利用序列化机制实现Session共享的原理：

1、Web Server 1的应用程序序列化Session信息为文本值（可以是Binary或Soap格式）

2、将序列化后的值写入文件，保存到File Server上

3、Web Server 2 对保存在File Server上的Session序列化后的值进行反序列化

4、在Web Server 2上重新构建Session值

创建一个类：SessionEntity  
创建一个序列化、反序列化操作的类：ShareSessionFormatter

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Collections;
using System.IO;
using System.Runtime.Serialization.Formatters.Soap;
using System.Runtime.Serialization.Formatters.Binary;

[Serializable]
public class SessionEntity
{
    [NonSerialized]
    public string AUTH_GUID = "";

    private Hashtable _HtShareSession;

    public Hashtable HtShareSession
    {
        get
        {
            return this._HtShareSession;
        }
        set
        {
            this._HtShareSession = value;
        }
    }
    public SessionEntity(string guid)
    {
        this.AUTH_GUID = guid;
    }

}
/// <summary>
/// 格式化操作器
/// </summary>
public class ShareSessionFormatter
{
    private static string _ShareSessionPath = System.Configuration.ConfigurationManager.AppSettings["ShareSessionPath"].ToString();
    /// <summary>
    /// 序列化格式器类型
    /// </summary>
    public enum FormatterType
    {
        Binary,
        Soap
    }
    /// <summary>
    /// 执行序列化
    /// </summary>
    /// <param name="formatterType">类型</param>
    public static void Serialize(FormatterType formatterType)
    {
        if (HttpContext.Current.Session["AUTH_GUID"] == null)
        {
            HttpContext.Current.Session["AUTH_GUID"] = Guid.NewGuid().ToString();
        }
        Hashtable ht = new Hashtable();

        //遍历Session           
        foreach (string key in HttpContext.Current.Session.Contents.Keys)
        {
            ht.Add(key, HttpContext.Current.Session[key]);
        }

        /**/
        ////执行序列化
        switch (formatterType)
        {
            case FormatterType.Binary:
          
      BinarySerialize(ht);
                break;
            case FormatterType.Soap:
                SoapSerialize(ht);
                break;
            default:
                break;
        }

    }
    /// <summary>
    /// 按照Binary格式序列化
    /// </summary>
    /// <param name="ht"></param>
    private static void BinarySerialize(Hashtable ht)
    {
        string guid = HttpContext.Current.Session["AUTH_GUID"].ToString();
        SessionEntity obj = new SessionEntity(guid);
        obj.HtShareSession = ht;

        // 创建一个文件guid.xml
        Stream stream = File.Open(_ShareSessionPath + guid + ".xml", FileMode.Create);
        BinaryFormatter formatter = new BinaryFormatter();

        //执行序列化
        formatter.Serialize(stream, obj);
        stream.Close();

        // 将对象置空
        obj = null;
    }
    /// <summary>
    /// 按照Soap格式序列化
    /// </summary>
    /// <param name="ht"></param>
    private static void SoapSerialize(Hashtable ht)
    {
        string guid = HttpContext.Current.Session["AUTH_GUID"].ToString();
        SessionEntity obj = new SessionEntity(guid);
        obj.HtShareSession = ht;

        // 创建一个文件guid.xml
        Stream stream = File.Open(_ShareSessionPath + guid + ".xml", FileMode.Create);
        SoapFormatter formatter = new SoapFormatter();

        //执行序列化
        formatter.Serialize(stream, obj);
        stream.Close();

        // 将对象置空
        obj = null;
    }
    /// <summary>
    /// 反序列化
    /// </summary>
    /// <param name="formatterType">传送端的Session["AUTH_GUID"]</param>
    /// <param name="guid"></param>
    public static void Deserialize(FormatterType formatterType, string guid)
    {
        switch (formatterType)
        {
            case FormatterType.Binary:
                BinaryDeserialize(guid);
                break;
            case FormatterType.Soap:
                SoapDeserialize(guid);
                break;
            default:
                break;
        }
    }
    /// <summary>
    /// 以Binary方式反序列化
    /// </summary>
    private static void BinaryDeserialize(string guid)
    {
        SessionEntity obj = new SessionEntity(guid);

        // 打开文件guid.xml
        Stream stream = File.Open(_ShareSessionPath + g
uid + ".xml", FileMode.Open);
        BinaryFormatter formatter = new BinaryFormatter();

        obj = (SessionEntity)formatter.Deserialize(stream);
        stream.Close();

        Hashtable ht = obj.HtShareSession;
        obj = null;

        //遍历ht，生成Session
        CreateSession(ht);
    }
    /// <summary>
    /// 以Soap方式反序列化
    /// </summary>
    private static void SoapDeserialize(string guid)
    {
        SessionEntity obj = new SessionEntity(guid);

        // 打开文件guid.xml
        Stream stream = File.Open(_ShareSessionPath + guid + ".xml", FileMode.Open);
        SoapFormatter formatter = new SoapFormatter();

        obj = (SessionEntity)formatter.Deserialize(stream);
        stream.Close();

        Hashtable ht = obj.HtShareSession;
        obj = null;

        //遍历ht，生成Session
        CreateSession(ht);
    }
    /// <summary>
    /// 遍历Hashtable，同时创建Session
    /// </summary>
    /// <param name="ht"></param>
    private static void CreateSession(Hashtable ht)
    {
        foreach (DictionaryEntry de in ht)
        {
            HttpContext.Current.Session[de.Key.ToString()] = de.Value;
        }
    }
}

编译项目，生成ShareSession.dll

把ShareSession.dll引入 你需要共享的站点 配置web.config