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### Instruction:
What is the purpose of the 'mpls ldp discovery hello interval' command in IOS XR?
### Response:
The 'mpls ldp discovery hello interval' command is used to configure the frequency at which LDP hello messages are sent. Hello messages are used to establish and maintain LDP sessions. A lower hello interval means faster detection of topology changes and quicker LDP convergence, but also results in more LDP traffic. The hello interval should be set to a lower value than the hello holdtime.
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