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razor
razor
Visitor III
July 2, 2018
Question

Configuring specific dhcp options within same subnet

  • July 2, 2018
  • 2 replies
  • 9611 views

Hi Fortinet Guru's,

 

I have a question regarding the DHCP functionality within the FortiOS.

 

We're asked to replace a CISCO device within a couple of weeks, so far so good. But the Cisco device used DHCP pools to distribute DHCP options for specific desk phone's, within the same subset.

 

A piece of the config file:

ip dhcp excluded-address 192.168.2.1 192.168.2.9
ip dhcp excluded-address 192.168.2.200 192.168.2.254
!
ip dhcp pool VLAN1
network 192.168.2.0 255.255.255.0 domain-name xxx.local default-router 192.168.2.254 dns-server 192.168.2.254
lease 0 8 !
ip dhcp pool phone1
host 192.168.2.5 255.255.255.0
hardware-address 0004.f269.39d5
default-router 192.168.2.254
dns-server 192.168.2.254 213.144.235.1
option 66 ascii "http://xxx100:xxhoofd75@xxx.nl/dms/polyucauth" lease 0 0 30
!
ip dhcp pool phone2
host 192.168.2.6 255.255.255.0
hardware-address 0004.f269.3d88
default-router 192.168.2.254
dns-server 192.168.2.254 213.144.235.1
option 66 ascii "http://xxx200:xxhoofd75@xxx.nl/dms/polyucauth" lease 0 0 30

 

It seems FortiOS doesn't have the capability to provide the same functionality; but I need someone to confirm. For instance, if I try to make multiple DHCP servers within the FortiOS config, it will complain about the subnet which cannot be used in multiple DHCP servers.

 

Who can help me out? Thanks in advance!

    2 replies

    bommi
    bommi
    New Member
    July 2, 2018

     

     

    sw2090
    SuperUser
    sw2090
    SuperUser
    July 3, 2018

    hm yes,

     

    FortiOS does only support one DHCP Server per Interface. It though does support multiple ip pools per dhcp server and also dhcp reservations/assignments. So far that would be no problem.

    What kills it is your client specific dhcp option 66. You can set custom string as dhcp option on a dhcp server on a FGT Interface but you can not tag it to a specific client.

    So you would have to multiply the interfaces instead of the dhcp servers. You could setup a vlan for each telephone with its own dhcp server - that would do the trick but will be somehow overkill....

    Toshi_Esumi
    SuperUser
    Toshi_Esumi
    SuperUser
    July 3, 2018

    Option 66 is regularly per phone type or vendor. We have multiple phone type/vendor environment at customer locations and each type might require different settings (like Cisco requires option 150), often a combination between  Cisco and Polycom. We separate them by vlans and set different DHCP scope and options, so that it makes our troubleshooting process much easier, especially for Cisco phones. Most phones can learn own vlan via CDP or LLDP. If not, we set it at phones manually.

    irfansyah
    irfansyah
    New Member
    October 11, 2018

    i have same problem before,

     

    and i tried this command

    config system settings set allow-subnet-overlap enable end

    it works

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