VLSM Question 1

[kouloubj]

I came across this question on a practice test and I am stumped.

Which of the follwoing network masks would be most efficient when allocaiting IP addresses in a point-to-point WAN link on a network that supports VLSM?
1. /32
2. /18
3. /23
4. /30
5. /27

My test is next Wednesday, so any help is great!

 

[paulk29]

Hi there,
the best answer is number 4. /30 for a point to point link as the subnet 255.255.255.252 would provide only 2 useabble ip addresses, one at each end of the link. Therefore no ip addresses are wasted.
Hope this helps.

e.g
say netowrk address 192.168.1.0 255.255.255.252 (00)
first IP address 192.168.1.1 (01)
second ip address 192.168.1.2 (10)
broadcast address 192.168.1.3 (11)

252 in binary is 11111100 therefore only last two bits can be used for the hosts or each end of the ptp link.
00 would be the network addr.
01 the first ip host addr.
10 the second ip host addr.
11 the broadcast ip addr.

Paul Kilcoyne B eng. CCNA

 

[cisco1970]

4. /30

 

[CiscoGuy33]

I agree 100% with paulk29 - he had a text book answer.

One star for Paul !!

E.A. Broda
CCNA, CCDA, CCAI, Network +