DHCP server edit when DHCP Relay enabled

Part of Redmine #6997
1) Display the DHCP Server settings even when DHCP Relay is enabled, but
disable the "enable" checkbox in this case - so the user cannot enable
DHCP Server when DHCP Relay is enabled, but can view and modify the DHCP
Server parameters (ready for the day they want to use it).
2) Actually validate the POSTed DHCP Server parameters, even if it is
disabled. Previously you could put rubbish values in fields and they
would be "happily" saved when DHCP Server was disabled. We want users to
be able to setup DHCP Server ready-to-enable and knowing that they have
put validated stuff in.
3) When DHCP Server is disabled, allow Range From and Range To to be
left empty. When first setting up parameters (e.g. with the UI page up
for the first time) it is OK for the user to be able to just press
"Save". e.g. they are just pressing Save as a way to get out (as if it
is a Cancel button). We do not need to force them to enter range from/to
IP addresses.

1 files changed, 194 insertions, 185 deletions

diff --git a/src/usr/local/www/services_dhcp.php b/src/usr/local/www/services_dhcp.php
index c9c275a..5f244e9 100644
--- a/src/usr/local/www/services_dhcp.php
+++ b/src/usr/local/www/services_dhcp.php
@@ -232,222 +232,228 @@ if (isset($_POST['save'])) {
 	$pconfig['numberoptions'] = $numberoptions;
 
 	/* input validation */
+
+	// Note: if DHCP Server is not enabled, then it is OK to adjust other parameters without specifying range from-to.
 	if ($_POST['enable'] || is_numeric($pool) || $act == "newpool") {
 		$reqdfields = explode(" ", "range_from range_to");
 		$reqdfieldsn = array(gettext("Range begin"), gettext("Range end"));
 
 		do_input_validation($_POST, $reqdfields, $reqdfieldsn, $input_errors);
+	}
 
-		if (($_POST['nonak']) && !empty($_POST['failover_peerip'])) {
-			$input_errors[] = gettext("Ignore Denied Clients may not be used when a Failover Peer IP is defined.");
-		}
+	if (($_POST['nonak']) && !empty($_POST['failover_peerip'])) {
+		$input_errors[] = gettext("Ignore Denied Clients may not be used when a Failover Peer IP is defined.");
+	}
 
-		if (($_POST['range_from'] && !is_ipaddrv4($_POST['range_from']))) {
-			$input_errors[] = gettext("A valid range must be specified.");
-		}
-		if (($_POST['range_to'] && !is_ipaddrv4($_POST['range_to']))) {
-			$input_errors[] = gettext("A valid range must be specified.");
-		}
-		if (($_POST['gateway'] && $_POST['gateway'] != "none" && !is_ipaddrv4($_POST['gateway']))) {
-			$input_errors[] = gettext("A valid IP address must be specified for the gateway.");
-		}
-		if (($_POST['wins1'] && !is_ipaddrv4($_POST['wins1'])) || ($_POST['wins2'] && !is_ipaddrv4($_POST['wins2']))) {
-			$input_errors[] = gettext("A valid IP address must be specified for the primary/secondary WINS servers.");
-		}
-		$parent_ip = get_interface_ip($_POST['if']);
-		if (is_ipaddrv4($parent_ip) && $_POST['gateway'] && $_POST['gateway'] != "none") {
-			$parent_sn = get_interface_subnet($_POST['if']);
-			if (!ip_in_subnet($_POST['gateway'], gen_subnet($parent_ip, $parent_sn) . "/" . $parent_sn) && !ip_in_interface_alias_subnet($_POST['if'], $_POST['gateway'])) {
-				$input_errors[] = sprintf(gettext("The gateway address %s does not lie within the chosen interface's subnet."), $_POST['gateway']);
-			}
+	if ($_POST['range_from'] && !is_ipaddrv4($_POST['range_from'])) {
+		$input_errors[] = gettext("A valid IPv4 address must be specified for range from.");
+	}
+	if ($_POST['range_to'] && !is_ipaddrv4($_POST['range_to'])) {
+		$input_errors[] = gettext("A valid IPv4 address must be specified for range to.");
+	}
+	if (($_POST['range_from'] && !$_POST['range_to']) || ($_POST['range_to'] && !$_POST['range_from'])) {
+		$input_errors[] = gettext("Range From and Range To must both be entered.");
+	}
+	if (($_POST['gateway'] && $_POST['gateway'] != "none" && !is_ipaddrv4($_POST['gateway']))) {
+		$input_errors[] = gettext("A valid IP address must be specified for the gateway.");
+	}
+	if (($_POST['wins1'] && !is_ipaddrv4($_POST['wins1'])) || ($_POST['wins2'] && !is_ipaddrv4($_POST['wins2']))) {
+		$input_errors[] = gettext("A valid IP address must be specified for the primary/secondary WINS servers.");
+	}
+	$parent_ip = get_interface_ip($_POST['if']);
+	if (is_ipaddrv4($parent_ip) && $_POST['gateway'] && $_POST['gateway'] != "none") {
+		$parent_sn = get_interface_subnet($_POST['if']);
+		if (!ip_in_subnet($_POST['gateway'], gen_subnet($parent_ip, $parent_sn) . "/" . $parent_sn) && !ip_in_interface_alias_subnet($_POST['if'], $_POST['gateway'])) {
+			$input_errors[] = sprintf(gettext("The gateway address %s does not lie within the chosen interface's subnet."), $_POST['gateway']);
 		}
+	}
 
