The following points describe IGMP versions 2, and 3:

• IGMP Version 2 extends IGMP allowing such features as the IGMP query timeout and the maximum query-response time. See RFC 2236.

• IGMP Version 3 permits joins and leaves for certain source and group pairs instead of requesting traffic from all sources in the multicast group.

The IGMP Per Interface States Limit sets a limit on creating OLEs for the IGMP interface. When the set limit is reached, the group is not accounted against this interface but the group can exist in IGMP context for some other interface.

The following configuration sets a limit on the number of group memberships created on an interface as a result of receiving IGMP or MLD membership reports.

router igmp | mld [vrf <vrfname>]
            interface <ifname>
                        (no) maximum groups-per-interface <max> [threshold <threshold>] [<acl>]
            !
!

where,

<ifname> is the interface name

<max> is the maximum limit on the groups

<threshold> is the threshold number of groups at which point a syslog warning message will be issued

<acl> provides an option for selective accounting. If provided, only groups or (S,G)s that are permitted by the ACL is accounted against the limit. Groups or (S, G)s that are denied by the ACL are not accounted against the limit. If not provided, all the groups are accounted against the limit.

The following messages are displayed when the threshold limit is reached for IGMP:

igmp[1160]: %ROUTING-IPV4_IGMP-4-OOR_THRESHOLD_REACHED : Threshold for Maximum number of group per interface has been reached 3: Groups joining will soon be throttled. 
Config a higher max or take steps to reduce states

igmp[1160]: %ROUTING-IPV4_IGMP-4-OOR_LIMIT_REACHED : Maximum number of group per interface has been reached 6: Groups joining is throttled. 
Config a higher max or take steps to reduce states

Typically, PIM in sparse mode (PIM-SM) operation is used in a multicast network when relatively few routers are involved in each multicast. Routers do not forward multicast packets for a group, unless there is an explicit request for traffic. Requests are accomplished using PIM join messages, which are sent hop by hop toward the root node of the tree. The root node of a tree in PIM-SM is the rendezvous point (RP) in the case of a shared tree or the first-hop router that is directly connected to the multicast source in the case of a shortest path tree (SPT). The RP keeps track of multicast groups, and the sources that send multicast packets are registered with the RP by the first-hop router of the source.

As a PIM join travels up the tree, routers along the path set up the multicast forwarding state so that the requested multicast traffic is forwarded back down the tree. When multicast traffic is no longer needed, a router sends a PIM prune message up the tree toward the root node to prune (or remove) the unnecessary traffic. As this PIM prune travels hop by hop up the tree, each router updates its forwarding state appropriately. Ultimately, the forwarding state associated with a multicast group or source is removed. Additionally, if prunes are not explicitly sent, the PIM state will timeout and be removed in the absence of any further join messages.

PIM-SM is the best choice for multicast networks that have potential members at the end of WAN links.

When PIM-SM is used with SSM, multi-cast routing is easier to manage. This is because RPs (rendezvous points) are not required and therefore, no shared trees (*,G) are built.

There is no specific IETF document defining PIM-SSM. However, RFC4607 defines the overall SSM behavior.

In the rest of this document, we use the term PIM-SSM to describe PIM behavior and configuration when SSM is used.

In many multicast deployments where the source is known, protocol-independent multicast-source-specific multicast (PIM-SSM) mapping is the obvious multicast routing protocol choice to use because of its simplicity. Typical multicast deployments that benefit from PIM-SSM consist of entertainment-type solutions like the ETTH space, or financial deployments that completely rely on static forwarding.

In SSM, delivery of data grams is based on (S,G) channels. Traffic for one (S,G) channel consists of datagrams with an IP unicast source address S and the multicast group address G as the IP destination address. Systems receive traffic by becoming members of the (S,G) channel. Signaling is not required, but receivers must subscribe or unsubscribe to (S,G) channels to receive or not receive traffic from specific sources. Channel subscription signaling uses IGMP to include mode membership reports, which are supported only in Version 3 of IGMP (IGMPv3).

