1. Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 1 Lesson 3 Address Resolution Protocol (ARP)

2. Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 2 Address Resolution Protocol (ARP) ARP overview ARP cache ARP frames Gratuitous ARP Inverse ARP Proxy ARP

3. Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 3 Overview of ARP Resolve the next-hop IP address of a node to its corresponding media access control (MAC) address For direct deliveries, ARP resolves the datagram’s destination IP address For indirect deliveries, ARP resolves the IP address of a neighboring router ARP exchange: Broadcast ARP Request Unicast ARP Replay

4. Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 4 The ARP Cache Table of resolved IP addresses and their corresponding MAC addresses Checked before sending ARP Request Types of entries Dynamic Static MAC address for existing entry is updated if ARP Request from the IP address is received

5. Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 5 ARP Frame Structure Hardware Type Protocol Type Hardware Address Length Protocol Address Length Operation Sender Hardware Address Sender Protocol Address Target Hardware Address Target Protocol Address = 0x0800 = 6 = 4

6. Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 6 ARP Request and ARP Reply Example ARP Request SHA: 00-60-08-52-F9-D8 SPA: 10.0.0.99 THA: 00-00-00-00-00-00 TPA: 10.0.0.1 ARP Reply SHA: 00-10-54-CA-E1-40 SPA: 10.0.0.1 THA: 00-60-08-52-F9-D8 TPA: 10.0.0.99 Node 1 IP Address: 10.0.0.99 MAC Address: 00-60-08-52-F9-D8 Node 2 IP Address: 10.0.0.1 MAC Address: 00-10-54-CA-E1-40

7. Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 7 Gratuitous ARP and Duplicate IP Address Detection ARP Request for one’s own address Reply received: Duplicate IP address No reply received: Unique IP address for the network segment Duplicate address ARP exhange Gratuitous ARP sent by offending node Unicast APR Reply sent by defending node Gratuitous ARP sent by defending node

8. Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 8 Inverse ARP Used for non-broadcast multiple access (NBMA) technologies Example: Frame Relay MAC-level address is known, but IP address of node at the other end of the connection is not For Frame Relay, DLCI for virtual circuit known Inverse ARP exhange InARP Request InARP Reply

9. Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 9 Proxy ARP Proxy ARP Device Node 1 Node 2 Single Subnet

10. Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 10 A Windows Server 2003 Remote Access Server and Proxy ARP Remote Access Client Assigned address: 10.1.1.201 Windows Server 2003 Family Remote Access Server 10.1.1.0/24 10.1.1.50 10.1.1.8 Configured range: 10.1.1.200-10.1.1.254

11. Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 11 Review ARP overview ARP cache ARP frames Gratuitous ARP Inverse ARP Proxy ARP