H3C Technologies H3C S12500 Series Switches - Manual (Page 209)

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• Notification—A Notification message is sent when an error is detected. The BGP connection is
closed immediately after sending it.
BGP path attributes
BGP path attributes are a group of parameters carried in update messages. They give detailed route
attributes information that can be used for route filtering and selection.
• ORIGIN
The ORIGIN attribute defines the origin of routing information (how a route became a BGP route).
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. The
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 to reach the
destination. When a route is advertised from the local AS to another AS, each passed AS number
is added 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 73 , the number of the
AS closest to the receiver's AS is leftmost.
{
AS_SET—Requires no sequence when arranging AS numbers.
Figure 73 AS_PATH attribute
The AS_PATH attribute can be used to implement the following functions:
{
Avoid routing loops—A BGP router does not receive routes containing the local AS number to
avoid routing loops.