Telnet Config (Answer)

certskills
By certskills July 27, 2012 07:00

This blog post simply lists the answers to the earlier lab from a few days ago. No guile, no tricks, just a chance to exercise. The topic for this post: starting from a wiped-clean router, configure support for Telnet from a local PC client on a local LAN.

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: Router Triangle with IP Subnets

This lab does require that you do a little subnetting math as well. The requirements state the routers use the highest IP addresses in each subnet, but the lab did not list the specific IP address to be used for each router interface. R1 needs IP addresses for each interface, but to meet the requirements of the lab, it only needs an IP address on its F0/0 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.

Example 1: R1 Telnet Config

Telnet Config
Config Museum: SSH Config
certskills
By certskills July 27, 2012 07:00
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8 Comments

  1. adrikayak January 7, 07:38

    Hello Wendell

    Wouldn’t it be also necessary to issue a “transport input telnet”? As far as I now, “transport input” defaults to “none”

    Reply to this comment
  2. Oliwer June 26, 05:41

    Hello Wendell,

    If i’m not wrong the default transport input setting for the routers is none whereas all for switches only. Why don’t we need the transport input telnet command configured in this lab? What is the reason of default login command in vty lines on routers, whereas on swithes the default is no login?

    Reply to this comment
    • CCENTSkills July 5, 09:27

      Hi Oliwer,
      I agree, routers should default to “transport input none”, meaning that this lab should include “transport input telnet” or “transport input all”. My mistake; I’ll fix it in a moment.

      On your other question, I’m not sure of the intent – long history there, and never heard the story.
      Wendell

      Reply to this comment
  3. troyl June 26, 20:05

    I’m confused, the ICND1 100-105 Cert Guide book states at the bottom of page 178:
    “Cisco routers default to transport input none, so that you must add the transport input line subcommand to enable Telnet and/or SSH into a router.”

    Do some routers default to “input none” and some to “input all”? The Cisco 3725 I’m looking at seems to default to “input all”

    Reply to this comment
    • CCENTSkills July 5, 09:24

      Hi Troy,
      I don’t have a 3725 to test with. Per the IOS doc, through 15.5M at least, Cisco claims the default is “none” on routers. That’s the best I could tell you.

      If it’s a lab device, can you do an “erase startup-config” on the 3725 without harming others, and then a reload? And then do a “show terminal” and see what the transport input settings are. I’d personally be curious, if that’s an experiment you can run.
      Wendell

      Reply to this comment
      • Bav April 1, 10:16

        I’ve labbed this in packet tracer and on a 1941 router it seems to default to transport input all.

        Reply to this comment
        • CCENTSkills April 3, 10:43

          Hi Bav,
          Thanks for the additional data point. However, personally, I wouldn’t trust default behavior based on anyone’s Sim, even as nice a product as PT. Until I see real IOS for a router with “all” as default, I’ll stick with “none” as a current belief. Thanks again.
          W

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