What are some best practices and common pitfalls of using BGP community attribute for route filtering?

1 Understand the scope and meaning of communities

One of the first steps to use BGP community attribute effectively is to understand the scope and meaning of the communities you are using or receiving. BGP communities can be either standard or extended, and they can have either local or global significance. Standard communities are 32-bit values, while extended communities are 64-bit values that can include additional information such as route targets or origin AS. Local communities are only meaningful within a single AS or a group of ASes that agree on their interpretation, while global communities are registered and standardized by IANA or other authorities. You should always check the documentation and agreements of your peers and providers to know what communities they accept, send, and honor, and what actions they trigger.

2 Use a consistent and clear naming convention

Another best practice for using BGP community attribute is to use a consistent and clear naming convention for your own communities and policies. This will help you avoid confusion and errors when configuring and troubleshooting your BGP sessions and filters. You should use a naming convention that reflects the purpose and function of the communities, such as indicating the origin, destination, or action of the routes. For example, you could use a prefix like AS65000: to indicate your own AS number, followed by a suffix like :100 to indicate a specific policy, such as no-export or local-preference. You should also document your naming convention and the meaning of each community in a central and accessible place.

3 Test and verify your community filters

A common pitfall of using BGP community attribute is to assume that your community filters are working as intended without testing and verifying them. This could lead to unexpected or unwanted outcomes, such as leaking routes to unintended recipients, blocking routes from legitimate sources, or affecting the traffic engineering of your network. You should always test and verify your community filters before applying them to production traffic, using tools such as route servers, looking glasses, or traceroutes. You should also monitor and audit your BGP sessions and routes regularly to detect any anomalies or changes in the community values or policies.

4 Coordinate with your peers and providers

Another common pitfall of using BGP community attribute is to neglect the coordination and communication with your peers and providers. BGP communities are not mandatory or standardized, and different networks may have different interpretations or implementations of them. Therefore, you should always coordinate and communicate with your peers and providers to ensure that you have a mutual understanding and agreement on the use of BGP community attribute. You should also inform them of any changes or updates in your community values or policies, and request them to do the same. This will help you avoid conflicts, inconsistencies, or misconfigurations that could affect your BGP routing and performance.

5 Use community filters with caution and care

The final best practice for using BGP community attribute is to use community filters with caution and care. BGP community attribute is a powerful tool, but it also comes with risks and responsibilities. You should always be aware of the potential impact and consequences of your community filters, not only on your own network, but also on the networks of your peers and providers. You should also follow the best current practices and recommendations of the BGP community, such as respecting the well-known communities, avoiding the use of reserved or private communities, and using extended communities for more specific and granular control. You should also review and update your community filters periodically to ensure that they are still relevant and effective.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?