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Module 4 – Learning about other Devices
Testing network connections
Tools
• 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
– Device ID – Local Interface – Holdtime – Capability – Platform – Port ID
• CDPv2 (only) also displays
– VTP management domain name
– Native VLAN – Full or half-duplex
• Show details for a specific CDP neighbors entry
Show cdp 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
• Interface level cdp enable/disable
– interface FastEthernet 0/0– Router(config-interface)# cdp run– Router(config-interface)# no cdp run
Telnet
• Application-level tool• Mainly used to establish remote connections to network devices
Telnet Operation
• Available in User or Privileged EXEC mode• Default inactivity time – 10 minutes
• 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
• 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
U ICMP unreachable message received (no route)
C Source Quench ICMP unreachable message received
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:
– nn msec RTT for number of probes– * probe timed out– A administratively prohibited– Q source quench– H ICMP unreachable message received
Troubleshooting
• Ping• Traceroute• Telnet• show interfaces• show ip route• debug