Subnetting

Discussion in 'Cisco' started by AC, Jul 18, 2003.

  1. AC

    AC Guest

    Set up the scenario a little here:

    We have a /23 network coming in through a Cisco router. At the moment, our
    Linux box is using proxy arp and has the network divided into two pieces. I
    want to elimate proxy arp and use the Linux box as a proper router.
    Basically I want to take our /23 and cut it into two /24s.

    I'm pretty sure I can do the configuration on the Linux box, but the Cisco
    box has me a little confused. I think it might be as simple as the IOS
    command:

    ip route y.y.y.y 255.255.255.0 x.x.x.21

    (where y is the upper /24 and x is the lower /24).

    Is this right, or am I missing something?
     
    AC, Jul 18, 2003
    #1
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  2. You're right.
     
    Barry Margolin, Jul 18, 2003
    #2
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  3. AC

    AC Guest

    I'm glad I'm right about something. Let's try a more tangible example.

    We've got a /23:

    10.101.104.0/23

    Ethernet1 on the cisco unit has the following configuration:

    interface Ethernet1
    ip address 10.101.104.0 255.255.254.0
    no ip directed-broadcast

    To forward the upper /24 to the Linux router, the entry is:

    ip route 10.101.105.0 255.255.255.0 10.101.104.2

    (Where 10.101.104.2 is the Linux router's address on the lower /24)

    It's that simple from the Cisco box?
     
    AC, Jul 18, 2003
    #3
  4. Yes. You would also normally change the subnet mask in the "ip address"
    statement to 255.255.255.0.
     
    Barry Margolin, Jul 18, 2003
    #4
  5. AC

    AC Guest

    So the Ethernet1 config would like this?

    interface Ethernet1
    ip address 10.101.104.0 255.255.255.0
    no ip directed-broadcast
     
    AC, Jul 18, 2003
    #5
  6. Actually, the address needs to be in the range 10.101.104.1 through
    10.101.104.254. .0 is the network address and .255 is the broadcast
    address.
     
    Barry Margolin, Jul 18, 2003
    #6
  7. AC

    AC Guest

    Okay. Can you give me an example of how the Interface commands should look?
    Sorry to be a pain, but I feel like I'm missing something here.
     
    AC, Jul 21, 2003
    #7
  8. interface Ethernet1
    ip address 10.101.104.1 255.255.255.0
     
    Barry Margolin, Jul 21, 2003
    #8
  9. AC

    AC Guest

    Why do I suddenly feel like an idiot?

    Thanks for the help.
     
    AC, Jul 21, 2003
    #9
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