Subnet IP / What's the right term and what am I searching for.

Discussion in 'Cisco' started by Jeff Mac Pherson, Jan 14, 2004.

  1. I have a Class C IP, we're in the process of moving so I requested
    from my ISP (sprint) a temporary set of IP so I can test the new
    router. I couldn't understand what the tech was talking about, so I'm
    here. They say I can just subnet an IP off my class C and use it
    there. Is this subnetting or is the term something else ?

    Is there any problem or reconfiguration of my current router if I am
    subnetting ?
     
    Jeff Mac Pherson, Jan 14, 2004
    #1
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  2. :I have a Class C IP, we're in the process of moving so I requested
    :from my ISP (sprint) a temporary set of IP so I can test the new
    :router. I couldn't understand what the tech was talking about, so I'm
    :here. They say I can just subnet an IP off my class C and use it
    :there. Is this subnetting or is the term something else ?

    The tech is correct that subnetting can sometimes be used in that kind
    of situation.


    :Is there any problem or reconfiguration of my current router if I am
    :subnetting ?

    The most obvious problem is that it requires that you squeeze your
    existing hosts into a smaller block. If you have a host at (say) .3
    and another at (say) .200 then after subnetting they aren't going to be
    in the same subnet, which might require renumbering the .200 down to
    below .127. Setting up the subnets and renumbering hosts can range
    from being a small nuisance to being essentially impractical, depending
    on your current layout and service requirements.

    It's usually not hard to configure the router itself for subnets, but
    that depends on your setup. How does the link to sprint show up
    for you? If it shows up as an IP address within your class C, then
    you cannot just go ahead and subnet: you would need close co-operation
    with sprint as they would have to change their netmask at the same
    time, and they would have to ensure that they kept routing the whole
    range to you, which would require that they added routing entries
    on their end.

    If, though, instead you have a "carrier" network between you and
    sprint (that is, your router's next hop is in a different IP address
    range entirely that is shared between you and sprint), then you can
    subnet on your router without affecting the link. You'll have to
    connect the new router to the old one and add in a routing table
    entry though.

    The actual work involved on the router is not difficult for any of this.
    It does require good advance planning, though, and the renumbering
    of hosts can be a killer in some situaitons (and not a problem at all
    in other situations.)
     
    Walter Roberson, Jan 14, 2004
    #2
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