IP and Subnetting confusion?

Shy87Shy87 Member Posts: 21 ■□□□□□□□□□
While studying for my certification I am coming across a question which really confused me. I was solving a problem where I had to find why 2 routers with ip address 192.168.1.62 and 192.168.1.65 cant communicate.


My tutor emailed me this solution But I still cant get it..
In a serial network, we usually applies / 30 mask, which includes two IPs.
192.168.1.62 belongs to network 192.168.1.32 and 192.168.1.65 belongs to network 192.168.1.64.
The serial interfaces of the routers are not on the same subnet.

Can someone please explain and tell me how can I tell which ip belongs to which network.

Comments

  • CiskHoCiskHo Member Posts: 188
    Search google or this site for "how to subnet". You will need to master this in order to get your CCNA. Devices on different subnets cannot communicate with each other unless a router (or layer 3 switch) gets involved. That is kind of the whole purpose of subnetting.... making one network into multiple smaller networks.
    My Lab Gear:
    2811(+SW/POE/ABGwifi/DOCSIS) - 3560G-24-EI - 3550-12G - 3550POE - (2) 2950G-24 - 7206VXR - 2651XM - (2) 2611XM - 1760 - (2) CP-7940G - ESXi Server

    Just Finished: RHCT (1/8/11) and CCNA:S (Fall 2010)
    Prepping For: VCP and CCNP SWITCH, ROUTE, TSHOOT
  • Shy87Shy87 Member Posts: 21 ■□□□□□□□□□
    Hmm dats ok. but can you explain the above problem to me.
  • CiskHoCiskHo Member Posts: 188
    Shy87 wrote: »
    Hmm dats ok. but can you explain the above problem to me.
    Sorry, I dont have time to teach a Cisco student how to subnet over the interwebs. There are plenty of sites dedicated to doing that already. Besides, every entry level networking book will have a chapter dedicated to subnetting. All you have to do is follow my original advice.
    My Lab Gear:
    2811(+SW/POE/ABGwifi/DOCSIS) - 3560G-24-EI - 3550-12G - 3550POE - (2) 2950G-24 - 7206VXR - 2651XM - (2) 2611XM - 1760 - (2) CP-7940G - ESXi Server

    Just Finished: RHCT (1/8/11) and CCNA:S (Fall 2010)
    Prepping For: VCP and CCNP SWITCH, ROUTE, TSHOOT
  • notgoing2failnotgoing2fail Member Posts: 1,138
    Shy87 wrote: »
    While studying for my certification I am coming across a question which really confused me. I was solving a problem where I had to find why 2 routers with ip address 192.168.1.62 and 192.168.1.65 cant communicate.


    My tutor emailed me this solution But I still cant get it..
    In a serial network, we usually applies / 30 mask, which includes two IPs.
    192.168.1.62 belongs to network 192.168.1.32 and 192.168.1.65 belongs to network 192.168.1.64.
    The serial interfaces of the routers are not on the same subnet.
    
    Can someone please explain and tell me how can I tell which ip belongs to which network.


    No problem, it's a good question, and your teacher really should have spend more time explaining it. His response sounds a little quick...

    Anyways....

    He is right, they IP's are on the wrong subnet. The /30 prefix only allows for 2 IP's to communicate. The /30 prefix is the number one used prefix believe it or not. It's the best way to conserve IP addresses for point to point links. So for example, you don't want to use a /24 for a point to point link, you'd be wasting way too many IP's!!

    So the IP's in question are class C addresses.

    192.168.1.0 / 255.255.255.0 or if you go with the prefix, it would be /24.
    That's the default class C structure.

    For your case, it's a /30. So you need to borrow 6 bits from the host bits.

    11111111.11111111.11111111.11111100 <--That's your /30
    If you convert that, it becomes: 255.255.255.252

    So if you look at your HOST bits, what's left? Only 2 zeros.
    So 2^2 (2 to the power of 2) gets you 4. But since you can't use the subnet number or broadcast, you have to do 4-2 which gets you 2.
    Exactly the 2 IP addresses that you need for a serial link!

    Back to your 2 addresses in question. Now that you know the network subnet uses 6 bits. The last octet looks like this, just like above:

    11111100


    You now have to take the first ordered bit that's used by the subnet which is the 3rd bit. That becomes 4.

