Understanding the BGP Origin Code Attribute
Understanding the BGP Origin Code Attribute
The BGP Origin Code is a mandatory attribute attached to BGP routes, indicating the origin of a particular route in the BGP table. It specifies how a route was introduced into BGP and provides crucial information about its source. There are three possible origin codes:
- IGP (Interior Gateway Protocol): Routes marked with the IGP origin code were learned via an Interior Gateway Protocol like OSPF (Open Shortest Path First) or RIP (Routing Information Protocol) within the same Autonomous System (AS). These routes are typically manually configured or learned through an IGP and are considered the most trustworthy.
- EGP (Exterior Gateway Protocol): EGP-originated routes were learned via an Exterior Gateway Protocol, an older protocol used before BGP’s dominance. However, in modern networks, EGP-originated routes are rarely encountered as BGP has largely replaced older exterior protocols.
- Incomplete: Routes marked as Incomplete lack information about their origin. This code is typically assigned to routes redistributing into BGP from other routing protocols or statically configured.
Significance of the Origin Code Attribute
Route Selection Process: BGP routers utilize multiple attributes, including the Origin Code, to determine the best path for forwarding packets. The Origin Code is influential in the BGP best path selection process.
Routing Policy and Decision Making: Network administrators use the Origin Code as a component of routing policies. For instance, they prefer routes learned through IGP over those learned via redistribution from other protocols.
Troubleshooting and Analysis: Analyzing the Origin Code helps in diagnosing routing issues. It provides insights into how routes were introduced into BGP and aids in identifying potential misconfigurations or inconsistencies.
Implementing the Origin Code Attribute
BGP routers automatically assign an origin code to each route based on its source. However, network engineers can manually modify the origin code using route maps or policies. Careful consideration and understanding of the network’s design and requirements are essential when manipulating the Origin Code attribute.
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