subnets please help

[carl_townshend]

Hi all, can anyone tell me, if I split a class c network in 4 on a 192 mask, the subnet starting 192.168.11.0/192 etc.

how would i reach all 4 subnets via static route, could I just use 192.168.11.0 , would this reach all 4 subnets, or would I have to point each one ? also if I used eigrp would i advertise all 4 seperately ?

cheers

Carl

[ariela]

Hi,

your 4 nets are:

192.168.11. 00 | 000000

192.168.11. 01 | 000000

192.168.11. 10 | 000000

192.168.11. 11 | 000000

that is:

192.168.11.0/26

192.168.11.64/26

192.168.11.128/26

192.168.11.192/26

Please remember that the correct bit notation is /26 (24 C class + 2 subnetting) and not /192

for the static route, you have to use a single route that "summarize" all 4 routes: 192.168.11.0/24

for eigrp, something like

router eigrp 100

no auto-summary

network 192.168.11.0 0.0.0.255

would be ok.

If you need to work with eigrp routes, remember that by default, EIGRP summarizes subnet routes to the network level. The no auto-summary command can be entered to configure subnet level summarization, then use 'ip summary-address eigrp' on a specific interface. More infos:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cr/hirp_r/rte_eih.htm#wp1097180

HTH

Andrea

[carl_townshend]

Hi Andrea, thanks for your help, do I need to use the eigrp-summary address on my interface,or will it work fine without ? I guess this just stops all 3 networks being advertised out the interface right ?

Also is it possible for me to split the network

into a 128 subnet and 2 64's, how would I do this ?

[zerozerotito]

Hi carl,

It will work fine. As you mentioned, it makes advertisements smaller. In this case, it will advertise on network instead of 3 if you configure eigrp...

As i understand u wanna create a subnet which include 128 IP addresses, and two more subnet which includes 64 IP Addresses. Yes it is possible with a enough block of IPs.

Here is a simple calculation for 192.168.11.0/24

Subnet 1

Network Address: 192.168.11.0

Subnet Mask : 255.255.255.128

Subnet 2

Network Address: 192.168.11.128

Subnet Mask : 255.255.255.128

Both subnet has 128 IP address. Both u can use only 126 of them because the first one is network and the last one is for broadcast.

So lets have 64-IP Subnet

We will use the first one for 128-IP

So we have to subnet the second one to use as 64-IP

Subnet 2.1

Network Address:192.168.11.128

Subnet MAsk : 255.255.255.192

Subnet 2.2

Network Address: 192.168.11.192

Subnet MAsk : 255.255.255.192

After these calculations you have 3 subnets. The first one includes 128 IPs, and the others (Subnet 2.1 and 2.2) include 64 IPs

Regards.

Ahmet

Please Rate helpful posts.

[carl_townshend]

is it possible we can have the first 2 64 subnets first and the 128 subnet last (higher in the range) ?

[zerozerotito]

Exactly you can...

VLANs are like legos, you can build whatever u want...

But there is one important thing you have to consider is that:

If you wanna use first subnet (subnet zero), you have to configure your switches.

Here is the command:

router(config)# ip subnet-zero

Without enabling this, you cant use first subnet...

Regards...

Pls rate helpful posts...

[carl_townshend]

so can i have my first 2 64 ip addresses in the lower range ie 0-64-128 and 128-256, or do u have to use the bigger one first in the lower range ?