    128 64 32 16 8 4 2 1 <--- you see? Equals this---> 11111100

    So now your network segments are increments of 4.

    Your first IP address of 192.168.1.62, all you have to do is find out which subnet it belongs to.

    If you work on the network increments of 4. You find out that it belongs in 192.168.1.60 - 192.168.1.63

    The .60 is your subnet ID and the .63 is your broadcast. Leaving you with .61 and .62 as your ONLY 2 valid IP addresses for your serial link.


    The other IP address 192.168.1.65 belongs in the next network segment.

    192.168.1.64 - 192.168.1.67

    .64 is your network ID and .67 is your broadcast. Leaving you with .65 and .66 as your only valid IP addresses...


    Hope that helps!
  • phoeneousphoeneous Go ping yourself... Member Posts: 2,333 ■■■■■■■□□□
    Shy87 wrote: »
    Hmm dats ok. but can you explain the above problem to me.

    Don't be lazy, you're only hurting yourself. If you want to go anywhere with Networking, you have to know subnetting. It is easier than you think.
  • billscott92787billscott92787 Member Posts: 933
    Shy87 wrote: »
    While studying for my certification I am coming across a question which really confused me. I was solving a problem where I had to find why 2 routers with ip address 192.168.1.62 and 192.168.1.65 cant communicate.


    My tutor emailed me this solution But I still cant get it..
    In a serial network, we usually applies / 30 mask, which includes two IPs.
    192.168.1.62 belongs to network 192.168.1.32 and 192.168.1.65 belongs to network 192.168.1.64.
    The serial interfaces of the routers are not on the same subnet.
    

    Can someone please explain and tell me how can I tell which ip belongs to which network.






    /30 = 11111111.11111111.11111111.11111100 or 255.255.255.252

    To detect the size of each subnet block you take 256 - the octect in which you are concentrating in (this will be where ever your mask breaks from 1's into 0's) in this case as you can see it is the 4th octect, where we have 111111 | 00. The 1's stand for the network portion of your address, the 0's stand for the host portion of your address. Each max subnet block is 256. So take this reference number and subtract the mask that you are being given in this case /30 or 255.255.255.252. You are concentrating in the 4th octect, so you would do the following:


    256 - 252 = 4.

    Network address is: 192.168.1.0/30


    So since your subnet block is a size of 4, you would have the following:


    192.168.1.0
    192.168.1.4
    192.168.1.8
    192.168.1.12
    192.168.1.16
    192.168.1.20
    192.168.1.24
    192.168.1.28
    192.168.1.32
    192.168.1.36
    192.168.1.40
    192.168.1.44
    192.168.1.48
    192.168.1.52
    192.168.1.56
    192.168.1.60
    192.168.1.64
    etc..... and so on.

    These two routers IPs are 192.168.1.62 and 192.168.1.65

    The first IP address belong to the subnet 192.168.1.60 (which has an ip range of 192.168.1.61 - 192.168.1.62) broadcast address is 192.168.1.63.


    The second IP address belongs to the subnet 192.168.1.64 (which has an ip range of 192.168.1.65 - 192.168.1.66) broadcast adress is 192.168.1.67


    So these two devices are unable to communicate because they are on a totally different subnet. I hope this helps.
  • Shy87Shy87 Member Posts: 21 ■□□□□□□□□□
    CiskHo wrote: »
    Sorry, I dont have time to teach a Cisco student how to subnet over the interwebs.

    You have time to type all these.... thankss Its not all about subnetting, its about my confusion. But anyway if you dont have time just dont reply.. thanks anyway
  • Shy87Shy87 Member Posts: 21 ■□□□□□□□□□
    Thanks so muchh @ billscott92787 and notgoing2fail. Let me go though your answers and will get back to you if i cant understand anything... thanksssssss
  • CiskHoCiskHo Member Posts: 188
    Shy87 wrote: »
    You have time to type all these.... thankss Its not all about subnetting, its about my confusion. But anyway if you dont have time just dont reply.. thanks anyway
    Its about your confusion on how to subnet. Punching "How To Subnet" into Google would have saved both those poor guys above from having to write out an essay for you. I see no need for it as it is already available on many many many sites. I have plenty of time to reply. I just don't have time to teach what is in Chapter 1 of most books. As stated being lazy in your studies will hurt you. Being too lazy to run a Google search will keep you from ever getting a networking job. Best of luck in your studies.
    My Lab Gear:
    2811(+SW/POE/ABGwifi/DOCSIS) - 3560G-24-EI - 3550-12G - 3550POE - (2) 2950G-24 - 7206VXR - 2651XM - (2) 2611XM - 1760 - (2) CP-7940G - ESXi Server

