Sparsed in Many to One..

Internet Protocol Multicast is an Internet routing protocol designed to provide efficient data transmission to multiple users. Multicast uses Class D addressing to identify and route multicast traffic and Protocol Independent Multicast (PIM) to configure and structure the multicast network.

IP Multicast assembles users who wish to receive multicast traffic into multicast groups and assigns each group a specific Class D IP address. The Class D IP address range reserved for multicast addresses is 224.0.0.0 to 239.255.255.255. PIM is enabled on interfaces to provide the routing mechanism to structure the multicast traffic. When a message is sent to a multicast group, the sending host forwards a single copy of the data packet over the network. The intermediate routers replicate these data packets and distribute them to the multicast group members.

Enables/disables Protocol Independent Multicast (PIM) sparse-mode on an interface.
Syntax: ip pim sparse-mode
Description: The ip pim sparse-mode command enables PIM sparse-mode on the interface. Modes in multicast denote specific methods of routing multicast traffic.

Enabling PIM on an interface also enables IGMP operation on that interface. An interface can be configured to be in dense mode, sparse mode, or sparse-dense mode. The mode determines how the router populates its multicast routing table and how the router forwards multicast packets it receives from its directly connected LANs. You must enable PIM in one of these modes for an interface to perform IP multicast routing.
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 routers, 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 may send joins toward the source to build a source-based distribution tree.
There is no default mode setting. By default, multicast routing is disabled on an interface.

If you configure sparse-dense mode, the idea of sparseness or denseness is applied to the group on the router, and the network manager should apply the same concept throughout the network. Another benefit of sparse-dense mode is that Auto-RP information can be distributed in a dense mode manner; yet, multicast groups for user groups can be used in a sparse mode manner. Thus, there is no need to configure a default RP at the leaf routers.

To test this out we are going to configure on R4, R5, R3, R1 all interfaces of these routers in pim sparse mode.

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R1#conf ter
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)#ip multicast-routing
R1(config)#int lo0
R1(config-if)#ip pim sparse
R1(config-if)#int f0/0
R1(config-if)#ip pim sparse
R1(config-if)#int s0/0/0
R1(config-if)#ip pim sparse

 
R3#conf ter
Enter configuration commands, one per line.  End with CNTL/Z.
R3(config)#ip multicast-routing
R3(config)#int lo0
R3(config-if)#ip pim sparse
R3(config-if)#int f0/0
R3(config-if)#ip pim sparse
R3(config-if)#int s0/0/0
R3(config-if)#ip pim sparse
R3(config-if)#^Z
R4#conf ter
Enter configuration commands, one per line.  End with CNTL/Z.
R4(config)#ip multicast-routing
R4(config)#int f0/0
R4(config-if)#ip pim sparse
R4(config-if)#int f0/1
R4(config-if)#ip pim sparse
R4(config-if)#int lo0
R4(config-if)#ip pim sparse
R4(config-if)#int s0/0/0.45
R4(config-subif)#ip pim sparse
R4(config-subif)#exit
R4(config)#int s0/0/0.134
R4(config-subif)#ip pim sparse
R4(config-subif)#ip pim nbma
R4(config-subif)#exit
R4(config)#int lo0
R4(config-if)#ip pim sparse
R4(config-if)#exit
R5#conf ter
 Enter configuration commands, one per line.  End with CNTL/Z.
 R5(config)#ip multicast-routing
 R5(config)#int lo0
 R5(config-if)#ip pim sparse
 R5(config-if)#int f0/0
 R5(config-if)#ip pim sparse
 R5(config-if)#int s0/0/0.45
 R5(config-subif)#ip pim sparse
 R5(config-subif)#exit

R1 should be the RP for this group only, configures R4 as the Mapping Agent (AUTO-RP) also prevent from RP for this group in particular.

With Auto-RP, you configure the RPs themselves to announce their availability as RPs and mapping agents. The RPs send their announcements using 224.0.1.39. The RP mapping agent listens to the announced packets from the RPs, then sends RP-to-group mappings in a discovery message that is sent to 224.0.1.40. These discovery messages are what the rest of the routers use for their RP-to-group map. You can use one RP that also serves as the mapping agent, or you can configure multiple RPs and multiple mapping agents for redundancy purposes. Generally Auto-RP is used with sparse-dense mode, since then the Auto-RP information can be propagated in dense mode. If your routers are configured with pure sparse-mode on the interfaces, then you can shift to sparse-dense-mode, so we need to configure on the router ip auto-rp listener

ip pim autorp listener is a way of overiding the interface configuration and allowing dense mode operation. Therefore even if you have ip pim sparse mode configured it will override this command and allow the dense mode operation for the groups 224.0.1.39 and 224.0.1.40 to be distributed in dense mode.

