DHCP on Switch Configuration

Unanswered Question
Sep 9th, 2008

I have 3750 switch with Version 12.2(25)SEE3. I am running DHCP server on it for data/voice

I am running 172.28.92.0/24 for data and 172.28.93.0/24 for voice.

Ports are configured both for data/voice.

Now i want to add another subnet because users are getting IP address outage.

Please let me know how to add another subnet for voice and data and how to confiugre this subnet for DHCP server. How to configure the VLAN for this.

I will be very greatful to you.

I have this problem too.
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wasim,

If you need to add addresses - you need to look at your IP Subneting structure.

What subnet is running out of addresses Data or Voice or both?

I would recommend the following:-

Change Data from 172.28.92.0/24 to 172.19.92/23

Which expands your data subnet from 254 to 510 addresses, you just make the mask change to the SVI and the DHCP pool.

The I would re-configure the Voice from 172.28.93.0/24 to 172.28.90.0/23

Which expands your voice subnet from 254 to 510 addresses - you will need to re-ip your Voice SVI completly, but since you change

your data SVI first - you will not lose connectivity.

HTH>

wasiimcisco Tue, 09/09/2008 - 01:36

Thanks for the reply, one more question what i m getting from ur reply is that i have to play around with the already mentioned IP pool. I cant assign new IP pool for example i want to assign 172.28.94.0/24 for data and 172.28.95.0/24 for voice.

If i want to do this is this possible, if yes then what will be the DHCP Configuration and what will be the VLAN Configuration.

wasiimcisco Tue, 09/09/2008 - 02:52

I will make another DHCP POOl for new subnet addition.

Old POOL look like this

ip dhcp pool AB_DATA

network 172.28.92.0 255.255.255.0

default-router 172.28.92.254

dns-server 172.28.32.32

!

ip dhcp pool AB_VOICE

network 172.28.93.0 255.255.255.0

default-router 172.28.93.254

option 150 ip 172.28.10.10

dns-server 172.28.32.32

The new IP pool will be like this

ip dhcp pool NEW_DATA

network 172.28.94.0 255.255.255.0

default-router 172.28.92.254

dns-server 172.28.32.32

!

ip dhcp pool NEW_VOICE

network 172.28.95.0 255.255.255.0

default-router 172.28.93.254

option 150 ip 172.28.10.10

dns-server 172.28.32.32

Is there any need to creat additional VLAN bcz right now i have two vlan 100 for data and 110 for voice.

By adding another pool how the VLAN will react and how to configure the ports for this newly added IP Pool.

Giuseppe Larosa Tue, 09/09/2008 - 01:22

Hello Waasim,

you need to redefine one of the address pool to allow more users on the subnet

an example is the following:

you can adapt it to your needs

ip dhcp pool DATA

network 10.110.224.128 255.255.255.240

default-router 10.110.224.129

dns-server 10.98.112.32 10.55.0.32

netbios-name-server 10.52.64.37 10.24.128.151

lease 0 1

!

ip dhcp pool VOICE

network 10.110.224.144 255.255.255.248

default-router 10.110.224.145

dns-server 10.98.112.32 10.55.0.32

netbios-name-server 10.52.64.37 10.24.128.151

option 150 ip 10.98.67.5 10.55.61.4

lease 0 1

!

in the voice pool you need to specify in the option 150 the ip addresses of your TFTP servers that are part of the CM cluster.

Note: this config is done starting in global config mode.

The SVI Vlan has no special config: its ip address is used as the gateway address in the pool.

Edit

I didn't catch the problem was to increase the size of one subnet . Sorry ..

Hope to help

Giuseppe

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