    Just Finished: RHCT (1/8/11) and CCNA:S (Fall 2010)
    Prepping For: VCP and CCNP SWITCH, ROUTE, TSHOOT
  • Shy87Shy87 Member Posts: 21 ■□□□□□□□□□
    CiskHo wrote: »
    Its about your confusion on how to subnet. Punching "How To Subnet" into Google would have saved both those poor guys above from having to write out an essay for you. I see no need for it as it is already available on many many many sites. I have plenty of time to reply. I just don't have time to teach what is in Chapter 1 of most books. As stated being lazy in your studies will hurt you. Being too lazy to run a Google search will keep you from ever getting a networking job. Best of luck in your studies.

    thanks for ur wishes lol..yh i got my masters degree bcos of my laziness and hopefully soon i will get my ccna as well. icon_wink.gif
  • loxleynewloxleynew Member Posts: 405
    CiskHo wrote: »
    Its about your confusion on how to subnet. Punching "How To Subnet" into Google would have saved both those poor guys above from having to write out an essay for you. I see no need for it as it is already available on many many many sites. I have plenty of time to reply. I just don't have time to teach what is in Chapter 1 of most books. As stated being lazy in your studies will hurt you. Being too lazy to run a Google search will keep you from ever getting a networking job. Best of luck in your studies.

    Don't be an @ss lol. You can say that about everything. What if someone asked how to partition their hard drive? Sure it is on many sites but she is asking on this site. Don't read post just to give some smart @ss reply. It's not helping anyone. Especially with subnetting everyone knows it just "clicks" after a while You can read it on 5 different sites and maybe it will only click that 5th time because of a certain way someone put it.
  • billscott92787billscott92787 Member Posts: 933
    loxleynew wrote: »
    Don't be an @ss lol. You can say that about everything. What if someone asked how to partition their hard drive? Sure it is on many sites but she is asking on this site. Don't read post just to give some smart @ss reply. It's not helping anyone. Especially with subnetting everyone knows it just "clicks" after a while You can read it on 5 different sites and maybe it will only click that 5th time because of a certain way someone put it.



    I have to agree. I read many websites, and ended up actually teaching myself through binary. Then I read a the CCENT subnetting portion of the CCNA Exam Certification Library and it TOTALLY confused me, I had to go back and re-teach myself everything. Subnetting is something that takes practice and time to learn. Some people think it is the hardest portion of the CCNA. I didn't think it was that bad, but I spent A LOT of time learning it. I enjoy helping out, especially since it makes me recall everything and I can keep it fresh in my mind as well.
  • notgoing2failnotgoing2fail Member Posts: 1,138
    I have to agree. I read many websites, and ended up actually teaching myself through binary. Then I read a the CCENT subnetting portion of the CCNA Exam Certification Library and it TOTALLY confused me, I had to go back and re-teach myself everything. Subnetting is something that takes practice and time to learn. Some people think it is the hardest portion of the CCNA. I didn't think it was that bad, but I spent A LOT of time learning it. I enjoy helping out, especially since it makes me recall everything and I can keep it fresh in my mind as well.


    It doesn't come easy for me. Especially since I don't do it everyday. When I am focused on it, I am like a dart, it is clear.

    But as soon as I step away for awhile, I get rusty. It's just not a normal way of thinking for most humans so it's not easy.

    There's also soooo many ways to learn it that it can get confusing. I am a fan of Wendell Odom and have many of his books. But his teaching style is tough. I'm not sure he's the best teacher....
  • billscott92787billscott92787 Member Posts: 933
    It doesn't come easy for me. Especially since I don't do it everyday. When I am focused on it, I am like a dart, it is clear.

