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Configuring Auto-RP Announcement, Mapping, and Discovery

Although auto-RP is a nonstandard (non-RFC-based) function requiring dense mode PIM to advertise control traffic, it provides an important failover advantage that static RP assignment does not: you can configure multiple routers as RP candidates. If the elected RP stops operating, one of the other preconfigured routers takes over the RP functions. This capability is controlled by the auto-RP mapping agent.

If PIM is operating in sparse or sparse-dense mode, configure how the router operates in auto-RP by specifying the following auto-RP options:

Add the discovery option to enable the router to receive and process discovery messages from the mapping agent. This is the most basic auto-RP option.
Add the announce option to enable the router to send announce messages in the network, advertising itself as a candidate RP. Routers configured with this option must also be configured as RPs, or announce messages are not sent.
Add the mapping option to enable the router to perform the mapping function. If the router is also an RP, the mapping option also allows the router to send auto-RP announcements (mapping on an RP allows the router to perform both the announcement and mapping functions).

The router joins the auto-RP groups on the configured interfaces and on the loopback interface lo0.0. For auto-RP to work correctly, configure a routable IP address on the loopback interface. The router ID is used as the address for auto-RP updates. You cannot use the loopback address 127.0.0.1. Also, you must enable PIM sparse-dense mode on the lo0.0 interface if you do not specify interface all.

In most cases, how the router handles auto-RP discovery, announce, or mapping messages depends on whether the router is an RP (configured as local RP) or not. Table 13 shows how the router behaves depending on the local RP configuration.

Table 13: Local RP and Auto-RP Message Types

Auto-RP Message Type	Local RP?	Router Behavior
discovery	No	Listen for auto-RP mapping messages.
discovery	Yes	Listen for auto-RP mapping messages.
announce	No	Listen for auto-RP mapping messages.
announce	Yes	Listen for auto-RP mapping messages. Send auto-RP announce messages.
mapping	No	Listen for auto-RP mapping messages. Listen for auto-RP announce messages. If elected mapping agent, send auto-RP mapping messages.
mapping	Yes	Listen for auto-RP mapping messages. Send auto-RP announce messages. Listen for auto-RP announce messages. If elected mapping agent, send auto-RP mapping messages.

To configure auto-RP at the main hierarchy level, follow these steps:

Include the mode statement, and specify the option sparse-dense on all interfaces at the [edit protocols pim] hierarchy level:[edit protocols pim] interface all { mode sparse-dense; }
This configuration allows the router to operate in sparse mode for most groups and dense mode for others. The default is to operate in sparse mode unless the router is specifically informed of a dense mode group.
Configure two multicast dense mode groups (224.0.1.39 and 224.0.1.40) using the dense-groups statement at the [edit protocols pim] hierarchy level:[edit protocols pim] dense-groups { 224.0.1.39/32; 224.0.1.40/32; }
Auto-RP requires multicast flooding to announce potential RP candidates and to discover the elected RPs in the network. Multicast flooding occurs through a PIM dense mode model where group 224.0.1.39 is used for announce messages and group 224.0.1.40 is used for discovery messages.
Include the auto-RP statement at the [edit protocols pim rp] hierarchy level to configure auto-RP on each router in the group. There are four possible categories for each router.
- If the router is not a local RP and listens only for auto-RP mapping messages, include the auto-rp discovery statement at the [edit protocols pim rp] hierarchy level:[edit protocols pim rp] auto-rp discovery;
- If the router is a local RP, sends auto-RP announcements, and listens for auto-RP mapping messages, configure the router as a local RP and include the auto-rp announce statement to the router RP configuration at the [edit protocols pim rp] hierarchy level:[edit protocols pim rp] local { address 10.0.1.1; } auto-rp announce;
- If the router performs only the mapping function to listen for auto-RP announcements, performs the auto-RP-to-group mapping, and sends auto-RP mapping messages, include the auto-rp mapping statement at the [edit protocols pim rp] hierarchy level. When multiple candidate RP routers announce their capabilities to support multicast groups, there must be a single router in the network to act as mapping agent. The mapping agent sends out discovery messages to the network, informing all routers in a multicast group of the RP to use:[edit protocols pim rp] auto-rp mapping;
- If the router combines the local RP function to send announcements and also perform the mapping function, configure the router as a local RP and include the auto-rp mapping statement at the [edit protocols pim rp] hierarchy level:[edit protocols pim rp] local { address 10.0.1.1; } auto-rp mapping;

All routers must also have a routable IP address on the lo0 interface:



interface lo0 {


unit 0 {


family inet {
address 127.0.0.1; # this address cannot be used by auto-rp


address 192.168.27.1 { # this example uses a private IP
address 
preferred;
}


}


}


}

You can include these statements at the following hierarchy levels (auto-RP announce is not supported in logical systems):

[edit protocols]
[edit routing-instances routing-instance-name protocols]
[edit logical-systems logical-system-name protocols] (all statements except auto-rp announce)
[edit logical-systems logical-system-name routing-instances routing-instance-name protocols] (all statements except auto-rp announce)

To verify auto-RP information, issue the show pim rps command :

user@host> show pim rps

RP address     Type    Holdtime    Timeout  Active groups   Group prefixes
192.168.5.1    auto-rp     150       123                1   224.0.0.0/4

Issue the show pim rps extensive command to see information about how an RP is learned, what groups it handles, and the number of groups actively using the RP:

user@host> show pim rps extensive

RP: 192.168.5.1
Learned from 192.168.5.1 via: auto-rp
Time Active: 00:34:29
Holdtime: 150 with 108 remaining
Device Index: 6
Subunit: 32769
Interface: pd-0/0/0.32769
Group Ranges:
        224.0.0.0/4
Active groups using RP:
        224.2.2.100
        total 1 groups active
Register State for RP:
Group      Source FirstHop        RP Address       StateRP address Type Holdtime Timeout

In the example, the RP at 192.168.5.1 was learned through auto-RP. The RP is able to support all groups in the 224.0.0.0/4 range (all possible groups). The local router has sent PIM control traffic for the 224.2.2.100 group to the RP.

Additionally, the presence of a Tunnel Physical Interface Card (PIC) in an RP router creates a de-encapsulation interface, which allows the RP to receive multicast traffic from the source. This interface is indicated by pd-0/0/0.32769.

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