Hi,
Regarding the support, ideally it would be the Chassis SN used and the an install base has to be updated with the parts related to the Chassis Id registered to have the contract active for the rest of the parts.
However, for more information regarding the service contracts, Configuration services, suggest you to reach out to the local reseller or Partner.
The below links might help regarding the contracts and finding a reseller.
https://www.juniper.net/assets/us/en/local/pdf/service-descriptions/9060093-en.pdf
https://kb.juniper.net/InfoCenter/index?page=content&id=KB9839&actp=METADATA
Hope this information helps.
Regards,
Pradeep.
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