Configuring PIM Auto-RP

You can configure a mode-dynamic way of assigning RPs in a multicast network by means of auto-RP. When you configure auto-RP for a routing device, the routing device learns the address of the RP in the network automatically. Auto-RP operates in PIM version 1 and version 2.

Note: If the routing device receives auto-RP announcements split across multiple messages, the routing device loses the information in the previous part of the message as soon as the next part of the message is received.

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 routing devices as RP candidates. If the elected RP stops operating, one of the other preconfigured routing devices 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 routing device operates in auto-RP by specifying the following auto-RP options:

• Add the discovery option to enable the routing device 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 routing device to send announce messages in the network, advertising itself as a candidate RP. Routing devices configured with this option must also be configured as RPs, or announce messages are not sent.
• Add the mapping option to enable the routing device to perform the mapping function. If the routing device is also an RP, the mapping option also allows the routing device to send auto-RP announcements (mapping on an RP allows the routing device to perform both the announcement and mapping functions).

The routing device 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 routing device handles auto-RP discovery, announce, or mapping messages depends on whether the routing device is an RP (configured as local RP) or not. Table 1 shows how the routing device behaves depending on the local RP configuration.

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

1. 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 routing device to operate in sparse mode for most groups and dense mode for others. The default is to operate in sparse mode unless the routing device is specifically informed of a dense mode group.

2. 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.

3. Include the auto-rp statement at the [edit protocols pim rp] hierarchy level to configure auto-RP on each routing device in the group. There are four possible categories for each routing device.
   • If the routing device 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 routing device is a local RP, sends auto-RP announcements, and listens for auto-RP mapping messages, configure the routing device as a local RP and include the auto-rp announce statement to the routing device 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 routing device 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 routing devices announce their capabilities to support multicast groups, there must be a single routing device in the network to act as mapping agent. The mapping agent sends out discovery messages to the network, informing all routing devices in a multicast group of the RP to use:
     [edit protocols pim rp]auto-rp mapping;
   • If the routing device combines the local RP function to send announcements and also perform the mapping function, configure the routing device 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 routing devices must also have a routable IP address on the lo0 interface:

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

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

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

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:

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.

Configuring Auto-RP Mapping Agent Election

Auto-RP specifications state that mapping agents do not send mapping messages if they receive messages from a mapping agent with a higher IP address. This process is called mapping agent election. However, some vendors' mapping agents continue to announce mappings, even in the presence of higher-addressed mapping agents. In other words, some mapping agents will always send mapping messages.

For compatibility, you can suppress mapping messages with the mapping-agent-election statement. When this option is configured, the mapping agent will stop sending mapping messages if it receives messages from a mapping agent with a higher IP address.

The default auto-RP operation is to perform mapping agent election. To explicitly enable mapping agent election, include the mapping-agent-election statement for an auto-RP mapping agent:

Mapping message suppression is disabled with the no-mapping-agent-election statement. When this option is configured, the mapping agent will always send mapping messages even in the presence of higher-addressed mapping agents.

To explicitly disable mapping agent election for compatibility with other vendors' equipment, include the no-mapping-agent-election statement for an auto-RP mapping agent:

You can include these statements at the following hierarchy levels:

• [edit protocols pim rp]
• [edit routing-instances routing-instance-name protocols pim rp]
• [edit logical-systems logical-system-name protocols pim rp]
• [edit logical-systems logical-system-name routing-instances routing-instance-name protocols pim rp]