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Troubleshooting Azure ExpressRoute connections In this lesson you’ll learn the practical steps, checks, and tools to diagnose and resolve connectivity and performance issues with Azure ExpressRoute circuits. The guidance focuses on validating circuit provisioning, verifying peerings and routing, confirming Layer 2 mappings, and isolating performance bottlenecks so you can restore reliable connectivity between on-premises networks and Azure. What you’ll learn:
  • How to confirm an ExpressRoute circuit is provisioned and in the correct state using the Azure Portal or Azure CLI.
  • How to validate Azure Private and Microsoft peerings and common misconfigurations that break connectivity. (Public peering has been retired.)
  • How to use ARP and Layer 2 checks to confirm MAC/IP mappings between on-premises equipment and Azure.
  • How to identify and mitigate network performance issues that affect ExpressRoute.
This lesson assumes familiarity with ExpressRoute concepts (circuits, peerings, BGP) and access to the Azure subscription where the ExpressRoute circuit is deployed. Recommended tools: the Azure Portal, the Azure CLI, and on‑premises network tools (router/switch show arp, BGP show commands, ping, traceroute, and packet captures).
Quick Azure CLI commands
  • Show ExpressRoute circuit details:
  • List peerings for a circuit:
  • Show a specific peering (e.g., AzurePrivate):
Troubleshooting checklist
  1. Circuit state: Confirm the ExpressRoute circuit is provisioned and in the expected status in the Portal or via CLI.
  2. Provider/Service Key: Verify the service key (SCK) and provider status if working with a connectivity partner.
  3. Peerings: Validate that Azure Private and Microsoft peerings exist, are enabled, and have correct IP addresses and VLAN IDs.
  4. BGP: Confirm BGP session establishment, route advertisement, and route acceptance on both sides. Check BGP state and prefix lists.
  5. Layer 2: Use ARP entries and MAC tables on on‑prem switches to confirm correct mapping to the ExpressRoute VLAN.
  6. Performance: Measure latency, jitter, throughput, and packet loss. Compare to SLA targets and baseline telemetry.
  7. Escalation: If the issue appears on the provider side, gather configuration snippets, packet captures, and BGP logs before contacting the connectivity provider or Microsoft support.
Links and references

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