To run SSM with IGMPv3, SSM must be supported on the multicast router, the host where the application is running, and the application itself. Cisco IOS XR Software allows SSM configuration for an arbitrary subset of the IP multicast address range 224.0.0.0 through 239.255.255.255.

When an SSM range is defined, existing IP multicast receiver applications do not receive any traffic when they try to use addresses in the SSM range, unless the application is modified to use explicit (S,G) channel subscription.

Protocol Independent Multicast (PIM) is a multicast routing protocol used to create multicast distribution trees, which are used to forward multicast data packets. PIM is an efficient IP routing protocol that is “independent” of a routing table, unlike other multicast protocols such as Multicast Open Shortest Path First (MOSPF) or Distance Vector Multicast Routing Protocol (DVMRP).

Cisco IOS XR Software supports Protocol Independent Multicast in sparse mode (PIM-SM) and Protocol Independent Multicast in Source-Specific Multicast (PIM-SSM), permitting these modes to operate on your router at the same time.

PIM-SM and PIM-SSM supports one-to-many applications by greatly simplifying the protocol mechanics for deployment ease.

• PIM in sparse mode operation is used in a multicast network when relatively few routers are involved in each multicast and these routers do not forward multicast packets for a group, unless there is an explicit request for the traffic.

• PIM in Source-Specific Multicast operation uses information found on source addresses for a multicast group provided by receivers and performs source filtering on traffic.

  • By default, PIM-SSM operates in the 232.0.0.0/8 multicast group range for IPv4 and ff3x::/32 (where x is any valid scope) in IPv6. To configure these values, use the ssm range command.

  • If SSM is deployed in a network already configured for PIM-SM, only the last-hop routers must be upgraded with Cisco IOS XR Software that supports the SSM feature.

  • No MSDP SA messages within the SSM range are accepted, generated, or forwarded.

Deploying PIM-SSM in legacy multicast-enabled networks can be problematic, because it requires changes to the multicast group management protocols used on the various devices attached to the network. Host, routers, and switches must all be upgraded in such cases.

To support legacy hosts and switches in a PIM-SSM deployment, this router offers a configurable mapping feature. Legacy group membership reports for groups in the SSM group range are mapped to a set of sources providing service for that set of (S,G) channels.

Router#configure
Tue Feb  4 05:15:56.544 UTC
Router(config)#ipv4 access-list mc3
Router(config-ipv4-acl)#permit 1 host 232.1.1.2 any
Router(config-ipv4-acl)#commit
Tue Feb  4 05:16:28.752 UTC
Router(config-ipv4-acl)#exit
Router(config)#exit 
Router:ios#

Router#configure
Router(config)#router igmp vrf vrf20
Router(config-igmp-vrf20)#ssm map static 232.1.1.1 mc2
Router(config-igmp-vrf20)#exit
Router(config-igmp)#commit

The PIM Per Interface States Limit sets a limit on creating OLEs for the PIM interface. When the set limit is reached, the group is not accounted against this interface but the group can exist in PIM context for some other interface.

The following configuration sets a limit on the number of routes for which the given interface may be an outgoing interface as a result of receiving a PIM J/P message.

router pim | pim6 [vrf <vrfname>]
interface <ifname>
          maximum route-interfaces <max> [threshold <threshold>] [<acl>]
!
!

where,

<ifname> is the interface name

<max> is the maximum limit on the groups

<threshold> is the threshold number of groups at which point a syslog warning message will be issued

<acl> provides an option for selective accounting. If provided, only groups or (S,G)s that are permitted by the ACL is accounted against the limit. Groups or (S, G)s that are denied by the ACL are not accounted against the limit. If not provided, all the groups are accounted against the limit.

