BGP route policies: Top 3 use cases by customer demand

When we first made BGP route policies for Cloud Router generally available over a year ago, our goal was to give network administrators deep, programmable control over how network paths are evaluated and propagated. Since then, we’ve been watching closely how our customers have adopted this feature. We've seen network engineering teams build incredibly sophisticated, resilient routing architectures that were previously difficult to achieve without third-party virtual appliances.

This year, we launched policy named sets for Cloud Router. As routing environments grow more complex, managing individual prefixes or communities within these policies can become cumbersome. 

Policy named sets solve this by allowing you to group lists of IPv4/IPv6 prefixes or BGP communities into a single, reusable entity. This significantly simplifies your configurations, making it easier to scale, manage, and update your routing rules across multiple Cloud Routers.

Powered by the Common Expression Language (CEL), BGP route policies allow you to define fine-grained, ordered rules to filter BGP routes and modify route attributes directly within Cloud Router.

To celebrate the launch of policy named sets, we want to highlight three of the most impactful ways we've seen customers use BGP route policies over the past year, along with resources on how you can build them yourself.

1. The foundation: Route filtering and network protection

Before manipulating traffic paths, network stability requires strict control over which routes are allowed into and out of your network. We've seen customers extensively use BGP route policies to filter out unwanted learned routes from peers or prevent specific subnet prefixes from being advertised out of their Virtual Private Cloud (VPC).

Operating on a "fail open" model by default, many security-conscious organizations have adapted BGP route policies to create a "fail closed" environment — appending a "drop all" policy as the final term in their evaluation list. This helps enable absolute certainty over accepted network routes, preventing routing loops and ensuring traffic isn't BGP hijacked or inadvertently blackholed.

• Dive deeper: For a foundational look at how to set up CEL expressions for route filtering, check out our deep-dive guide: Introduction to BGP policies.

2. Influencing traffic paths for active/standby architectures

Achieving optimal traffic distribution often requires forcing traffic down a specific path, whether for cost optimization or managing active/standby interconnects. Customers have used BGP route policies to influence the preferred BGP route without touching their on-premises hardware.

By dynamically modifying the BGP multi-exit discriminator (MED) attribute, network teams can make a specific peer preferred for incoming traffic. Conversely, if they want to steer traffic away from a congested or backup link, they are using AS-PATH prepending — adding one or more values to the route's AS-PATH to deprioritize it across the broader network.

• Dive deeper: To see the configuration steps for managing MED and AS-Path prepending, read: Using BGP policies to influence traffic paths.

3. Solving asymmetric routing with BGP communities

One of the most advanced and highly requested use cases we’ve seen over the last year is achieving traffic symmetry. When enterprises use stateful firewalls or specific network appliances on-premises, return traffic must flow back through the exact same appliance it originated from. If it doesn't, the traffic is dropped.

Customers are successfully solving this by using BGP route policies to match against specific standard BGP communities. By tagging routes with specific communities on-premises, Cloud Router can read those tags via inbound policies and adjust the route preference by manipulating the MED accordingly. This helps ensure that Google Cloud inherently understands the stateful topology of the on-premises network and routes the return traffic symmetrically.

• Dive deeper: To learn how to architect stateful traffic symmetry using BGP community tags, explore: Using BGP communities to create traffic symmetry.

Get started today

Taking control of your dynamic routing is now easier and more robust than ever. Using BGP route policies, it's a great time to optimize and secure your hybrid cloud connectivity.

We recommend testing your BGP route policies in a staging environment to verify your CEL expressions and routing logic before rolling them out to production. To explore the technical documentation, check out the BGP route policies overview.