• Basic multicast routing
• IP Multicast Routing for VRF Lite
• IGMP
• PIMv4 SSM
• PIMv4 SSM Mapping
• PIM MIB
• PIM sparse mode
• PIM BFD
• Static Rendezvous Point (RP)
• Auto RP
• Bootstrap router (BSR)

PIM SSM is the routing protocol that supports the implementation of SSM and is derived from the PIM sparse mode (PIM-SM). IGMP is the Internet Engineering Task Force (IETF) standards track protocol used for hosts to signal multicast group membership to routers. IGMPv3 supports source filtering, which is required for SSM. In order for SSM to run with IGMPv3, SSM must be supported in the device (the host where the application is running) and in the application itself.

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 the network with the use of special multicast queriers and hosts.

For more information on IGMP, see the IP Multicast: IGMP Configuration Guide at: http://www.cisco.com/en/US/docs/ios-xml/ios/ipmulti_igmp/configuration/xe-3s/imc_customizing_igmp.html

IGMP snooping allows a router to examine IGMP packets and make forwarding decisions based on their content. IGMP, which runs at Layer 3 on a multicast router, generates Layer 3 IGMP queries in subnets where the multicast traffic has to be routed. Using IGMP snooping, the router intercepts IGMP messages from the host and updates its multicast table accordingly.

You can configure the router to use IGMP snooping in subnets that receive IGMP queries from either IGMP or the IGMP snooping querier. IGMP snooping constrains IPv4 multicast traffic at Layer 2 by configuring Layer 2 LAN ports dynamically to forward IPv4 multicast traffic only to those ports that want to receive it.

You can configure the IGMP snooping lookup method for each VLAN. Layer 3 IGMP snooping lookup uses destination IP addresses in the Layer 2 multicast table (This is the default behavior). Layer 2 IGMP snooping lookup uses destination MAC addresses in the Layer 2 multicast table.

For more information on IGMP snooping, see the IPv4 Multicast IGMP Snooping document at: http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/15.0SY/configuration/guide/ipv4_igmp_snooping.html

PIM SSM mapping supports SSM transition in cases where neither the URD nor IGMP v3lite is available, or when supporting SSM on the end system is not feasible. SSM mapping enables you to leverage SSM for video delivery to legacy set-top boxes (STBs) that do not support IGMPv3 or for applications that do not take advantage of the IGMPv3 host stack. URD and IGMPv3lite are applications used on receivers which do not have SSM support.

SSM mapping introduces a means for the last hop router to discover sources sending to groups. When SSM mapping is configured, if a router receives an IGMPv1 or IGMPv2 membership report for a particular group G, the router translates this report into one or more (S, G) channel memberships for the well-known sources associated with this group.

SSM mapping only needs to be configured on the last hop router connected to receivers. No support is needed on any other routers in the network. When the router receives an IGMPv1 or IGMPv2 membership report for a group G, the router uses SSM mapping to determine one or more source IP addresses for the group G. SSM mapping then translates the membership report as an IGMPv3 report INCLUDE (G, [S1, G], [S2, G]...[Sn, G] and continues as if it had received an IGMPv3 report.

Reverse-path forwarding is used for forwarding multicast datagrams. It functions as follows:

• If a router receives a datagram on an interface it uses to send unicast packets to the source, it means the packet has arrived on the RPF interface.
• If the packet arrives on the RPF interface, a router forwards the packet out the interfaces present in the outgoing interface list of a multicast routing table entry.
• If the packet does not arrive on the RPF interface, the packet is silently discarded to prevent loops.

PIM SSM uses source trees to forward datagrams; the RPF check is performed as follows:

• If a PIM router has source-tree state (that is, an [S, G] entry is present in the multicast routing table), the router performs the RPF check against the IPv4 address of the source of the multicast packet.
• Sparse-mode PIM uses the RPF lookup function to determine where it needs to send joins and prunes. (S, G) joins (which are source-tree states) are sent toward the source.

For more information on Reverse Path Forwarding, see the Configuring Unicast Reverse Path Forwarding document at: http://www.cisco.com/en/US/docs/ios/12_2/security/configuration/guide/scfrpf.html

The IP Multicast VRF Lite feature provides IPv4 multicast support for multiple virtual routing and forwarding (VRF) contexts. The scope of these VRFs is limited to the router in which the VRFs are defined.

