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The Address Resolution Protocol (ARP) table on the Cloud Router maps Layer 3 IP addresses to Layer 2 MAC addresses. Every device that communicates through the Cloud Router must have a corresponding ARP entry so that the router can encapsulate IP packets into the correct Ethernet frames and forward them to the right physical or virtual interface. Use the ARP table to verify that adjacent devices (BGP neighbors, cloud gateways, data center routers) are reachable at Layer 2 before troubleshooting higher-layer issues.

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View the ARP table

You can view the ARP table from Network > Cloud Router > ARPs. The tab title shows the total number of active ARP entries. Each row in the table represents a resolved mapping between an IP address and a MAC address on a specific Cloud Router interface.

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Dynamic vs. static entries

  • Dynamic entries are created automatically when the Cloud Router sends an ARP request and receives a reply from a neighboring device.

    These entries age out if the neighbor stops responding, and are refreshed periodically while traffic flows.
  • Static entries are configured manually. Static entries do not age out and persist until they are removed.

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When to use the ARP table

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Verify Layer 2 reachability

If you cannot reach a next-hop gateway, cloud gateway, or BGP peer, check whether an ARP entry exists for that IP address. A missing entry indicates a Layer 2 problem — verify physical connectivity, VLAN tagging, and interface configuration before investigating routing or BGP.

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Confirm device connectivity

After provisioning a new Cloud Router connection, check the ARP table to confirm that the remote device has been learned on the expected virtual interface. A valid ARP entry confirms that the link is up and Layer 2 frames are being exchanged.

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Troubleshoot BGP peering failures

A valid ARP entry for a BGP neighbor’s IP address is a definitive confirmation that Layer 2 connectivity is working. If BGP will not establish but the ARP entry exists, the issue is almost certainly a Layer 3 BGP configuration problem — for example, an incorrect ASN, a mismatched MD5 password, or a route filter policy. This lets you skip physical and VLAN debugging and focus on BGP configuration directly.

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Identify stale or missing entries

If the Age value for an entry is unusually high, the remote device may have become unreachable. If an expected entry is missing entirely, there is likely a Layer 2 issue between the Cloud Router and the neighbor — check the physical link, VLAN assignment, and interface status.