First of all you must configure BGP router with router bgp command. To configure BGP router, you need AS number. AS number is an identification of autonomous system. BGP protocol uses the AS number for detecting whether the BGP connection is internal one or external one.
Enable a BGP protocol process with the specified asn. After this statement you can input any
BGP Commands. You can not create different BGP process under different asn without specifying
multiple-instance(see Multiple instance).
This command specifies the router-ID. If bgpd connects to zebra it gets interface and address information. In that case default router ID value is selected as the largest IP Address of the interfaces. When
router zebrais not enabled bgpd can't get interface information so
router-idis set to 0.0.0.0. So please set router-id by hand.