Diagnose a network problem

A layered method, from the network card to the Internet.

1. Addresses and routes:

   ip a
   ip r

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2. Does the gateway answer, then the Internet, then DNS?

   ping -c 4 192.168.1.1
   ping -c 4 1.1.1.1
   ping -c 4 exemple.fr

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3. Test name resolution:

   dig exemple.fr +short

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4. See what is listening on the machine:

   ss -tulpn

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5. With NetworkManager (Wi-Fi):

   nmcli device status
   nmcli dev wifi list

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6. If pinging an IP works but a name does not, the problem is DNS.