-		if (($_POST['dns1'] && !is_ipaddrv4($_POST['dns1'])) || ($_POST['dns2'] && !is_ipaddrv4($_POST['dns2'])) || ($_POST['dns3'] && !is_ipaddrv4($_POST['dns3'])) || ($_POST['dns4'] && !is_ipaddrv4($_POST['dns4']))) {
-			$input_errors[] = gettext("A valid IP address must be specified for each of the DNS servers.");
-		}
+	if (($_POST['dns1'] && !is_ipaddrv4($_POST['dns1'])) || ($_POST['dns2'] && !is_ipaddrv4($_POST['dns2'])) || ($_POST['dns3'] && !is_ipaddrv4($_POST['dns3'])) || ($_POST['dns4'] && !is_ipaddrv4($_POST['dns4']))) {
+		$input_errors[] = gettext("A valid IP address must be specified for each of the DNS servers.");
+	}
 
-		if ($_POST['deftime'] && (!is_numeric($_POST['deftime']) || ($_POST['deftime'] < 60))) {
-			$input_errors[] = gettext("The default lease time must be at least 60 seconds.");
+	if ($_POST['deftime'] && (!is_numeric($_POST['deftime']) || ($_POST['deftime'] < 60))) {
+		$input_errors[] = gettext("The default lease time must be at least 60 seconds.");
+	}
+
+	if (isset($config['captiveportal']) && is_array($config['captiveportal'])) {
+		$deftime = 7200; // Default value if it's empty
+		if (is_numeric($_POST['deftime'])) {
+			$deftime = $_POST['deftime'];
 		}
 
-		if (isset($config['captiveportal']) && is_array($config['captiveportal'])) {
-			$deftime = 7200; // Default value if it's empty
-			if (is_numeric($_POST['deftime'])) {
-				$deftime = $_POST['deftime'];
+		foreach ($config['captiveportal'] as $cpZone => $cpdata) {
+			if (!isset($cpdata['enable'])) {
+				continue;
 			}
-
-			foreach ($config['captiveportal'] as $cpZone => $cpdata) {
-				if (!isset($cpdata['enable'])) {
-					continue;
-				}
-				if (!isset($cpdata['timeout']) || !is_numeric($cpdata['timeout'])) {
-					continue;
-				}
-				$cp_ifs = explode(',', $cpdata['interface']);
-				if (!in_array($if, $cp_ifs)) {
-					continue;
-				}
-				if ($cpdata['timeout'] > $deftime) {
-					$input_errors[] = sprintf(gettext(
-						'The Captive Portal zone (%1$s) has Hard Timeout parameter set to a value bigger than Default lease time (%2$s).'), $cpZone, $deftime);
-				}
+			if (!isset($cpdata['timeout']) || !is_numeric($cpdata['timeout'])) {
+				continue;
+			}
+			$cp_ifs = explode(',', $cpdata['interface']);
+			if (!in_array($if, $cp_ifs)) {
+				continue;
+			}
+			if ($cpdata['timeout'] > $deftime) {
+				$input_errors[] = sprintf(gettext(
+					'The Captive Portal zone (%1$s) has Hard Timeout parameter set to a value bigger than Default lease time (%2$s).'), $cpZone, $deftime);
 			}
 		}
+	}
 
