Network Architecture & Design

  • 1.  Setting up a secondary IP address range

    Posted 10-25-2016 12:54
    We are running out of IP's in our DHCP range and do not have 'room' in our IPv4 to enlarge the current scope. Can you setup a secondary IP range to use DHCP?

    Like so:

    interface vlan.0.100
    ip address 10.10.1.0 255.255.255.0 primary
    ip address 10.10.7.0 255.255.255.0 secondary



  • 2.  RE: Setting up a secondary IP address range

    Posted 10-25-2016 12:57
    Hi Jeremy,
    working with secondary IP addresses on a router interface is possible but alway a nasty workaround.

    Regards
    André


  • 3.  RE: Setting up a secondary IP address range

    Posted 10-25-2016 12:57
    Why 'nasty'?


  • 4.  RE: Setting up a secondary IP address range

    Posted 10-25-2016 12:57
    Both subnets are broadcastdomains - usually broadcastdomains are separated by routers - you plan to connect them with a bridge.

    You better create a second vlan with its own IP range and use tagging on the uplinks.

    /André


  • 5.  RE: Setting up a secondary IP address range

    Posted 10-25-2016 12:57
    I am not sure I would use the adjective "nasty". Adding the secondary address with another class c address is not much different than backing off the mask by 1 bit. That said I understand and agree with the sentiment of keeping broadcast domains as small a possible.


  • 6.  RE: Setting up a secondary IP address range

    Posted 10-25-2016 12:57
    When it stops with the first secondary IP - I agree. But you are opening the door to a bad style of networking (I have customers with 12 secondary IPs in a subnet). Creating a second vlan shouldn't be a problem.



  • 7.  RE: Setting up a secondary IP address range

    Posted 10-25-2016 12:57
    Another thing is the DHCP request - I assume DHCP relay will be used,
    In that case the router will send out 2 requests for the different scopes and the first reply will decide which IP (subnet) is used by the client.

    In my opinion it's better to configure a new VLAN instead of using a secondary IP.


  • 8.  RE: Setting up a secondary IP address range

    Posted 10-25-2016 12:57
    Your DHCP server will need to be configured to show the different subnets are actually a part of the same network. Our BlueCat DHCP servers are able to do that.


  • 9.  RE: Setting up a secondary IP address range

    Posted 10-26-2016 05:42
    Hi Jeremy,

    you can add a secondary IP address to a VLAN:
    configure vlan <NAME> add secondary-ipaddress <ADDRESS> [/code]You can configure the BOOTP Relay service to include the secondary address(es):
    configure bootprelay ipv4 include-secondary [/code]Br,
    Erik