Troubleshooting · Networking
Device cannot reach the internet
A device has no connectivity, or reaches some destinations but not others.
Work through these in order
- 01
Check link and address
Interface up? Address from the expected range, or a link local address indicating DHCP failure?
- 02
Test the gateway
Ping the default gateway. Failure points to local switching, VLAN or DHCP configuration.
- 03
Test name resolution separately from routing
Resolve a name, then reach an IP address directly. Distinguishing the two saves most of the time spent here.
- 04
Check the path
Traceroute to identify where packets stop; compare with a working device on the same segment.
- 05
Check policy
Firewall egress rules, web filtering categories, NAC posture, or a captive portal awaiting authentication.
- 06
Check MTU for tunnels
If small requests succeed and large transfers hang, suspect MTU or MSS clamping.
Background reading
DHCP
Dynamic Host Configuration Protocol automatically issues IP addresses and network configuration to clients as they join a network.
DNS
The Domain Name System is the distributed, hierarchical directory that resolves names to addresses and service records for nearly every other service.
Routing
Forwarding packets between networks by selecting the best available path from a route table.
Firewalls
Policy enforcement points that permit or deny traffic between network zones based on connection state, identity and application context.
TCP/IP
The protocol suite that actually runs the internet and virtually every enterprise network, organised into link, internet, transport and application layers.