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Example: Configuring the Multicast Forwarding Cache

Requirements

Before you begin:

• Configure the router interfaces. See the Junos® OS Network Interfaces.
• Configure an interior gateway protocol. See the Junos OS Routing Protocols Configuration Guide.
• Configure a multicast protocol. This feature works with the following multicast protocols:
  • DVMRP
  • PIM-DM
  • PIM-SM
  • PIM-SSM

Overview

• forwarding-cache—Specifies how forwarding entries are aged out and how the number of entries is controlled.
• timeout—Specifies an idle period after which entries are aged out and removed from inet.1. You can specify a timeout in the range from 1 through 720 minutes.
• threshold—Enables you to specify threshold values on the forwarding cache to suppress (suspend) entries from being added when the cache entries reach a certain maximum and begin adding entries to the cache when the number falls to another threshold value. By default, no threshold values are enabled on the routing device.

  The suppress threshold suspends the addition of new multicast forwarding cache entries. If you do not specify a suppress value, multicast forwarding cache entries are created as necessary. If you specify a suppress threshold, you can optionally specify a reuse threshold, which sets the point at which the device resumes adding new multicast forwarding cache entries. During suspension, forwarding cache entries time out. After a certain number of entries time out, the reuse threshold is reached, and new entries are added. The range for both thresholds is from 1 through 200,000. If configured, the reuse value must be less than the suppression value. If you do not specify a reuse value, the number of multicast forwarding cache entries is limited to the suppression value. A new entry is created as soon as the number of multicast forwarding cache entries falls below the suppression value.

  Beginning with Junos OS 12.2, you can optionally configure a warning threshold so the device can log warning messages in the system log when a certain number of entries have been added to the cache. It is helpful to review the system log messages for troubleshooting purposes and to detect if an excessive amount of entries are filling up the cache. When the number of entries exceeds the configured warning threshold, but remains below the suppress threshold, traffic continues to be accepted, and the device logs warning messages in the system log.

  The warning threshold is a percentage of the suppress threshold, so you must configure the suppress threshold to configure the warning threshold. The range for the warning threshold is 1 through 100 percent. In this example, you set a warning threshold of 40 percent. With a configured suppress value of 150,000, and a warning threshold of 40 percent, the device logs a warning message in the system log after it receives 60,000 entries.

Configuration

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

Step-by-Step Procedure

1. Configure the maximum size of the forwarding cache.

   [edit routing-options multicast forwarding-cache]user@host# set threshold suppress 150000

2. Configure the amount of time (in minutes) entries can remain idle before being removed.

   [edit routing-options multicast forwarding-cache]user@host# set timeout 60

3. Configure the size of the forwarding cache when suppression stops and new entries can be added.

   [edit routing-options multicast forwarding-cache]user@host# set threshold reuse 70000
4. (Optional) Configure when warning messages are logged in the system log.
   [edit routing-options multicast forwarding-cache]user@host# set threshold log-warning 40
5. If you are done configuring the device, commit the configuration.
   [edit routing-options multicast forwarding-cache]user@host# commit

Results

Confirm your configuration by entering the show routing-options command.

Verification

Confirm that the configuration is working properly.

• Displaying Entries in the IP Multicast Forwarding Table
• Verifying the IP Multicast Forwarding Cache Configuration

Displaying Entries in the IP Multicast Forwarding Table

Purpose

Verify that entries are in the IP multicast forwarding table and that the configured timeout value is displayed.

Action

From operational mode, enter the show multicast route extensive command.

Family: INET
Group: 232.0.0.1
    Source: 11.11.11.11/32
    Upstream interface: fe-0/2/0.200
    Downstream interface list:
        fe-0/2/1.210
    Downstream interface list rejected by CAC:
        fe-0/2/1.220
    Session description: Source specific multicast
    Statistics: 0 kBps, 0 pps, 0 packets
    Next-hop ID: 337
    Upstream protocol: PIM
    Route state: Active
    Forwarding state: Forwarding
    Cache lifetime/timeout: 60 minutes
Wrong incoming interface notifications: 0

Verifying the IP Multicast Forwarding Cache Configuration

Purpose

Verify that the suppress threshold, reuse value, and warning threshold have been configured correctly.

Action

From operation mode, enter the show multicast forwarding-cache statistics command.

Instance: master Family: INET
Suppress Threshold                      150000
Reuse Value                              70000
Warning Threshold                           40
Currently Used Entries                      17