Answers: Configuring Telnet

This lab asks for the required, non-default configuration to enabled Telnet on router R1, with other conditions. Check out the original lab problem statement for the details. Figure 1 repeats the network diagram, and Example 1 lists the answer.

Figure 1: Lab Topology with IP Subnet

This lab does require that you do a little subnetting math as well. The requirements state for the router to use the highest IP addresses in the subnet, but the lab did not list the specific IP address to be used for each router interface. R1 needs an IP address on its G0/0 interface, which is shown in subnet 172.18.1.0/26. That subnet has a range of usable addresses from 172.18.1.1 – 172.18.1.62, so the configuration uses the .62 address for R1’s F0/0.

interface GigabitEthernet0/0
 no shutdown
 ip address 172.18.1.62 255.255.255.192
!
line vty 0 15
 password Certskills
 transport input telnet
 
! Note – if you only did VTY’s 0 through 4, that’s ok.
! The config relies on a default vty subcommand of login

Example 1: R1 Telnet Config

Cisco routers and switches allow a simple security method for both console and Telnet access. Basically, all you have to do is tell the device to use that method by supplying a prompt for the password (the login subcommand) and defining the password’s value (the password subcommand).

Note that the answer shows the configuration of the VTY password (to support Telnet) with VTYs 0 through 4 as separate from the configuration of VTYs 5 through 15. This quirk of Cisco output has to do with the fact that older IOS versions support only VTYs 0 through 4. You could have used the commands literally shown in the answer example, or you could have used the command line vty 0 15, followed by those same password and login commands.

Known Issues in this Lab

This section of each Config Lab Answers post hopes to help with those issues by listing any known issues with Packet Tracer related to this lab. In this case, the issues are:

Why Would Cisco Packet Tracer Have Issues?

(Note: The below text is the same in every Config Lab.)

Cisco Packet Tracer (CPT) simulates Cisco routers and switches. However, CPT does not run the same software that runs in real Cisco routers and switches. Instead, developers wrote CPT to predict the output a real router or switch would display given the same topology and configuration – but without performing all the same tasks, an actual device has to do. On a positive note, CPT requires far less CPU and RAM than a lab full of devices so that you can run CPT on your computer as an app. In addition, simulators like CPT help you learn about the Cisco router/switch user interface – the Command Line Interface (CLI) – without having to own real devices.

CPT can have issues compared to real devices because CPT does not run the same software as Cisco devices. CPT does not support all commands or parameters of a command. CPT may supply output from a command that differs in some ways from what an actual device would give. Those differences can be a problem for anyone learning networking technology because you may not have experience with that technology on real gear – so you may not notice the differences. So this section lists differences and issues that we have seen when using CPT to do this lab.

Beyond comparing your answers to this lab’s Answers post, you can test in Cisco Packet Tracer (CPT) or Cisco Modeling Labs (CML). In fact, you can and should explore the lab once configured. For this lab, once you have completed the configuration, try these verification steps. 

1. Open a command prompt on the PC and test connectivity to R1’s G0/0 IP address using the ping command.
2. If successful, test Telnet using the telnet command to that same IP address. If successful, you should be prompted for a password, and if you supply the password you just configured, you should reach the user mode prompt of the router.