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Network plus exam

Posted on 2013-12-27
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Hope someone can help me with this one.  Can some one explain to me why  172.16.128.0/15  is not a private non routable ip address.   Isnt this  within the class B range within the 172.16.0.0    172.31.255.255     Ive seen this address in practice test 172.16.128.0/15 and it isnt flagged as a private address  What am I missing
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Question by:openjohn
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LVL 11

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by:Miftaul
Miftaul earned 1400 total points
ID: 39742277
RFC1918 states 3 blocks of IP for private internal use. They are

10.0.0.0/8
172.16.0.0/12
192.168.0.0/16

They are not routed because ISPs block them entering their bgp because multiple customers can have similar IP range. But in your lab, you can route them. They are not routable in a sence they should be for internal use and reserve for that.
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by:tmoore1962
ID: 39742388
Because of the subnet /15 makes the range 172.16.0.0 to 172.17.255.255 so technically its netowork  falls outside of 'private' reserved networks, think kind of a trick question.
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by:CompProbSolv
CompProbSolv earned 200 total points
ID: 39742460
Isn't 172.16.0.0 to 172.17.255.255 (subnet for 172.16.128.0/15) completely contained within 172.16.0.0 to 172.31.255.255 (172.16.0.0/12)?  It seems to me that this IS a private non-routable address.
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Miftaul earned 1400 total points
ID: 39742650
tmoore1962 is wrong here.

172.16.128.0/15 aka subnet 172.16.0.0 mask 255.254.0.0 (range 172.16.0.0-172.17.255.255) completely contains within 172.16.0.0/12 (range 172.16.0.0 - 172.31.255.255) private range and not routable.
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Hope someone can help me with this one.  Can some one explain to me why  172.16.128.0/15  is not a private non routable ip address.  

Yes, It is a Private non routable address.

Isnt this  within the class B range within the 172.16.0.0    172.31.255.255  

Yes, it falls within.

Ive seen this address in practice test 172.16.128.0/15 and it isnt flagged as a private address  What am I missing

Practice test answer seems to be wrong here. Is Comptia selling practice tests? You know,  dumps are blindly followed by DUMBs.

/Miftaul
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LVL 47

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by:Craig Beck
Craig Beck earned 200 total points
ID: 39742681
The 172.16.0.0/15 range is completely private - it must be.

The 172.16.0.0/12 range is private, so a smaller mask must be contained within that range.  Check here...

http://jodies.de/ipcalc

Address:   172.16.128.0          10101100.0001000 0.10000000.00000000
Netmask:   255.254.0.0 = 15      11111111.1111111 0.00000000.00000000
Wildcard:  0.1.255.255           00000000.0000000 1.11111111.11111111
=>
Network:   172.16.0.0/15         10101100.0001000 0.00000000.00000000 (Class B)
Broadcast: 172.17.255.255        10101100.0001000 1.11111111.11111111
HostMin:   172.16.0.1            10101100.0001000 0.00000000.00000001
HostMax:   172.17.255.254        10101100.0001000 1.11111111.11111110
Hosts/Net: 131070                (Private Internet)
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LVL 71

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by:Qlemo
Qlemo earned 200 total points
ID: 39742978
And if you need another confirmation: Yes, it is private, The only "issue" is that 172.16.0.0/12 is usually divided into Class B subnets, which are /16, but in fact it doesn't matter as long as the mask does not exceed /12. 172.16.0.0/11 would certainly not been considered as "private" anymore.
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by:Miftaul
ID: 39751387
This post will be read by many other as it comes up in Google search.

"Because of the subnet /15 makes the range 172.16.0.0 to 172.17.255.255 so technically its network falls outside of 'private' reserved networks," is definitely not an accepted excellent answer.

(sorry I am not asking points, please don't take me otherwise)
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