Cisco DHCP Multiple Subnets

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QuadZeroRoute's Avatar (by Gravatar) posted on
September 1, 2008, 8:29 pm
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When on a Cisco router, configuring DHCP I assume that I can have
multiple subnets although I have never seen an example at Cisco on
this.  Would I just have multiple "network" statements for those
subnets?

Example

ip dhcp pool academy
network 172.16.0.0 255.255.255.0
network 172.16.10.0 255.255.255.0
network 172.16.20.0 255.255.255.0


The reason that I ask is that for InterVLAN routing you end up with
multiple subnets but I was never told how to manage DHCP for that
situation and while it looks straightforward I do not know that the
solution fits because I do not have equipment to try it on.

Thanks.

Brian V's Avatar (by Gravatar) posted on
September 1, 2008, 11:46 pm
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Re: Cisco DHCP Multiple Subnets



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You would create different pools, ie pool_subnet1, then the gateway, dns
yada yada, then pool_subnet2 with it's gateway etc.

-Brian


QuadZeroRoute's Avatar (by Gravatar) posted on
September 2, 2008, 1:12 am
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Re: Cisco DHCP Multiple Subnets


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Ahhhhh....excellent.  Good thing I asked!  Thank you very much.

QuadZeroRoute's Avatar (by Gravatar) posted on
September 2, 2008, 1:27 am
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Re: Cisco DHCP Multiple Subnets


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For those who have not seen the DHCP commands are are studying this, I
thought that I would throw out the solution so you can see it
according to what Brian explained.

For interVLAN communications according to Cisco you would configure:

    Router_Two# config terminal
    Router_Two(config)# interface fa 0/1
    Router_Two(config-if)# no shutdown
    Router_Two(config-if)# interface fa 0/1.1
    Router_Two(config-if)# encapsulation dot1q 1 native
    Router_Two(config-if)# ip address 172.16.0.1 255.255.255.0
    Router_Two(config-if)# interface fa 0/1.10
    Router_Two(config-if)# encapsulation dot1q 10
    Router_Two(config-if)# ip address 172.16.10.1 255.255.255.0
    Router_Two(config-if)# interface fa 0/1.20
    Router_Two(config-if)# encapsulation dot1q 20
    Router_Two(config-if)# ip address 172.16.20.1 255.255.255.0
...
    Router_Two# show ip interface brief
    FastEthernet 0/1        unassigned
    FastEthernet 0/1.1        172.16.0.1
    FastEthernet 0/1.10        172.16.10.1
    FastEthernet 0/1.20        172.16.20.1
    Serial 0/1            unassigned
...
and the DHCP solution would be:
    Router_Two(config)# service dhcp
    Router_Two(config)# ip dhcp pool native_VLAN
    Router_Two(dhcp-config)# network 172.16.0.0 255.255.255.0
    Router_Two(dhcp-config)# default-router 172.16.0.1
    Router_Two(dhcp-config)# dns-server 172.16.0.10
    Router_Two(dhcp-config)# netbios-name-server 172.16.0.10
    Router_Two(dhcp-config)# domain-name cisco.com
    Router_Two(dhcp-config)# lease infinite
    Router_Two(dhcp-config)# exit
    Router_Two(config)# ip dhcp pool accounting
    Router_Two(dhcp-config)# network 172.16.10.0 255.255.255.0
    Router_Two(dhcp-config)# default-router 172.16.10.1
    Router_Two(dhcp-config)# dns-server 172.16.10.10
    Router_Two(dhcp-config)# netbios-name-server 172.16.10.10
    Router_Two(dhcp-config)# domain-name cisco.com
    Router_Two(dhcp-config)# lease 0 24 0
    Router_Two(dhcp-config)# exit
    Router_Two(config)# ip dhcp pool sales
    Router_Two(dhcp-config)# network 172.16.20.0 255.255.255.0
    Router_Two(dhcp-config)# default-router 172.16.20.1
    Router_Two(dhcp-config)# dns-server 172.16.20.10
    Router_Two(dhcp-config)# netbios-name-server 172.16.20.10
    Router_Two(dhcp-config)# domain-name cisco.com
    Router_Two(dhcp-config)# lease 0 24 0
    Router_Two(dhcp-config)# exit

QuadZeroRoute's Avatar (by Gravatar) posted on
September 9, 2008, 6:34 pm
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Re: Cisco DHCP Multiple Subnets


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I have found a problem in what I wrote.  I did not include multiple
statements for the dhcp exclude.... do I need three statements or is
there another way to do it?

Router_Two(config)# ip dhcp excluded-address 172.10.0.0 172.16.0.10
Router_Two(config)# ip dhcp excluded-address 172.16.10.0 172.16.10.10
Router_Two(config)# ip dhcp excluded-address 172.16.20.0 172.16.20.10



Thanks

Scott Perry's Avatar (by Gravatar) posted on
September 9, 2008, 7:40 pm
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Re: Cisco DHCP Multiple Subnets


You use all three statements.

-----
Scott Perry
Indianapolis, IN
-----



I have found a problem in what I wrote.  I did not include multiple
statements for the dhcp exclude.... do I need three statements or is
there another way to do it?

Router_Two(config)# ip dhcp excluded-address 172.10.0.0 172.16.0.10
Router_Two(config)# ip dhcp excluded-address 172.16.10.0 172.16.10.10
Router_Two(config)# ip dhcp excluded-address 172.16.20.0 172.16.20.10



Thanks



QuadZeroRoute's Avatar (by Gravatar) posted on
September 9, 2008, 8:13 pm
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Re: Cisco DHCP Multiple Subnets


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Good to know just in case.

Thanks Scott!

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