(Optional) Configuring SPT Switchover Conditions

PIM-SM enables a Rendezvous Point (RP) or a receiver's Designated router (DR) to trigger a shortest path tree (SPT) switchover when the rate of IPv6 multicast packets is high. You can configure the SPT switchover conditions and the interval for checking the rate at which IPv6 multicast data is forwarded on the receiver's DR.

Context

During the forwarding of IPv6 multicast packets in a PIM-SM domain, only one rendezvous point tree (RPT) is set for each multicast group. All multicast sources encapsulate multicast data in Register messages, and then unicast the Register messages to the RP. After receiving the Register messages, the RP decapsulates them and then forwards multicast data along the RPT to group members.

Forwarding IPv6 multicast data along an RPT has the following disadvantages:

The source's DR and the RP need to frequently encapsulate and decapsulate messages.
The forwarding path may not be the shortest path from the source to receivers.
Heavy IPv6 multicast traffic increases the load of the RP, which easily causes a fault.

The solutions to the preceding disadvantages are as follows:

SPT switchover triggered by the RP

The RP sends a Join message to the source to create an IPv6 multicast route along the shortest path from the source's DR to the RP to build an MDT. Then, subsequent packets are forwarded along this path.
SPT switchover triggered by the receiver's DR

The receiver's DR checks the forwarding rate of IPv6 multicast data. If the receiver's DR finds that the rate exceeds the threshold, the receiver's DR triggers the SPT switchover immediately. The receiver's DR sends a Join message to the source to set up an IPv6 multicast route along the shortest path from the source's DR to the receiver's DR. Subsequent IPv6 multicast packets are forwarded along this path.

By default, the RP triggers the SPT switchover immediately after receiving the first Register message, and the receiver's DR triggers the SPT switchover immediately after receiving the first IPv6 multicast data packet. The router can work normally with default control parameters. You are allowed to adjust SPT switchover parameters based on the specific networking environment.

If there is no special requirement, default parameter values are recommended.

Procedure

Run system-view
The system view is displayed.
Configure a basic numbered ACL6 or a naming ACL6 as needed.
- Configure a basic numbered ACL6.
  1. Run acl ipv6 [ number ] basic-acl6-number [ match-order { auto | config } ]
    A basic numbered ACL6 is created, and the basic numbered ACL6 view is displayed.
  2. Run rule [ rule-id ] [ name rule-name ] { deny | permit } [ fragment | source { source-ipv6-address prefix-length | source-ipv6-address/prefix-length | any } ] ^*
    Rules are configured for the basic numbered ACL6.
- Configure a naming ACL6.
  1. Run acl ipv6 name acl6-name basic [ match-order { auto | config } ]
    A naming ACL6 is created, and the naming ACL6 view is displayed.
  2. Run rule [ rule-id ] [ name rule-name ] { deny | permit } [ fragment | source { source-ipv6-address prefix-length | source-ipv6-address/prefix-length | any } ] ^*
    Rules are configured for the naming ACL6.
Run the rule command and set the source parameter to a multicast group range to which the specified rate threshold applies.
Run quit
Return to the system view.
Run pim-ipv6
The IPv6 PIM view is displayed.
Run spt-switch-threshold { traffic-rate | infinity } [ group-policy { basic-acl6-number |acl6-name acl6-name } [ order order-value ] ]
SPT switchover conditions are configured.

This command takes effect on all routers that may become the receiver's DR, but does not take effect on the RP.
- traffic-rate: specifies the threshold for the rate of IPv6 multicast data. When the rate of IPv6 multicast data exceeds the threshold, the receiver's DR triggers the SPT switchover.
  
  The configuration in Step 4 makes sense only after traffic-rate is set.
- infinity: indicates that the receiver's DR never triggers the SPT switchover. IPv6 multicast data can be transmitted to receivers only along the RPT.
- group-policy { basic-acl6-number | acl6-name acl6-name }: specifies the range of multicast groups to which the threshold is applied. By default, the threshold is applicable to all multicast groups.
- order order-value: adjusts the order of the IPv6 ACLs in the group-policy list. If a group matches multiple IPv6 ACLs, the threshold is selected in the order specified by order-value.
- If no ACL is configured, the device applies the specified rate threshold to all multicast groups.
- If an ACL is configured, the device uses configured ACL rules to determine whether to apply the specified rate threshold to a multicast group.
  - If a multicast group matches an ACL rule and the action is permit, the device applies the specified rate threshold to this group.
  - If a multicast group matches an ACL rule and the action is deny, the device performs an SPT switchover immediately after the SPT switchover condition is met.
  - If a multicast group does not match any ACL rule or if the specified ACL does not exist or does not contain rules, the device performs an SPT switchover immediately after the SPT switchover condition is met.
(Optional) Run timer spt-switch interval
The interval for checking the forwarding rate of multicast packets is set.
Run commit
The configuration is committed.