If a CCIE Lab question restricted you to using ip pim sparse mode only yet still required Auto-RP then this could be the solution for you

R1#conf ter
 Enter configuration commands, one per line.  End with CNTL/Z.
 R1(config)#ip pim autorp list
 R1(config)#
R3#conf ter
 Enter configuration commands, one per line.  End with CNTL/Z.
 R3(config)#ip pim autorp list
 R3(config)#
R4(config)#ip pim autorp list
R5(config)#ip pim autorp list
 R5(config)#

The RP itself would have “send-rp-discovery,” while the Mapping Agent has “send-rp-announce.”

R1(config)#ip pim send-rp-announce Loopback0 scope 10 group-list 10 bidir
 R1(config)#access-list 10 permit 224.1.1.1
 R1(config)#ip pim bidir-enable
R3(config)#ip pim bidir-enable
R4(config)#ip pim bidir-enable
R5(config)#ip pim bidir-enable

PIM-SM cannot forward traffic in the upstream direction of a tree, because it only accepts traffic from one Reverse Path Forwarding (RPF) interface. This interface (for the shared tree) points toward the RP, therefore allowing only downstream traffic flow. In this case, upstream traffic is first encapsulated into unicast register messages, which are passed from the designated router (DR) of the source toward the RP. In a second step, the RP joins an SPT that is rooted at the source. Therefore, in PIM-SM, traffic from sources traveling toward the RP does not flow upstream in the shared tree, but downstream along the SPT of the source until it reaches the RP. From the RP, traffic flows along the shared tree toward all receivers.

To influence which router is the RP for a particular group, when two RPs are announcing for that group, you can configure each router with a loopback address. Place the higher IP address on the preferred RP, then use the loopback interface as the source of the announce packets; for example, ip pim send-RP-announce loopback0. When multiple mapping agents are used, they listen to each other’s discovery packets and the mapping agent with the highest IP address wins and becomes the only forwarder of 224.0.1.40.

To configure bidir-PIM, use the following commands in global configuration mode, depending on which method you use to distribute group-to-RP mappings:

Command Purpose
Router(config)# ip pim rp-address rp-address [access-list] [override] bidir Configures the address of a PIM RP for a particular group, and specifies bidirectional mode. Use this command when you are not distributing group-to-RP mappings using either Auto-RP or the PIMv2 BSR mechanism.
Router(config)# ip pim rp-candidate type number [group-list access-list] bidir Configures the router to advertise itself as a PIM Version 2 candidate RP to the BSR, and specifies bidirectional mode. Use this command when you are using the PIMv2 BSR mechanism to distribute group-to-RP mappings.
Router(config)# ip pim send-rp-announce type number scope ttl-value [group-list access-list] [interval seconds] bidir Configures the router to use Auto-RP to configure for which groups the router is willing to act as RP, and specifies bidirectional mode. Use this command when you are using Auto-RP to distribute group-to-RP mappings.

PIM-SM constructs uni-directional shared trees that are used to forward data from senders to receivers of a multicast group. PIM-SM also allows the construction of source specific trees, but this capability is not related to the protocol described in this document.

The shared tree for each multicast group is rooted at a multicast router called the Rendezvous Point (RP). Different multicast groups can use separate RPs within a PIM domain.

In unidirectional PIM-SM, there are two possible methods for distributing data packets on the shared tree. These differ in the way packets are forwarded from a source to the RP:

Initially when a source starts transmitting, its first hop router encapsulates data packets in special control messages (Registers) which are unicast to the RP. After reaching the RP the packets are decapsulated and distributed on the shared tree.

