Youtube Video

Summary published at 10/9/2024

👋 Advanced Path Manipulation in BGP

📈 This video is essential for network engineers and those preparing for networking interviews.

🛣️ To understand path manipulation, one must first grasp best path selection in BGP, which relies on various attributes.

🔍 The first attribute is Next Hop. It checks if the next hop IP address is reachable. If both next hops are reachable, the router checks the next attribute.

⚖️ The second attribute is Weight. BGP does not carry weight information in updates, but self-advertised prefixes have a weight of 32768, while received prefixes have a weight of 0.

🏷️ The third attribute is Local Preference (LP). This is only carried for iBGP neighbors. If LP values are the same, the router checks the next attribute.

🔗 The fourth attribute is AS Path. A shorter AS path is preferred. If AS paths are equal, the router checks the next attribute.

📜 The fifth attribute is Origin Code. It can be I (IGP), E (EGP), or ? (incomplete). I is preferred over E.

📊 The sixth attribute is Metric. BGP does not carry metric information in updates.

🌐 The seventh attribute is External vs. Internal. External paths are preferred over internal paths.

💰 The eighth attribute is IGP Cost to reach the next hop. Lower costs are preferred.

⏳ The ninth attribute is Oldest Path. The oldest path is preferred if all other attributes are equal.

🔢 The tenth attribute is Router ID. The router with the lower ID is preferred.

🔄 Path Manipulation Techniques:

  • Using Weight to influence path selection.
  • Using Local Preference to prefer certain paths.
  • Using AS Path Prepend to manipulate path selection.
  • Using Origin Code to influence path selection.
  • Using Metric for outgoing path selection.

📊 Load Balancing: BGP can perform load balancing if the IGP cost to reach the next hop is the same.

🔄 Aggregation in BGP: This is used to summarize multiple prefixes into a single route to reduce the size of the routing table.

📜 Community Attribute: This is used for tagging and path manipulation. It includes predefined communities like No Export, No Advertise, and Internet.

🔑 Key Takeaways:

  • Understand the attributes used in BGP for path selection.
  • Learn how to manipulate paths using various techniques.
  • Know the importance of aggregation and community attributes in BGP.

📅 Stay tuned for more detailed discussions in future videos!

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