package main

import (
    "fmt"
    "net"
)

func main() {
    network := "192.168.5.0/24"
    addrs := []string{
        "192.168.5.1",
        "192.168.6.1",
    }

    _, subnet, err := net.ParseCIDR(network)
    if err != nil {
        panic(err)
    }

    for _, addr := range addrs {
        if subnet.Contains(net.ParseIP(addr)) {
            fmt.Println("addr:", addr, "in subnet")
        }
    }
}