# Perform Fault-Tolerant Lookups

TIBCO Enterprise Message Service can perform fault-tolerant JNDI lookups. If the active server fails and the standby server becomes active, the JNDI provider automatically uses the new active server for JNDI lookups. You accomplish this by providing multiple URLs in the `Context.PROVIDER_URL` property when creating the `InitialContext`. Specify more than one URL separated by commas (,) in the property.

## Example

The following illustrates setting up the `Context.PROVIDER_URL` property with the URLs of a primary EMS server on the machine named `emshost` and a secondary EMS server on the machine named `backuphost`.

    env.put(Context.PROVIDER_URL, "tibjmsnaming://jmshost:7222,tibjmsnaming://backuphost:7222");

Assuming `emshost` starts out as active, if at any time it fails the JNDI provider automatically switches to the EMS server on the host `backuphost` for JNDI lookups. If `emshost` is repaired and restarted, it then becomes the standby EMS server.

## Limitations of Fault-Tolerant JNDI Lookups

Fault-tolerant JNDI lookups do not occur in scenarios:

- When using full URL names in argument to the lookup method.
- When looking up an object that has been bound into a foreign naming/directory service such as LDAP.

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