Stumped on subnet question
bnturnbo
Member Posts: 3 ■□□□□□□□□□
in CCNA & CCENT
In subnetting, when a question asks to configure the router with the last IP in the 4th usable subnet, what exactly are they looking for? For example, in a Class B network 130.4.0.0 / 255.255.252.0 (in the question, subnet 130.4.4.0 has already been assigned and is unavailable), would the answer be 130.4.12.2 or 130.4.16.2? I hope this makes sense. [/b]
Comments
130.4.4.0 - 1st usable subnet
130.4.8.0 - 2nd usable subnet
130.4.12.0 - 3rd usable subnet
130.4.16.0 - 4th usable subnet (host range 130.4.16.1 - 130.4.19.254, broadcast 130.4.19.255)
130.4.20.0 - 5th usable subnet
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130.4.19.254 would be my answer for the last IP in the 4th usable subnet.
class type inspect BELL
drop log
130.4.8.0 - 130.4.11.255 - 1st range
.12.0 - 15.255 - 2nd range
.16.0 - 19.255 - 3rd range
.20.0 - 23.255 - 4th range
So your last usable host would be 130.4.23.254 assuming the 130.4.8.0 is your first usable range. Obviously it cant be 23.255 as that is the broadcast. but if you can start at the 130.4.4.0 range then 130.4.19.254 would be the last usable host
I think that correct anyway - my subnetting is a little rusty!
Bsc (hons) Network Computing - 1st Class
WIP: Msc advanced networking
130.4.4.0 subnet cannot be used
130.4.8.0 1st avialable subnet
130.4.12.0 2nd available subnet
13.4.1.16.0 3rd available subnet
134.4.1.20.0 4th available subnet
based on that the first available address of the subnet is 134.4.1.20.1
the last useable address in the subnet would be 134.4.1.23.254
the broadcast address would be 134.4.23.255
the fifith subnet would be one address higher 134.4.24.0
as you can see the subnets are going up in blocks of 4
the mask is 252 and the max available in each octet is 256
256-252=4 which tells the increment for the subnet.
Quest for 11K pages read in 2011
Page Count total to date - 1283
Bsc (hons) Network Computing - 1st Class
WIP: Msc advanced networking
class type inspect BELL
drop log
Step 1: Work out the subnet boudaries. (look straight at the subnet mask bearing in mind class a, b, c) Do not even look at the ip address execpt for the first octect to give you a clue about the class.
255.255.252.0 (with a 130 first octect of ip address) implies the class B so ....
... 256
... 252 -
...
... 4
as it is 252.0, that makes the subnet 4.0
so the boundaries are 4.0, 8.0, 12.0, 16.0, 20.0, etc...
4th subnet starts at 16.0 but they are asking for the last usuable address. Quickest way to do this is go for the start of the 5th subnet (20.0) and subtract 1 (19.255) for the broadcast of the previous subnet and then one more for the last usuable host address. 130.4.19.254
Do it this way and it is soo quick to work out you will save yourself major time in the exam.
Damn you ambiguity!
class type inspect BELL
drop log
i) question asks to configure the router with the last IP in the 4th usable subnet
ii) in the question, subnet 130.4.4.0 has already been assigned and is unavailable
Someone already did the first subnet..... You are being asked to do the 4th !
Above posters read this to mean unavailable so +1 on the subnet boundaries incorrectly.
I agree.