H3C S5600 Series Operation Manual page 388

Operation Manual – Routing Protocol
H3C S5600 Series Ethernet Switches
Figure 5-3 BGP Update message format
An Update message can advertise a group of reachable routes with the same path
attribute. These routes are set in the NLRI (network layer reachability information)
field. The Path Attributes field carries the attributes of these routes, according to
which BGP chooses routes. An Update message can also carry multiple unreachable
routes. The withdrawn routes are set in the Withdrawn Routes field.
The fields of an Update message are described as follows.
Unfeasible Routes Length: Length (in bytes) of the unreachable routes field. A
value of 0 indicates that there is no Withdrawn Routes filed in the message.
Withdrawn Routes: Unreachable route list.
Total Path Attribute Length: Length (in bytes) of the Path Attributes field. A value
of 0 indicates that there is no Path Attributes filed in the message.
Path Attributes: Attributes list of all the paths related to NLRI. Each path attribute
is a TLV (Type-Length-Value) triplet. In BGP, loop avoidance, routing, and
protocol extensions are implemented through these attribute values.
NLRI (Network Layer Reachability Information): Contains the information such
reachable route suffix and the corresponding suffix length.
IV. Notification
When BGP detects error state, it sends the Notification message to peers and then
tear down the BGP connection.
message.
Figure 5-4 BGP Notification message format
The fields of a Notification message are described as follows.
Error Code: Error code used to identify the error type.
Error Subcode: Error subcode used to identify the detailed information about the
error type.
Figure 5-4 shows the format of an Notification
5-4
Chapter 5 BGP Configuration