At 01:53 PM 2/1/01, Fred Danson wrote:
>I dont understand why the answer "C) Routing protocols must carry the
>prefix length with the 32bit address" doesn't apply to the question of
>"When you develop a subent routing scheme, to which guideline must you adhere?"
"Subnet routing scheme" isn't a technical term. You'll notice that the most
experienced people on the group just scratched their heads when they heard
it. Maybe Cisco has started using the term, but it would be unfortunate if
they were. The technical term for the number of bits that mean network
instead of host is "prefix length." Routing based on prefix length rather
than classes is called classless interdomain routing (CIDR).
CIDR allows routers to group routes together in order to cut down on the
quantity of routing information carried by core routers. With CIDR, several
IP networks appear to networks outside the group as a single, larger
entity. The grouping of routes is also known as summarization, aggregation,
or supernetting.
Somebody at Cisco (and we need to find them and take them out) learned
subnetting and thinks that supernetting is the same thing. I ran into this
before. The e-learning version of Designing Cisco Networks had this problem
too. (I think they pulled that product, I complained so bitterly about it,
though it might have resurfaced. &;-)
Priscilla
>When you develop any subnet routing scheme, you must use a classless
>routing protocol that can factor in the subnet with the network address.
>Summarization is similar, but the answer seems right to me.
>
>Could anyone explain why the question is wrong?
>
>Thanks,
>Fred
>
>
>>From: Priscilla Oppenheimer <[EMAIL PROTECTED]>
>>Reply-To: Priscilla Oppenheimer <[EMAIL PROTECTED]>
>>To: Hunt Lee <[EMAIL PROTECTED]>, [EMAIL PROTECTED]
>>Subject: Re: subnet routing scheme question
>>Date: Wed, 31 Jan 2001 16:56:24 -0800
>>
>>Hee, hee. This is very funny. As soon as I saw it I said too myself, "this
>>looks really familiar." These are bullet points in my book, Top-Down
>>Network Design. The bullets are in the CID class also and are based on
>>concepts that Howard Berkowitz and Peter Welcher taught me. They might be
>>in BSCN also because Howard had a big influence on that class also.
>>
>>However, some clueless person screwed it up! This must be from a COLT test.
>>&:-)
>>
>>At 07:50 AM 2/1/01, Hunt Lee wrote:
>> >I have got the following question, but I don't understand the answer...
>> >
>> >When you develop a subent routing scheme, to which guideline must you
>> >adhere?
>>
>>The question is supposed to be "When you develop a route summarization
>>scheme..."
>>
>>
>> >A) IP addresses must share the same right-most bits.
>>
>>They changed left-most to right-most to make this a wrong answer. If IP
>>addresses share left-most bits, then they can be summarized.
>>
>>
>> >B) Routers must base routing decisions on a 16bit or 32bit address
>>
>>They added 16-bit to make this a wrong answer. It would be right if it
>>simply said "must base routing decisions on a 32-bit address."
>>
>>
>> >C) Routing protocols must carry the prefix length with the 32bit
>> >address
>>
>>This one is true (because the question is supposed to be about
>>summarization).
>>
>>
>> >D) Routers must base routing decisions on a prefix length that is 16bit
>> >or 32bit long.
>>
>>They added 16-bit to make this wrong. Routing must be based on a 32-bit
>>prefix in case there are host-specific routes. In other words, the router
>>must look at all 32 bits.
>>
>>
>> >I thought the answer is C, but the answer is B. Any help would be
>> >greatly appreciated.
>>
>>
>>Priscilla
>>
>>
>> >Regards,
>> >Hunt Lee
>> >IP Solution Analyst
>> >Cable and Wireless (Sydney)
>> >
>> >_________________________________
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>>
>>
>>________________________
>>
>>Priscilla Oppenheimer
>>http://www.priscilla.com
>>
>>_________________________________
>>FAQ, list archives, and subscription info:
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>>Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
>
>_________________________________________________________________
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________________________
Priscilla Oppenheimer
http://www.priscilla.com
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