What version of Go are you using (go version)?

$ go version
go version devel +master Sat Jun 20 01:48:54 EDT 2020 plan9/amd64

What did you do?

Run:

package main

import (
	"fmt"
	"net"
)

func main() {
	la, err := net.ResolveTCPAddr("tcp", ":1234")
	if err != nil {
		panic(err)
	}
	d := net.Dialer{
		LocalAddr: la,
	}
	c, err := d.Dial("tcp", "golang.org:80")
	if err != nil {
		panic(err)
	}
	defer c.Close()
	fmt.Printf("local=%v remote=%v\n", c.LocalAddr(), c.RemoteAddr())
}

What did you expect to see?

local=192.168.1.254:1234 remote=172.253.63.141:80

What did you see instead?

local=192.168.1.254:41592 remote=172.253.63.141:80

It should be possible to support this on Plan 9. The control message takes the local port (but not IP) as an argument. From ip(3):

connect ip–address!port!r local

Establish a connection to the remote ip–address and port. If local is specified, it is used as the local port number. If local is not specified but !r is, the system will allocate a restricted port number (less than 1024) for the connection to allow communication with Unix login and exec services. Otherwise a free port number starting at 5000 is chosen. The connect fails if the combination of local and remote address/port pairs are already assigned to another port.

@gopherbot Add labels OS-Plan9, NeedsFix