-		if ($_POST['maxtime'] && (!is_numeric($_POST['maxtime']) || ($_POST['maxtime'] < 60) || ($_POST['maxtime'] <= $_POST['deftime']))) {
-			$input_errors[] = gettext("The maximum lease time must be at least 60 seconds and higher than the default lease time.");
-		}
-		if (($_POST['ddnsdomain'] && !is_domain($_POST['ddnsdomain']))) {
-			$input_errors[] = gettext("A valid domain name must be specified for the dynamic DNS registration.");
-		}
-		if (($_POST['ddnsdomain'] && !is_ipaddrv4($_POST['ddnsdomainprimary']))) {
-			$input_errors[] = gettext("A valid primary domain name server IP address must be specified for the dynamic domain name.");
-		}
-		if (($_POST['ddnsdomainkey'] && !$_POST['ddnsdomainkeyname']) ||
-		    ($_POST['ddnsdomainkeyname'] && !$_POST['ddnsdomainkey'])) {
-			$input_errors[] = gettext("Both a valid domain key and key name must be specified.");
-		}
-		if ($_POST['domainsearchlist']) {
-			$domain_array = preg_split("/[ ;]+/", $_POST['domainsearchlist']);
-			foreach ($domain_array as $curdomain) {
-				if (!is_domain($curdomain)) {
-					$input_errors[] = gettext("A valid domain search list must be specified.");
-					break;
-				}
+	if ($_POST['maxtime'] && (!is_numeric($_POST['maxtime']) || ($_POST['maxtime'] < 60) || ($_POST['maxtime'] <= $_POST['deftime']))) {
+		$input_errors[] = gettext("The maximum lease time must be at least 60 seconds and higher than the default lease time.");
+	}
+	if (($_POST['ddnsdomain'] && !is_domain($_POST['ddnsdomain']))) {
+		$input_errors[] = gettext("A valid domain name must be specified for the dynamic DNS registration.");
+	}
+	if (($_POST['ddnsdomain'] && !is_ipaddrv4($_POST['ddnsdomainprimary']))) {
+		$input_errors[] = gettext("A valid primary domain name server IP address must be specified for the dynamic domain name.");
+	}
+	if (($_POST['ddnsdomainkey'] && !$_POST['ddnsdomainkeyname']) ||
+		($_POST['ddnsdomainkeyname'] && !$_POST['ddnsdomainkey'])) {
+		$input_errors[] = gettext("Both a valid domain key and key name must be specified.");
+	}
+	if ($_POST['domainsearchlist']) {
+		$domain_array = preg_split("/[ ;]+/", $_POST['domainsearchlist']);
+		foreach ($domain_array as $curdomain) {
+			if (!is_domain($curdomain)) {
+				$input_errors[] = gettext("A valid domain search list must be specified.");
+				break;
 			}
 		}
+	}
 
-		// Validate MACs
-		if (!empty($_POST['mac_allow']) && !validate_partial_mac_list($_POST['mac_allow'])) {
-			$input_errors[] = gettext("If a mac allow list is specified, it must contain only valid partial MAC addresses.");
-		}
-		if (!empty($_POST['mac_deny']) && !validate_partial_mac_list($_POST['mac_deny'])) {
-			$input_errors[] = gettext("If a mac deny list is specified, it must contain only valid partial MAC addresses.");
-		}
+	// Validate MACs
+	if (!empty($_POST['mac_allow']) && !validate_partial_mac_list($_POST['mac_allow'])) {
+		$input_errors[] = gettext("If a mac allow list is specified, it must contain only valid partial MAC addresses.");
+	}
+	if (!empty($_POST['mac_deny']) && !validate_partial_mac_list($_POST['mac_deny'])) {
+		$input_errors[] = gettext("If a mac deny list is specified, it must contain only valid partial MAC addresses.");
+	}
 
