Andrew
There are multiple ways that you could work through this problem and come up with the right answer. Here is the process that worked for me - but it is probably not the only way to work through this logic:
- I started from the part of the instruction that said there should be a single summarized static route that minimizes wasted addresses.
- Since there will be 2 subnets with a /28 mask that we want to summarize the mask that summarizes them and minimizes wasted addresses would be a /27.
- remember that the subnet mask for /28 is 255.255.255.240 and the mask for /27 is 255.255.255.224.
- this eliminates two possible answers about static routes that use mask of 255.255.255.192.
- take the existing subnet of 10.0.155.80 with /28 and figure out what would be the subnet if the mask were /27. There are several ways to figure this out, but the basic way is to work out the values in binary.
First write out the existing address and mask in binary (and we only need to worry about the fourth octet)
existing mask binary value of address decimal value
1111 0000 0101 0000 80
note that the existing mask says that the first 4 bits are significant in determining the subnet address.
then write out the new mask and apply it to the address
new mask binary value of address decimal value
1110 0000 0100 0000 64
note that the new mask says that only the first 3 bits are significant in determining the subnet address. So the new subnet is 64.
- this allows you to eliminate the incorrect choice for subnet and the incorrect choice for static route.
- now you have the 2 correct answers.
HTH
Rick
HTH
Rick
