Troubleshoot routing and BGP

This guide helps you diagnose and resolve common routing and BGP issues with Cloudflare WAN. These issues can affect traffic delivery, cause unexpected latency, or result in connectivity loss.

If you are experiencing routing or BGP issues, check these items first:

1. BGP session state: Verify session is Established, not stuck in Connect or Active.
2. Firewall rules: Ensure TCP port 179 is permitted bidirectionally between your router and Cloudflare.
3. Tunnel or CNI health: Check that underlying connectivity is healthy. Degraded tunnels affect route priority.
4. Static route conflicts: Static routes take precedence over BGP routes at equal priority.

This section covers BGP peering sessions (beta) between your network and Cloudflare, established over CNI or tunnels.

• BGP session never reaches Established state
• No routes being advertised or received
• Router logs show repeated connection attempts

1. Verify your firewall permits TCP port 179 bidirectionally between your router and the Cloudflare peering address.
2. Confirm the neighbor IP matches the Cloudflare-provided peering address exactly.
3. Verify your ASN configuration matches the dashboard settings. Only eBGP is supported, so your ASN must differ from the Cloudflare account ASN.
4. If using MD5 authentication, verify the password matches on both sides.

• Traffic from specific regions routed through distant data centers
• Higher than expected latency for regional users
• Traffic not using the closest tunnel or CNI

• Tunnel health degradation causing route deprioritization
• Regional route scoping misconfiguration
• BGP route priorities not set as expected
• Static routes overriding BGP routes

1. Check tunnel health: Degraded tunnels have 500,000 added to their route priority. Down tunnels have 1,000,000 added. Traffic shifts to healthier paths, which may be in different regions. Refer to Troubleshoot tunnel health for diagnostic steps.

2. Review route priorities: Lower priority values indicate higher preference. Verify your routes have the expected priority configuration.

   • Default BGP route priority: 100
   • Static routes at priority 100 take precedence over BGP routes at 100

3. Check regional scoping: If you use region-scoped routes, ensure all regions have route coverage. Traffic arriving at a region without a matching route is dropped.

4. Use Network Analytics: Review traffic patterns to identify where traffic is landing and which paths it follows. Refer to Network Analytics for usage instructions.

• CNI shows down in dashboard
• BGP session over CNI drops
• Traffic fails over to tunnels or alternate CNIs

CNI issues can occur at multiple layers:

A healthy physical link can still have BGP issues. A healthy BGP session can exist while specific prefixes are withdrawn.

Check physical layer (your side):

1. Verify the interface is administratively up on your router.
2. Check optical light levels (Tx/Rx dBm). Abnormal readings indicate fiber or transceiver issues.
3. If light levels are low or absent on your receive side, contact your data center to verify cross-connect status.

Check BGP session:

1. Verify BGP neighbor state on your router shows Established.
2. Check for MD5 authentication mismatches if authentication is configured.
3. Review BGP logs for error messages indicating why the session may have dropped.

Check for maintenance:

1. Review Cloudflare Status ↗ for scheduled maintenance affecting your CNI location.
2. Some maintenance events may temporarily affect CNI connectivity even when marked as non-disruptive.

Refer to Network Interconnect for CNI configuration and setup information.

• BGP routes not being used despite being learned
• Traffic not following expected BGP path
• Route changes not taking effect as expected

Cloudflare prefers static routes when static and BGP routes share the same prefix and priority. This ensures manually configured routes take precedence unless explicitly deprioritized.

Adjust route priorities based on your preference:

• To prefer BGP routes: Set static route priority to a higher number (for example, 150 or 200). Higher numbers indicate lower preference.
• To prefer static routes: Keep static route priority at or below 100. BGP routes default to priority 100.