The following messages are displayed when the threshold limit is reached for PIM:

pim[1157]: %ROUTING-IPV4_PIM-4-CAC_STATE_THRESHOLD : The interface GigabitEthernet0_2_0_0 threshold number (4) allowed states has been reached.
State creation will soon be throttled. Configure a higher state limit value or take steps to reduce the number of states.

pim[1157]: %ROUTING-IPV4_PIM-3-CAC_STATE_LIMIT : The interface GigabitEthernet0_2_0_0 maximum number (5) of allowed states has been reached. 
State creation will not be allowed from here on. Configure a higher maximum value or take steps to reduce the number of states

In PIM-SM, the rendezvous point (RP) is used to bridge sources sending data to a particular group with receivers sending joins for that group. In the initial setup of state, interested receivers receive data from senders to the group across a single data distribution tree rooted at the RP. This type of distribution tree is called a shared tree or rendezvous point tree (RPT) as illustrated in the below image. Data from senders is delivered to the RP for distribution to group members joined to the shared tree.

Unless the spt-threshold infinity command is configured, this initial state gives way as soon as traffic is received on the leaf routers (designated router closest to the host receivers). When the leaf router receives traffic from the RP on the RPT, the router initiates a switch to a data distribution tree rooted at the source sending traffic. This type of distribution tree is called a shortest path tree or source tree . By default, the Cisco IOS XR Software switches to a source tree when it receives the first data packet from a source.

The following process describes the move from shared tree to source tree in more detail:

1. Receiver joins a group; leaf Router C sends a join message toward RP.

2. RP puts link to Router C in its outgoing interface list.

3. Source sends data; Router A encapsulates data in Register and sends it to RP.

4. RP forwards data down the shared tree to Router C and sends a join message toward Source. At this point, data may arrive twice at the RP, once encapsulated and once natively.

5. When data arrives natively (unencapsulated) at RP, RP sends a register-stop message to Router A.

6. By default, receipt of the first data packet prompts Router C to send a join message toward Source.

7. When Router C receives data on (S,G), it sends a prune message for Source up the shared tree.

8. RP deletes the link to Router C from outgoing interface of (S,G). RP triggers a prune message toward Source.

Join and prune messages are sent for sources and RPs. They are sent hop by hop and are processed by each PIM router along the path to the source or RP. Register and register-stop messages are not sent hop by hop. They are exchanged using direct unicast communication between the designated router that is directly connected to a source and the RP for the group.

Tip	The spt-threshold infinity command lets you configure the router so that it never switches to the shortest path tree (SPT).

The multicast-intact feature provides the ability to run multicast routing (PIM) when Interior Gateway Protocol (IGP) shortcuts are configured and active on the router. Both Open Shortest Path First, version 2 (OSPFv2), and Intermediate System-to-Intermediate System (IS-IS) support the multicast-intact feature. Multiprotocol Label Switching Traffic Engineering (MPLS-TE) and IP multicast coexistence is supported in Cisco IOS XR Software by using the mpls traffic-eng multicast-intact IS-IS or OSPF router command. See the Routing Configuration Guide for Cisco 8000 Series Routers for information on configuring multicast intact using IS-IS and OSPF commands.

You can enable multicast-intact in the IGP when multicast routing protocols (PIM) are configured and IGP shortcuts are configured on the router. IGP shortcuts are MPLS tunnels that are exposed to IGP. The IGPs route the IP traffic over these tunnels to destinations that are downstream from the egress router of the tunnel (from an SPF perspective). PIM cannot use IGP shortcuts for propagating PIM joins because reverse path forwarding (RPF) cannot work across a unidirectional tunnel.

When you enable multicast-intact on an IGP, the IGP publishes a parallel or alternate set of equal-cost next-hops for use by PIM. These next-hops are called mcast-intact next-hops . The mcast-intact next-hops have the following attributes:

• They are guaranteed not to contain any IGP shortcuts.

• They are not used for unicast routing but are used only by PIM to look up an IPv4 next hop to a PIM source.

• They are not published to the Forwarding Information Base (FIB).

• When multicast-intact is enabled on an IGP, all IPv4 destinations that were learned through link-state advertisements are published with a set equal-cost mcast-intact next-hops to the RIB. This attribute applies even when the native next-hops have no IGP shortcuts.

