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TOPIC: Intro Exam - reserved IP Addresses

Intro Exam - reserved IP Addresses 8 years 6 months ago #26483

  • SteveP
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I've been reading the Cisco Intro Exam book (by Wendell Odom) and several IP Address ranges are said to be reserved. I know about 0.0.0.0/8, 127.0.0.0/8, 169.254.0.0/16 and the Class A, B and C private networks, but what about 128.0.0.0/16, 191.255.0.0/16, 192.0.0.0/24 and 223.255.255.0/24?

I've checked using Packet Tracer 4.11 and it won't let me assign anything from 0.0.0.0/8 or 127.0.0.0/8 to a host but it will allow me to assign any of the other reserved address ranges.

I'm confused - I realise that 128.0.0.0/16 and 191.255.0.0/16 are the first and last of Class B whilst 192.0.0.0/24 and 223.255.255.0/24 are the first and last of Class C, but why are they reserved? I can apply them to hosts in Packet Tracer so does that mean that I can apply them in real life (I don't have a spare PC to set up a peer-peer to check it out)? If asked in an exam whether these are, in fact, reserved, how do I answer? This is the first time that I've come across these additional reserved address ranges.

Thanks for your time.
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Re: Intro Exam - reserved IP Addresses 8 years 5 months ago #26487

  • Chojin
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128.0.0.0/16 - This block, corresponding to the numerically lowest of
the former Class B addresses, was initially and is still reserved by
the IANA. Given the present classless nature of the IP address
space, the basis for the reservation no longer applies and addresses
in this block are subject to future allocation to a Regional Internet
Registry for assignment in the normal manner.

191.255.0.0/16 - This block, corresponding to the numerically highest
to the former Class B addresses, was initially and is still reserved
by the IANA. Given the present classless nature of the IP address
space, the basis for the reservation no longer applies and addresses
in this block are subject to future allocation to a Regional Internet
Registry for assignment in the normal manner.

192.0.0.0/24 - This block, corresponding to the numerically lowest of
the former Class C addresses, was initially and is still reserved by
the IANA. Given the present classless nature of the IP address
space, the basis for the reservation no longer applies and addresses
in this block are subject to future allocation to a Regional Internet
Registry for assignment in the normal manner.

223.255.255.0/24 - This block, corresponding to the numerically
highest of the former Class C addresses, was initially and is still
reserved by the IANA. Given the present classless nature of the IP address space, the basis for the reservation no longer applies and addresses in this block are subject to future allocation to a
Regional Internet Registry for assignment in the normal manner.
CCNA / CCNP / CCNA - Security / CCIP / Prince2 / Checkpoint CCSA
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Re: Intro Exam - reserved IP Addresses 8 years 5 months ago #26490

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Yes, I saw that in the RFC. The thing that triggered my question was a question in a sample exam. It asked which of several IP Addresses were valid. Some options such as 192.168.275.3 were obviously wrong but one was 223.255.255.4 and I saw no reason why this was invalid. Needless to say, I got it wrong!

I suppose the problem is with multiple choice questions (rather than an oral exam) is I don't have the opportunity of explaining my reasoning. Similarly, if asked about the number of addresses on the 192.168.4.0/24 network, do I answer 256 (the total) or 254 (the total number of usable addresses)?

I do hate MCQs, probably as much as the examiners hate them because they're so difficult to construct in a fair manner to assess a candidate's knowledge!
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Re: Intro Exam - reserved IP Addresses 8 years 5 months ago #26491

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For your question, the ammount of addresses is not the ammount of hosts available.

256 are the addresses, 254 are the hosts as you said be very aware of the terms they use (this can really kill ya :()

For 223.255.255.4 being an invalid address, seems totaly nonsens to mee.

As you have read in the RFC the block was reserved BEFORE (so. in the past) It will be available for use.. so this is just a matter of age of your exam.

I think that is a very difficult thing to keep in mind what exam you are taking and it is more then ridiculous that you have to keep in mind what rules applies on your question because of the time the question is asked :s.

The exams you are taking to prepare are most likely things like Testkings or other preparation, do take note that these exams are not the most up-to-date questions. I hope Cisco will update there questions, but on this one I can't guarantee you how this will be.

Just read your book, see what they say.. and don't 'think' on your exam... thats fatal :).

Hope you'll pass very soon m8, Goodluck.
CCNA / CCNP / CCNA - Security / CCIP / Prince2 / Checkpoint CCSA
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Re: Intro Exam - reserved IP Addresses 8 years 5 months ago #26492

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Thank you.

I've been advised by several folks not to think too much but to put down a first impression (obviously making sure that they're not asking for "what is NOT ..." rather than "what IS ..."). When doing MCQs normally, I go through the paper answering those questions that I can, almost as a knee-jerk reaction and leave those which need a bit of thinking (or calculation). I know that it's not possible to go back over the Intro Exam questions, so I've been practicing doing exams in one fell swoop, and not being tempted to go back over and check my answers.

Oh well, we'll see how it goes when I take it in a few weeks.
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