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Chapter 7 - Protocol Independent Multicast-Sparse Mode

Cisco Multicast Routing & Switching
William R. Parkhurst
  Copyright © 1999 The McGraw-Hill Companies

PIM-SM Router Configuration Commands
PIM-SM is more complicated to configure than PIM-DM because an RP is required for each group. One RP can handle all groups, which can be spread across multiple RPs. The first step is to enable multicast routing in Global Configuration mode using the command
ip multicast-routing
Next, enable PIM-SM on the router interfaces using the interface command
ip pim sparse-mode
or
ip pim sparse-dense-mode
PIM-Sparse-Dense-Mode is used when there are groups with no RP. In this case, groups with an assigned RP are treated as Sparse Mode groups, and groups without an RP are treated as Dense Mode groups.
Rendezvous Point Configuration and Static RP Configuration
There is not a default RP and one or more must be configured using one of the three methods. For the static case, the RP does not need to be configured, only the leaf routers. To configure the static RP, use the global configuration command
ip pim rp-address ip-address [access-list-number] [override]
ip-address
ip address of the RP
group-access-list-number
Optional. Standard IP access list number, 1—100. If no access list is used, then the RP can handle all groups. Use an access list to limit the groups that the RP will service.
override
Optional. If there is a conflict between the static RP and one configured using Auto-RP, then the static RP takes precedence.
For example, to configure an RP that handles all groups, use
ip pim rp-address 172.16.1.1
where 172.16.1.1 is the address of the RP. If we want the RP to only handle a subset of multicast groups, then an access list is needed. If the RP is to handle only group 239.252.1.1, then we would use the following commands:
ip pim rp-address 172.16.1.1 1
access-list 1 permit 239.252.1.1 0.0.0.0
If the RP is to service the groups 239.252.1.0 through 239.252.1.255, then the access list would contain
access-list 1 permit 239.252.1.0 0.0.0.255.
Auto-RP Configuration
For Auto-RP, the RPs and a mapping agent need to be configured. The RPs are configured using the Global Configuration command:
ip pim send-rp-announce interface-type interface-number scope ttl
group-list access-list-number
interface-type interface-number
The address of the specified interface is used to identify the RP.
scope
TTL value of the announcements. Limits the distance an RP announcement can travel.
access-list-number
An access-list determines the groups that the RP is announcing that it can service.
The router sends RP announcements on all PIM-enabled interfaces for a maximum number of hops specified by the scope parameter. The announcements are sent to the group CISCO-RP-ANNOUNCE (224.0.1.39). To enable the RP to announce all multicast groups, use the command below.
ip pim send-rp-announce ethernet 0 scope 30 group-list 2
access-list 2 permit 224.0.0.0 15.255.255.255
The next step in configuring Auto-RP is to configure the RP mapping agent using the global command
ip pim send-rp-discovery scope ttl
TTL of the Discovery messages. Used to limit the scope of the message.
The router configured as a mapping agent will listen for RP announcements to group CISCO-RP-ANNOUNCE (224.0.1.39). The RP mapping agent then sends the RP-to-group mappings to the group CISCO-RP-DISCOVERY (224.0.1.40), and PIM routers get their RP information from the Discovery messages.

 


 
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