https://www.juniper.net/documentation/us/en/software/junos/is-is/topics/task/junos-software-router-is-system-identifier-configuring.html
Configuring an ISO System Identifier for the Router | Junos OS | Juniper Networks
For IS-IS to operate on the router, you can optionally configure a system identifier (system ID). The system identifier is commonly the media access control...
system identifierfor the