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### Instruction:
What is the purpose of the 'bgp bestpath med missing-as-worst' command in IOS XR BGP configuration?
### Response:
The 'bgp bestpath med missing-as-worst' command is used to treat routes without a MED attribute as having the highest possible MED value for best path selection. By default, if a route is missing the MED attribute, it is treated as having a MED of 0, making it the most preferred route. This command changes the behavior to make routes without a MED the least preferred.
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