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Just looking for a little help on the evil 70-291

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  • Just looking for a little help on the evil 70-291

    Well I think Microsoft should be pretty happy since I have failed this test 9 times (125 x 9=$$$)


    I am struggling in the following:

    TCP/IP Subnetting
    DNS

    Everything else was pretty high on the bar.

    Thanks
    David

  • #2
    Re: Just looking for a little help on the evil 70-291

    I will try to put together a teachme on subnetting... give me some time to write it though

    Are you perfectly happy with binary and hexadecimal?


    Tom
    For my own and your protection, I do not provide support by private message under any circumstances. All such messages will be deleted and ignored.

    Anything you say will be misquoted and used against you

    Comment


    • #3
      Re: Just looking for a little help on the evil 70-291

      Originally posted by Stonelaughter View Post
      I will try to put together a teachme on subnetting... give me some time to write it though

      Are you perfectly happy with binary and hexadecimal?
      Let me get this straight... you're going to put a little something together on a topic that takes some authors 600 pages to write about? Most would have thrown him a few ISBN numbers. You are definitely the man
      VCDX3 #34, VCDX4, VCDX5, VCAP4-DCA #14, VCAP4-DCD #35, VCAP5-DCD, VCPx4, vEXPERTx4, MCSEx3, MCSAx2, MCP, CCAx2, A+
      boche.net - VMware Virtualization Evangelist
      My advice has no warranties. Follow at your own risk.

      Comment


      • #4
        Re: Just looking for a little help on the evil 70-291

        Until Tom gets that "teachme" together check out these:

        http://www.3com.com/other/pdfs/infra..._US/501302.pdf

        http://www.trainsignal.com/index.asp...WPROD&ProdID=8 (biggles77 swears by it)

        http://www.petri.com/dns.htm
        Regards,
        Jeremy

        Network Consultant/Engineer
        Baltimore - Washington area and beyond
        www.gma-cpa.com

        Comment


        • #5
          Re: Just looking for a little help on the evil 70-291

          OK... Basic IP as it was before we got too big for it:

          An IP address is a 32 bit binary number which is used to "address" a particular "host" on the network. The TCP/IP "Stack" programs in a "host" take the "Destination IP Address" from each packet it receives and perform a Logical NOR with it's own IP address. If it gets all zeroes, the packet is for this host. (i.e. if the "destination" and "local IP address" are the same). The TCP/IP stack then processes the packet and life is good.

          For convenience, the IP address is written for humans as 4 eight-bit numbers represented in decimal - the "dotted decimal" notation.

          However - one day people realised that 32 bits wasn't going to be enough; especially with a large quantity of the available addresses being "reserved" for special uses. So - they came up with subnetting and a more modern version of routing. (In the days of the original TCP/IP standard, all you had to know was the destination IP and the routers would know which direction to send the packet).

          Because of subnetting, the same "network" can appear in unlimited places all over the world. Because of subnetting, you can have lots of hosts in a building which has only one "live" internet IP address, and all of those hosts can access the internet.

          How we do it is, we split up the IP address into "Network ID" and "Host ID". On the "live internet", we have three main "classes" of IP address - Class A, Class B and Class C. In Class A addresses, the first eight bits make up the network ID and the other 24 make up the host ID. Lots of hosts, you will acknowledge - a 24 bit number is very big. In Class B addresses, the first sixteen bits make up the network ID, and the second sixteen make up the host ID. In Class C, the first 24 bits are network and the last 8 make the host. So - with a Class C network, you can only have 254 hosts (host ID's of all 1's or all 0's are not permitted); so you lose 0000 0000 and 1111 1111 (0 and 255) and are left with 1 to 254. All addresses which are "live" on the internet are either Class A, B or C. Full stop. There are no more.

          So - that's Basic TCP/IP covered.

          Now we can make more networks OUTSIDE the internet by using different numbers of bits for network ID and host ID. For instance, there is no reason why on our internal network we couldn't use 3 bits for network ID and 29 for host ID. We could have a LOT of computers, all on the same IP network. Or, if our organisation only has 5 computers, we could have a 29 bit network ID and a 3 bit host ID. That way, we can add more networks later because we have LOADS of them.

          The way we make this change is using a "subnet mask". You match up a subnet mask, in binary, with an IP address, also in binary. Line up bit 0 with bit 0 and bit 31 with bit 31. Now - any bit in the IP address which lines up with a "1" in the subnet mask is part of the network ID. Any part which lines up with a "0" in the subnet mask is part of the host ID.

          There are a couple of rules. The Network ID MUST be the "most significant bits" and MUST be contiguous (i.e. all the "1"s in the subnet mask must be all together and on the left). The Host ID MUST be the least significant bits and contiguous (i.e. all the zeros in the subnet mask must be together and on the right).