• In IS-IS, the max-paths limit is applied by counting both the native and mcast-intact next-hops together. (In OSPFv2, the behavior is slightly different.)

Cisco routers use PIM-SM to forward multicast traffic and follow an election process to select a designated router (DR) when there is more than one router on a LAN segment.

The designated router is responsible for sending PIM register and PIM join and prune messages toward the RP to inform it about host group membership.

If there are multiple PIM-SM routers on a LAN, a designated router must be elected to avoid duplicating multicast traffic for connected hosts. The PIM router with the highest IP address becomes the DR for the LAN unless you choose to force the DR election by use of the dr-priority command. The DR priority option allows you to specify the DR priority of each router on the LAN segment (default priority = 1) so that the router with the highest priority is elected as the DR. If all routers on the LAN segment have the same priority, the highest IP address is again used as the tiebreaker.

Note	DR election process is required only on multi access LANs. The last-hop router directly connected to the host is the DR.

The figure "Designated Router Election on a Multiaccess Segment", below illustrates what happens on a multi access segment. Router A (10.0.0.253) and Router B (10.0.0.251) are connected to a common multi access Ethernet segment with Host A (10.0.0.1) as an active receiver for Group A. As the Explicit Join model is used, only Router A, operating as the DR, sends joins to the RP to construct the shared tree for Group A. If Router B were also permitted to send (*,G) joins to the RP, parallel paths would be created and Host A would receive duplicate multicast traffic. When Host A begins to source multicast traffic to the group, the DR's responsibility is to send register messages to the RP. Again, if both routers were assigned the responsibility, the RP would receive duplicate multicast packets.

If the DR fails, the PIM-SM provides a way to detect the failure of Router A and to elect a failover DR. If the DR (Router A) were to become inoperable, Router B would detect this situation when its neighbor adjacency with Router A timed out. Because Router B has been hearing IGMP membership reports from Host A, it already has IGMP state for Group A on this interface and immediately sends a join to the RP when it becomes the new DR. This step reestablishes traffic flow down a new branch of the shared tree using Router B. Additionally, if Host A were sourcing traffic, Router B would initiate a new register process immediately after receiving the next multicast packet from Host A. This action would trigger the RP to join the SPT to Host A, using a new branch through Router B.

Note	Two PIM routers are neighbors if there is a direct connection between them. To display your PIM neighbors, use the show pim neighbor command in EXEC mode.

• They are not used for unicast routing but are used only by PIM to look up an IPv4 next hop to a PIM source.

• They are not published to the Forwarding Information Base (FIB).

• When multicast-intact is enabled on an IGP, all IPv4 destinations that were learned through link-state advertisements are published with a set equal-cost mcast-intact next-hops to the RIB. This attribute applies even when the native next-hops have no IGP shortcuts.

• In IS-IS, the max-paths limit is applied by counting both the native and mcast-intact next-hops together. (In OSPFv2, the behavior is slightly different.)

Router#configure
Router(config)#router pim
Router(config-pim-default)#address-family ipv4
Router(config-pim-default-ipv4)#dr-priority 2 
Router(config-pim-default-ipv4)#interface TenGigE0/0/0/1 
Router(config-pim-ipv4-if)#dr-priority 4
Router(config-ipv4-acl)#commit

Router#show run router pim
router pim
 address-family ipv4
  dr-priority 2
  spt-threshold infinity
  interface TenGigE 0/0/0/1
   dr-priority 4
   hello-interval 45

Router#show pim interface
PIM interfaces in VRF default
Address           Interface           PIM  Nbr   Hello  DR    DR Count Intvl  Prior
100.1.1.1        TenGigE0/0/0/1        on   1     45     4     this system
26.1.1.1         TenGigE0/0/0/26       on   1     30     2     this system

When PIM is configured in sparse mode, you must choose one or more routers to operate as a rendezvous point (RP). A rendezvous point is a single common root placed at a chosen point of a shared distribution tree, as illustrated in PIM Shared Tree and Source Tree (Shortest Path Tree). A rendezvous point can be either configured statically in each box or learned through a dynamic mechanism.

