1. MAC AddressesCS-502 (EMC) Fall 20091 Clarification — MAC Addresses and IP Networks CS-502, Operating Systems Fall 2009 (EMC) (Slides include materials from Modern Operating Systems, 3 rd ed., by Andrew Tanenbaum and from Operating System Concepts, 7 th ed., by Silbershatz, Galvin, & Gagne)

2. MAC AddressesCS-502 (EMC) Fall 20092 MAC Address MAC  Media Access Control –Unique identifier assigned to most network adapters –By manufacturer Implemented by Level 2, Data Link layer –MAC address is prefixed to every packet –Enables network devices to recognize packets addressed to them Promiscuous modes and software MAC addresses are possible and legal

3. MAC AddressesCS-502 (EMC) Fall 20093 Address Resolution Protocol (ARP) A protocol by which Level 3 (Network layer) implementations exchange MAC addresses See Linux man page about “arp” man 7 arp ARP cache Maps IP addresses to MAC addresses on local subnet

4. MAC AddressesCS-502 (EMC) Fall 20094 ARP (continued) Every host maintains ARP cache Level 3 implementations fill it by Broadcast and enquiry Watching other traffic Exchanging information with neighboring Level 3 implementations Static information When packet arrives at Level 3 network interface Look up IP address in ARP cache  MAC address Hand off to Level 2 for transmission to MAC address –On appropriate subnet

5. MAC AddressesCS-502 (EMC) Fall 20095 Summary — OSI 7-layer model Physical Layer Data Link Layer Network Layer Transport Layer Session Layer Presentation Layer Application Layer Sending Process Physical Layer Data Link Layer Network Layer Transport Layer Session Layer Presentation Layer Application Layer Receiving Process Bits DHDataDT NHData THData SHData PHData AHData Maintains ARP cache Gets MAC addresses Uses MAC addresses to transmit packets

6. MAC AddressesCS-502 (EMC) Fall 20096 Questions?