Mastering Network Traffic Control: A Guide to Influencing Traffic with BGP Attributes

As a network engineer, one of the most powerful tools in your arsenal for managing and controlling network traffic is Border Gateway Protocol (BGP). BGP allows you to influence the flow of traffic within and across autonomous systems by manipulating various attributes associated with route advertisements. In this article, we'll delve into the intricacies of BGP attributes and explore how you can use them effectively to shape and optimize network traffic according to your organization's needs.

Before we dive into the practical aspects of influencing network traffic, let's first establish a solid understanding of BGP attributes. BGP routes are accompanied by a set of attributes that describe various characteristics of the route. These attributes are crucial for BGP routers to make routing decisions. Some of the key BGP attributes include:

1. AS_Path: This attribute specifies the sequence of autonomous systems that a route has traversed. It helps prevent routing loops and influences the selection of the best path.
2. Next Hop: The Next Hop attribute indicates the IP address of the next router along the path to the destination network.
3. Weight: Weight is a Cisco-specific attribute used to influence the preferred route for outbound traffic from a router.
4. Local Preference: Local Preference is an attribute used to influence the outbound routing decision within an autonomous system (AS).
5. Multi-Exit Discriminator (MED): MED is used to influence the inbound routing decision when multiple entry points exist into an AS.
6. Community: Communities are tags that can be attached to routes to influence routing policies within and across ASes.

Now that we have a basic understanding of BGP attributes, let's explore how we can leverage them to influence network traffic:

Inbound Traffic Management: Using attributes like AS_Path Prepending or MED, you can influence how traffic enters your network from external peers or providers. This allows you to control which entry points traffic takes into your network, thereby optimizing inbound traffic flows.

router bgp 65001
  neighbor 203.0.113.1 remote-as 65002
  neighbor 203.0.113.1 route-map PrependAS out
  
route-map PrependAS permit 10
  match as-path 1
  set as-path prepend 65001 65001 65001 

This is an actual prepending, here we tell other AS how many ASes traffic would travesre until it reaches us. Traffic would choose path with less ASes.

clear ip bgp 203.0.113.1 soft

Here we gently clearing current sessions so traffic gently would choose new path 
when current sessions end

Outbound Traffic Control: By adjusting attributes like Local Preference or Weight, you can influence the selection of outbound routes from your network. This is particularly useful for directing traffic towards preferred egress points or optimizing the use of available network resources.

router bgp 65001
  neighbor 192.0.2.1 remote-as 65002
  neighbor 192.0.2.1 route-map OutboundTrafficControl out
  
ip prefix-list Network-Prefixes seq 10 permit 10.0.0.0/24
route-map OutboundTrafficControl permit 10
  match ip address prefix-list Network-Prefixes
  set local-preference 200

Default local-preference 100. Traffic would choose path with higher local preference

Policy-based Routing: BGP communities provide a mechanism for implementing policy-based routing. By tagging routes with specific communities, you can apply routing policies based on predefined criteria such as geographic location, customer type, or service level agreements (SLAs).

Best Practices and Considerations:
While manipulating BGP attributes offers significant flexibility in controlling network traffic, it's essential to approach it with caution and adhere to best practices:

• Document Your Changes: Keep detailed documentation of any BGP attribute modifications to ensure clarity and facilitate troubleshooting.
• Monitor and Analyze: Regularly monitor and analyze network traffic patterns to assess the effectiveness of your BGP attribute manipulations and make adjustments as necessary.
• Testing and Validation: Before implementing changes in a production environment, conduct thorough testing and validation to minimize the risk of disruptions. From my experience it is also a good idea to get a peer review.

Conclusion:
In summary, BGP attributes are powerful tools that network engineers can use to influence the flow of traffic within and across their networks. By understanding the various BGP attributes and how they can be manipulated, you can effectively optimize network performance, improve reliability, and ensure efficient resource utilization. However, it's crucial to approach BGP attribute manipulation with care, following best practices and exercising caution to avoid unintended consequences. With careful planning and implementation, you can leverage BGP attributes to masterfully control network traffic according to your organization's specific requirements and objectives.