    But as soon as I step away for awhile, I get rusty. It's just not a normal way of thinking for most humans so it's not easy.

    There's also soooo many ways to learn it that it can get confusing. I am a fan of Wendell Odom and have many of his books. But his teaching style is tough. I'm not sure he's the best teacher....



    I agree I like his books, I used his series to study for my CCNA. Very good stuff. But, I totally skipped the subnetting section in that book because it confused me.
  • mikem2temikem2te Member Posts: 407
    Shy87 wrote: »
    Thanks so muchh @ billscott92787 and notgoing2fail. Let me go though your answers and will get back to you if i cant understand anything... thanksssssss

    If you do have any more questions just ask, don't let the odd unhelpful post put you off. It's a friendly helpful forum (most of the time).

    Subnetting is a tricky one, there's lots of concepts to grasp and every web site you look at describes it in different ways. I'm not surprised the email you had from your tutor didn't help, it doesn't seem to make much sense, he is mentioning a /30 network but describing a /27
    Blog : http://www.caerffili.co.uk/

    Previous : Passed Configuring Microsoft Office SharePoint Server 2007 (70-630)
    Currently : EIGRP & OSPF
    Next : CCNP Route
  • thenjdukethenjduke Member Posts: 894 ■■■■□□□□□□
    Shy basically it is subnet to /30 which is usually the case with serial links. That give them 2 host on the subnet. The two ip address are in different subnets this is the reason for it.
    CCNA, MCP, MCSA, MCSE, MCDST, MCITP Enterprise Administrator, Working towards Networking BS. CCNP is Next.
  • mikem2temikem2te Member Posts: 407
    I use this when I'm feeling lazy-

    Online IP Subnet Calculator
    Blog : http://www.caerffili.co.uk/

    Previous : Passed Configuring Microsoft Office SharePoint Server 2007 (70-630)
    Currently : EIGRP & OSPF
    Next : CCNP Route
  • billscott92787billscott92787 Member Posts: 933
    mikem2te wrote: »
    I use this when I'm feeling lazy-

    Online IP Subnet Calculator



    Mike I think Most network engineers use the calculator. I asked a few of our network engineers here a subnetting question when I was studying for my CCNA, none of them could answer it. Honestly, none of them even have their CCNA at the facility I work for.
  • notgoing2failnotgoing2fail Member Posts: 1,138
    Mike I think Most network engineers use the calculator. I asked a few of our network engineers here a subnetting question when I was studying for my CCNA, none of them could answer it. Honestly, none of them even have their CCNA at the facility I work for.


    I think you're right about this. The subnet calculator is very easy to use but I honestly think, one should only use it if they understand the concepts behind it.

    Anyways, back to Wendell Odom, I wasn't going to say it, but I too skip his chapter on subnetting, he confuses the HECK out of me with his style.

    He has a very in-depth approach I noticed, for example, I'm currently reading his chapter on IPv6, which is chapter 17. And this guy gets really really in depth....and appreciate it, and I think he's doing his best to prepare you, but when it comes to subnetting, I think one is better off looking elsewhere.....

    Once you get your CCNA or you want to go back and get some really good deep stuff, he's good for that....but for newbies, I think he can really make a topic sound "too big of a deal" when it doesn't have to be...
  • miller811miller811 Member Posts: 897
    Shy87 wrote: »
    Hmm dats ok. but can you explain the above problem to me.

    http://www.techexams.net/forums/ccna-ccent/38772-subnetting-made-easy.html
    I don't claim to be an expert, but I sure would like to become one someday.

    Quest for 11K pages read in 2011
    Page Count total to date - 1283
  • binargsbinargs Member Posts: 55 ■■□□□□□□□□
    you better get good at subneting and understand it thoroughly, or there is no way in hell that you can pass the ccent exam
  • mella060mella060 Member Posts: 196
    I agree I like his books, I used his series to study for my CCNA. Very good stuff. But, I totally skipped the subnetting section in that book because it confused me.

    Same for me. I went through it briefly but that was about it. I found it too confusing after going through Todd Lammles book.

    The best way to learn subnetting is to go through the chapter in Lammles book and the method Jeremy uses in the CBTs. Done
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