PIM Allow RP

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A rendezvous point (RP) is a role that a device performs when operating in Protocol Independent Multicast (PIM) Sparse Mode (SM). An RP is required only in networks running PIM SM. In the PIM-SM model, only network segments with active receivers that have explicitly requested multicast data will be forwarded the traffic. This method of delivering multicast data is in contrast to PIM Dense Mode (PIM DM). In PIM DM, multicast traffic is initially flooded to all segments of the network. Routers that have no downstream neighbors or directly connected receivers prune back the unwanted traffic.

An RP acts as the meeting place for sources and receivers of multicast data. In a PIM-SM network, sources must send their traffic to the RP. This traffic is then forwarded to receivers down a shared distribution tree. By default, when the first hop device of the receiver learns about the source, it will send a Join message directly to the source, creating a source-based distribution tree from the source to the receiver. This source tree does not include the RP unless the RP is located within the shortest path between the source and receiver.

In most cases, the placement of the RP in the network is not a complex decision. By default, the RP is needed only to start new sessions with sources and receivers. Consequently, the RP experiences little overhead from traffic flow or processing. In PIM version 2, the RP performs less processing than in PIM version 1 because sources must only periodically register with the RP to create state.

There are three types of networks: publisher, consumer, and transport. Many publisher networks can originate content and many consumer networks can be interested in the content. The transport network, owned and operated by a service provider, connects the publisher and the consumer networks.

The consumer and the transport networks are connected as follows:

For a specific group range, or all-groups range (similar to a default route), the service provider defines a particular rendezvous point (RP), such as RP-A. Reverse path forwarding of RP-A from a consumer device will cause a (*,G) Join to be sent towards the transport network.

For the same group, the service provider may define a different RP, such as RP-B, that is used to build the shared tree within the transport network for G. RP-A and RP-B are typically different RPs and each RP is defined for different group ranges.

RFC 4601 dictates that if a device receives a (*, G) Join and the RP that is specified in the (*, G) Join is different than what the receiving device expects (unknown RPs), the incoming (*, G) Join must be ignored. The PIM Allow RP feature enables the receiving device to use its own RP to create state and build shared trees when an incoming (*, G) Join is processed and a different RP is identified. This allows the receiving device to accept the (*, G) Join from the different RP.

PIM Allow RP is only applicable for downstream traffic, for building the shared tree. It does not work with Auto-RP or BSR. Only static configuration is supported. However, PIM Allow RP does compensate for the embedded RP in the consumer network to be different than the one configured statically in the transport network.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.   

4.    interface type number

5.   

6.   ipv6 address {ipv6-address | prefix-length | prefix-name sub-bits | prefix-length}

7.   no shut

8.    exit

9.    Repeat Steps 4 through 8 on every interface that uses IP multicast.

10.   

11.    exit

12.    show ip pim rp [mapping] [rp-address]

13.    show ip mroute

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Device> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Device# configure terminal	Enters global configuration mode.
Step 3	ip multicast-routing [vrf vrf-name] distributed ipv6 multicast-routing [vrf vrf-name] Example: Device(config)# ip multicast-routing Device(config)# ipv6 multicast-routing	For IPv4: Enables multicast routing on all interfaces of the device. In Cisco IOS XE Release 3.2S and earlier releases, the distributed keyword is optional. For IPv6: Enables multicast routing on all interfaces of the device and also enables multicast forwarding for PIM and MLD on all multicast-enabled interfaces of the device. Note    IPv6 multicast routing is disabled by default when IPv6 unicast routing is enabled. On certain devices, the IPv6 multicast routing must also be enabled in order to use IPv6 unicast routing.
Step 4	interface type number Example: Device(config)# interface gigabitethernet 1/0/0	Selects an interface that is connected to hosts on which PIM can be enabled.
Step 5	ip pim sparse-mode ipv6 pim enable Example: Device(config-if)# ip pim sparse-mode Device(config-if)# ipv6 pim enable	For IPv4: Enables PIM. You must use sparse mode. For IPv6: Enables IPv6 and by default, IPv6 PIM.
Step 6	ipv6 address {ipv6-address | prefix-length | prefix-name sub-bits | prefix-length} Example: Device(config-if)# ipv6 address 2001:DB8::4:4/64	For IPv6 only: Configures an IPv6 address based on an IPv6 general prefix and enables IPv6 processing on an interface.
Step 7	no shut Example: Device(config-if)# no shut	Enables an interface.
Step 8	exit Example: Device(config-if)# exit	-- Returns to global configuration mode.
Step 9	Repeat Steps 4 through 8 on every interface that uses IP multicast.
Step 10	ip pim [vrf vrf-name] rp-address rp-address [access-list] [override] ipv6 pim [vrf vrf-name] rp-address ipv6-address [group-address-list] Example: Device(config)# ip pim rp-address 192.0.2.1 acl-sparse Device(config)# ipv6 pim rp-address 2001:DB8::1:1 acl_sparse1	For IPv4: Configures the address of a PIM RP. If no access list is specified, the RP address is applied to all multicast groups, 224/4. For IPv6: Configures the address of a PIM RP. If no group-address list is specified, the RP address is applied to the entire routable IPv6 multicast group range, excluding SSM, which ranges from FFX[3-f]::/8 to FF3X::/96.
Step 11	exit Example: Device(config)# exit	Exits global configuration mode.
Step 12	show ip pim rp [mapping] [rp-address] Example: Device# show ip pim rp mapping	(Optional) Displays RPs known in the network and shows how the router learned about each RP.
Step 13	show ip mroute Example: Device# show ip mroute	(Optional) Displays the contents of the IP mroute table.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.   

4.    exit

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Device> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Device# configure terminal	Enters global configuration mode.
Step 3	ip pim allow-rp [group-list access-list | rp-list access-list [group-list access-list]] ipv6 pim allow-rp [group-list access-list | rp-list access-list [group-list access-list]] Example: Device(config)# ip pim allow-rp Device(config)# ipv6 pim allow-rp	Enables PIM Allow RP.
Step 4	exit Example: Device(config)# exit	Returns to privileged EXEC mode.

SUMMARY STEPS

1.    enable

2.   

3.   

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Device> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	show ip pim [vrf vrf-name] rp [metric] [rp-address] show ipv6 pim [vrf vrf-name] interface [state-on] [state-off] [type number] Example: Device# show ip pim interface Device# show ipv6 pim interface	Displays information about interfaces configured for PIM.
Step 3	show ip pim [ vrf vrf-name] rp mapping [rp-address] show ipv6 pim [vrf vrf-name] group-map [group-name | group-address] | [group-range | group-mask] [info-source {bsr | default | embedded-rp | static}] Example: Device# show ipv6 pim rp mapping Device# show ipv6 pim group-map static	Displays the mappings for the PIM group to the active rendezvous points.