          Some Examples:


          IP address 35.15.250.126 (hex 23.0F.FA.7E)

          in binary is:
          0010 0011 * 0000 1111 * 1111 1010 * 0111 1110
          1111 1111 * 0000 0000 * 0000 0000 * 0000 0000 (Class A subnet mask as per the Internet - 255.0.0.0)
          0010 0011 * 0000 0000 * 0000 0000 * 0000 0000 The network ID with a Class A mask - 35.0.0.0 (the Host ID is therefore 0.15.250.126 within the 35 network)


          HOWEVER

          If we decided to change our subnet mask to give us more flexibility on networks and to reduce the vast number of hosts available (because we don't need them) we can change the subnet mask to a Class C one - reducing us to 254 Hosts but VASTLY increasing the number of networks we can use internally. Example 2 below...


          IP address 35.15.250.126 (hex 23.0F.FA.7E)

          in binary is:
          0010 0011 * 0000 1111 * 1111 1010 * 0111 1110
          1111 1111 * 1111 1111 * 1111 1111 * 0000 0000 (Class C subnet mask or 255.255.255.0)

          0010 0011 * 0000 1111 * 1111 1010 * 0000 0000 is now the network ID (35.15.250.0) and the host ID is 126.


          To appreciate the value of this, if I now put another bunch of PC's on the network with the SAME subnet mask but with a different IP address scheme of 35.15.240.n, they are on a different network and CANNOT talk to the first set! They can all talk to each other, but not to computers with 35.15.250.n addresses. Before subnet masks came along, any IP could talk to any other IP. Now, we would need a ROUTER between these two sets of PCs to allow them to talk to one another.

          ** to be continued **
          Last edited by Stonelaughter; 13th April 2007, 00:06.


          Tom
          For my own and your protection, I do not provide support by private message under any circumstances. All such messages will be deleted and ignored.

          Anything you say will be misquoted and used against you

          Comment


          • #6
            Re: Just looking for a little help on the evil 70-291

            Now I want to have a look at this but with even more variety in the subnet mask...

            Consider an IP address of 9A.BC.DE.F0 (154.188.222.240)

            Instead of using a "Class" subnet mask, let's use 255.255.192.0 (FF.FF.C0.00)

            Have a look at the binary:

            1001 1010 * 1011 1100 * 1101 1110 * 1111 0000 (IP address)
            1111 1111 * 1111 1111 * 1100 0000 * 0000 0000 (Subnet Mask)


            You can see that the last **14** bits are the host ID, now... so you can have a host ID which LOOKS in decimal like it's zero - but it's not. For instance the IP address shown has a host ID of 1E.F0 (30.240) (line up the bits above). The network ID is 9A.BC.C0.00 (154.188.192.0) - so the third "octet" in Decimal is part host and part network... better to work in binary or hex!!!

            If we zeroed the last eight bits of the IP address, it's STILL A VALID ADDRESS, of 154.188.222.0.

            Last thing before my head explodes and to allow for any questions:

            There are TWO WAYS to write IP/Network IDs. You can write them complete with the full subnet mask (e.g. 192.168.0.1, 255.255.255.0) or you can use the more popular way these days of putting the number of bits in the network ID after the IP address (for instance 192.168.0.1/24 is the same meaning as the first example).

            The network ID from earlier would be written 154.188.192.0/18.


            Tom
            For my own and your protection, I do not provide support by private message under any circumstances. All such messages will be deleted and ignored.

            Anything you say will be misquoted and used against you

            Comment


            • #7
              Re: Just looking for a little help on the evil 70-291

              I'm surprised no one has posted this

              http://www.learntosubnet.com/

              Comment


              • #8
                Re: Just looking for a little help on the evil 70-291

                http://www.trainsignal.com/index.asp...PROD&ProdID=35

                Chris Bryant has a very good lesson on subnetting in this video. Well worth having.
                1 1 was a racehorse.
                2 2 was 1 2.
                1 1 1 1 race 1 day,
                2 2 1 1 2

                Comment


                • #9
                  Re: Just looking for a little help on the evil 70-291

                  Do the last two replies mean that my lesson was [email protected]? It was 11.30pm when I began writing... LOL


                  Tom
                  For my own and your protection, I do not provide support by private message under any circumstances. All such messages will be deleted and ignored.

                  Anything you say will be misquoted and used against you

                  Comment


                  • #10
                    Re: Just looking for a little help on the evil 70-291

                    Originally posted by Stonelaughter View Post
                    Do the last two replies mean that my lesson was [email protected]? It was 11.30pm when I began writing... LOL
                    Not at all m8.

                    I only posted that site as i used it when i was learning.

                    I haven't actually read yours yet.

                    Comment


                    • #11
                      Re: Just looking for a little help on the evil 70-291

                      Ditto Wuliie's post.
                      1 1 was a racehorse.
                      2 2 was 1 2.
                      1 1 1 1 race 1 day,
                      2 2 1 1 2

                      Comment


                      • #12
                        Re: Just looking for a little help on the evil 70-291

                        Just to add a little to Toms teach me...

                        These are some terms Tom used I thought might need to be defined for some people.

