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Another Subnetting Question!

Discussion in 'Routing & Switching' started by Crazydave1990, Jun 18, 2012.

  1. Crazydave1990

    Crazydave1990 Bit Poster

    Hey folks!

    Ok... So, I think I have my head around the BASICS of subnetting. I'm no pro yet, so, if this is a stupid question, then I apologise.

    Right ok, so, lets imagine that we have an I.P address - And let's imagine we need to subnet that into 5 networks.

    Now, I know a concept atm that basically allowed me to split this I.P into enough pieces that I require, I'm not going to bore you with all the details of this method, but I'll write down my results - /24 (
    Networks Required: 5

    Subnet =

    IP Ranges:

    (R1 = Router 1, R2 = Router 2 etc.)
    R1 Network: -
    R1 WAN to R2: -
    R2 Network: -
    R2 WAN to R3: -
    R3 Network: -

    Now, if we imagine that this network is segregated over a WAN, and we have two WAN lines, linking R1 to R2 and R2 to R3, this WAN line will only need two IP's - so that means in total for the WANs, I only need four (data transferable IP addresses) addresses! That is a Mahoosive waste isn't it!

    So my question is this, how do I route the WANS together, without wasting 28 addresses!

    I know this is really detailed, and I know it's probably a nightmare to read/understand, thank you for your patience, and thank you in advance for your answers.
  2. soundian

    soundian Gigabyte Poster

    Variable length subnet masks.
    IP Addressing and Subnetting for New Users - Cisco Systems
    Last edited by a moderator: Jun 19, 2012
    Certifications: A+, N+,MCDST,MCTS(680), MCP(270, 271, 272), ITILv3F, CCENT
    WIP: Knuckling down at my new job
  3. Coupe2T

    Coupe2T Megabyte Poster

    As Soundian says, you will learn about it under VLSM, which is basically subnetting a subnet. Which probably sounds really confusing, but you soon get your head around it.
    Certifications: ECDL, Does that Count!?!
  4. Straylight

    Straylight Bit Poster

    Currently revising for ICND2 again, saw this, thought I'd practise by trying an answer. Excuse long post, maybe it will help someone else or they can tell me I've gone way wrong here. :)

    Making efficient use of the network space. Assumed as per OP, we need 5 subnets with 30 hosts and best use of remaining space.

    Subnets with 30 hosts / 27

    Ranges - 31
    ...32 - 63
    ...64 - 91
    ...92 - 127
    ...128 - 159

    Subnets with 14 hosts / 28

    Ranges - 175
    ...176 - 191
    ...192 - 207
    ...208 - 223
    ...224 - 239

    Smallest subnet, 6 hosts. / 29

    Range - 247

    WAN links. 2 hosts. / 30

    Ranges - 251
    ...252 - 255

    supernets for your routing protocols. / 27 / 28 / 29 / 30
    Certifications: CCENT
    WIP: CCNA MS 70-680

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