Network Troubleshooting / IT Support Guides
Inspect Linux ARP and NDP state with ip neigh
A local-link connectivity problem can stem from address resolution rather than DNS. Inspect the neighbor table for the destination or its gateway.
Environment and inputs: Mixed platforms · each example identifies its shell or required tool
Try the diagnostic command
Use the stated shell and platform. Replace sample domains, addresses, services and paths with values from the system you are authorized to support.
ip neigh showHow to read the result
The table reports IPv4 ARP and IPv6 neighbor discovery entries with states such as REACHABLE, STALE or FAILED. STALE is an ordinary cache state, while repeated resolution failures warrant investigation.
What to do next
Compare the selected route and interface with the neighbor entry. Check the cable, VLAN and gateway availability, and use switch evidence to investigate duplicate addressing.
Before you make a change
Neighbor entries do not identify the final hardware address of a remote internet server. Do not flush the table before preserving the relevant evidence.