                        Definitions: (Tom, correct me if I'm wrong on any of these)

                        Host http://www.uwo.ca/its/doc/manuals/handbook/node17.html
                        Live IP address (aka public IP address) http://www.vicomsoft.com/glossary/addresses.html
                        Logical NOR http://en.wikipedia.org/wiki/Logical_NOR
                        Network http://en.wikipedia.org/wiki/Computer_network


                        Nice write up Tom.
                        Let me just nitpick it a little.
                        Originally posted by Stonelaughter View Post
                        Because of subnetting, the same "network" can appear in unlimited places all over the world. Because of subnetting, you can have lots of hosts in a building which has only one "live" internet IP address, and all of those hosts can access the internet.
                        Don't you mean PAT or NAT?
                        Technically speaking, subnetting is the act of "borrowing" host bits and adding them to the network bits.

                        e.g. Lets use 10.0.0.1/15. Because it's in the class A range, the first 8 bits are the network bits.
                        Code:
                        0 0 0 0 1 0 1 0   0 0 0 0 0 0 0 0   0 0 0 0 0 0 0 0   0 0 0 0 0 0 0 1 
                        1 1 1 1 1 1 1 1   1 1 1 1 1 1 1 0   0 0 0 0 0 0 0 0   0 0 0 0 0 0 0 0 
                        |-------------|   |-----------| |-----------------------------------|
                           Network 	     Subnet	 		Host
                            Bits	      Bits			Bits


                        All addresses which are "live" on the internet are either Class A, B or C. Full stop. There are no more.
                        There's plenty of subnetting on the Internet. In fact the depletion of IP addresses is what led to subnetting. (Necessity is the mother of invention) My company has a /29 network on the Internet.
                        Maybe I misunderstood what you're saying.

                        Before subnet masks came along, any IP could talk to any other IP. Now, we would need a ROUTER between these two sets of PCs to allow them to talk to one another.
                        Correct me if I'm wrong (and I very well may be) but the Internet originally had it so that every network had an 8-bit mask. This means that there needed to be routers back then.
                        It then moved to having Classes and then to Classless (CIDR).



                        Originally posted by biggles77 View Post
                        http://www.trainsignal.com/index.asp...PROD&ProdID=35

                        Chris Bryant has a very good lesson on subnetting in this video. Well worth having.
                        Wholeheartedly agree. I watched that whole series and it was excellent.
                        Last edited by JeremyW; 13th April 2007, 15:14.
                        Regards,
                        Jeremy

                        Network Consultant/Engineer
                        Baltimore - Washington area and beyond
                        www.gma-cpa.com

                        Comment


                        • #13
                          Re: Just looking for a little help on the evil 70-291

                          OK Jeremy you have me there; I am a little hazy on the history...!

                          Regarding subnets on the Internet; ARE they ACTUALLY on the Internet though? To my mind if they're behind a router with a subnet mask outside the 8,16,24 rule, that puts them OUTSIDE "The Internet" by definition... As I understood it, the Internet was that portion of the world-wide network which was composed entirely of the original scope of unmodified "Live" IP addresses with Class A, B and C subnet masks. As soon as you chop off a bit and subnet it, it's a separate network CONNECTED to the Internet.

                          Regarding PAT/NAT, yes, they are what makes possible the one-to-many mapping of internal to external IP's and I always get the effects and reasons mixed up without getting the actual functions mixed up?! Silly me!
                          Last edited by Stonelaughter; 13th April 2007, 15:28.


                          Tom
                          For my own and your protection, I do not provide support by private message under any circumstances. All such messages will be deleted and ignored.

                          Anything you say will be misquoted and used against you

                          Comment


                          • #14
                            Re: Just looking for a little help on the evil 70-291

                            Anyone want to collate the info and dump it into a document. I think there is too much to put into one post as is otherwise it could be made a Sticky.

                            Thoughts?
                            1 1 was a racehorse.
                            2 2 was 1 2.
                            1 1 1 1 race 1 day,
                            2 2 1 1 2

                            Comment


                            • #15
                              Re: Just looking for a little help on the evil 70-291

                              Originally posted by Stonelaughter View Post
                              Regarding subnets on the Internet; ARE they ACTUALLY on the Internet though? To my mind if they're behind a router with a subnet mask outside the 8,16,24 rule, that puts them OUTSIDE "The Internet" by definition... As I understood it, the Internet was that portion of the world-wide network which was composed entirely of the original scope of unmodified "Live" IP addresses with Class A, B and C subnet masks. As soon as you chop off a bit and subnet it, it's a separate network CONNECTED to the Internet.
                              Well I'm almost positive that anything that is connected to the Internet and has a routable address is part of the Internet.

                              A few articles:
                              http://computer.howstuffworks.com/in....htm/printable
                              http://en.wikipedia.org/wiki/Internet
                              http://www.searchandgo.com/articles/...xplained-1.php This one looks pretty good. I haven't read it all though.

                              An RFC from 1985 talking about subnetting procedures for the Internet
                              ftp://ftp.rfc-editor.org/in-notes/rfc950.txt
                              Last edited by JeremyW; 13th April 2007, 15:47. Reason: Added another link
                              Regards,
                              Jeremy

                              Network Consultant/Engineer
                              Baltimore - Washington area and beyond
                              www.gma-cpa.com

                              Comment

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