""s vermill"" wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > The Long and Winding Road wrote: > > > The question sucks and so do the answer choices. Eight > > *addresses* per > > > subnet or eight subnets? If the former, a mask of > > 255.255.255.248 would > > be > > > required - not 255.255.248.0. If the latter, I'd go with you > > (sorta). Or > > > perhaps a. if subnet zero weren't allowed for some reason > > (but then you'd > > > have 15 subnets plus subnet zero - not eight!). > > > > > > Nothing you do with a subnet mask makes a class B a class C. > > If it was > > > class B before you subnetted it, it isn't going to fall into > > the class C > > > range of addresses all of the sudden is it? If by "class C" > > they mean a > > > subnet with 254 host addresses, your answer isn't right > > either. Your > > > subnets (/21) would have 8190 hosts. In that case, there > > isn't a valid > > > answer at all because a class B subnetted for 254 hosts will > > have > > somewhere > > > in the neighborhood of 255 subnets. > > > > > > CL: I disagree. 172.16.0.0/21 gives you eight subnets, each > > with a mask of > > /24 - subnets 172.16.0.0/24 through 172.16.7.0/24, for example. > > Think ISP / > > BGP :-) > > > > Chuck, > > Interesting. As you pointed out, > > 172.16.0.0 /21 has networks: > > 172.16.0.0 - 172.16.7.255 > 172.16.8.0 - 172.16.15.255 > so on and so on. > > Each of which, of course, can be further subnetted to /24: > > 172.16.0.0 /24 > through > 172.16.7.0 /24 > > so on and so on.. > > So I guess you came up with the most correct answer by looking ahead to the > next step. I still think the question sucks. If you subnet a class B with > a /21 mask, you wind up with 2046 usable hosts until you subnet it > further. Somehow I came up with 8190 host for a /21 mask the first time > around. Don't know why I though /21 left 13 host bits?
CL: yeah, the point is that given ANY "class B" address, using a /21 ( .248 mask in the third octet ) yields the possibility of 8 /24's CL: OTOH, a /19 ( .224 in the third octet ) give you eight subnets, but they are in no way shape or form anything close to "class C's" CL: the N2-2 argument is really moot these days. According to the Cisco docs, IP subnet-zero is now the default on routers. The "all ones" subnet has not been an issue as long as I've been touching routers, dating back to 11.1 or so. CL: if Cisco course materials are still using the old N2-2 philosophy with regards to subnets, it is well past time for them to update the materials. Tom? > > What's funny is that Todd Lammle is coming to our Cisco User's group next > week. The title of his presentation is something to the effect of "Learn to > Subnet in Your Head in XX Minutes." I elected not to reserve a seat on the > basis that it would be a waste of my time. Hmmmm..... > > Thanks Chuck, > > Scott Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=58655&t=58569 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
