Multicast Forwarding Information Base Overview

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Multicast Forwarding Information Base
           Overview

           First Published: October 2, 2009
           Last Updated: November 20, 2009

           The Multicast Forwarding Information Base (MFIB) architecture provides 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 and Cisco IOS XR multicast implementations. With the introduction of the IPv4 MFIB
           infrastructure, the Cisco IOS IPv4 multicast implementation has been enhanced, making the MFIB
           forwarding model the only forwarding engine used.



Finding Feature Information
           Your software release may not support all the features documented in this module. For the latest feature
           information and caveats, see 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 for the Multicast Forwarding Information Base" section on page 12.
           Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS
           software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An
           account on Cisco.com is not required.



Contents
               Information About the Multicast Forwarding Information Base, page 2
               Additional References, page 10
               Feature Information for the Multicast Forwarding Information Base, page 12




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            Cisco Systems, Inc., 170 West Tasman Drive, San Jose, CA 95134-1706 USA
                                                                                       Multicast Forwarding Information Base Overview
  Information About the Multicast Forwarding Information Base




Information About the Multicast Forwarding Information Base
                       Before implementing a multicast network that supports the MFIB, you should be familiar with the
                       following concepts:
                            Benefits of the MFIB Architecture, page 2
                            Types of Multicast Tables, page 2
                            Types of Multicast Entries, page 3
                            MFIB Components, page 3
                            Multicast Packet Forwarding Using the MFIB, page 6
                            MFIB and MRIB Entry and Interface Flags, page 6
                            Introduction of (*, G/Mask) Entries, page 9
                            Introduction of PIM Tunnel Interfaces, page 9
                            MFIB Statistics Support, page 9


Benefits of the MFIB Architecture
                            Simplifies multicast operation through the separation of the control and forwarding planes.
                            Protects mission critical multicast applications by enabling new services such as multicast high
                             availability (HA).
                            Eliminates the need for the route cache maintenance associated with demand caching schemes such
                             as multicast fast switching.


Types of Multicast Tables
                       The following tables are used for general multicast routing and forwarding:
                            IGMP--Contains local IGMP memberships on the router.
                            Multicast Route (Mroute)--Contains (*, G) and (S, G) multicast states on the router (including PIM
                             mode, incoming interfaces, and outgoing interfaces).
                            Multicast Source Discovery Protocol (MSDP)--Contains all Source-Active (SA) messages.
                            Multicast Routing Information Base (MRIB)--Contains (*, G), (S, G), and (*, G/m) MRIB entries.
                            MFIB--Contains (*, G), (S, G), and (*, G/m) MFIB entries




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 Multicast Forwarding Information Base Overview
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                         Multicast tables can be further be defined by the following contexts:
                             Global--Non-VRF context.
                             VRF--Layer-3 VPN context.
                             IPv4--IPv4 address family context.
                             IPv6--IPv6 address family context.


Types of Multicast Entries
                             (*, G)--Shared tree entries used by PIM sparse mode (PIM-SM) and bidirectional PIM (bidir-PIM).
                             (S, G)--Source tree entries used by PIM-SM and Source Specific Multicast (PIM-SSM).
                             (*, G/mask)--Shared tree entries used by the bidir-PIM and the MFIB.


               Note      For more information about (*, G/mask) entries, see the "Introduction of (*, G/Mask) Entries" section.



MFIB Components
                         The following sections describe the components that make up the MFIB architecture:
                             MFIB
                             Distributed MFIB
                             MRIB
                             Multicast Control Plane




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                                                                                          Multicast Forwarding Information Base Overview
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                     Figure 1 illustrates the components that make up the MFIB architecture.

                     Figure 1              IPv4 MFIB Architecture




                                PIM                Mroute           IGMP



                                                    MRIB



                                                    MFIB



                                    Platform Dependent Forwarding




                                                                                 252565
           Note      When you enter the show ip mrib client command on a multicast router in an IP multicast network, PIM,
                     the mroute table, and IGMP will appear as one client to the MRIB. For more information, see the
                     Cisco IOS IP Multicast Command Reference.

                     Figure 2 illustrates the IPv4 MFIB distributed architecture.

                     Figure 2              IPv4 MFIB Distributed Architecture




                                      RP (Route Processor)                                LC/DFC



                           PIM                 Mroute          IGMP


                          Platform                            MRIB                           MRIB
                         annotations            MRIB          Proxy                          Proxy


                                                MFIB                                         MFIB



                                 Platform Dependent Forwarding                  Platform Dependent Forwarding
                                                                                                                      252566




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 Multicast Forwarding Information Base Overview
                                                                              Information About the Multicast Forwarding Information Base




MFIB
                         The MFIB 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


Distributed MFIB
                         Distributed MFIB (dMFIB) is used to switch multicast packets on distributed platforms. dMFIB may
                         also contain platform-specific information on replication across line cards. The basic MFIB routines that
                         implement the core of the forwarding logic are common to all forwarding environments.
                         dMFIB implements the following functions:
                             Distributes a copy of the MFIB to the line cards.
                             Relays data-driven protocol events generated in the line cards to PIM.
                             Provides an MFIB platform application program interface (API) to propagate MFIB changes to
                              platform-specific code responsible for programming the hardware acceleration engine. This API
                              also includes entry points to switch a packet in software (necessary if the packet is triggering a
                              data-driven event) and to upload traffic statistics to the software.
                             Provides hooks to allow clients residing on the route processor (RP) to read traffic statistics on
                              demand. (dMFIB does not periodically upload these statistics to the RP.)
                         The combination of dMFIB and MRIB subsystem (MRIB proxy) also allows the router to have a
                         "customized" copy of the MFIB database in each line card and to transport MFIB-related
                         platform-specific information from the RP to the line cards.


MRIB
                         The MRIB is the communication channel between MRIB clients. Examples of MRIB clients are PIM,
                         IGMP, the multicast routing (mroute) table, and the MFIB.
                         MRIB communication is based on the setting and clearing of entry and interface flags. MRIB entries are
                         keyed on source, group, and group mask; and appear as (*, G), (S, G), and (*, G/m) multicast entries in
                         the output of the show ip mrib route commands. In addition, every MRIB entry will have a list of
                         interfaces associated with it and each interface will have flags set that describe its forwarding state.
                         The MRIB does not interpret any entry or interface flags. The flags are significant only to MRIB clients.


               Note      The MRIB uses different tables for different contexts. MRIB tables are separated by address family to
                         distinguish between IPv4 and IPv6 multicast entries. Each table can further be divided within a VRF or
                         global context.




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