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Community Member

Second DHCP Range

Hello Everyone,

If I have a 2811 router with 10.70.0.1 as the inside interface IP address and it is handing out DHCP ip addresses in teh 10.70.0.x range to clients and telling them to use 10.70.0.1 as teh Default Gateway how do I configure a second range of 10.80.0x for DHCP and have them use the same interface for the DG?  WIll it just work if I configure the second range or do I have to do something else to make the 10.80.0 x clients use the same DG?

Thanks in advance!

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1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Second DHCP Range

Hi,

Oh, I see. This should have been stated from the very beginning.

Frankly, there is no way of doing this without modifying your addressing plan. You are basically running short on IP addresses because the IP network itself is small. It is not possible to force the stations on your single LAN to use two distinct IP ranges from two different IP networks and yet have them consider themselves to be members of just a single LAN (and a single network). That would go against the basic principles of IP operation.

Technically, the easiest solution would be to modify the netmask of your network to /23 or less so that your network becomes 10.70.0.0/23 which provides you with a range from 10.70.0.0 to 10.70.1.255. However, that would require:

  • Readdressing the interface on your router (changing its netmask)
  • Reconfiguring the DHCP pool (modifying the netmask in the network command)
  • Modifying all other parts of the router's configuration that refer to the previous network (ACLs, routing protocols, ...)
  • Readdressing all statically addressed devices in your network (changing their netmasks)

There is quite a lot of administrative overhead involved. Sadly, I do not see any other reliable solution.

Best regards,

Peter

3 REPLIES
Cisco Employee

Second DHCP Range

Hi,

For a new range, you must create a new DHCP pool with the network command specifying the range 10.80.0.x/24. All DHCP-provided options (DNS, domain name, default gateway, etc.) must be explicitly specified in this new pool.

However, I do not understand why you want the clients from the 10.80.0.x range use the default gateway 10.70.0.1. Such addressing would be incorrect, as the IP address of the default gateway must always be in the same IP network as the clients that are using it. Can you clarify your requirement please?

Best regards,

Peter

Community Member

Second DHCP Range

Thanks for the response.  All I really want to do is be able to have more clients via DHCP that the current range allows.  Right now I can only use 10.70.0.100-254 and I need more IP addresses.  10,70.0.1-99 are reserved and can't be handed out.

Cisco Employee

Second DHCP Range

Hi,

Oh, I see. This should have been stated from the very beginning.

Frankly, there is no way of doing this without modifying your addressing plan. You are basically running short on IP addresses because the IP network itself is small. It is not possible to force the stations on your single LAN to use two distinct IP ranges from two different IP networks and yet have them consider themselves to be members of just a single LAN (and a single network). That would go against the basic principles of IP operation.

Technically, the easiest solution would be to modify the netmask of your network to /23 or less so that your network becomes 10.70.0.0/23 which provides you with a range from 10.70.0.0 to 10.70.1.255. However, that would require:

  • Readdressing the interface on your router (changing its netmask)
  • Reconfiguring the DHCP pool (modifying the netmask in the network command)
  • Modifying all other parts of the router's configuration that refer to the previous network (ACLs, routing protocols, ...)
  • Readdressing all statically addressed devices in your network (changing their netmasks)

There is quite a lot of administrative overhead involved. Sadly, I do not see any other reliable solution.

Best regards,

Peter

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