dividing a class C network into two subnets

hitman0577

Hello,

Has anyone ever that if you divide the a class C network into two subnets the second subnet (255.255.255.12 that will cause problems in the network? I am not sure if I am expressing myself in a way that can be understood, but if anyone has heard about anything similar to that please let me know.

Thanks

Hitman0577

keenon

yep,

thats all that subnetting is about...

first network would start 1-126
second would be 129-254

hitman0577

keenon wrote:

yep,

thats all that subnetting is about...

first network would start 1-126
second would be 129-254

No, my friend. I understand that. What I am refering to is the following question.:

Is there any cisco documentation that advises not to use the second subnet of a class C address that has been divided into two subnets. For example:

Subnet# Subnetmask Start End Broadcast
Address Address Address

---

1 255.255.255.128 200.10.44.1 200.10.44.126 200.10.44.127
2 200.10.44.129 200.10.44.254 200.10.44.255


is there anything that says in Cisco Documentation that advises not to use the second subnet that starts at 129 ip address?

Thanks for the reply.

hitman0577

Subnet# Subnetmask Start End Broadcast

---

1 255.255.255.128 200.10.44.1 200.10.44.126 200.10.44.127
2 200.10.44.129 200.10.44.254 200.10.44.255


sorry about all the garbage in the example above. Hopefully this comes out better.

hitman0577

Subnet# Subnetmask Start End Broadcast

---

1 200.10.44.1 200.10.44.126 200.10.44.127
2 200.10.44.129 200.10.44.254 200.10.44.255


sorry about all the garbage in the example above. Hopefully this comes out better.

mikej412

Are you referring to the subnet zero issue -- from way back in the old days?

EricO

I don't know about documentation against it....... But I have used this subnet on a class c network without issue on Cisco equipment. In fact it will work on L3 switches, and now through a firewall.

hitman0577

You know what? Thanks again for the reply. I know about subnet-zero and that it can be enabled if needed. We are using a class C network divided into two subnets at the company I work for, the problem is the second subnets is showing timeouts from time to time and we have checked every possibility and nothing appears to be the source of that minor problem.
I read in a book and saw something in a google group that said that the use of the .128 subnet is invalid (which I think not) and that same use could have an impact in security and bandwidth as well.

Something I had never heard before but it's out there to create some confusion on newbies like me.

forbesl

What you're refering to is the "all 1's subnet".

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080093f18.shtml#theallonesubnet

There is no problem with using it as long as you have no misconfigured equipment.

hitman0577

Great Link to clear any doubts. Thanks again...

mikej412

hitman0577 wrote:

the problem is the second subnets is showing timeouts from time to time and we have checked every possibility and nothing appears to be the source of that minor problem.

Ah, an intermittent timeout problem..... Where are you seeing the issue -- on a router or host/server? If you've double checked your configurations and everything still looks correct, it then sounds like a job for a packet sniffer.

If you have sniffed, was there any particular type of traffic timing out, or was it random? One specific source/destination address? Any other exciting traffic (broadcast storms, p2p traffic, multi-user games, streaming video, etc) happening when the timeouts occur.