# Configuring Timing

You can use the timing source command to configure three timing sources for the system. These sources are known as the primary, secondary, and tertiary sources. The system periodically polls the status of the current timing source. If the system discovers that the current source has become unavailable, it polls the timing source you specified as next in line. If this source is available, it switches to this source; if not, it then polls the next source in line. If the lowest source is unavailable, the system maintains the SRP clock as the source.

If you enable auto-upgrade, in the event of a source failure, the system—after switching to a lower source—polls all higher configured sources and automatically switches back to the highest timing source when that source becomes available.

The timing select command enables you to specify which source (primary, secondary, or tertiary) the system is to use by default. The system will never attempt to upgrade to a source higher than the selected source.

timing disable-auto-upgrade

- Use to disable the auto-upgrade feature of the system’s timing selector.
- The system starts out by setting the operational timing selector to the administratively configured selector. See the timing select command.
- Example
  host1(config)#timing disable-auto-upgrade
- Use the no version to restore the factory default, which is auto-upgrade enabled.
- See timing disable-auto-upgrade.

timing select

- Use to specify which of the configured timing sources is used by default.
- Primary timing source is preferred over secondary, and secondary is preferred over tertiary. See the timing source command.
- If you enable the auto-upgrade feature, the system does not try to upgrade beyond the administratively configured selector.
- Example
  host1(config)#timing select secondary
- There is no no version.
- See timing select.

timing source

- Use to specify how the SRP module exchanges timing signals with an interface.
- You can specify primary, secondary, and tertiary timing sources.
- You can specify one external source received on an I/O module or IOA other than the SRP I/O module or SRP IOA.
- You can specify two or more internal sources or external sources received through the SRP I/O module or SRP IOA external timing ports.
- On the E120 and E320 routers, you can specify sonet for only two of the available three timing sources (primary, secondary, or tertiary).
- The available sources to choose are:
  - ds1—DS1 interface
  - ds3—DS3 interface
  - e1—E1 interface
  - e3—E3 interface
  - sonet—SONET interface
  - internal—Internal system controller (SC) oscillator
  - line—External timing input on SRP module
- Example
  host1#timing source secondary sonet 3/0
- There is no no version.
- See timing source.

## Monitoring Timing

Use the show timing command to view the timing settings for the system.

show timing

- Use to display the timing settings and the operational status of the system timing.
- If a timing source fails, the system uses the next time source in the hierarchy, and a message appears in the system log at the warning level. If auto-upgrade is enabled, the system upgrades to a higher-priority timing source when one becomes available, and a message appears in the system log at the notice level.
- Example

      host1#show timing
      timing: tertiary (failover from primary)
      primary: external SC E1 (A) (ERROR)
      secondary: ds3 3/0 (ERROR)
      tertiary: internal SC oscillator (ok)
      auto-upgrade enabled

- See show timing.