L4 learning about other devices

Discovering and Connecting to Neighbors Objectives • Cisco Discovery Protocol • Getting information about remote devices Introduction to CDP • Cisco Discovery Protocol (CDP) is a Layer protocol that connects lower physical media and upper network layer protocols • CDP is used to obtain information about neighboring devices Introduction to CDP • CDP is media and protocol independent, and runs on all Cisco equipment over the Subnetwork Access Protocol (SNAP) • When a Cisco device boots up, CDP starts up automatically and allows the device to detect neighboring devices that are also running CDP Information obtained with CDP • CDP provides information about each CDP neighbor device by transmitting type length values (TLVs), which are blocks of information embedded in CDP advertisements Information obtained with CDP • Device TLVs displayed by the show cdp neighbors command include the following: – – – – – – – – – Device ID Local Interface Holdtime Capability Platform Port ID VTP Management Domain Name (CDPv2 only) Native VLAN (CDPv2 only) Full/Half-Duplex (CDPv2 only) CDP Example Cisco RouterD CDP Neighbors • CDP information can only be collected from: – Cisco devices – Operational over layer – Directly connected • Update timer: 60s • Hold timer: 180s CDP commands • • • • • cdp run cdp enable clear cdp counters show cdp show cdp entry {*|device-name[*][protocol | version]} • show cdp interface [type number] • show cdp neighbors [type number] [detail] • If CDP is disabled globally, individual interfaces cannot be enabled for CDP CDP Commands Show cdp neighbor detail Device ID: SCA0425051J Entry address(es): IP address: 192.168.4.254 Platform: WS-C6509, Capabilities: Trans-Bridge Switch Interface: FastEthernet0/24, Port ID (outgoing port): 3/20 Holdtime : 138 sec Version : WS-C6509 Software, Version McpSW: 5.4(2) NmpSW: 5.4(2) Copyright (c) 1995-2000 by Cisco Systems advertisement version: VTP Management Domain: 'SSP' Native VLAN: 20 Duplex: full Device ID: Switch Entry address(es): Platform: cisco WS-C2924-XL, Interface: FastEthernet0/23, Holdtime : 127 sec Capabilities: Trans-Bridge Switch Port ID (outgoing port): FastEthernet0/24 Creating a network map of the environment • CDP was designed and implemented as a simple, low-overhead protocol • Though a CDP frame can be small, it can retrieve a great deal of useful information about connected neighboring Cisco devices Troubleshooting CDP Getting Information about Remote Devices Telnet • Telnet is a virtual terminal protocol that is part of the TCP/IP protocol suite • It allows connections to be made to remote hosts Telnet provides a network terminal or remote login capability • Telnet is an IOS EXEC command used to verify the application layer software between source and destination • This is the most complete test mechanism available Telnet • • Telnet functions at the application layer of the OSI model and depends on TCP to guarantee the correct and orderly delivery of data between the client and server A router can have multiple simultaneous incoming Telnet sessions The range through is used to specify VTY or Telnet lines for standard IOS Establishing a Telnet connection • To initiate a Telnet session any of the following alternatives can be used: Denver>connect paris (if DNS available) Denver#paris Denver>131.108.100.152 Denver>telnet paris Disconnecting Telnet sessions • To terminate a Telnet session any of the following alternatives can be used: Denver>disconnect paris Denver>exit • To suspend a Telnet session: Press Ctrl-Shift-6, then x • To set ideal timeout (default is 10 mins): (config-line)#exec-timeout minute [second] Telnet process LAB_A Telnet LAB_B Connect LAB_B Ctrl-Shift-6 x Enter Disconnect Resume Exit LAB_B - Enter key will resume the most recent connection -The resume is used with connection ID Ping •The ping command first sends an echo request packet to an address, then waits for a reply The ping is successful only if: the echo request gets to the destination, and · the destination is able to get an echo reply back to the source Ping Result • A successful echo-reply is expressed with a ! symbol • Echo-reply timeout in seconds (default) is expressed with Symbol • Change default ping settings with extended ping command (Router)#ping [Enter] • Use Ctrl-Shift-6 escape sequence stop ping process Traceroute • The traceroute command is the ideal tool for finding where data is being sent in a network • The traceroute command is similar to the ping command, except that instead of testing endto-end connectivity, traceroute tests each step along the way • asterisk indication means one router is unreachable • Use Ctrl-Shift-6 escape sequence stop traceroute process Trace Process Summary • Cisco Discovery Protocol-CDP • Telnet command • Ping command • Traceroute command Lab Topology • Given access to a running network topology, find out the following: – How devices are interconnected (physical topology) – Device name, platform – Interface name and address ... can retrieve a great deal of useful information about connected neighboring Cisco devices Troubleshooting CDP Getting Information about Remote Devices Telnet • Telnet is a virtual terminal protocol... lower physical media and upper network layer protocols • CDP is used to obtain information about neighboring devices Introduction to CDP • CDP is media and protocol independent, and runs on all Cisco... automatically and allows the device to detect neighboring devices that are also running CDP Information obtained with CDP • CDP provides information about each CDP neighbor device by transmitting type