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Is BGP4 packet directly encapsulated in IP datagram for transmission?
BGP4 packets are directly encapsulated in IP datagrams for transmission. The BGP4 message is carried by tcp, and the port number is 179. Whether ospf carried on the ip layer or is-is protocol directly carried on the link layer, there are confirmation messages of routing information. OSPF is Sack, and Isis is PSNP.

Therefore, although ip is an unreliable protocol, you can know whether the route has reached the opposite end by confirming the message, otherwise it will be retransmitted. Bgp has no acknowledgement message, so if you want to know whether the published routing information is received by neighbors, you must rely on the acknowledgement and timeout retransmission mechanism of TCP protocol.

BGP is mainly used for interconnection between Internet AS (autonomous systems), and its main function is to control the propagation of routes and select the best routes. China Unicom, China Telecom, China Tietong and some large private IDC operators all have AS numbers, and most major domestic network operators realize multi-line interconnection with their AS numbers through BGP protocol.

Using this scheme to realize multi-line interconnection, IDC needs to apply for its own IP address segment and AS number in CNNIC (China Internet Information Center) or APNIC (Asia-Pacific Network Information Center), and then broadcast the IP address segment to the networks of other network operators through BGP protocol. After interconnection using BGP protocol, all backbone routing equipment of network operators will judge the best route of IP section of IDC computer room, so as to ensure high-speed access for users of different network operators.