H3C Technologies H3C SR8800 - Manual (Page 211)

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• Route-refresh
They have the same header.
Figure 71 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 72 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.
• BGP identifier—An IP address that identifies the BGP router.
• Opt Parm Len (Optional Parameters Length)—Length of optional parameters, which is set to 0 if no
optional parameter is available.
• Optional parameters—Used for multiprotocol extensions, and other functions.