| Demijohn 2003-12-10, 10:26 am |
| No question really, just sharing my adventure.
So I skim through chapter 9 of my Bruno & Kim CCDA cert guide because I think I’m solid on IPV4, and start working on the Q&A.
In the scenario, they show a remote site router B, with two LANs w/100 hosts each. Then the question:
The remote site uses the network prefix 192.168.10.0/24. What subnets and masks can you use for the LANs at the remote site and conserve address space?
a. 192.168.10.64/26 and 192.168.10.192/26
b. 192.168.10.0/25 and 192.168.10.128/25
c. 192.168.10.32/28 and 192.168.10.64.28
d. 192.168.10.0/30 and 192.168.10.129/30
…and they give the answer as b.
Now I’ve been doing this a long time and I didn’t think it was legal to use just 1 bit for subnetting.
(i.e. (2**1 –2) = 0 valid subnets)
So I go back through the chapter more thoroughly and read “With Cisco routers you can use the all 1s subnet for a subnet”) Oh well, learn something new every day.
I know there are mistakes in this book so I double check and go off to cisco.com and find subnet zero and the all ones subnet.
This makes it all perfectly clear, except for what to do if I get a “how many valid subnets” question. Maybe they don't ask those on the CCDA exam any more. |