OSI Model, OSI Troubleshooting + DNS Issues

[DarkMaster]

Layer 1
-Do you have link lights?
-Are the network cables plugged in?
-Are the network cables plugged into the correct ports?
-Is the network adapter enabled?
-Is the switch port enabled?
-Are the cables in working condition? (test the cables)

Layer 2
-Can you ping the loopback address 127.0.0.1?
-Do you have an IP address?
-Can you ping your own IP address?
-Can you ping other hosts in your own subnet?
-Are you in the correct VLAN?
-Is the IP address in the expected network / subnet?

Layer 3
-Can you ping hosts outside of your network?
-Is your subnet mask correct?
-Do you have a default gateway configured?
-Is the default gateway correct?
-Can you ping the default gateway? (if not, you may have a layer 2 issue)

DNS Issues
-Do you have DNS servers configured?
-Can you ping the DNS server?
-Can you ping hosts by name?
-Can you ping hosts by IP address?

If you can ping a host by IP but not by name, then you may have a DNS issue.

-Can you perform nslookup against your own DNS server(s)?
-Can you perform nslookup against other DNS server(s)?