C# work with local IP address

/// 
/// Ref: How To Get IP Address Of A Machine
/// Ref: WMI or How to change my IP address
/// using System.Management;
///

public string getLocalIP() 
{
  string localIP = "";
  string strHostName = Dns.GetHostName();

  IPHostEntry ipEntry = Dns.GetHostByName (strHostName);
  IPAddress [] addr = ipEntry.AddressList;

  /* what if more than one instance exists? */
  for (int i = 0; i < addr.Length; i++)  
  {
    localIP = addr[i].ToString();
  }

  return localIP;
}


public bool setLocalIP(string newIP) {
  try 
  {
    ManagementBaseObject inPar = null;
    ManagementBaseObject outPar = null;
    ManagementClass mc = new ManagementClass("Win32_NetworkAdapterConfiguration");
    ManagementObjectCollection moc = mc.GetInstances();
    foreach (ManagementObject mo in moc) 
    {
      if (!(bool) mo["IPEnabled"]) continue;
      inPar = mo.GetMethodParameters("EnableStatic");
      inPar["IPAddress"] = new string[] {newIP};
      inPar["SubnetMask"] = new string[] {subnetMask};
      outPar = mo.InvokeMethod("EnableStatic", inPar, null);
      break;
    }
  
    this.currentIP = newIP;
    return true;
  } 
  catch (Exception e) 
  {
    this.setErrMsg(e.Message + "\nsource: " + e.Source);
    return false;
  }
}


static void SwitchToDHCP()
{
  ManagementBaseObject inPar = null;
  ManagementBaseObject outPar = null;
  ManagementClass mc = new ManagementClass("Win32_NetworkAdapterConfiguration");
  ManagementObjectCollection moc = mc.GetInstances();
  foreach( ManagementObject mo in moc )
  {
    if( ! (bool) mo["IPEnabled"] )
      continue;

    inPar = mo.GetMethodParameters("EnableDHCP");
    outPar = mo.InvokeMethod( "EnableDHCP", inPar, null );
    break;
  }
}


static void SwitchToStatic()
{
  string newIP;
  string subnetMask = "255.255.255.0";
  newIP = (curIP.Equals("192.168.168.209"))?"192.168.168.204":"192.168.168.209";

  ManagementBaseObject inPar = null;
  ManagementBaseObject outPar = null;
  ManagementClass mc = new ManagementClass("Win32_NetworkAdapterConfiguration");
  ManagementObjectCollection moc = mc.GetInstances();
  foreach( ManagementObject mo in moc )
  {
    if( ! (bool) mo[ "IPEnabled" ] )
      continue;

    inPar = mo.GetMethodParameters( "EnableStatic" );
    inPar["IPAddress"] = new string[] { newIP };
    inPar["SubnetMask"] = new string[] { subnetMask };
    outPar = mo.InvokeMethod( "EnableStatic", inPar, null );
    break;
  }
}


static void ReportIP()
{
  Console.WriteLine( "****** Current IP addresses:" );
  ManagementClass mc = new ManagementClass("Win32_NetworkAdapterConfiguration");
  ManagementObjectCollection moc = mc.GetInstances();
  foreach( ManagementObject mo in moc )
  {
    if( ! (bool) mo[ "IPEnabled" ] )
      continue;

    Console.WriteLine( "{0}\n SVC: '{1}' MAC: [{2}]", (string) mo["Caption"],
      (string) mo["ServiceName"], (string) mo["MACAddress"] );

    string[] addresses = (string[]) mo[ "IPAddress" ];
    string[] subnets = (string[]) mo[ "IPSubnet" ];

    Console.WriteLine( " Addresses :" );
    foreach(string sad in addresses)
      Console.WriteLine( "\t'{0}'", sad );

    Console.WriteLine( " Subnets :" );
    foreach(string sub in subnets )
      Console.WriteLine( "\t'{0}'", sub );

    curIP = addresses[0];
  }
}

Sams Teach Yourself TCP/IP in 24 Hours

Sams Teach Yourself TCP/IP in 24 Hours (4th Edition) - by Joe Casad, 2008, 456 pages. ISBN-10: 0672329964.

I caught this book in sight at Barns and Noble. It is a short book to read, to the point and clear on basic concepts. Short is good.

I. TCP/IP basics

II. TCP/IP Protocol system

2. Correspondence of TCP/IP model and OSI model.
  TCP/IP                      OSI         Relevant protocols
  ----------------------------------------------------------------------------------
  Application layer           A,P,S          
  Transport layer             T           TCP/UDP
  Internet layer              N           IP, ARP, RARP, ICMP, router(RIP, OSPF etc.)
  Network access layer        D,P         FTS, FDDI, PPP, 802.11, 802.3, 802.16

  note: 802.3 - ethernet, 802.11 - wireless, 802.16 - winmax

3. Network access layer
  - physical addressing.
  - LAN - ethernet.
    CSMA/CS (Carrier Sense Multiple Access with Collision Detect)
    ethernet frame: preamble|dest addr|sr addr|length|data|FCS(CRC)

4. Internet layer
  - IP, IP header
  - IP addressing: class A(8/24), B(16/16), C(24/8), D, E
  - ARP (Address Resolution Protocol)
  - RARP (Reverse ARP)
  - ICMP
  - BGP (Border Gateway Protocol), RIP (Routing Information Protocol)

5. Subnetting & CIDR (Classless Inter-Domain Routing)
  - subnet mask/host ID
  - split and combine networks.

6. Transport layer
  - TCP/UDP
  - ports, sockets
  - multiplexing, demultiplexing.
  - TCP: stream, resequencing, flow control, precedence & security, graceful close.

7. Application layer
  - use socket/port to communicate with transport layer.
  - target of multiplexing/de-multiplexing

III. Networking with TCP/IP

8. Routing
  - routing table
  - IP forwarding
  - Dynamic routing algorithm
    - DV (Distance vector). e.g. RIP
    - LS (Link state). e.g. OSPF (Open Shortest Path First)
      LS is more popular than DV now.
  - Complex network routing
    1) core router - backbone network (GGP)
    2) exterior router - on border of autonomous systems (EGP: e.g. BGP)
    3) interior router - within autonomous system (IGP: OSPF/RIP)
  - classless routing: CIDR.
  - OSPF: implemented as routed on unix/linux, builds SPT (Shortest Path Tree)

10. Firewall
  - DMZ (Demilitarized Zone)
  - rules
  - proxy service
  - reverse proxy

11. Name resolution
  - DNS (Domain Name Server)

IV. TCP/IP utilities.

V. TCP/IP and the internet

18. Email
  - outgoing email: SMTP
  - incoming email: POP3/IMAP

19. Streaming and casting
  - stack:
    RTP
    UDP
    Internet layer
    Network Access layer

VI. Advanced topics

Network tools

To find out what server (IIS/Apache etc.) a site is running:
http://uptime.netcraft.com/up/graph
or: http://whois.domaintools.com/thedomainname.com

Many tools for analyzing web stuff:
http://www.dnsstuff.com/tools/

Socket communication in C#

http://topic.csdn.net/u/20080623/08/4bbd2475-45f1-42e3-a613-16b094759ade.html