DNS resolution failed
Why FTP/SFTP DNS lookups fail and how to fix hostname resolution issues quickly.
Diagnose this automatically
Check whether the hostname resolves before debugging credentials or firewall rules.
Shareable output
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If DNS resolution fails, the hostname can’t be converted into an IP address.
This is usually a typo, missing DNS record, or a DNS/VPN/network resolver issue.
Common causes
- Misspelled hostname
- DNS record does not exist (NXDOMAIN)
- Internal hostname used outside the VPN/network
- Local DNS resolver misconfiguration
- Intermittent DNS failures (timeouts / SERVFAIL)
Fix checklist
- Verify the hostname spelling (copy/paste; watch trailing spaces).
- Run `nslookup <host>` or `dig <host>` from your network.
- If the hostname is internal-only, connect via VPN or run checks from inside the network.
- Try an alternate resolver (1.1.1.1 / 8.8.8.8) if allowed.
Quick commands
nslookup <host>
dig +short <host>
ping <host> # only to test resolution; ICMP may be blockedRelated
- TCP connection timeout (firewall issue) — Why FTP/SFTP connections time out and how to diagnose firewall, routing, or allowlist blocking.
- TCP connection failed — General TCP failure causes when connecting to FTP, FTPS, or SFTP services.
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