H3C Technologies H3C SecPath F1000-E - Manual (Page 328)

2
• Open
• Update
• Notification
• Keep-alive
• Route-refresh
They have the same header, as shown below:
Figure 1 BGP message header
• Marker: The 16-byte field is used to delimit BGP messages. The Marker must be all ones.
• Length: The 2-byte unsigned integer indicates the total length of the message.
• Type: This 1-byte unsigned integer indicates the type code of the message. The following type codes
are defined: 1–Open, 2-Update, 3-Notification, 4–Keepalive, and 5–Route-refresh. The former four
are defined in RFC1771, and the last one is defined in RFC2918.
Open
After a TCP connection is established, the first message sent by each side is an Open message for peer
relationship establishment. An Open message contains the following fields:
Figure 2 BGP open message format
• Version: This 1-byte unsigned integer indicates the protocol version number. The current BGP version
is 4.
• My autonomous system: This 2-byte unsigned integer indicates the Autonomous System number of
the sender.
• Hold time: When establishing a peer relationship, two parties negotiate an identical hold time. If
no Keepalive or Update is received from a peer within the hold time, the BGP connection is
considered down.