Overlap

So I have 1 router and i'm attempting to add some ips to a couple of interfaces.

I've placed 10.0.0.1/30 on my serial interface.

I try to put 10.0.0.5/28 on another interface but it complains of a conflict with the serial interface on 10.0.0.0

As far as I can tell there is no overlap. The complaint of overlapping with 10.0.0.0 suggests to me that the router can't handle classless?

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Comments

daveccna

Interestingly if I put the /30 at the top of the range it's allowed so

s0/0 ip 10.0.0.253/30 and
fa1/0 ip 10.0.0.1/28

works just fine.

gecco

Change the 3rd octet to something other than ZERO in one of your interfaces.
Also, just curious why you're using IP subnet zero?
I wouldn't use this if you can help it.

You may have to turn on IP SUBNET ZERO which is not needed in a lab environment.
Just go 10.0.1.x and 10.0.2.x and make your life easy.

networker050184

10.0.0.1/30 = 10.0.0.0 - 10.0.0.4

10.0.0.5/28 = 10.0.0.0 - 10.0.0.15

They certainly do overlap.

networker050184

gecco wrote: »

Change the 3rd octet to something other than ZERO in one of your interfaces.
Also, just curious why you're using IP subnet zero?
I wouldn't use this if you can help it.

You may have to turn on IP SUBNET ZERO which is not needed in a lab environment.
Just go 10.0.1.x and 10.0.2.x and make your life easy.

Why would you not use subnet zero? Thats just a waste of perfectly good IPs.

daveccna

networker050184 wrote: »

10.0.0.1/30 = 10.0.0.0 - 10.0.0.4

10.0.0.5/28 = 10.0.0.0 - 10.0.0.15

They certainly do overlap.

Ahh for some reason I had assumed that the router would reserve the first 4 as belonging to the first network entry and be ok with the starting address of .5 for the next network.

With this in mind would it have been alright with .17/28?

networker050184

daveccna wrote: »

Ahh for some reason I had assumed that the router would reserve the first 4 as belonging to the first network entry and be ok with the starting address of .5 for the next network.

With this in mind would it have been alright with .17/28?

Yes, .17 would work fine. The router can't just "reserve" some addresses out of another range. Its all just 1's and 0's to the router.

gecco

networker050184 wrote: »

Why would you not use subnet zero? Thats just a waste of perfectly good IPs.

In real life with many networks, sure. In a lab environment with ONE router...no reason to add complexity, Keep it simple.

networker050184

gecco wrote: »

In real life with many networks, sure. In a lab environment with ONE router...no reason to add complexity, Keep it simple.

I guess if you think using the zero subnet is complex. I always thought the reservation of the zero subnet to be more complex then just being able to use it.

mikem2te

gecco wrote: »

In real life with many networks, sure. In a lab environment with ONE router...no reason to add complexity, Keep it simple.

Surely the lab environment for CCNA is the place to learn about "subnet zero"

hexem

the use of subnet zero has been accepted and used for along time, no need not to use it, i certainly use it in real world and lab.