3Com S7902E, Руководство по настройке

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z
NLRI (Network Layer Reachability Information): Each feasible route is represented as <length,
prefix>.
Notification
A Notification message is sent when an error is detected. The BGP connection is closed immediately
after sending it. The Notification message format is shown below:
Figure 1-4 BGP Notification message format
z
Error code: Type of Notification.
z
Error subcode: Specific information about the nature of the reported error.
z
Data: Used to diagnose the reason for the Notification. The contents of the Data field depend upon
the Error Code and Error Subcode. Erroneous part of data is recorded. The Data field length is
variable.
Keepalive
Keepalive messages are sent between peers to maintain connectivity. Its format contains only the
message header.
Route-refresh
A Route-refresh message is sent to a peer to request the resending of the specified address family
routing information. Its format is shown below:
Figure 1-5 BGP Route-refresh message format
z
AFI: Address family identifier.
z
Res: Reserved. Set to 0.
z
SAFI: Subsequent Address Family Identifier.
BGP Path Attributes
Classification of path attributes
Path attributes fall into four categories:
z
Well-known mandatory: Must be recognized by all BGP routers and must be included in every
Update message. Routing information errors occur without this attribute.
z
Well-known discretionary: Can be recognized by all BGP routers and optional to be included in
every Update message as needed.
z
Optional transitive: Transitive attribute between ASs. A BGP router not supporting this attribute can
still receive routes with this attribute and advertise them to other peers.