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192.168.1.64/26 192.168.1.128/26The two routers have been configured with the "no ip subnet zero" command. Which of the following VLSM network addresses can be used between the routers? (Choose two answers.)
a) 192.168.1.0/30 b) 192.168.1.4/30 c) 192.168.1.8/30 d) 192.168.1.96/30 e) 192.168.1.138/30 f) 192.168.1.190/30
Correct answers are B and C.
It is my understanding that when working with VLSM, one starts by using smaller masks and working up (more hosts to less hosts). Since the LANs are using /26 (.0 -> .63, .64 -> .127, .128 -> .191. and .192 -> .255) and the "no ip subnet zero" command is being used on both routers, subnet #0 (.0 -> .63) is not available. How can answers B and C be correct?
I wrote Cisco and received the following answer:
"The issue would be valid if a 255.255.255.192 (/26) mask was used with either the 192.168.1.4 or 192.168.1.8 addresses, however with VLSM, the /30 mask creates a new series of subnets within the 192.168.1.0 through 192.168.1.63 range, all of which can be used with the exception of the 192.168.1.0/30 subnet unless the ip subnet-zero use is enabled."
Can anyone clarify this for me?
Many thanks!
Joey Lanza