webapi获取IP的方式

using System.Net.Http;

public static class HttpRequestMessageExtensions
{
    private const string HttpContext = "MS_HttpContext";
    private const string RemoteEndpointMessage =
        "System.ServiceModel.Channels.RemoteEndpointMessageProperty";
    private const string OwinContext = "MS_OwinContext";

    public static string GetClientIpAddress(this HttpRequestMessage request)
    {
       // Web-hosting. Needs reference to System.Web.dll
       if (request.Properties.ContainsKey(HttpContext))
       {
           dynamic ctx = request.Properties[HttpContext];
           if (ctx != null)
           {
               return ctx.Request.UserHostAddress;
           }
       }

       // Self-hosting. Needs reference to System.ServiceModel.dll. 
       if (request.Properties.ContainsKey(RemoteEndpointMessage))
       {
            dynamic remoteEndpoint = request.Properties[RemoteEndpointMessage];
            if (remoteEndpoint != null)
            {
                return remoteEndpoint.Address;
            }
        }

       // Self-hosting using Owin. Needs reference to Microsoft.Owin.dll. 
       if (request.Properties.ContainsKey(OwinContext))
       {
           dynamic owinContext = request.Properties[OwinContext];
           if (owinContext != null)
           {
               return owinContext.Request.RemoteIpAddress;
           }
       }

        return null;
    }
}

References required:

• HttpContextWrapper - System.Web.dll
• RemoteEndpointMessageProperty - System.ServiceModel.dll
• OwinContext - Microsoft.Owin.dll (you will have it already if you use Owin package)

第二种：
((System.Web.HttpContextWrapper)Request.Properties["MS_HttpContext"]).Request.UserHostAddress;

原文：http://www.cnblogs.com/damsoft/p/6059434.html