CCNA WTF



  • Hi guys...
    I'm studying for the CCNA exam and just got this test. As I see it the crappy cisco software has made an /31 address, but doesn't treat it as a special case...
    WTF 1: generating an /31 subnet when /30 has ust been declared as the smallest possible unit.
    WTF 2: not handling said /31 subnet right.
    wtf 3: uber crappy software*

    • their software doesn't allow me to scroll (with the wheel on my mouse) or zoom in/out at all. And if i divide the screen 50/50 in packet tracer/CCNA-browser-thingy, the images in the CCNA window will simply re-size, to something like 30% magnification... extremely aggravating software...

    WTH?! damn you CS... someone please fix the formatting...



  • i might add that i filled in the bottom four rows, the rest was auto generated...



  • @swayde said:

    Hi guys...

    I'm studying for the CCNA exam and just got this test. As I see it the crappy cisco software has made an /31 address, but doesn't treat it as a special case...

    WTF 1: generating an /31 subnet when /30 has ust been declared as the smallest possible unit.

    WTF 2: not handling said /31 subnet right.

    wtf 3: uber crappy software*



    * their software doesn't allow me to scroll (with the wheel on my mouse) or zoom in/out at all. And if i divide the screen 50/50 in packet tracer/CCNA-browser-thingy, the images in the CCNA window will simply re-size, to something like 30% magnification... extremely aggravating software...

    FTFY. I have no idea what any of this means, but FTFY.



  • @swayde said:

    i might add that i filled in the bottom four rows, the rest was auto generated...

    So.... it was you who set the first usable IP address to be greater than the last usable IP address?  Why?




  •  Cheetas never prosper.

     



  • @DaveK said:

    @swayde said:
    i might add that i filled in the bottom four rows, the rest was auto generated...
    So.... it was you who set the first usable IP address to be greater than the last usable IP address? Why?

    I wanted to know what the software considered "Correct" (as pictured)... I tried a few times, and entered the appropriate values. If i enter anything else the software will consider it "Incorrect"... (even if it makes sense in /31 terms... eg first usable is 66, and last is 67, the software will see that as incorrect...)



  • I've long thought that there's something about Cisco's training that fucks up otherwise normal human beings.  They no longer will be satisfied with simple, effective solutions and will always look to add complexity to any system, or add "Enterpriseishness' to all networks.  Now, I have no proof that this is the case yet, but the anecdotal evidence is piling up. 

    For instance, we're currently in a project to re-IP our network because the clusterfuck we have inherited is, well, a clusterfuck.  10.x.x.x. with a /24, which I suppose is OK, except they made it so the second octect indicates building (or building/floor for bigger buildings) and the third octect is always 0, making an effective netmask of 255.0.255.0.  We have 10.10.0.x, 10.20.0.x, 10.30.0.x, then 10.132.0.x, 10.134.0.x, 10.136.0.x, all the way up to 10.204.0.x at this point.  Keep in mind this is for somewhere around 1200 devices.  

    I understand the need to plan for expansion, but this is a little ridiculous.

     



  •  @swayde said:

    an /31 address

     How do you pronounce "/31"?



  • @mahlerrd said:

    I've long thought that there's something about Cisco's training that fucks up otherwise normal human beings.  They no longer will be satisfied with simple, effective solutions and will always look to add complexity to any system, or add "Enterpriseishness' to all networks.  Now, I have no proof that this is the case yet, but the anecdotal evidence is piling up. 

    For instance, we're currently in a project to re-IP our network because the clusterfuck we have inherited is, well, a clusterfuck.  10.x.x.x. with a /24, which I suppose is OK, except they made it so the second octect indicates building (or building/floor for bigger buildings) and the third octect is always 0, making an effective netmask of 255.0.255.0.  We have 10.10.0.x, 10.20.0.x, 10.30.0.x, then 10.132.0.x, 10.134.0.x, 10.136.0.x, all the way up to 10.204.0.x at this point.  Keep in mind this is for somewhere around 1200 devices.  

    I understand the need to plan for expansion, but this is a little ridiculous.

     

    So, why do you consider the third octet to be part of the subnet if it is always zero? Also, 255.0.225.0 would mean that 10.10.0.22 and 10.20.0.22 would be on the same subnet, but clearly your description of the situation says that these two addresses are in different buildings. Sensible subnet number allocation would be to allocate bits from the left first so you don't tie yourself down to a /24 forever. Their scheme is rather simplistic, but fits the bill. The "book way" to do it is to assign subnets in this order: 10.0.0.x, 10.128.0.x, 10.64.0.x, 10.192.0.x, 10.32.0.x, 10.96.0.x, 10.160.0.x, 10.224.0.x, etc...



    I have it much worse. Our network guys just set up our new site with a "servers" switch and a "workstations" switch, which are connected together with 1G fiber. Unfortunately, we have gigabit to the desktop and every packet on the network goes either to or from one of the servers. They also put multiple NICs in each server, giving us about 8 gigs of aggregate bandwidth between the servers and the switches, 87% of which can never be used.



  • @swayde said:

    @DaveK said:
    @swayde said:
    i might add that i filled in the bottom four rows, the rest was auto generated...
    So.... it was you who set the first usable IP address to be greater than the last usable IP address? Why?

