Netmask issue

Reissom Beshir Reissom_Beshir at
Fri Oct 2 22:52:55 UTC 2009

Simon Hobson wrote:

>>So does this bug exist in dhcp-4.0?
> Is it a bug ? The OP didn't specify a netmask option to send to clients. 
> You could argue that the logic is wrong in how the value is chosen, but if 
> the admin specifies the right value then it works just fine.

If I am not mistaken the expected behaviour is for dhcpd to take the netmask 
set in the subnet statement and place that in the netmask option when the 
option is not explicitly specified.  In this case the OP did specify the 
right value in the subnet decl, but dhcpd chose its own value.  This is 
incorrect.  Does that not make it a bug?

And according to the documentation...
man dhcpd.conf:
  The subnet statement
  Although a netmask must be given with every subnet declaration,
  it is recommended that if there is any variance in  subnet  masks
  at  a  site,  a subnet-mask option statement be used in each subnet
  declaration to set the desired subnet mask, since any subnet-mask
  option statement will override the subnet mask declared in the
  subnet statement.

man dhcp-options:
  option subnet-mask ip-address;

  The  subnet  mask  option specifies the client's subnet mask as
  per RFC 950.  If no subnet mask option is provided anywhere in
  scope, as a last resort dhcpd will use the subnet mask from the
  subnet declaration for the network  on  which  an  address  is
  being assigned.  However, any subnet-mask option declaration that
  is in scope for the address being assigned will override the
  subnet mask specified in the subnet declaration.


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