© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Connecting Networks Exploring the IP Packet Delivery Process

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Outline Overview Overview of IP Packet Delivery IP Packet Structure Protocol Field Internet Control Message Protocol Using Internet Control Message Protocol Testing Summary

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v IP Packet Delivery 1. Host sends packet to default gateway 2. Packet placed in frame 3. Router receives frame 4. Router finds destination network in route table 5. Router chooses next hop toward destination 6. MAC address of next hop determined 7. Packet placed in frame 8. Repeats steps 2 through 7 as necessary 9. Router receives frame 10. Router finds network directly connected 11. MAC address of end host determined 12. Packet placed in frame to final destination

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v IP Datagram Header

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Protocol Field

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v ICMP Announces network problems –Destination unreachable Announces network congestion –Source Quench Assists in troubleshooting –Echo request and Echo reply Announces timeouts –Time to Live exceeded

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v ICMP Testing Process D:\>ping Pinging with 32 bytes of data: Request timed out D:\>ping Pinging with 32 bytes of data: Reply from : bytes=32 timeping Pinging with 32 bytes of data: Destination unreachable

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Summary The steps involved in transmitting an IP packet over a routed network are similar to those of sending a letter through a mail delivery service, and include finding the destination address in a routing table, putting the data into a frame and sending it to a router at the destination location, unpacking the frame, and sending the data to its destination. The structure of an IP packet (datagram) includes the necessary information to deliver the packet. This information includes items such as version, header length, priority and type of service, total length, identification, and so on.

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v Summary (Cont.) IP uses a protocol number in the datagram header to identify which protocol to use for a particular datagram. ICMP defines a small number of messages used for diagnostic and management purposes in the IP transmission process. These messages include announcing network errors, congestion and timeouts, and assisting with troubleshooting. The ping command is used to test the connectivity. The ping command uses the echo function in ICMP.

© 2005 Cisco Systems, Inc. All rights reserved.INTRO v