Paste ipconfig, ip addr, or show interface output above to begin diagnosis
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Fix-it commands for:
No issues detected
Gateway in same subnet · Subnet mask valid IP not reserved · MTU standard · IPv6 stack clean
Static analysis of the pasted config only. Nothing was pinged. Run ping or traceroute in your terminal to test real reachability.
Diagnostic engine ready
Paste CLI output to trigger inference
IPv4: gateway · subnet · APIPA · MTU · DNS
IPv6: scope · SLAAC · overlap · link-local GW
Static analysis only · no packets are sent
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Spot network misconfigurations in seconds
A wrong subnet mask or a gateway outside the subnet is easy to miss in a wall of ipconfig /all output. Paste the output from Windows, Linux, macOS or a Cisco device and RouteLens checks each interface’s addressing, flags problems and gives the commands to fix them.
Common questions
Why can I reach local devices but not the internet?
Usually a missing or wrong default gateway, or a gateway outside your subnet. Check that the gateway shares the network part of your address (for 192.168.1.50/24, a gateway of 192.168.1.1, not 192.168.0.1), that it answers a ping, and that DNS servers are set.
What does a 169.254.x.x address mean?
It’s a link-local (APIPA) address that the machine gives itself when DHCP doesn’t answer. Check the cable or Wi-Fi, the DHCP server and the switch port’s VLAN, then renew with ipconfig /renew on Windows or by restarting the connection on Linux.
How do I show my IP address, mask and gateway on Linux?
ip -br addr lists addresses with their prefix length, ip route shows the default gateway, and resolvectl status shows DNS servers on systemd-based systems. ifconfig is deprecated and often not installed.
What happens if the subnet mask is wrong?
Too small a subnet (a /25 instead of /24) and the host thinks local neighbours are remote, sending their traffic to the gateway; too large and it tries to reach remote hosts directly and fails. Both show up as some destinations working and others not.
Does it check IPv6 too?
Yes. It reads IPv6 addresses alongside IPv4 and flags common dual-stack problems, such as having only a link-local fe80:: address and no global one.