removing an interface does not remove the dhcp entry

[hboetes]

So the error is: "DHCP Server is currently enabled. Cannot enable the DHCP Relay service while the DHCP Server is enabled on any interface."

Well it's not enabled.

After googling that I found this: https://forum.netgate.com/topic/42997/can-t-enable-dhcp-relay

So I made a config backup and searched for dhcp and found:

  <dhcpd>                                                                                                                                                                                                                                                      
    <lan>                                                                                                                                                                                                                                                      
      <range>                                                                                                                                                                                                                                                  
        <from>10.10.10.10</from>                                                                                                                                                                                                                               
        <to>10.10.10.245</to>                                                                                                                                                                                                                                  
      </range>                                                                                                                                                                                                                                                 
    </lan>                                                                                                                                                                                                                                                     
    <opt2>                                                                                                                                                                                                                                                     
      <enable>1</enable>                                                                                                                                                                                                                                       
      <gateway>10.10.30.1</gateway>                                                                                                                                                                                                                            
      <domain>guest-lan</domain>                                                                                                                                                                                                                              
      <ddnsdomainalgorithm>hmac-md5</ddnsdomainalgorithm>                                                                                                                                                                                                      
      <numberoptions/>                                                                                                                                                                                                                                         
      <range>                                                                                                                                                                                                                                                  
        <from>10.10.30.100</from>                                                                                                                                                                                                                              
        <to>10.10.30.200</to>                                                                                                                                                                                                                                  
      </range>                                                                                                                                                                                                                                                 
      <dnsserver>1.1.1.1</dnsserver>                                                                                                                                                                                                                           
      <dnsserver>8.8.8.8</dnsserver>                                                                                                                                                                                                                           
    </opt2>                                                                                                                                                                                                                                                    
    <opt3>                                                                                                                                                                                                                                                     
      <ddnsdomainalgorithm>hmac-md5</ddnsdomainalgorithm>                                                                                                                                                                                                      
      <numberoptions/>                                                                                                                                                                                                                                         
      <range>                                                                                                                                                                                                                                                  
        <from>10.10.40.10</from>                                                                                                                                                                                                                               
        <to>10.10.40.240</to>                                                                                                                                                                                                                                  
      </range>                                                                                                                                                                                                                                                 
      <dnsserver>10.10.10.11</dnsserver>                                                                                                                                                                                                                       
      <dnsserver>10.10.10.12</dnsserver>                                                                                                                                                                                                                       
    </opt3>                                                                                                                                                                                                                                                    
    <opt5>                                                                                                                                                                                                                                                     
      <ddnsdomainalgorithm>hmac-md5</ddnsdomainalgorithm>                                                                                                                                                                                                      
      <numberoptions>                                                                                                                                                                                                                                          
        <item/>                                                                                                                                                                                                                                                
      </numberoptions>                                                                                                                                                                                                                                         
      <range>                                                                                                                                                                                                                                                  
        <from>172.16.6.200</from>                                                                                                                                                                                                                              
        <to>172.16.6.250</to>                                                                                                                                                                                                                                  
      </range>                                                                                                                                                                                                                                                 
      <winsserver/>                                                                                                                                                                                                                                            
      <dnsserver/>                                                                                                                                                                                                                                             
      <ntpserver/>                                                                                                                                                                                                                                             
    </opt5>                                                                                                                                                                                                                                                    
  </dhcpd>

That opt2 config with the enabled dhcp entry is from an old removed interface. So apparently removing an interface does not remove the dhcp entry and after that you can't remove the matching dhcp entry.
I tried working around the issue by enabling dhcp on another interface and then removing it again. Still the same entry remains.

After downloading the config and editing it, as mentioned in the linked URL, the problem was gone.

[AdSchellevis]

3df9968 should fix the issue (validate if interface is active and dhcpd is enabled).

[fichtner]

the same is probably true for dhcpv6 as well

[AdSchellevis]

missed the IPv6 page, I'll check.

[hboetes]

Wouldn't it be nice to remove the DHCP configuration for an interface after removing the interface?

[AdSchellevis]

We don't have a mechanism in place to clean those sections, it would be confusing if we do this in some sections for some components. I rather keep it like it is now.