After preferred values are set for BGP routes, the route with the greatest value is preferred
when multiple routes to the same destination exist in the BGP routing table.
l
Local_Pref
The Local_Pref attribute has the same function as the preferred value of a route. If both of
them are configured for a BGP route, the preferred value takes precedence over the
Local_Pref attribute.
l
MED
The MED attribute is used to determine the optimal route for traffic that enters an AS. The
route with the smallest MED value is selected as the optimal route if the other attributes of
the routes are the same.
l
Next_Hop
BGP route selection can be flexibly controlled by changing Next_Hop attributes for routes.
l
AS_Path
The AS_Path attribute is used to prevent rooting loops and control route selection.
Pre-configuration Tasks
Before configuring BGP route attributes, complete the following tasks:
l
Configuring IP addresses for interfaces to ensure IP connectivity between neighboring
nodes
l
Configuring Basic BGP Functions
Data Preparation
To configure BGP route attributes, you need the following data.
No.
Data
1
AS number
2
BGP preference value
3
Local_Pref value
4
MED value
7.4.2 Configuring the BGP Preference
Setting the BGP preference can affect route selection between BGP routes and other routing
protocols' routes.
Context
Multiple dynamic routing protocols can be run on a device at the same time. In this case, there
is a problem of route sharing and selecting among routing protocols. To address this problem,
the system sets a default preference for each routing protocol. If different protocols have routes
to the same destination, the protocol with the highest preference is selected to forward IP packets.
Perform the following steps on a device running BGP.
S6700 Series Ethernet Switches
Configuration Guide - IP Routing
7 BGP Configuration
Issue 01 (2012-03-15)
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