A Question?

ritamshomeritamshome MemberMember Posts: 57 ■■□□□□□□□□
Hi. Am new to CCNA forum.Was just wondering what the ans to this question is?

10.0.0.0/26

subnet mask is:255.255.255.192
S=262144
Hosts per Subnet=62
Block Size=64


How do you find the 262138th Subnet directly from a formula (including the first host,the last host,the broadcast address) instead of like working backwards manually from 262144th Subnet?

The (Subnet position number-1)*block size supposedly does not stand valid ?Or am i missing something?

signing out--ritamshome.

Comments

  • QUIX0TICQUIX0TIC Senior Member Member Posts: 277
    Omitting my question. I think the crack is getting to me!
    "To realize one's destiny is a person's only obligation."
  • milliampmilliamp Senior Member Member Posts: 135
    I think working backwards would have to be your best bet.

    10.0.0.0/26

    Broadcast address of last subnet would be 10.255.255.255

    Here are our bit boundries for that address space.

    Mask = /26
    0-63
    64-127
    128-191
    192-255

    262144 - 262138 = 6

    So we need to go back 6 subnets from 10.255.255.255 to get the one we need.

    4 /26's per /24 so that puts us half way through

    4 of them are in 10.255.255.0/24, and we are half way through 10.255.254.0 (at 10.255.254.12icon_cool.gif

    So our subnet should be 10.255.254.128/26

    10.255.254.128 - network
    10.255.254.129 - first host
    10.255.254.190 - last host
    10.255.254.191 - broadcast

    here is a list of bit boundries, you can't use them for the exam, but they are useful in "real life"

    Mask = /24
    0-255

    Mask = /25
    0-127
    128-255

    Mask = /26
    0-63
    64-127
    128-191
    192-255

    Mask = /27
    0-31
    32-63
    64-95
    96-127
    128-159
    160-193
    192-223
    224-255

    Mask = /28
    0-15
    16-31
    32-47
    48-63
    64-79
    80-95
    96-111
    112-127
    128-143
    144-159
    160-175
    176-191
    192-207
    208-223
    224-239
    240-255

    Mask = /29
    0-7
    8-15
    16-23
    24-31
    32-39
    40-47
    48-55
    56-63
    64-71
    72-79
    80-87
    88-95
    96-103
    104-111
    112-119
    120-127
    128-135
    136-145
    146-151
    152-159
    160-167
    168-175
    176-183
    184-191
    192-199
    200-207
    208-215
    216-223
    224-231
    232-239
    240-247
    248-255

    /30 is not listed because there are to omany, but they are easy because the network address is anything divisible by 4.

    eg. if you had 10.10.10.14/30 you know that is a host address because 12 is divisible by 4 but 14 is not.
  • ritamshomeritamshome Member Member Posts: 57 ■■□□□□□□□□
    Thanks for answering. You are quite right. Working backwards seems to be the answer.-Although tedious.Heck, i am still working on the formula to directly find out the ans.Will inform all as soon as i finish working it out.

    signing out--ritamshome.
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