Module 4 – Learning about other Devices
Testing network connections
Tools
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CDP Ping – Packet Internet Groper
Traceroute (Trace, Tracert) –
Telnet
CDP
• Used to obtain information about neighboring Cisco devices
• Uses a Layer 2 *proprietary* protocol
• CDP Version 2 (CDPv2) latest version – needs IOS
12.0(3)T or later
• CDP Version 1 used from IOS 10.3 to 12.0(3)T
CDP
• Protocol independent
– Layer 2 protocol
• therefore Layer-3 independent
– media independent
Show cdp neighbors
• CDP discovers all Cisco devices that are directly connected to a local
device
• Show CDP Neighbors Command displays a summary of info about
the neighbors
Show cdp neighbors
• CDP v1 and CDPv2 displays
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Device ID
Local Interface
Holdtime
Capability
Platform
Port ID
• CDPv2 (only) also displays
– VTP management domain
name
– Native VLAN
– Full or half-duplex
Show cdp entry
• Show details for a specific CDP neighbors entry
Show cdp interface
• Show CDP setup parameters for the specified interface
The show cdp traffic Command
CDP commands
Starting and Stopping CDP
• Global cdp enable/disable
– Router(config)# cdp run
– Router(config)# no cdp run
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Interface level cdp enable/disable
– interface FastEthernet 0/0
– Router(config-interface)# cdp run
– Router(config-interface)# no cdp run
Telnet
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Application-level tool
Mainly used to establish remote connections to network devices
Telnet Operation
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Available in User or Privileged EXEC mode
Default inactivity time – 10 minutes
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Can remotely connect to the Paris router from the Denver router
– if both routers have been previously configured
Denver> telnet Paris
(or connect Paris)
or
Denver> telnet 131.108.100.152
Paris> ….
Paris> exit
Denver>
Telnet
Advanced Telnet Operation
Multiple Telnet sessions can be used and suspended with the
Ctrl+Shift+6 then x sequence.
Ping
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Packet Internet Groper (PING)
Operates at Layer 3
Uses ICMP echo request and echo response
Tests end-to-end connectivity
PING
• Uses ICMP messages
• Sends an ICMP echo request and waits for an ICPM echo
reply
• Cisco codes:
!
receipt of an echo reply message
.
time out
ICMP unreachable message received (no route)
Source Quench
ICMP unreachable message received
U
C
Traceroute (trace)
Traceroute
• Operates at Layer 3
• Sets TTL in IP packet header to expire at subsequent routers
from the closest router to the furtherest router
• Tests each step along the route to destination
• Cisco codes:
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nn msec
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A
Q
H
RTT for number of probes
probe timed out
administratively prohibited
source quench
ICMP unreachable message received
Troubleshooting
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Ping
Traceroute
Telnet
show interfaces
show ip route
debug