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