Docker DNS & Networking Fixes

What this is

Reference for fixing Docker container networking and DNS resolution issues within my homelab.

Why I needed this

Containers were unable to resolve hostnames or access external services reliably.
This caused issues with updates, API calls, and inter-container communication.

Where this applies

Mainly on: micropc
Docker-based services across both hosts
Affects containers using default bridge networking

Symptoms

Containers cannot resolve domains:
```
ping google.com → fails
```
Slow or failed internet access inside containers
Services unable to reach APIs or external endpoints
Intermittent networking issues

Root Cause (Observed)

Docker DNS not reliably using router DNS
Inconsistent DNS resolution inside containers
Possible MTU mismatch causing packet issues

Fix: Docker Daemon Configuration

Edit:

sudo nano /etc/docker/daemon.json

Add / update:

{
  "dns": ["192.168.86.1", "8.8.8.8", "1.1.1.1"],
  "ipv6": false,
  "mtu": 1380
}

Apply Changes

Restart Docker:

sudo systemctl restart docker

Key Configuration Notes

DNS Servers

192.168.86.1 → local router (primary)
8.8.8.8 → Google DNS (fallback)
1.1.1.1 → Cloudflare DNS (fallback)

MTU Setting

Set to 1380
Helps avoid packet fragmentation issues
Especially important when using:
- VPNs
- Cloudflare Tunnel

IPv6

Disabled (ipv6: false)
Avoids conflicts where IPv6 is partially configured but not functional

Verification Steps

Test DNS inside container

docker exec -it <container_name> ping google.com

Test HTTP connectivity

docker exec -it <container_name> curl https://example.com

Check container DNS config

docker exec -it <container_name> cat /etc/resolv.conf

Common Problems / Fixes

DNS still not resolving

Restart affected containers:
```
docker restart <container_name>
```

Only some containers affected

Check if container overrides DNS
Verify network mode (bridge vs host)

Issues after reboot

Ensure Docker starts after network is ready
Confirm /etc/docker/daemon.json is still applied

Host works but containers don’t

Confirms Docker-level DNS issue
Re-check daemon.json configuration

Result

Stable DNS resolution across all containers
Reliable external connectivity
No more intermittent network failures

Notes

Applies globally to all containers on host
Important baseline configuration for homelab stability
Particularly relevant when using Cloudflare Tunnel