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Setting up a loopback address

Discussion in 'Routing & Switching' started by morph, Apr 10, 2009.

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  1. morph

    morph Byte Poster

    Little help requireed :)

    So i'm messing around with my routers and switches - i've got my laptop connected to my switch which is connected to a cisco 1721 router running dhcp (via fast ethernet port).

    The dhcp is working great i'v got an ip and i can ping the gateway. I wanted to set up one of the serial ports as a loopback just so i could pretend its my isp or whatever - so i've configured the interface with an ip and set it to loopback but i cant seem to bring the interface up - no shut doesnt bring it up - i know i've probably made a fatal error, just been googling it to try and find out what that might be - help :blink
    Certifications: Network +, ITIL Foundation, CCENT, CCNA
    WIP: server/ccna security
  2. morph

    morph Byte Poster

    someones just told me somthing needs to be plugged into the serial port to bring it up - i thought maybe as i had it as a loopback, nothing would need to be plugged in ?:blink
    Certifications: Network +, ITIL Foundation, CCENT, CCNA
    WIP: server/ccna security
  3. albertc30

    albertc30 Kilobyte Poster

    It is true about the serial connection but you can just have a loopback interface set and it works as you want it.
    Just go to
    conf t#interface loopback 0
    ip address [whatever you whant here]
    no shut
    copy run start
    and you shoul be able to ping the IP of the loopback interface

    Hope it helps.
    Certifications: CCNA
    WIP: 220-701 - A+
  4. brick-it

    brick-it Bit Poster

    I'm new to this, but i remember something i read about disabling the keep alive timer on the interface so it will always be up up.... just a thought
    Certifications: HNC comp, C&G Electronics, CCNA voice
    WIP: CCNA security
  5. Richie1888

    Richie1888 Byte Poster

    are you thinking of no-keepalives ?

    i agree with albert though on his way to create a loopback is the way I would have done it.

    also something would have to be placed in the serial to bring the line protocol up ie HDLC etc if i remember correctly.
    Certifications: See Sig
    WIP: Security+

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