H3C S7500E Series Ethernet Switches Operation Manual

Operation Manual – IPv4 Routing
H3C S7500E Series Ethernet Switches Chapter 5 BGP Configuration
5-5
V. Keepalive
Keepalive messages are sent between peers to maintain connectivity. Its format
contains only the message header.
VI. 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 5-5 BGP Route-refresh message format
AFI: Address Family Identifier.
Res: Reserved. Set to 0.
SAFI: Subsequent Address Family Identifier.
5.1.2 BGP Path Attributes
I. 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 error occurs 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.
z 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 5-1 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