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Subnetting Vs Different Network Ranges

Discussion in 'Networks' started by Twonk, Oct 15, 2008.

  1. Twonk

    Twonk New Member

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    Hi all,

    Noob here so please go easy :oops:

    I'm planning on taking my CCNA next year, I do bits and bobs of networking in my current job but find it quite interesting and would like to pursue it further and as a starting point to that, have taught myself subnetting.

    After much practice I now understand it inside out and back to front but it raised a couple of questions for me that I wondered if you could help me with.

    The first I think I may already know the answer to, but essentially it's this - With subnetting, obviously you are cutting down on broadcasts, you are using your router(s) to segment unnessecary (sp) trafffic to it's own intended network which is fine, but what is the advantage in subnetting rather than just using a different network range anyway, seeing as both methods require the packet to be routed anyway.

    A rough example, say I had a bog standard class c network of 192.168.x.x with a subnet mask of 255.255.240.0 so my first useable address on my first subnet subnet is 192.168.0.1 up to 192.168.15.254 (assuming subnet 0 is allowed) and my next subnet would be 192.168.16.1 up to 192.168.31.254

    What is the advantage in doing the above over say, just creating two network ranges - 192.168.1.x and 192.168.2.x and setting up a static route between them?

    However, as I mentioned earlier, I think I may already know at least some of the answer to this question, and I'm assuming it's scalability, i.e. with two different network ranges, at least class c ones, you are limited to 254 hosts on each network

    Would appreciate some network guru's thoughts on this!!

    My second question is a bit quicker, I was at a customers the other day, and noticed that one of their sites was using an internal IP Range of 192.0.x.x.

    Am I being stupid or are they external / public ip's? I thought on a class c network, it was only 192.168.x.x addresses that were non-routeable or is it anything thats 192.x.x.x?

    Thanks for your help and sorry if these are really stupid questions!!
     
  2. jiggy

    jiggy Nibble Poster

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    hi Twonk, welcome to the forums. Might pay to introduce yourself in the new members section...just to say hi.

    To be honest Im not entirely sure what you are asking in your first question but maybe someone with a bit more networking "nouse" can answer it for you. Yes a standard class C only has 254 hosts but what if you have 500 pc's that need addresses and you want them on the same subnet so you dont have to setup a route or for ease of management...then you have to go with a /23. Anyway Im not sure Im answering your question so Ill leave it.

    Re question 2, I have seen this at client sites that have been around for a long time, back when every machine used to have its own publicly addressable ip number. As time has gone on the addresses were hard coded into a number of applications on the network that reference servers with these ip's (very bad idea) and now cant be changed without a whole heap of work. Hence it was easier just to leave them as they are. No traffic can get to them from external because of the firewall setup and nat takes care of outgoing traffic.

    Hope that helps

    Jiggy.

    by the way...there are no stupid questions :D
     
    Certifications: MCSE
    WIP: ABC's
  3. FlashDangerpants

    FlashDangerpants Nibble Poster

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    Imagine your company has 2 sites, and each site has 3 small networks (one each for two in house VLANs, and a third for a guest wireless network for instance). You could use a single class C address space at each site and subnet it. Or you could use a whole class c space for each network.

    Now consider the routers at each site. If you subnet a single class C then, then each router only need to know the where that C range is to find any of the subnets. So that's one entry per site. If you took the second option it would be 3 entries per site.

    Now assume that the company has 20 sites... If you use subnetting you will have much shorter and more efficient routing tables, which means among other things that your routers will perform better, and you will have a much easier time maintaining your set up. The downside is that you have to take much more care about what you are doing. Although that's kind of the upside too.

    you will notice that using subnetting would also have avoided wasting hundreds of IP addresses, which can be important sometimes.
     
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  4. supernova

    supernova Gigabyte Poster

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    why would you want to break down a private class into multiple subnets

    Well think about ...

    what if you had routers between floors in a building and a backbone linking them up.

