1 Pertemuan 8 Getting Information about Remote Devices

Discussion Topics Telnet Establishing and verifying a Telnet connection Disconnecting and suspending Telnet sessions Advanced Telnet operation Alternate connectivity tests Troubleshooting IP address issues 2

3 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.

4 Establishing and verifying a Telnet connection To initiate a Telnet session any of the following alternatives can be used: Denver>connect paris Denver>paris Denver> Denver>telnet paris A hostname table or access to DNS for Telnet must be present for a name to work. Otherwise, the IP address of the remote router must be entered.

5 RouterA#conf t Enter configuration commands, one per line. End with CNTL/Z. RouterA(config)#ip host RouterA RouterA(config)#exit RouterA#telnet routera Trying RouterA ( )... Open User Access Verification Password: RouterB> This is where the ip host commands can be helpful. Does not have to be the router-name but it is generally a good idea. Not case sensitive. Establishing and verifying a Telnet connection

6 RouterA>telnet Trying Open Password required, but none set [Connection to closed by foreign host] RouterA> RouterA>telnet Trying Open User Access Verification Password:cisco RouterB> RouterB>exit [Connection to closed by foreign host] RouterA> RouterB(config)#line vty 0 4 RouterB(config-line)#login RouterB(config-line)#password cisco Configure vty password on RouterB Telnet works! Enter vty password Exit closes (ends) telnet session Telnet password – line vty

7 RouterA>telnet Trying Open User Access Verification Password:cisco RouterB>ena % No password set RouterB>exit RouterA>telnet Trying Open User Access Verification Password:cisco RouterB>ena Password:class RouterB#exit [Connection to closed by foreign host] RouterA> Cannot enter privilege mode because there is no privilege password (enable secret). Can only enter this mode from the console until the password is created. RouterB(config)#enable secret class Configure vty password on RouterB Telnet and the privilege password

8 Disconnecting and suspending Telnet sessions A session is suspended for a limited time, to resume a Telnet session that has been suspended, just press Enter. The command show sessions will show what Telnet sessions are taking place.

9 RouterA>connect Host: Trying Open User Access Verification Password:cisco RouterB> RouterA>show sessions Conn Host Address Byte Idle Conn Name * RouterA> [Resuming connection 1 to ] RouterB>exit [Connection to closed by foreign host] RouterA>show sessions % No connections open RouterA> Or the “telnet” command Disconnecting and suspending Telnet sessions

10 Advanced Telnet operation

11 Alternative connectivity tests As an aid to diagnosing basic network connectivity, many network protocols support an echo protocol. The ping target in Figure responded successfully to all five datagrams sent. The exclamation points (!) indicate each successful echo. If one or more periods (.) are received instead of exclamations on the display, the application on the router (or source device) timed out waiting for a given packet echo from the ping target.

12 Alternative connectivity tests More on ping (ICMP Echo) in a special presentation.

13 Alternative connectivity tests

14 Troubleshooting IP addressing issues ping uses the ICMP protocol to verify the hardware connection and the IP address of the network layer. This is a basic testing mechanism. telnet verifies the application layer software between source and destination. This is the most complete test mechanism available. traceroute allows the location of failures in the path from the source to the destination. Trace uses Time to Live values to generate messages from each router along the path.