R21xx-HP FlexFabric 11900 Layer 3 IP Routing Configuration Guide

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• Keepalive—BGP sends Keepalive messages between peers to maintain connectivity.
• Route-refresh—BGP sends a Route-refresh message to request the routing information of a specified
address family from a peer.
• Notification—BGP sends a Notification message upon detecting an error and immediately closes
the connection.
BGP path attributes
BGP uses the following path attributes in update messages for route filtering and selection:
• ORIGIN
The ORIGIN attribute specifies the origin of BGP routes. This attribute has the following types:
{ IGP—Has the highest priority. Routes generated in the local AS have the IGP attribute.
{ EGP—Has the second highest priority. Routes obtained through EGP have the EGP attribute.
{ INCOMPLETE—Has the lowest priority. The source of routes with this attribute is unknown.
Routes redistributed from other routing protocols have the INCOMPLETE attribute.
• AS_PATH
The AS_PATH attribute identifies the ASs through which a route has passed. Before advertising a
route to another AS, BGP adds the local AS number into the AS_PATH attribute, so the receiver can
determine ASs to route the message back.
The AS_PATH attribute has the following types:
{ AS_SEQUENCE—Arranges AS numbers in sequence. As shown in Figure 44, the number of the
AS closest to the receiver's AS is leftmost.
{ AS_SET—Arranges AS numbers randomly.