Cisco CCNA Study Guide - Router Alley

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CCNA Study Guide v2.62 – Aaron Balchunas 90 Troubleshooting IP using ICMP The Internet Control Message Protocol (ICMP) is used for a multitude of informational and error messaging purposes. The following is a list of common ICMP types and codes: Type Code Description 0 0 Echo Reply 3 - Destination Unreachable 0 Network Unreachable 1 Host Unreachable 2 Protocol Unreachable 3 Port Unreachable 4 Fragmentation Needed – Don’t Fragment Flag Set 6 Destination Network Unknown 7 Destination Host Unknown 9 Destination Network Administratively Prohibited 10 Destination Host Administratively Prohibited 5 Redirect 8 Echo 11 TTL Exceeded The two most common troubleshooting tools that utilize ICMP are: • Packet Internet Groper (ping) • Traceroute Ping is a core connectivity troubleshooting tool, which utilizes the Echo Request and Echo Reply ICMP messages to determine if an IP address is reachable and responding. Ping will additionally provide the round-trip time between the source and destination, usually measured in milliseconds. Traceroute determines the routing path a packet takes to reach its destination. Traceroute will not only identify each router the packet has been forwarded through, but will also measure the delay experienced at each router hop. * * * All original material copyright © 2013 by Aaron Balchunas (aaron@routeralley.com), unless otherwise noted. All other material copyright © of their respective owners. This material may be copied and used freely, but may not be altered or sold without the expressed written consent of the owner of the above copyright. Updated material may be found at http://www.routeralley.com.
CCNA Study Guide v2.62 – Aaron Balchunas 91 Transport Layer Protocols Section 7 - TCP and UDP - The Transport layer (OSI Layer-4) does not actually transport data, despite its name. Instead, this layer is responsible for the reliable transfer of data, by ensuring that data arrives at its destination error-free and in order. The Transport layer is referred to as the Host-to-Host layer in the Department of Defense (DoD) reference model. Transport layer communication falls under two categories: • Connection-oriented – requires that a connection with specific agreed-upon parameters be established before data is sent. • Connectionless – requires no connection before data is sent. Connection-oriented protocols provide several important services: • Connection establishment – connections are established, maintained, and ultimately terminated between devices. • Segmentation and sequencing – data is segmented into smaller pieces for transport. Each segment is assigned a sequence number, so that the receiving device can reassemble the data on arrival. • Acknowledgments – receipt of data is confirmed through the use of acknowledgments. If a segment is lost, data can be retransmitted to guarantee delivery. • Flow control (or windowing) – data transfer rate is negotiated to prevent congestion. The TCP/IP protocol suite incorporates two Transport layer protocols: • Transmission Control Protocol (TCP) – connection-oriented • User Datagram Protocol (UDP) - connectionless Both TCP and UDP provide a mechanism to differentiate applications running on the same host, through the use of port numbers. When a host receives a packet, the port number tells the transport layer which higherlayer application to hand the packet off to. Both TCP and UDP will be covered in detail in this guide. Please note that the best resource on the Internet for TCP/UDP information is the exemplary TCP/IP Guide, found here: http://www.tcpipguide.com/free/index.htm * * * All original material copyright © 2013 by Aaron Balchunas (aaron@routeralley.com), unless otherwise noted. All other material copyright © of their respective owners. This material may be copied and used freely, but may not be altered or sold without the expressed written consent of the owner of the above copyright. Updated material may be found at http://www.routeralley.com.
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