No problem. I was hoping you would quibble. &;-) That's how I learn.
Priscilla
At 07:16 PM 2/1/01, Howard C. Berkowitz wrote:
> >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).
>
>I'd quibble with you a little bit here. The basic mechanism is simply
>classless routing, which, IIRC, was introduced under the term
>supernetting:
>
>RFC 1338 Supernetting: an Address Assignment and Aggregation Strategy. V.
> Fuller, T. Li, J. Yu, K. Varadhan. June 1992.
>
>The broader CIDR effort was a little later, and the main documents are:
>
>1517 Applicability Statement for the Implementation of Classless
> Inter-Domain Routing (CIDR). Internet Engineering Steering Group, R.
> Hinden. September 1993. (Format: TXT=7357 bytes) (Status: PROPOSED
> STANDARD)
>
>1518 An Architecture for IP Address Allocation with CIDR. Y. Rekhter,
> T. Li. September 1993. (Format: TXT=72609 bytes) (Status: PROPOSED
> STANDARD)
>
>1519 Classless Inter-Domain Routing (CIDR): an Address Assignment and
> Aggregation Strategy. V. Fuller, T. Li, J. Yu, K. Varadhan. September
> 1993. (Format: TXT=59998 bytes) (Obsoletes RFC1338) (Status: PROPOSED
> STANDARD)
>
>1520 Exchanging Routing Information Across Provider Boundaries in the
> CIDR Environment. Y. Rekhter, C. Topolcic. September 1993. (Format:
> TXT=20389 bytes) (Status: INFORMATIONAL)
>
>The distinction I'd make between CIDR and generic prefix routing:
>
> 1. CIDR was specifically intended to solve some address exhaustion
> and routing table size problems in the public Internet.
>
> 2. CIDR does not consider the "subnetting a subnet" or VLSM approach.
> VLSM certainly is an arbitrary prefix length technique, but its
> applicability is inside enterprises rather than among providers.
>
> VLSM is truly a terrible name -- subnet masks are always 32 bits
> long.
> They can contain different numbers of one bits.
>
> 3. CIDR includes administrative procedures for global address
> assignment.
>
> 4. There are an assortment of problems caused by workarounds to
> classful addressing, such as discontiguous networks, that are
> primarily enterprise problems and outside the CIDR scope.
> >
> >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.
>
>It's probably the same copywriter that, when Sprint announced they
>were installing GSR's, boasted how the new hardware was going to
>provide customers with greater bandwidth and latency.
>
> >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
>
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Priscilla Oppenheimer
http://www.priscilla.com
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