Troubleshooting and fixing Delta airlines in-flight WiFi page can’t be reached issue

The Issue: No Captive Portal on Delta WiFi

Summer 2024. I was on an 8-hour flight from London to the US. I connected to Delta’s in-flight WiFi just fine on my phone. But on my Linux laptop? No captive portal. No redirect. Nothing. I spent the flight troubleshooting it. After a bit of digging, I found the culprit: Docker.

Turns out Delta’s WiFi runs on the 172.19.0.0/23 network which happens to be the same range Docker uses by default.

The Fix (TL;DR)

Fast-forward to Summer 2025 on a flight to Denver, I finally resolved the issue:

1. Docker’s default bridge network (172.17.0.0/16 or 172.19.0.0/16) conflicts with Delta’s in-flight WiFi (172.19.0.0/23).
2. I changed Docker’s bridge to a safe range: 172.31.0.0/24.
3. Then I removed all container networks overlapping with 172.19.x.x using Portainer and docker network rm.

The Delta captive portal appeared immediately after. Problem solved.

Error Message:

Attempt to connect to the deltawifi.com

Step-by-Step: Fixing Docker & Delta WiFi Conflict

1. Validate Delta WiFi IP Range

Connect to Delta WiFi and run:

ip a | grep inet

Look for your wireless interface (e.g., wlp4s0). You might see:

inet 172.19.1.32  netmask 255.255.254.0  broadcast 172.19.1.255

Using the UI

That confirms Delta uses 172.19.0.0/23.

2. Check Docker Network

List docker networks:

docker network ls

Inspect any custom or bridge networks:

docker network inspect <network-name>

If you see something like:

"Subnet": "172.19.0.0/16",
"Gateway": "172.19.0.1"

You’ve got a conflict.

3. Change Docker’s Default Bridge Subnet

Edit Docker daemon config (if the file does not exist create it):

sudo nano /etc/docker/daemon.json

If the daemon file exists and the base subnet IP conflicts with the Delta in-flight subnet, change it to a non-conflicting range:

{
 "default-address-pools": [
   {
     "base": "172.31.0.0/16",
     "size": 24
   }
 ]
}

Restart services:

sudo systemctl restart docker.socket
sudo systemctl restart docker

4 Remove Conflicting Networks

Even after changing the default subnet, you might have leftover container networks using 172.19.x.x.

Use Portainer or run the following to get the container network details:

echo -e "NETWORK ID        NAME                  DRIVER    SCOPE     SUBNET"
docker network ls --format '{{.ID}} {{.Name}} {{.Driver}} {{.Scope}}' | while read id name driver scope; do
  subnet=$(docker network inspect "$id" --format '{{range .IPAM.Config}}{{.Subnet}}{{end}}')
  printf "%-18s %-21s %-9s %-9s %s\n" "$id" "$name" "$driver" "$scope" "$subnet"
done

Then remove any conflicting networks:

docker network rm <network-id>

In my case, I had 15 container networks. I removed all inactive ones. You can just remove the ones that conflict with Delta’s range.

After the Fix

Docker bridge:

docker0: inet 172.31.0.1  netmask 255.255.255.0

Delta WiFi:

wlp4s0: inet 172.19.1.32  netmask 255.255.254.0

No more overlap. Captive portal worked instantly.

---

Takeaway

If you’re a developer running Docker and can’t connect to Delta’s WiFi:

• Check your Docker bridge and container networks
• Make sure nothing uses 172.19.0.0/23
• Change to a safe subnet like 172.31.0.0/24

Hope this saves someone a headache on their next flight!

Happy travels ✈️

Tags: Delta-Inflight-WiFi Docker Troubleshooting