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  • Allow only telnet to device (Cisco)

    Design & Configure

    Allow only telnet to device (Cisco)

    Technology: Security
    Area: Device Hardening
    Vendor: Cisco
    Title: How to allow SSH only to Cisco device
    Software: 12.X , 15.X
    Platform: Catalyst switches, Routers

    Telnet protocol enables TCP/IP connections to a host fro management purposes. To allow only telnet sessions to device use configuration under line vty as below.

    To restrict Telnet Session one has to:

    Router# configure terminal
    Router(config)#line vty 0 4
    Router(config-line)#transport input telnet

    Verifying the command by trying to connect to telnet one has to Open Command Prompt:

    PC> telnet
    Trying ……Open
    User Access Verification

    Verifying if ssh connection is possible:

    PC> ssh -l admin


    Hint: remember to user telnet carefully. Telnet is a protocol that sends the content with clear text so is susceptible to sniffing attacks. You can verify telnet’s behavior easy with wireshark. Connect to any device with telnet, run the wireshark and login with user/pass. You should see your original password.

    Author: Marcin Bialy