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You have been assigned the address block 10.255.255.224 /28 to create the network address for point to point wan links. How many of these WANS can you support with this address block?
A. 1
B. 4
C. 7
D. 14

Can someone please explain this to me.

I swear the answer in the book is wrong.

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mikem2te

thenjduke wrote: »

You have been assigned the address block 10.255.255.224 /28 to create the network address for point to point wan links. How many of these WANS can you support with this address block?
A. 1
B. 4
C. 7
D. 14

Can someone please explain this to me.

I swear the answer in the book is wrong.

What did the book say. 4?

thenjduke

Yes 4 was the answer in the book.

mikem2te

thenjduke wrote: »

Yes 4 was the answer in the book.

You mentioned point to point link, these usually are given a 30 bit mask as there are only two hosts on the point to point. using a 30 wastes no IP addresses.

mikem2te

So out of your 10.255.255.224 /28 if this is subnetted down to a thirty mask you get

10.255.255.224 / 30 with 225 & 226 useable
10.255.255.228 / 30 with 229 & 230 useable
10.255.255.232 / 30 with 233 & 234 useable
10.255.255.236 / 30 with 237 & 238 useable

Or something like that!!

thenjduke

Mike thanks that answers the question.
I forget about VLSM all the time.

Aldur

mikem2te wrote: »

...using a 30 wastes no IP addresses.

Actually a /30 does waste IP addresses. On a point to point link there is no need for a network or a broadcast address. If you really want to conserve IP address space use a /31.

mikem2te

Aldur wrote: »

Actually a /30 does waste IP addresses. On a point to point link there is no need for a network or a broadcast address. If you really want to conserve IP address space use a /31.

Oooh! Nice. RFC3021 ??

I've used unnumbered links before - no ip addresses - no waste. A complete PITA though.

Bl8ckr0uter

mikem2te wrote: »

Oooh! Nice. RFC3021 ??

I've used unnumbered links before - no ip addresses - no waste. A complete PITA though.

Never heard of this one. Cool. The RFC is a good read.

Aldur

mikem2te wrote: »

Oooh! Nice. RFC3021 ??

I've used unnumbered links before - no ip addresses - no waste. A complete PITA though.

haha true, unnumbered links work. Would have to agree on the PITA aspect of it too. Plus you lose alot of functionality that having an IP address on an interface gives you. Although from a strictly IP conserving standpoint this is the 'best' option.

Lets hope it doesn't get to this point when IPv4 address space starts really getting slim.