PIM DRs forward data from directly connected multicast sources to the rendezvous point for distribution down the shared tree. Data is forwarded to the rendezvous point in one of two ways:

• Encapsulated in register packets and unicast directly to the rendezvous point by the first-hop router operating as the DR.

• Multicast forwarded by the RPF forwarding algorithm, described in the Reverse-Path Forwarding, if the rendezvous point has itself joined the source tree.

The rendezvous point address is used by first-hop routers to send PIM register messages on behalf of a host sending a packet to the group. The rendezvous point address is also used by last-hop routers to send PIM join and prune messages to the rendezvous point to inform it about group membership. You must configure the rendezvous point address on all routers (including the rendezvous point router).

A PIM router can be a rendezvous point for more than one group. Only one rendezvous point address can be used at a time within a PIM domain. The conditions specified by the access list determine for which groups the router is a rendezvous point.

You must manually configure a PIM router to function as a rendezvous point.

RP/0/RP0/CPU0:ios#configure
Thu Jan 30 08:30:02.187 UTC
RP/0/RP0/CPU0:ios(config)#router pim
RP/0/RP0/CPU0:ios(config-pim)#old-register-checksum
RP/0/RP0/CPU0:ios(config-pim)#exit
RP/0/RP0/CPU0:ios(config)#ipv4 access-list rp-access
RP/0/RP0/CPU0:ios(config-ipv4-acl)#permit 239.1.1.0 0.0.255.255
RP/0/RP0/CPU0:ios(config-ipv4-acl)#commit
Thu Jan 30 08:31:22.679 UTC
RP/0/RP0/CPU0:ios(config-ipv4-acl)#

Automatic route processing (Auto-RP) is a feature that automates the distribution of group-to-RP mappings in a PIM network. This feature has these benefits:

• It is easy to use multiple RPs within a network to serve different group ranges.

• It allows load splitting among different RPs.

• It facilitates the arrangement of RPs according to the location of group participants.

• It avoids inconsistent, manual RP configurations that might cause connectivity problems.

Multiple RPs can be used to serve different group ranges or to serve as hot backups for each other. To ensure that Auto-RP functions, configure routers as candidate RPs so that they can announce their interest in operating as an RP for certain group ranges. Additionally, a router must be designated as an RP-mapping agent that receives the RP-announcement messages from the candidate RPs, and arbitrates conflicts. The RP-mapping agent sends the consistent group-to-RP mappings to all remaining routers. Thus, all routers automatically determine which RP to use for the groups they support.

Tip	By default, if a given group address is covered by group-to-RP mappings from both static RP configuration, and is discovered using Auto-RP or PIM BSR, the Auto-RP or PIM BSR range is preferred. To override the default, and use only the RP mapping, use the rp-address override keyword.

Note

Auto-RP is not supported on VRF interfaces. Auto-RP Lite allows you to configure auto-RP on the CE router. It allows the PE router that has the VRF interface to relay auto-RP discovery, and announce messages across the core and eventually to the remote CE. Auto-RP is supported in only the IPv4 address family.

Router#configure
Router(config)# router pim
Router(config-pim-ipv4)# auto-rp candidate-rp GigabitEthernet0/1/0/1 scope 31 group-list 2 bidir
Router(config-pim-ipv4)# auto-rp mapping-agent GigabitEthernet0/1/0/1 scope 20
Router(config-pim-ipv4)# exit
Router(config)# ipv4 access-list 2
Router(config-ipv4-acl)# permit 239.1.1.1 0.0.0.0
Router(config-ipv4-acl)#commit

ipv4 access-list 111 
 10 permit 224.1.0.0 0.0.255.255  
 20 permit 224.2.0.0 0.0.255.255  
! 
!Access list 111 is used by the Auto-RP candidate.
!
ipv4 access-list 222 
 10 deny any host 224.0.1.39 
 20 deny any host 224.0.1.40 
! 
!Access list 222 is used by the boundary command to contain traffic (on GigabitEthernet0/3/0/0) that is sent to groups 224.0.1.39 and 224.0.1.40.
!
router pim
 auto-rp mapping-agent loopback 2 scope 32 interval 30 
 auto-rp candidate-rp loopback 2 scope 15 group-list 111 interval 30 
multicast-routing
 interface hundredGigE 0/0/0/25 
 boundary 222
!

