Document new netmask behaviour; document new requirement that all interfaces correspond to a declared subnet

1 files changed, 20 insertions, 7 deletions

diff --git a/server/dhcpd.conf.5 b/server/dhcpd.conf.5
index 462e636b..73b796e5 100644
--- a/server/dhcpd.conf.5
+++ b/server/dhcpd.conf.5
@@ -77,12 +77,13 @@ related strictly on a per-subnet basis, the \fIgroup\fR declaration
 can be used.
 .PP
 Each dhcpd.conf file must have one (and only one)
-\fIserver-identifier\fR declaration, which tells dhcpd the identifier
-to use when issuing leases.   For every subnet which will be served,
-there must be one \fIsubnet\fR declaration, which tells dhcpd how to
-recognize that an address is on that subnet.   A \fIsubnet\fR
-declaration is required for each subnet even if no addresses will be
-dynamically allocated on that subnet.
+.I server-identifier
+declaration, which tells dhcpd the identifier to use when issuing
+leases.  For every subnet which will be served, and for every subnet
+to which the dhcp server is connected, there must be one \fIsubnet\fR
+declaration, which tells dhcpd how to recognize that an address is on
+that subnet.  A \fIsubnet\fR declaration is required for each subnet
+even if no addresses will be dynamically allocated on that subnet.
 .PP
 Some installations have physical networks on which more than one IP
 subnet operates.   For example, if there is a site-wide requirement
@@ -353,6 +354,12 @@ of the subnet being described.   The subnet number, together with the
 netmask, are sufficient to determine whether any given IP address is
 on the specified subnet.
 .PP
+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.
+.PP
 .B The
 .I range
 .B statement
@@ -688,7 +695,13 @@ The standard options are:
  \fBoption subnet-mask\fR \fIip-address\fR\fB;\fR
 .PP
 The subnet mask option specifies the client's subnet mask as per RFC
-950.
+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,
+.I any
+subnet-mask option declaration that is in scope for the address being
+assigned will override the subnet mask specified in the subnet
+declaration.
 .PP
  \fBoption time-offset\fR \fIint32\fR\fB;\fR
 .PP