    I wanted to know what the software considered "Correct" (as pictured)... I tried a few times, and entered the appropriate values. If i enter anything else the software will consider it "Incorrect"... (even if it makes sense in /31 terms... eg first usable is 66, and last is 67, the software will see that as incorrect...)

    RFC 3021 talks all about /31 assignments. Essentially, it says that the subnet address and the broadcast address don't exist for a /31. In the way that it's written, it uses -1 to indicate certain addresses. Such an address is supposed to represent an address where the host portion is all ones, since binary -1 is 1 to the length you need it (-1 in 5 bits is 11111; -1 in 27 bits is 111 1111 1111 1111 1111 1111 1111; etc.). It looks to me like someone misread section 2.1, which says:

    If a 31-bit subnet mask is assigned to a point-to-point link, it
       leaves the <Host-number> with only 1 bit.  Consequently, only two
       possible addresses may result:
    
            {<Network-number>, 0} and {<Network-number>, -1}

    I can see how someone could misread that and think that the second usable address is considered to be the address before the first address, although about 30 seconds of critical thought makes one understand what's wrong with that.

    Correctly, it should be the first usable address is 10.216.119.66, the last usable address is 10.216.119.67, the broadcast address doesn't exist, and the next available subnet is 10.216.119.68.

    I was going to try to put this back on the user (i.e. you), but no, I agree, that software is screwed up.

    When I studied for the CCNA, I literally had to cram for it. I had no hardware with which to practice, and I hated the Boson simulator. It asked me to come up with an addressing scheme for a network, and I did. When I tried to enter the addresses I'd chosen, it essentially said "Screw your plan, use the addresses we expect you to use." It didn't say develop the addressing in a particular subnet, so I think I used 192.168 and it wanted the addresses to be . . . something in network 100? Whatever it was, it didn't specify planning the addresses in that network. I did something different, something that would have worked, and it told me to buzz off. It didn't help.



  • @fourchan said:

     @swayde said:

    an /31 address

     How do you pronounce "/31"?

    We pronounce them as "slash-(something)", so

    /24 = "slash twenty-four"
    /12 = "slash twelve"
    /29 = "slash twenty-nine"
    /31 = "slash thirty-one"



  • @nonpartisan said:

    @fourchan said:

     @swayde said:

    an /31 address

     How do you pronounce "/31"?

    We pronounce them as "slash-(something)", so

    /24 = "slash twenty-four"
    /12 = "slash twelve"
    /29 = "slash twenty-nine"
    /31 = "slash thirty-one"

     

    Okay maybe I was too subtle.  Would you say "an slash thirty-one"?

     



  • @nonpartisan said:

    I did something different, something that would have worked, and it told me to buzz off.
    See, that's exactly what an actual boss in the real world would do, so it was obviously only trying to prepare you for that scenario.



  • @fourchan said:

    Okay maybe I was too subtle.  Would you say "an slash thirty-one"?
     

    May be it's an 'ir'y-one, guv.



  • General rule of exam simulation software: When you know enough about the topic to realize that the exam simulation software is crap, then you are almost ready to take the test.



  • @fourchan said:

    @nonpartisan said:

    @fourchan said:

     @swayde said:

    an /31 address

     How do you pronounce "/31"?

    We pronounce them as "slash-(something)", so

    /24 = "slash twenty-four"
    /12 = "slash twelve"
    /29 = "slash twenty-nine"
    /31 = "slash thirty-one"

     

    Okay maybe I was too subtle.  Would you say "an slash thirty-one"?

     


    Not sure why you'd think that. "Slash" doesn't start with a vowel sound. So even /8 would be pronounced "a slash eight."



  • @Anonymouse said:

    @nonpartisan said:

    I did something different, something that would have worked, and it told me to buzz off.
    See, that's exactly what an actual boss in the real world would do, so it was obviously only trying to prepare you for that scenario.

     

    I was already low confidence trying to run the simulator thing in the first place anyway, and this sure as hell didn't help.

    I heard about a junior network engineering position open up in our organization and I was encouraged to apply for it.  Problem was, I would need my CCNA.  First stop was to the job board to file the application.  Second stop was to Amazon for the CCNA study kit.  I had no hardware but I had some socket programming in my background and had a respectable understanding of TCP/IP.  Unfortunately, I'm a hands-on person, so I was struggling with the simulator anyway because I didn't have cables to plug in, couldn't hear the sound of the switch whirring, etc.  I ended up just cramming for the test.  Each time I failed, I had to think back and figure out what questions I'd missed, then study those sections.  Finally passed on my fourth try.  I was given hire date + 90 days to pass the CCNA, and I passed it on the first day I reported for work.  All in all, roughly a three-month ordeal (end of April to mid-July) in 2006.

     



  • @nonpartisan said:

    Not sure why you'd think that.
     

    Because the OP did it. Twice.

    So I believe that in his language, 31 starts with a vowel, as it does in, for example, Dutch.



  • @fourchan said:

     @swayde said:

    an /31 address

     How do you pronounce "/31"?

     

    Italic i one score and eleven.


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