The PIM bootstrap router (BSR) provides a fault-tolerant, automated RP discovery and distribution mechanism.

To avoid a single point of failure, you can configure several candidate BSRs in a PIM domain. A BSR is elected among the candidate BSRs automatically.

Candidates use bootstrap messages to discover which BSR has the highest priority. The candidate with the highest priority sends an announcement to all PIM routers in the PIM domain that it is the BSR.

Routers that are configured as candidate RPs unicast to the BSR the group range for which they are responsible. The BSR includes this information in its bootstrap messages and disseminates it to all PIM routers in the domain. Based on this information, all routers are able to map multicast groups to specific RPs. As long as a router is receiving the bootstrap message, it has a current RP map.

Router# configure
Router:(config)# router pim
Router:(config-pim)# bsr candidate-bsr 10.0.0.1 hash-mask-len 30
Router:(config-ipv4-acl)#commit

RP/0/RP0/CPU0:ios#configure 
Thu Jan 30 08:03:47.952 UTC
RP/0/RP0/CPU0:ios(config)#router pim
RP/0/RP0/CPU0:ios(config-pim)#bsr candidate-bsr 10.0.0.1 hash-mask-len 30
RP/0/RP0/CPU0:ios(config-pim)#bsr candidate-rp 172.3.2.1 group-list 4 bidir
RP/0/RP0/CPU0:ios(config-pim)#interface fourHundredGigE 0/0/0/1
RP/0/RP0/CPU0:ios(config-pim-ipv4-if)# bsr-border
RP/0/RP0/CPU0:ios(config-pim-ipv4-if)#exit
RP/0/RP0/CPU0:ios(config-pim-default-ipv4)#exit
RP/0/RP0/CPU0:ios(config-pim)#exit
RP/0/RP0/CPU0:ios(config)#ipv4 access-list 4
RP/0/RP0/CPU0:ios(config-ipv4-acl)#permit 239.1.1.1 0.255.255.255
RP/0/RP0/CPU0:ios(config-ipv4-acl)#commit
Thu Jan 30 08:05:36.780 UTC
RP/0/RP0/CPU0:ios(config-ipv4-acl)#exit
RP/0/RP0/CPU0:ios(config)#exit

RP/0/RP0/CPU0:ios#show running-config router pim
Thu Jan 30 08:08:06.568 UTC
router pim
 address-family ipv4
  interface FourHundredGigE0/0/0/1
   bsr-border
  !
  bsr candidate-bsr 10.0.0.1 hash-mask-len 30 priority 1
  bsr candidate-rp 172.3.2.1 group-list 4 priority 192 interval 60 bidir
 !
!

RP/0/RP0/CPU0:ios#show pim bsr candidate-rp
Thu Jan 30 08:08:32.851 UTC
PIM BSR Candidate RP Info 

Cand-RP          mode  scope priority uptime    group-list
172.3.2.1        BD    16    192      00:00:00  4

RP/0/RP0/CPU0:ios#show pim bsr election
Thu Jan 30 08:08:58.846 UTC
PIM BSR Election State 

Cand/Elect-State        Uptime   BS-Timer BSR                C-BSR

Inactive/Accept-Any     00:00:00 00:00:00 0.0.0.0 [0, 0]     10.0.0.1 [1, 30]

RP/0/RP0/CPU0:ios#show pim bsr rp-cache
Thu Jan 30 08:09:44.901 UTC
PIM BSR Candidate RP Cache 

RP/0/RP0/CPU0:ios#show pim ipv4 group-map
Thu Jan 30 08:10:14.793 UTC
No ranges found.

