Serial interface addresing
![Mikdilly](https://us.v-cdn.net/6030959/uploads/defaultavatar/nE1RZK93BLG3K.jpg)
in CCNA & CCENT
From the cisco prep practice exams a question says use the most efficient addressing scheme and vlsm to configure a serial connection between two routers, which address can be configured on one of the serial interfaces?
A) 192.168.16.63/27
192.168.16.158/27
C) 192.168.16.192/27
D) 192.168.16.113/30
E) 192.168.16.145/30
F) 192.168.16.193/30
They say F is correct, why wouldn't D and E be correct as well?
A) 192.168.16.63/27
![B) B)](https://community.infosecinstitute.com/resources/emoji/sunglasses.png)
C) 192.168.16.192/27
D) 192.168.16.113/30
E) 192.168.16.145/30
F) 192.168.16.193/30
They say F is correct, why wouldn't D and E be correct as well?
Comments
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Netstudent Member Posts: 1,693 ■■■□□□□□□□
good question.
Looks to me like 145 is in the 144 subnet.There is no place like 127.0.0.1 BUT 209.62.5.3 is my 127.0.0.1 away from 127.0.0.1! -
r_durant Member Posts: 486 ■■■□□□□□□□
Hmmmmm...good question!! From what I calculated, D, E & F seem to be valid addresses in the scheme of the question asked...CCNA (Expired...), MCSE, CWNA, BSc Computer Science
Working on renewing CCNA! -
Paul Boz Member Posts: 2,620 ■■■■■■■■□□
Idiologically speaking, you want to reserve /30 masks for point to point links, as they only afford two usable ip addresses, which means absolutely no waste with your IP allocation. That should answer r_durant's question. [edit] r_durant edited his reply. For the sake of anyone that doesn't know this, he asked what the point is in using a /30 over the other choices, since the others would technically work.
As far as the original poster:
A) 192.168.16.63/27192.168.16.158/27
C) 192.168.16.192/27
D) 192.168.16.113/30
E) 192.168.16.145/30
F) 192.168.16.193/30
A, B, and C are instantly out because using wasteful addressing space is against Cisco best practice (and common sense).
Between D, E, and F,
D is correct because 192.168.16.113 is a part of the 112 subnet. It breaks down like this:
192.168.16.112 is the subnet
192.168.16.113-114 are the valid usable host addresses
192.168.16.115 is the broadcast address
192.168.16.116 is the next subnet.
E is correct because 192.168.16.145 is a part of the 144 subnet. It breaks down like this:
192.168.16.144 is the subnet
192.168.16.145-146 are the valid usable host addresses
192.168.16.147 is the broadcast address
192.168.16.148 is the next subnet.
F is correct because 192.168.16.193 is a part of the 192 subnet. It breaks down like this:
192.168.16.192 is the subnet
192.168.16.193-194 are the valid usable host addresses
192.168.16.195 is the broadcast address
192.168.16.196 is the next subnetCCNP | CCIP | CCDP | CCNA, CCDA
CCNA Security | GSEC |GCFW | GCIH | GCIA
pbosworth@gmail.com
http://twitter.com/paul_bosworth
Blog: http://www.infosiege.net/ -
r_durant Member Posts: 486 ■■■□□□□□□□
Paul Boz wrote:That should answer r_durant's question. [edit] r_durant edited his reply. For the sake of anyone that doesn't know this, he asked what the point is in using a /30 over the other choices, since the others would technically work.
I did??
I agreed with D, E & F...CCNA (Expired...), MCSE, CWNA, BSc Computer Science
Working on renewing CCNA! -
Mikdilly Member Posts: 309
It'd be helpful if they could give an explanation for their answers within the practice exam. Was thinking of submitting this question to them, would i get an answer? -
Pash Member Posts: 1,600 ■■■■■□□□□□
I totally agree Mikdilly, questions should always be backed up with explanations. Ever done a google search looking for a topic that is quiet hard to find specific information on...you find a post by some chap somewhere who has EXACTLY the same issue/problem you had....you follow his thread down to the end where he kindly puts.....got it working, thanks everyone for your help......no explanation on how. Yup, i bet most have.
So please, always always post an explanation to a an issue or problem, just like paul did for us. Back on topic.....yes that question is wrong and yup you probably should let them know.DevOps Engineer and Security Champion. https://blog.pash.by - I am trying to find my writing style, so please bear with me. -
Paul Boz Member Posts: 2,620 ■■■■■■■■□□
r_durant wrote:Paul Boz wrote:That should answer r_durant's question. [edit] r_durant edited his reply. For the sake of anyone that doesn't know this, he asked what the point is in using a /30 over the other choices, since the others would technically work.
I did??
I agreed with D, E & F...
Hmm, could have sworn you did. Oh well, at any rate it's still good infoCCNP | CCIP | CCDP | CCNA, CCDA
CCNA Security | GSEC |GCFW | GCIH | GCIA
pbosworth@gmail.com
http://twitter.com/paul_bosworth
Blog: http://www.infosiege.net/ -
Mikdilly Member Posts: 309
Sorry, my mistake, there was a graphic on the ques that showed the 2 routers with subnets of 192.168.16.64/27, 192.168.16.96/27, and 192.168.16.128/27. Answers D and E would fall into those ranges. I thought since they used a diff mask they wouldn't apply. -
Netstudent Member Posts: 1,693 ■■■□□□□□□□
ya be very careful of overlaps when using VLSM and manual route summarization.There is no place like 127.0.0.1 BUT 209.62.5.3 is my 127.0.0.1 away from 127.0.0.1!