H3C Technologies H3C SecPath F1000-E - Manual (Page 330)

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• 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 5 BGP Route-refresh message format
• AFI: Address family identifier.
• Res: Reserved. Set to 0.
• SAFI: Subsequent Address Family Identifier.
BGP Path Attributes
Classification of path attributes
Path attributes fall into four categories:
• 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.
• Well-known discretionary: Can be recognized by all BGP routers and optional to be included in
every update message as needed.
• 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.
• Optional non-transitive: If a BGP router does not support this attribute, it will not advertise routes
with this attribute.
The usage of each BGP path attribute is described in the following table.
Table 1 Usage of BGP path attributes
Name Category
ORIGIN Well-known mandatory
AS_PATH Well-known mandatory
NEXT_HOP Well-known mandatory
LOCAL_PREF Well-known discretionary
ATOMIC_AGGREGATE Well-known discretionary
AGGREGATOR Optional transitive
COMMUNITY Optional transitive