Learning about Neighboring and Remote Devices
PJC CCNA Semester 2 Ver. 3.0by
William Kelly
Cisco Discovery Protocol (CDP) Basics CDP’s primary purpose is to discover all directly CDP’s primary purpose is to discover all directly
connected Cisco devicesconnected Cisco devices CDP is a layer 2 protocol linking physical layer CDP is a layer 2 protocol linking physical layer
and upper layer protocolsand upper layer protocols CDP provides info. about connected devices, CDP provides info. about connected devices,
the model number of those devices, and the the model number of those devices, and the connected interfacesconnected interfaces
CDP is a Cisco proprietary protocolCDP is a Cisco proprietary protocol CDP is media and protocol independent (can CDP is media and protocol independent (can
learn info. even if other devices use different learn info. even if other devices use different protocols)protocols)
CDP v2 is the most recent release and runs on CDP v2 is the most recent release and runs on IOS 12.0(3) and laterIOS 12.0(3) and later
Common CDP Commands
Info. from show cdp neighbors Command
Device IDDevice ID AddressAddress Port IDPort ID CapabilitiesCapabilities VersionVersion PlatformPlatform IP Network PrefixIP Network Prefix VTP Management Domain Name (CDPv2 only)VTP Management Domain Name (CDPv2 only) Native VLAN (CDP v2 only)Native VLAN (CDP v2 only) Full/Half-Duplex (CDPv2 only)Full/Half-Duplex (CDPv2 only)
Overview of Testing
Application
Presentation
Session
Transport
Network
Data Link
Physical1
2
3
4
5
6
7 Telnet
pingtrace
show ip route
show interface
Telnet and Advanced Telnet Telnet is used to verify the application layer
between the source and the destination A router can have 5 simultaneous telnet sessions
(vty 0 – 4) Telnet depends on the TCP to accurately deliver the
data Ctrl + Shift + 6 followed by hitting the letter x will
escape the current telnet session The show sessions command will display all the
current telnet sessions The resume session# will resume a particular telnet
session
Alternate Connectivity Tests ping traceroute show ip route show interfaces serial show interfaces/clear counter debug
The ping Command Ping is an echo protocol that helps evaluate
path reliability Ping is used to troubleshoot lower level OSI
connectivity The basic ping can be used in both the user
and privileged mode
Ping Return Codes
The traceroute Command Traceroute follows the route data travels
through a network and can be used to find broken network connections (broken end to end connectivity)
Traceroute can be used at the user and privileged level
Traceroute operates by sending pings with ever increasing Time to Live (TTL) values
Ctrl-Shift-6 can be used to cancel a traceroute
Traceroute Return Codes
The show ip route Command The show ip route command lists the map the
router has constructed to switch packets The output of this command is referred to as
the routing table
The show interfaces serial Command
The show interfaces serial command displays information about the serial connection between two routers The hardware including cables and interfaces The software including protocols
The states of a serial interface1. Serial0 is up, line protocol is up –
OPERATIONAL
2. Serial0 is up, line protocol is down – CONNECTION PROBLEM
3. Serial0 is down, line protocol is down – INTERFACE PROBLEM
4. Serial0 is administratively down, line protocol is down - DISABLED
Debug Commands Debug all should not be used on a
production router as it will slow down or crash your network
Use debug ? to find the appropriate debug command
Use undebug all to turn off all debugging
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