也就是判断 HttpContext.Connection.RemoteIpAddress 是 IPv4 地址还是 IPv6 地址, RemoteIpAddress 的类型是 System.Net.IPAddress
可以通过 AddressFamily 判断
var protocol = HttpContext.Connection.RemoteIpAddress.AddressFamily switch
{
AddressFamily.InterNetwork => "IPv4",
AddressFamily.InterNetworkV6 => "IPv6",
_ => "non-ip"
};