Local Preference BGP vs. Preference BGP

Attribute	Local Preference BGP	Preference BGP
Definition	Used to influence outbound traffic within an autonomous system	Used to influence inbound traffic from external autonomous systems
Scope	Applies within the same autonomous system	Applies between different autonomous systems
Value Range	0-100	0-255
Default Value	100	100
Path Selection	Used after the AS_PATH attribute	Used before the AS_PATH attribute

Introduction

Border Gateway Protocol (BGP) is a crucial routing protocol used in the internet to exchange routing information between different networks. BGP allows routers to make decisions on the best path to reach a destination network based on various attributes. Two important attributes in BGP are Local Preference BGP and Preference BGP. In this article, we will compare the attributes of Local Preference BGP and Preference BGP to understand their differences and similarities.

Local Preference BGP

Local Preference BGP is an attribute used within an autonomous system (AS) to influence the outbound traffic flow. It is a non-transitive attribute, meaning it is not passed on to other ASes. Local Preference is used to determine the preferred exit point for traffic leaving an AS. The higher the Local Preference value, the more preferred the route is. Local Preference is typically set by the network administrator within the AS and is used to control the flow of traffic within the network.

Local Preference BGP is often used in scenarios where an AS has multiple exit points to other ASes. By setting different Local Preference values for each exit point, the network administrator can control which exit point is preferred for outbound traffic. This allows for better traffic engineering within the AS and can help optimize network performance.

Preference BGP

Preference BGP, on the other hand, is an attribute used to influence the inbound traffic flow from external ASes. It is also a non-transitive attribute and is not passed on to other ASes. Preference BGP is used by an AS to signal to its neighboring ASes the preferred route for inbound traffic. The higher the Preference BGP value, the more preferred the route is for incoming traffic.

Preference BGP is typically set by the network administrator of the receiving AS to influence the routing decisions made by neighboring ASes. By setting a higher Preference BGP value for a specific route, the receiving AS can signal to its neighbors that this route is the preferred path for inbound traffic. This can help optimize the inbound traffic flow and improve network performance.

Comparison

While Local Preference BGP and Preference BGP serve similar purposes in influencing traffic flow, they operate at different levels within the BGP routing process. Local Preference BGP is used within an AS to control outbound traffic flow, while Preference BGP is used between ASes to influence inbound traffic flow. Both attributes are non-transitive and are not passed on to other ASes, making them internal to the respective AS.

Another key difference between Local Preference BGP and Preference BGP is the direction in which they influence traffic flow. Local Preference BGP affects outbound traffic leaving an AS, while Preference BGP affects inbound traffic coming into an AS. By using both attributes in conjunction, network administrators can effectively control both outbound and inbound traffic flows to optimize network performance.

Conclusion

In conclusion, Local Preference BGP and Preference BGP are important attributes in BGP routing that allow network administrators to influence traffic flow within and between ASes. While Local Preference BGP is used within an AS to control outbound traffic flow, Preference BGP is used between ASes to influence inbound traffic flow. By understanding the differences and similarities between these attributes, network administrators can effectively optimize their network performance and ensure efficient routing of traffic.