Bgp Path Attributes - HP MSR2000 series Configuration Manual

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 specified address family routing information.
Figure 75 BGP route-refresh message format
AFI—Address family identifier.
•
• Res—Reserved; set to 0.
SAFI—Subsequent address family identifier.
•

BGP path attributes

Path attributes classification
BGP path attributes are a group of parameters encapsulated in the path attributes field of update
messages. They give detailed route attributes information that can be used for route filtering and
selection.
Path attributes fall into the following categories:
• Well-known mandatory—Must be recognized by all BGP routers and be included in every Update
message. Routing information errors occur without this attribute.
Well-known discretionary—Can be recognized by all BGP routers and optionally 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 7 Usage of BGP path attributes
Name
ORIGIN
AS_PATH
NEXT_HOP
LOCAL_PREF
ATOMIC_AGGREGATE
AGGREGATOR
COMMUNITY
MULTI_EXIT_DISC (MED)
ORIGINATOR_ID
Category
Well-known mandatory
Well-known mandatory
Well-known mandatory
Well-known discretionary
Well-known discretionary
Optional transitive
Optional transitive
Optional non-transitive
Optional non-transitive
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