Configuring the Drop Timeout Period on Multilink and Link Services Logical Interfaces
By default, the drop timeout parameter is disabled. You can configure a drop timeout value to provide a recovery mechanism if individual links in the multilink or link services bundle drop one or more packets. Drop timeout is not a differential delay tolerance setting, and does not limit the overall latency. However, you need to make sure the value you set is larger than the expected differential delay across the links, so that the timeout period does not elapse under normal jitter conditions, but only when there is actual packet loss. You can configure differential delay tolerance for link services interfaces only. For more information, see Configuring Differential Delay Alarms on Link Services Physical Interfaces with MLFR FRF.16.
To configure the drop timeout value, include the drop-timeout statement:
You can include this statement at the following hierarchy levels:
- [edit interfaces interface-name unit logical-unit-number]
- [edit logical-systems logical-system-name interfaces interface-name unit logical-unit-number]
For link services interfaces, you also can configure the drop timeout value at the physical interface level by including the drop-timeout statement at the [edit interfaces ls-fpc/pic/port:channel mlfr-uni-nni-bundle-options] hierarchy level:
By default, the drop timer has a value of 500 ms for bundles greater than or equal to the T1 bandwidth value, and 1500 ms for other bundles. Any CLI-configured value overrides these defaults. Values can range from 1 through 2000 milliseconds. Values less than 5 milliseconds are not recommended, and a configured value of 0 reverts to the default value of 2000 milliseconds.
 | Note: For multilink or link services interfaces, if a packet or fragment encounters an error condition and is destined for a disabled bundle or link, it does not contribute to the dropped packet and frame counts in the per-bundle statistics. The packet is counted under the global error statistics and is not included in the global output bytes and output packet counts. This unusual accounting happens only if the error conditions are generated inside the multilink interface, not if the packet encounters errors on the wire or elsewhere in the network. |
If you configure the drop-timeout statement with a value of 0, it disables any resequencing by the PIC for the specified class of MLPPP traffic. Packets are forwarded with the assumption that they arrived in sequence, and forwarding of fragmented packets is disabled for all classes. Fragments dropped as a result of this setting will increment the counter at the class level.
Alternatively, you can configure the drop-timeout statement at the [edit class-of-service fragmentation-maps map-name forwarding-class class] hierarchy level. The behavior and the default and range values are identical, but the setting applies only to the specified forwarding class. Configuration at the bundle level overrides configuration at the class-of-service level.
By default, compression of the inner PPP header in the MLPPP payload is enabled. To disable compression, include the disable-mlppp-inner-ppp-pfc statement at the [edit interfaces interface-name unit logical-unit-number] hierarchy level. For example:
For more information about CoS configuration, see the Junos OS Class of Service Configuration Guide. You can view the configured drop-timeout value and the status of inner PPP header compression by issuing the show interfaces interface-name extensive command.
