When i requested to 'localhost' host, the Postman sends SYN to IPv6, and then connects to IPv4.

[heli-os]

Is there an existing issue for this?

• I have searched the existing issues

Describe the Issue

When I send a requested to 'localhost' host, it attempts to connect without having a Request Header in IPv6 (probably SYN).

Why is it working like this? Isn't it common to send either IPv4 or IPv6 requests?

If [::1] is a host, it is normal (including request headers).
If 127.0.0.1 is a host, it is normal (including request headers).

Steps To Reproduce

1. Open the Postman App
2. Set up Request
   • Method: Any(i tried GET / POST)
   • URL: http://localhost:8080/test?asdasdas=afdasfads
3. Send a Request

Screenshots or Videos

No response

Environment Information

- Operating System: MacOS 11.4
- Platform Type: Native App
- Postman Version: 8.10.0

Additional Context?

No response

[DannyDainton]

Closing due to age and inactivity. If this is still an issue you're facing in the latest version of the platform, we can look at reopening this again.

[montdidier]

The reason this happens is because localhost exists in both ipv6 (as ::1) and ipv4 (as 127.0.0.1). It checks first to see if an ipv6 connection is available as RFC 3484 states
prefer ipv6 over ipv4 if both resolve and system supports ipv6. This is done with a connection check.

[heli-os]

@montdidier OMG! Thank you for your comment.