Reverse-path forwarding (RPF) is an algorithm 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, 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 uses both source trees and RP-rooted shared trees to forward datagrams; the RPF check is performed differently for each, as follows:

• If a PIM router has an (S,G) entry present in the multicast routing table (a source-tree state), the router performs the RPF check against the IP address of the source for the multicast packet.

• If a PIM router has no explicit source-tree state, this is considered a shared-tree state. The router performs the RPF check on the address of the RP, which is known when members join the group.

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. (*,G) joins (which are shared-tree states) are sent toward the RP.

Multicast Non-Stop Routing (NSR) enables the router to synchronize the multicast routing tables on both the active and standby RSPs so that during an HA scenario like an RSP failover there is no loss of multicast data. Multicast NSR is enabled through the multicast processes being hot standby. Multicast NSR supports both Zero Packet Loss (ZPL) and Zero Topology Loss (ZTL). With Multicast NSR, there is less CPU churn and no multicast session flaps during a failover event.

Multicast NSR is enabled by default, however, if any unsupported features like BNG or Snooping are configured, Multicast performs Non-Stop Forwarding (NSF) functionality during failover events. When Multicast NSR is enabled, multicast routing state is synchronized between the active and standby RSPs. Once the synchronization occurs, each of the multicast processes signal the NSR readiness to the system. For the multicast processes to support NSR, the processes must be hot standby compliant. That is, the processes on active and standby RSPs both have to be in synchronization at all times. The active RSP receives packets from the network and makes local decisions while the standby receives packet from the network and synchronizes it with the active RSPs for all the local decisions. Once the state is determined, a check is performed to verify if the states are synchronized. If the states are synchronized, a signal in the form NSR_READY is conveyed to the NSR system.

With NSR, in the case of a failover event, routing changes are updated to the forwarding plane immediately. With NSF, there is an NSF hold time delay before routing changes can be updated.

RP/0/RP0/CPU0:ios#configure 
Fri Feb  7 08:53:51.603 UTC
RP/0/RP0/CPU0:ios(config)#router pim address-family ipv4
RP/0/RP0/CPU0:ios(config-pim-default-ipv4)#nsf lifetime 30
RP/0/RP0/CPU0:ios(config-pim-default-ipv4)#exit
RP/0/RP0/CPU0:ios(config-pim)#router igmp
RP/0/RP0/CPU0:ios(config-igmp)#nsf lifetime 30
RP/0/RP0/CPU0:ios(config-igmp)#commit
Fri Feb  7 08:54:45.747 UTC
RP/0/RP0/CPU0:ios(config-igmp)#exit
RP/0/RP0/CPU0:ios(config)#exit
RP/0/RP0/CPU0:ios#show igmp nsf
Fri Feb  7 08:55:02.046 UTC
IGMP Non-Stop Forwarding Status:
Multicast routing state: Normal
   NSF Lifetime:       00:00:30

RP/0/RP0/CPU0:ios#show mfib nsf
Fri Feb  7 08:55:12.462 UTC
IP MFWD Non-Stop Forwarding Status:
	NSF Lifetime:          00:15:00

On node 0/RP0/CPU0 :
Multicast routing state: Normal

RP/0/RP0/CPU0:ios#show mrib nsf
Fri Feb  7 08:55:24.228 UTC
IP MRIB Non-Stop Forwarding Status:
Multicast routing state: Normal
   NSF Lifetime:       00:01:30
RP/0/RP0/CPU0:ios#show pim nsf
Fri Feb  7 08:55:33.499 UTC
IP PIM Non-Stop Forwarding Status:
Multicast routing state: Normal
   NSF Lifetime:       00:00:30
RP/0/RP0/CPU0:ios#

RP/0/RP0/CPU0:ios#show igmp nsf
Fri Feb  7 08:55:02.046 UTC
IGMP Non-Stop Forwarding Status:
Multicast routing state: Normal
   NSF Lifetime:       00:00:30

