Objective 5.3Network Troubleshooting· 1 min read
Common Network Service Issues
Common network service issues
What you will learn
- Recall DHCP failure's typical symptom (an APIPA address).
- Explain DHCP scope exhaustion and its impact.
- Recall common DNS problem symptoms despite an actual network connection.
- Distinguish a DNS fault from a DHCP fault by symptoms alone.
DHCP and DNS are completely different services, even though either one's failure looks to the user like "the internet isn't working." DHCP failure prevents getting an IP address in the first place, while DNS failure only prevents name resolution while a valid IP address and actual network connectivity exist.
DHCP failure symptom vs. DNS failure symptom
| DHCP failure | DNS failure | |
|---|---|---|
| Visible IP address | An APIPA address (169.254.x.x) | A normal valid IP address |
| Access by raw IP address | Doesn't work at all — no actual connectivity | Works normally |
| Access by domain name | Doesn't work | Specifically doesn't work — this is DNS's signature |
Core concepts
| APIPA | An address a device self-assigns automatically when it fails to reach a DHCP server for any reason. |
|---|---|
| DHCP Scope Exhaustion | All addresses in the DHCP scope run out, so any new device fails to get an address even though the DHCP server itself is running. |
Quick check
Answer in your head first, then reveal.
What symptom specifically indicates DHCP failure?Reveal the answer
The device getting an APIPA address (169.254.x.x).
What's the decisive difference between DHCP and DNS failure regarding raw IP access?Reveal the answer
Raw IP access works with DNS failure, but doesn't work at all with DHCP failure.
What happens when the DHCP scope exhausts all its addresses?Reveal the answer
Any new device fails to get an address, even though the DHCP server itself is running fine.
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Your next step
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Sources
Used to verify the facts. The writing is original to Passuit.