco 12000 series router,
you need to configure all interfaces for MDS. MDS is the only multicast switching mode for the Cisco 12000 series router.
you need to configure all interfaces for MDS. MDS is the only multicast switching mode for the Cisco 12000 series router.
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