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DHCP on additional addresses

Christoffer Möller
Hi

I'm currently migrating an existing network from and old version of smoothwall to ASG7. The old network has the subnet of 172.16.0.1/24. The problem is that there is no obvius space to put the DHCP addresses. My plan was to add another subnet 172.16.1.1/24 on the same interface and use that for DHCP.

However, it seems i can only add a DHCP server on the primary subnet. The sulution would be to use 172.16.1.1/24 as the primary and add 172.16.0.1/24 as an additional subnet.

Will this work? What else do I need to do so everything works as expected?

I don't have lots experience with bigger networks.

Thanks!


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  • 0
    The problem is that there is no obvius space to put the DHCP addresses.


    Hi, could you elaborate on this sentence? I'm not sure what your goal is.

    Barry
  • 0 in reply to BarryG
    Sure. From the start we had 172.16.0.2-99 for static ip and everything above as dhcp space. Due to several reasons we now have many static ip configured in the 172.16.0.100-254 range.

    This makes it messy, and it is at this point not feasible to change this without breaking a lot of things. So my hopes was to run dhcp from a completly different subnet.
  • 0
    I'm still a little confused about what your issue is, but I'll guess...

    Change the definition of the Internal interface from 172.16.0.0/24 to 172.16.0.0/23.  Change the DHCP range to 172.16.0.1-172.16.0.254.

    Cheers - Bob
     
    Sophos UTM Community Moderator
    Sophos Certified Architect - UTM
    Sophos Certified Engineer - XG
    Gold Solution Partner since 2005
    MediaSoft, Inc. USA
  • 0 in reply to BAlfson
    Hmm, I don't think that will work in my case since all static servers are configured with a netmask of 255.255.255.0.

    My basic question, I guess, is: Is it posible to have two diffrent subnets on the same physical interface?
  • 0
    That is, in essence, what you have with that suggestion, and you just configure the DHCP server to hand out addresses on the subnet without all the servers:

    [172.16.0.0/255.255.255.0 + 172.16.1.0/255.255.255.0] = [172.16.0.0/255.255.254.0]
    as
    [172.16.0.0/24 + 172.16.1.0/24] = [172.16.0.0/23]

    Here's a handy tool: Online IP CIDR / VLSM Supernet Calculator

    Cheers - Bob
     
    Sophos UTM Community Moderator
    Sophos Certified Architect - UTM
    Sophos Certified Engineer - XG
    Gold Solution Partner since 2005
    MediaSoft, Inc. USA
  • 0
    That seems logical [:)] Thanks!

    Is there anything else that I need to change? Can both subnets comunicate without problems?
  • 0
    Yes, you do need to change the subnet mask on the servers to 255.255.254.0 also.  DHCP wil handle that for the clients as it pulls the netmask from the Internal interface definition.

    Cheers - Bob
     
    Sophos UTM Community Moderator
    Sophos Certified Architect - UTM
    Sophos Certified Engineer - XG
    Gold Solution Partner since 2005
    MediaSoft, Inc. USA
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