IP, routing and IPv6

IPv6 problems on a Mac

Q: What is a link-local address?

An address that starts with fe80 works only on the local link. It does not reach the internet.

Most networks give a Mac both IPv4 and IPv6 addresses. If the IPv6 path is broken, some connections wait or fail.

Applies to: macOS 13 Ventura and later for the System Settings steps. The Terminal commands work on all current macOS versions.Checked: 29 October 2026

Symptoms

Some sites or APIs hang, but others load at once.
A tool connects after a delay, or after some retries.
Connections work on one network but not on another network.

Likely causes

A router that announces IPv6 but does not route it. The Mac gets an IPv6 address, but traffic over IPv6 does not reach the internet.
A provider or VPN without full IPv6. Some VPNs carry only IPv4. IPv6 traffic then goes outside the tunnel or fails.
A firewall that blocks IPv6. A router or company firewall can block IPv6 traffic while it allows IPv4.

How to check

Find the device name of each network port, for example en0 for Wi-Fi.
```
networksetup -listallhardwareports
```
Show the IPv6 addresses of the Wi-Fi interface. Addresses that start with fe80 are link-local only.
```
ifconfig en0 inet6
```
Show the router advertisement that the Mac accepted. An error means that no IPv6 router answered.
```
ipconfig getra en0
```
Send pings over IPv6 to a public address.
```
ping6 -c 3 2606:4700:4700::1111
```
Request a site over IPv4 only, then over IPv6 only. Compare the results.
```
curl -4 -I https://www.apple.com
```
If the IPv4 request works and the IPv6 request fails, the IPv6 path is broken.
```
curl -6 -I https://www.apple.com
```

How to fix it

Restart the router. Then test again.
Update the router's firmware, or ask the provider about IPv6 on your line.
For a test, turn IPv6 off on the service.
```
networksetup -setv6off Wi-Fi
```
Needs an administrator password.
Turn IPv6 on again after the test. Use the automatic setting.
```
networksetup -setv6automatic Wi-Fi
```
Needs an administrator password.
You can also use the Configure IPv6 menu in System Settings > Network > the service > Details > TCP/IP.
If the problem stops only with IPv6 off, report it to the network owner or the provider.

With Kilobat

why tries IPv4 and IPv6 apart and says which one fails.
```
kilobat why api.example.com
```
The MCP tool diagnose_connection returns the same steps for an agent. See Find why one site or API won't connect.

Questions

Should I keep IPv6 off?

No. Turn it off only for a test. Ask the network owner to fix IPv6, then turn it on again.

What is a link-local address?

An address that starts with fe80 works only on the local link. It does not reach the internet.

Sources

networksetup(8), man page installed with macOS 27.2
ipconfig(8), man page installed with macOS 27.2
ping6(8), man page installed with macOS 27.2
curl(1), man page installed with macOS 27.2
Apple Support: Change TCP/IP settings on Mac

Sources checked on 29 October 2026. Man pages are the ones installed with macOS; open one with man <name> in Terminal.