1. Network Layer 3 Application Presentation Session Transport Network Data Link Physical OSI Model

2. Overview Layer 3 Network Layer Layer 3 Network Layer Layer 3 responsibilitiesLayer 3 responsibilities IP as an exampleIP as an example

3. Network Layer Overview Responsible to route data (datagrams) through an internetwork to destination host. Responsible to route data (datagrams) through an internetwork to destination host. Data packetsData packets User data User data Route update packetsRoute update packets Information to map and navigate layer 3 networks Information to map and navigate layer 3 networks Not responsible for error-free communications Not responsible for error-free communications Communications are connectionless Communications are connectionless Communications are not ordered Communications are not ordered Defines broadcast domains Defines broadcast domains Requires an addressing scheme Requires an addressing scheme Primary device is router Primary device is router Examples: IP and IPX Examples: IP and IPX

4. TCP/IP Suite Layer 3 protocols IP (Internet Protocol) IP (Internet Protocol) ARP (Address Resolution Protocol) ARP (Address Resolution Protocol) ICMP (Internet Control Messaging Protocol) ICMP (Internet Control Messaging Protocol) IGMP (Internet Group Messaging Protocol) IGMP (Internet Group Messaging Protocol)

5. The Internet Protocol IP The Internet Protocol (IP) is the Network Layer protocol used in the Internet suite of protocols. IP provides: The Internet Protocol (IP) is the Network Layer protocol used in the Internet suite of protocols. IP provides: Datagram Delivery without reliability checkingDatagram Delivery without reliability checking Addressing through a fixed length IP addressAddressing through a fixed length IP address No method of flow controlNo method of flow control No ordering of packetsNo ordering of packets Connectionless serviceConnectionless service Fragmentation and reassembly of long packetsFragmentation and reassembly of long packets The full specification is described in RFC 791 1 The full specification is described in RFC 791 1 1 All internet protocols are described by specifications called Request for comments (RFC)

6. IP Packet Structure

7. Address Resolution Protocol (ARP) ARP is used to discover the MAC address for the destination device or the “Next Hop” router on the path to the destination. ARP is used to discover the MAC address for the destination device or the “Next Hop” router on the path to the destination. It does this by broadcasting a message to all asking for the MAC address that matches the known IP address. It does this by broadcasting a message to all asking for the MAC address that matches the known IP address. The device who owns the IP address answers back with its own MAC address The device who owns the IP address answers back with its own MAC address Some argue that ARP should be at layer 2 Some argue that ARP should be at layer 2

8. ARP Packet Structure Target's IP Address Sender's Hardware Address Sender's IP Address Target's Hardware Address 08 06 Operation (Opcode) Protocol Type Hardware Address Length Protocol Address Length Hardware Type 04 00

9. Internet Control Messaging Protocol (ICMP) Sends control and error messages throughout the IP network Sends control and error messages throughout the IP network Examples: Examples: Echo and Echo replyEcho and Echo reply Ping is a utility that sends an ICMP echo to the destination host. The host replies with an ICMP echo reply Ping is a utility that sends an ICMP echo to the destination host. The host replies with an ICMP echo reply Source QuenchSource Quench If a device is sending data faster than it can be received, a source squelch message is sent to the sender telling it to SLOW DOWN. If a device is sending data faster than it can be received, a source squelch message is sent to the sender telling it to SLOW DOWN. Destination UnreachableDestination Unreachable There is no way to get to the network you have requested There is no way to get to the network you have requested

10. Internet Group Messaging Protocol (IGMP) Used between IP hosts and their immediate neighbor multicast agents to support the allocation of temporary group addresses and the addition and deletion of members of a group. Used between IP hosts and their immediate neighbor multicast agents to support the allocation of temporary group addresses and the addition and deletion of members of a group. A multicast group is a set of hosts that wish to receive the same data as others within their group. A multicast group is a set of hosts that wish to receive the same data as others within their group. A multicast transmission is addressed to a group, not to an individual machine. Streaming media is a good example of a use for multicastingA multicast transmission is addressed to a group, not to an individual machine. Streaming media is a good example of a use for multicasting

11. Unicast Datagrams A unicast message is sent from one host to exactly one host. A unicast message is sent from one host to exactly one host. Host A wants to send a 5 meg message to hosts B,C and D. Host A wants to send a 5 meg message to hosts B,C and D. The message is sent 3 times requiring 15 meg of bandwidth The message is sent 3 times requiring 15 meg of bandwidth

12. Multicast Datagrams Multicast datagrams are sent once to the multicast group address and received by all hosts in the multicast group. Multicast datagrams are sent once to the multicast group address and received by all hosts in the multicast group. Host A wants to send a 5 meg message to hosts B,C and D. Host A wants to send a 5 meg message to hosts B,C and D. IGMP is used to create a multicast group IGMP is used to create a multicast group Host A sends the message to the Multicast group address Host A sends the message to the Multicast group address Hosts B,C and D receive the datagram(s) Hosts B,C and D receive the datagram(s) Total bandwidth used is 5 meg. Total bandwidth used is 5 meg.