RP/0/RP0/CPU0:ios#show mfib nsf
Fri Feb  7 08:55:12.462 UTC
IP MFWD Non-Stop Forwarding Status:
	NSF Lifetime:          00:15:00

On node 0/RP0/CPU0 :
Multicast routing state: Normal

RP/0/RP0/CPU0:ios#show mrib nsf
Fri Feb  7 08:55:24.228 UTC
IP MRIB Non-Stop Forwarding Status:
Multicast routing state: Normal
   NSF Lifetime:       00:01:30

RP/0/RP0/CPU0:ios#show pim nsf
Fri Feb  7 08:55:33.499 UTC
IP PIM Non-Stop Forwarding Status:
Multicast routing state: Normal
   NSF Lifetime:       00:00:30
RP/0/RP0/CPU0:ios#

Basic multicast services start automatically without any explicit configuration required. The following multicast services are started automatically:

• MFWD

• MRIB

• PIM

• IGMP

Other multicast services require explicit configuration before they start. For example, to start the MSDP process, you must enter the router msdp command and explicitly configure it.

When you issue the multicast-routing ipv4 or multicast-routing ipv6 command, all default multicast components (PIM, IGMP, MLD, MFWD, and MRIB) are automatically started, and the CLI prompt changes to “config-mcast-ipv4” or “config-mcast-ipv6”, indicating that you have entered multicast-routing configuration submode.

When you issue the router pim command, the CLI prompt changes to “config-pim-ipv4,” indicating that you have entered the default pim address-family configuration submode.

To enter pim address-family configuration submode for IPv6, type the address-family ipv6 keyword together with the router pim command before pressing Enter.

When you issue the router igmp command, the CLI prompt changes to “config-igmp,” indicating that you have entered IGMP configuration submode.

When you issue the router mld command, the CLI prompt changes to “config-mld,” indicating that you have entered MLD configuration submode.

When you issue the router msdp command, the CLI prompt changes to “config-msdp,” indicating that you have entered router MSDP configuration submode.

The MLDP MVPN configuration enables IPv4 and IPV6 multicast packet delivery using MPLS. This configuration uses MPLS labels to construct default and data Multicast Distribution Trees (MDTs). The MPLS replication is used as a forwarding mechanism in the core and edge network. For MLDP MVPN configuration to work, ensure that the global MPLS MLDP configuration is enabled. To configure MVPN extranet support, configure the source multicast VPN Routing and Forwarding (mVRF) on the receiver Provider Edge (PE) router or configure the receiver mVRF on the source PE. MLDP MVPN is supported for both intranet and extranet.

For each packet coming in, MPLS creates multiple out-labels. Packets from the source network are replicated along the path to the receiver network. The CE1 router sends out the native IP multicast traffic. The Provider Edge1 (PE1) router imposes a label on the incoming multicast packet and replicates the labeled packet towards the MPLS core network. When the packet reaches the core router (P), the packet is replicated with the appropriate labels for the MP2MP default MDT or the P2MP data MDT and transported to all the egress PEs. Once the packet reaches the egress PE (edge routers), the label is removed and the IP multicast packet is replicated onto the VRF interface. Basically, the packets are encapsulated at headend and decapsulated at tailend on the PE routers.

Multicast Label Distribution Protocol (MLDP) provides extensions to the Label Distribution Protocol (LDP) for the setup of point-to-multipoint (P2MP) and multipoint-to-multipoint (MP2MP) Label Switched Paths (LSPs) in Multiprotocol Label Switching (MPLS) networks.

MLDP eliminates the use of native multicast PIM to transport multicast packets across the core. In MLDP multicast traffic is label switched across the core. This saves a lot of control plane processing effort.

IP multicast was traditionally used for IPTV broadcasting and content delivery services. Point-to-Multipoint (P2MP) Traffic-Engineering is fast replacing the IP multicast technique because of the various advantages of MPLS-TE, such as:

• Fast re-routing (FRR) and restoration in case of link/ node failure

• Bandwidth guarantee