This feature enables separation between routing and forwarding, providing an additional level of security because no communication between devices belonging to different VRFs is allowed unless explicitly configured. The IPv4 Multicast VRF Lite feature simplifies the management and troubleshooting of traffic belonging to a specific VRF.

Bidirectional Forwarding Detection (BFD) is a detection protocol designed to provide fast forwarding path failure detection times for all media types, encapsulations, topologies, and routing protocols and independent of the higher layer protocols. In addition to fast forwarding path failure detection, BFD provides a consistent failure detection method for network administrators. Because the network administrator can use BFD to detect forwarding path failures at a uniform rate, rather than the variable rates for different routing protocol hello mechanisms, network profiling and planning is easier and reconvergence time is consistent and predictable.

Protocol Independent Multicast (PIM) uses a hello mechanism for discovering new neighbors and for detecting failures between adjacent nodes. The minimum failure detection time in PIM is 3 times the PIM Query-Interval. To enable faster failure detection, the rate at which a PIM Hello message is transmitted on an interface is configurable. However, lower intervals increase the load on the protocol and can increase CPU and memory utilization and cause a system-wide negative impact on performance. Lower intervals can also cause PIM neighbors to expire frequently as the neighbor expiry can occur before the hello messages received from those neighbors are processed.

The BFD Support for Multicast (PIM) feature, also known as PIM BFD, registers PIM as a client of BFD. PIM can then utilize BFD to initiate a session with an adjacent PIM node to support BFD's fast adjacency failure detection in the protocol layer. PIM registers just once for both PIM and IPv6 PIM.

At PIMs request (as a BFD client), BFD establishes and maintains a session with an adjacent node for maintaining liveness and detecting forwarding path failure to the adjacent node. PIM hellos will continue to be exchanged between the neighbors even after BFD establishes and maintains a BFD session with the neighbor. The behavior of the PIM hello mechanism is not altered due to the introduction of this feature.

Although PIM depends on the Interior Gateway Protocol (IGP) and BFD is supported in IGP, PIM BFD is independent of IGP's BFD.

IGMP snooping allows switches to examine IGMP packets and make forwarding decisions based on their content.

Use the following show command to verify the IPv4 multicast routing.

Router# show asr901 multicast-support 

Platform support for IPv4(v6) Multicast: ENABLED

Use the show commands listed below to verify the PIM SSM configuration.

To display the multicast groups with receivers that are directly connected to the router and that were learned through IGMP, use the show ip igmp groups command described in the following example.

Router# show ip igmp groups 

IGMP Connected Group Membership
Group Address    Interface                Uptime    Expires   Last Reporter   Group Accounted
232.1.1.1        Vlan70                   04:10:01  stopped   70.1.1.10       
224.0.1.40       Vlan16                   04:17:35  00:02:58  16.1.1.3        
224.0.1.40       Vlan23                   05:08:03  00:02:54  23.1.1.1  
      

To display the contents of the IP multicast routing table, use the show command described in the following example.

Router# show ip mroute 

IP Multicast Routing Table
Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected,
       L - Local, P - Pruned, R - RP-bit set, F - Register flag,
       T - SPT-bit set, J - Join SPT, M - MSDP created entry, E - Extranet,
       X - Proxy Join Timer Running, A - Candidate for MSDP Advertisement,
       U - URD, I - Received Source Specific Host Report, 
       Z - Multicast Tunnel, z - MDT-data group sender, 
       Y - Joined MDT-data group, y - Sending to MDT-data group, 
       G - Received BGP C-Mroute, g - Sent BGP C-Mroute, 
       N - Received BGP Shared-Tree Prune, n - BGP C-Mroute suppressed, 
       Q - Received BGP S-A Route, q - Sent BGP S-A Route, 
       V - RD & Vector, v - Vector, p - PIM Joins on route, 
       x - VxLAN group
Outgoing interface flags: H - Hardware switched, A - Assert winner, p - PIM Join
Timers: Uptime/Expires
Interface state: Interface, Next-Hop or VCD, State/Mode
(9.1.1.1, 232.1.1.1), 00:00:03/00:02:57, flags: sTI
  Incoming interface: Vlan16, RPF nbr 16.1.1.1
  Outgoing interface list:
    Vlan70, Forward/Sparse, 00:00:04/00:02:56
(5.1.1.1, 232.1.1.1), 00:00:04/00:02:56, flags: sTI
  Incoming interface: Vlan16, RPF nbr 16.1.1.1
  Outgoing interface list:
    Vlan70, Forward/Sparse, 00:00:04/00:02:56
(*, 224.0.1.40), 00:00:12/00:02:47, RP 6.6.6.6, flags: SJCL
  Incoming interface: Vlan16, RPF nbr 16.1.1.1
  Outgoing interface list:
    Vlan23, Forward/Sparse, 00:00:12/00:02:47

Use the show commands listed below to verify the PIM SSM Mapping configuration.