A transition from the above distribution mode can be made at a later stage. This is achieved by building source specific state on all routers along the path between the source and the RP. This state is then used to natively forward packets from that source.
Both these mechanisms suffer from problems. Encapsulation results in significant processing, bandwidth and delay overheads. Forwarding using source specific state has additional protocol and memory requirements. Bi-directional PIM dispenses with both encapsulation and source state by allowing packets to be natively forwarded from a source to the RP using shared tree state. In contrast to PIM-SM this mode of forwarding does not require any data-driven events.

Auto-RP relies on a router designated as RP mapping agent. Potential RP’s announce themselves to the mapping agent, and it resolves any conflicts. The mapping agent then sends out the multicast group-RP mapping information to the other routers.

R4(config)#ip pim send-rp-discovery Loopback0 scope 10

• There is a client at Vlan 173 that is joining group 224.1.1.1

R1(config)#int f0/0
 R1(config-if)#ip igmp jopi224.1.1.1
 R1(config-if)#ip igmp join 224.1.1.1

Verify the Multicast configuration by pinging the IGMP group address.

R5(config)#do ping 224.1.1.1

Type escape sequence to abort.
 Sending 1, 100-byte ICMP Echos to 224.1.1.1, timeout is 2 seconds:

Reply to request 0 from 192.168.134.1, 132 ms
Reply to request 0 from 192.168.134.1, 156 ms

In regards to prevent RP for this group in particular we configure a test RP with a higher IP Address (preferred by AUTORP) to test the configuration.

R5(config)#access-list 10 permit 224.1.1.1
 R5(config)#ip pim send-rp-announce Loopback0 scope 10 group-list 10 bidir
R4#show ip pim rp map
 PIM Group-to-RP Mappings
 This system is an RP-mapping agent (Loopback0)

Group(s) 224.1.1.1/32
 RP 110.110.5.5 (?), v2v1, bidir
 Info source: 110.110.5.5 (?), elected via Auto-RP
 Uptime: 00:00:07, expires: 00:02:52
 RP 110.110.1.1 (?), v2v1, bidir
 Info source: 110.110.1.1 (?), via Auto-RP
 Uptime: 00:11:13, expires: 00:02:44
R1#show ip pim rp map
 PIM Group-to-RP Mappings
 This system is an RP (Auto-RP)

Group(s) 224.1.1.1/32
 RP 110.110.5.5 (?), v2v1, bidir
 Info source: 110.110.4.4 (?), elected via Auto-RP
 Uptime: 00:03:23, expires: 00:02:32
R4(config)#do show ip access-list

R4(config)#!No Access-list Configured
 R4(config)#
 R4(config)#access-list 1 deny 110.110.1.1
 R4(config)#access-list 2 deny 224.1.1.1
 R4(config)#ip pim rp-announce-filter rp-list 1 group-list 2
R1#show ip pim rp map
 PIM Group-to-RP Mappings
 This system is an RP (Auto-RP)

Group(s) 224.1.1.1/32
 RP 110.110.1.1 (?), v2v1, bidir
 Info source: 110.110.4.4 (?), elected via Auto-RP
 Uptime: 00:00:00, expires: 00:02:56
 R1#
R3#show ip pim rp map
 PIM Group-to-RP Mappings

Group(s) 224.1.1.1/32
 RP 110.110.1.1 (?), v2v1, bidir
 Info source: 110.110.4.4 (?), elected via Auto-RP
 Uptime: 00:00:05, expires: 00:02:50
R4#show ip pim rp map
 PIM Group-to-RP Mappings
 This system is an RP-mapping agent (Loopback0)

Group(s) 224.1.1.1/32
 RP 110.110.5.5 (?), v2v1, bidir
 Info source: 110.110.5.5 (?), elected via Auto-RP
 Uptime: 00:00:13, expires: 00:02:42
 RP 110.110.1.1 (?), v2v1, bidir
 Info source: 110.110.1.1 (?), via Auto-RP
 Uptime: 00:00:19, expires: 00:02:36

!

R4#show ip access-list
 Standard IP access list 1
 10 deny   110.110.1.1 (4 matches)
 Standard IP access list 2
 10 deny   224.1.1.1
 R4#


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2 thoughts on “Sparsed in Many to One..

  1. Pingback: CCIE Candidate - A technical blog for Cisco CCIE candidates pursuing the routing & switching specialization. » GroupStudy.com CCIE-LAB List - Best of 12/31/2007

  2. I loved that article i learned a lot from it thx.
    Q why did you use bi-directional mode, can u please elaborate

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