    Or several buildings interconnected via fibre

    what does routeable traffic mean and does routeable traffic mean in terms of traffic control?

    why would you preferably want a building or site to be based on the same private class?


    or have i miss understood your post?
     
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  5. supernova

    supernova Gigabyte Poster

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    Ahh i think i got you...

    no with class c you have to base it on the default class c subnet 255.255.255.0

    so if you want to use class C and have 5 networks of 30 devices it would be 255.255.255.254

    the first three octets must still be 255 for a class c network

    you can break these rules, however, big headache. Many companies have a policy for this type of stuff
    (really you can do nearly any thing really as long as it doesn't conflict..lol)

    I would select a bigger class range and subnet, if you needed more hosts (254) per network, but i dont know much about planning such things

    Andi
     
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  6. Twonk

    Twonk New Member

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    Thanks for your reply Andi, taking the time to reply is appreciated.

    I would however, disagree with the above, regardless of class, you can subnet any IP range with any subnet mask you like, IP Classes are fairly irrelevant as it's obviously the subnet mask that defines how much / which parts of the IP Address are network and which are host.

    Also, a subnet mask of 255.255.255.254 doesn't give you any useable hosts per subnet. If you think of 254 written out in binary it's - 11111110, so your next subnet would be the lowest '1' in that binary figure, which is a '2'

    So your first subnet (assuming IP Zero and a IP Range of 192.168.1.x) is 192.168.1.0 (network address) up to 192.168.1.1 (broadcast address), from there you'd go to 192.168.1.2 (network address) up to 192.168.1.3 (broadcast address)
     
  7. supernova

    supernova Gigabyte Poster

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    I did say you can in fact do anything you like, its true we dont often use default subnets but for such a small network is it worth the hassle?

    Also that your company will probably have a policy in place for this type of thing.

    I used foundation examples because i thought you were someone that was diving into a CCNA , your obviously not.

    Yeap because i was meant to type 255.255.255.224 .. lmao

    2048 subnets of 30 hosts

    Network----------Host Range---------------------Broadcast
    192.168.0.0------192.168.0.1 to 192.168.0.30-----192.168.0.31
    192.168.0.32-----192.168.0.33 to 192.168.0.62----192.168.0.63
    192.168.0.64-----192.168.0.65 to 192.168.0.94----192.168.0.95

    ..... and so on


    Sorry about that typo :cracking

    Andi
     
    Certifications: Loads
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  8. andrewleighton657

    andrewleighton657 New Member

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    hi, i know what you're saying... the answer is no, it makes no difference whatsoever how you network. you could have, say, four departments, each on their own subnet and you could have a 10. on one 172. on the other 169. (not recommended) on the third and 192. on the fourth... each using different subnet masks as well.

    it makes no difference because as long as the router is set up with the two ip's on each subnet it would still forward traffic (no difference from a home network and the internet)

    the reason people dont do this and its not recommended is just for convenience... it would be a lot cleaner and more professional to divide the network up with the same range of ip's and the same class... a lot easier to remember as well.

    however, i once worked in a government building and one department had highly confidential data and they were on a completely difference range from the rest of the company (172.31.), everyone else was on 10.10.; they didnt sign in to the domain either and had their own workgroup. however, to access the internet they went through the 10.10. network to acccess the router... difference ranges, but it all still worked
     
  9. andrewleighton657

    andrewleighton657 New Member

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    in response to andi c... thats not strictly true, a subnet mask of 255.255 for 192.168 is still a private range and would still work and is not routable on the net... you dont have to use 255.255.255
     
  10. John Neerdael

    John Neerdael Nibble Poster

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    It is a private range and theoretically possible but isnt this not in range with the 'rules' in place on ip addressing, if you need subnetting on a Class B scale you would design your network on a 172.16.0.0/12 range I would suppose? Or am I just totally off here, would be nice to get some input on this from real job experience. As towards your 192.0.x.x question, yes only 192.168.x.x is a private network range and 192.0.x.x is not a valid ip address to use on a private lan.

    http://en.wikipedia.org/wiki/Private_network
    http://tools.ietf.org/html/rfc1918
     
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