To display information about SSM mapping, use the show command described in the following example.

Router# show ip igmp ssm-mapping

SSM Mapping  : Enabled
DNS Lookup   : Disabled
Cast domain : ssm-map.cisco.com
Name servers : 255.255.255.255

To display the sources that SSM mapping uses for a particular group, use the show command described in the following example.

Router# show ip igmp ssm-mapping 232.1.1.1

Group address: 232.1.1.1
Database     : Static
Source list  : 5.1.1.1
               9.1.1.1

To display the multicast groups with receivers that are directly connected to the router and that were learned through IGMP, use the show command described in the following examples.

• show ip igmp groups group-address

Router# show ip igmp groups 232.1.1.1 

IGMP Connected Group Membership
Group Address    Interface                Uptime    Expires   Last Reporter   Group Accounted
232.1.1.1        Vlan70                   04:14:26  stopped   70.1.1.10     
  

• show ip igmp groups interface-type interface-number

Router# show ip igmp groups vlan70

IGMP Connected Group Membership
Group Address    Interface                Uptime    Expires   Last Reporter   Group Accounted
232.1.1.1        Vlan70                   04:15:33  stopped   70.1.1.10       

• show ip igmp groups interface-type detail

Router# show ip igmp groups vlan70 detail 

Flags: L - Local, U - User, SG - Static Group, VG - Virtual Group,
       SS - Static Source, VS - Virtual Source,
       Ac - Group accounted towards access control limit
Interface:      Vlan70
Group:          232.1.1.1
Flags:          SSM 
Uptime:         04:15:37
Group mode:     INCLUDE
Last reporter:  70.1.1.10
CSR Grp Exp:    00:02:04
Group source list: (C - Cisco Src Report, U - URD, R - Remote, S - Static,
                    V - Virtual, M - SSM Mapping, L - Local,
                    Ac - Channel accounted towards access control limit)
  Source Address   Uptime    v3 Exp   CSR Exp   Fwd  Flags
  5.1.1.1          04:15:37  stopped   00:02:04  Yes  CM
  9.1.1.1          04:15:37  stopped   00:02:04  Yes  CM

To display information about static mroute, use the show ip mroute [vrf vrf-name ] group-address command described in the following examples.

Router# show ip mroute

mroute vrf VPN_A 239.1.1.1
IP Multicast Routing Table
Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected,
       L - Local, P - Pruned, R - RP-bit set, F - Register flag,
       T - SPT-bit set, J - Join SPT, M - MSDP created entry, E - Extranet,
       X - Proxy Join Timer Running, A - Candidate for MSDP Advertisement,
       U - URD, I - Received Source Specific Host Report,
       Z - Multicast Tunnel, z - MDT-data group sender,
       Y - Joined MDT-data group, y - Sending to MDT-data group,
       G - Received BGP C-Mroute, g - Sent BGP C-Mroute,
       N - Received BGP Shared-Tree Prune, n - BGP C-Mroute suppressed,
       Q - Received BGP S-A Route, q - Sent BGP S-A Route,
       V - RD & Vector, v - Vector, p - PIM Joins on route,
       x - VxLAN group
Outgoing interface flags: H - Hardware switched, A - Assert winner, p - PIM Join
Timers: Uptime/Expires
Interface state: Interface, Next-Hop or VCD, State/Mode
 
(*, 239.1.1.1), 00:03:57/stopped, RP 4.4.4.4, flags: SJCL
  Incoming interface: Vlan21, RPF nbr 21.1.1.1, using vrf IPv4 default
  Outgoing interface list:
    Vlan72, Forward/Sparse, 00:03:56/00:02:10
 
(70.1.1.10, 239.1.1.1), 00:00:49/stopped, flags: LT
  Incoming interface: Vlan22, RPF nbr 22.1.1.2, using vrf IPv4 default
  Outgoing interface list:
    Vlan72, Forward/Sparse, 00:00:49/00:02:10