What is the benefit of VLSM?
A.
reduces configuration complexity by using the same subnet mask length
B.
reduces the routing table size by using automatic route summarization
C.
reduces the routing table size by using manual route summarization
D.
allows the subnet mask and classful routing updates to be advertised
E.
secures the hosts on a subnet by using RFC 1918 addresses
Explanation:
This is a dumb question. The real benefit of VLSM is to provide the ability to subnet an already subnetted network address, providing more efficient use of IP addresses.
The question could have said “which of these is a consideration when using VLSM?” since you don’t do VLSM to reduce your routing table size, you do VLSM first, and then you want to reduce your routing table size afterward.
Anyway, to read up on VLSM:
http://www.trainsignal.com/blog/cisco-ccna-vlsm
A: is wrong as name says variable,
B : is wrong, as its not a VLXM thing, its routing protocol behavior
C: is wrong, as VLSM will result in more routes not less. Summarization is Routing protocol feature and behavior is different between RIP, EIGRP or OSPF.
D: is wrong. it allows for subnet-mask to be sent in updates. But updates are classless ( includes subnet mask). With change of class-ful to class-less the option is true.
E: irrelevant