-		if (($_POST['ntp1'] && (!is_ipaddrv4($_POST['ntp1']) && !is_hostname($_POST['ntp1']))) || ($_POST['ntp2'] && (!is_ipaddrv4($_POST['ntp2']) && !is_hostname($_POST['ntp2'])))) {
-			$input_errors[] = gettext("A valid IP address or hostname must be specified for the primary/secondary NTP servers.");
-		}
-		if (($_POST['domain'] && !is_domain($_POST['domain']))) {
-			$input_errors[] = gettext("A valid domain name must be specified for the DNS domain.");
-		}
-		if ($_POST['tftp'] && !is_ipaddrv4($_POST['tftp']) && !is_domain($_POST['tftp']) && !filter_var($_POST['tftp'], FILTER_VALIDATE_URL)) {
-			$input_errors[] = gettext("A valid IP address, hostname or URL must be specified for the TFTP server.");
-		}
-		if (($_POST['nextserver'] && !is_ipaddrv4($_POST['nextserver']))) {
-			$input_errors[] = gettext("A valid IP address must be specified for the network boot server.");
-		}
+	if (($_POST['ntp1'] && (!is_ipaddrv4($_POST['ntp1']) && !is_hostname($_POST['ntp1']))) || ($_POST['ntp2'] && (!is_ipaddrv4($_POST['ntp2']) && !is_hostname($_POST['ntp2'])))) {
+		$input_errors[] = gettext("A valid IP address or hostname must be specified for the primary/secondary NTP servers.");
+	}
+	if (($_POST['domain'] && !is_domain($_POST['domain']))) {
+		$input_errors[] = gettext("A valid domain name must be specified for the DNS domain.");
+	}
+	if ($_POST['tftp'] && !is_ipaddrv4($_POST['tftp']) && !is_domain($_POST['tftp']) && !filter_var($_POST['tftp'], FILTER_VALIDATE_URL)) {
+		$input_errors[] = gettext("A valid IP address, hostname or URL must be specified for the TFTP server.");
+	}
+	if (($_POST['nextserver'] && !is_ipaddrv4($_POST['nextserver']))) {
+		$input_errors[] = gettext("A valid IP address must be specified for the network boot server.");
+	}
 
-		if (gen_subnet($ifcfgip, $ifcfgsn) == $_POST['range_from']) {
-			$input_errors[] = gettext("The network address cannot be used in the starting subnet range.");
-		}
-		if (gen_subnet_max($ifcfgip, $ifcfgsn) == $_POST['range_to']) {
-			$input_errors[] = gettext("The broadcast address cannot be used in the ending subnet range.");
-		}
+	if (gen_subnet($ifcfgip, $ifcfgsn) == $_POST['range_from']) {
+		$input_errors[] = gettext("The network address cannot be used in the starting subnet range.");
+	}
+	if (gen_subnet_max($ifcfgip, $ifcfgsn) == $_POST['range_to']) {
+		$input_errors[] = gettext("The broadcast address cannot be used in the ending subnet range.");
+	}
 
-		// Disallow a range that includes the virtualip
-		if (is_array($config['virtualip']['vip'])) {
-			foreach ($config['virtualip']['vip'] as $vip) {
-				if ($vip['interface'] == $if) {
-					if ($vip['subnet'] && is_inrange_v4($vip['subnet'], $_POST['range_from'], $_POST['range_to'])) {
-						$input_errors[] = sprintf(gettext("The subnet range cannot overlap with virtual IP address %s."), $vip['subnet']);
-					}
+	// Disallow a range that includes the virtualip
+	if (is_array($config['virtualip']['vip'])) {
+		foreach ($config['virtualip']['vip'] as $vip) {
+			if ($vip['interface'] == $if) {
+				if ($vip['subnet'] && is_inrange_v4($vip['subnet'], $_POST['range_from'], $_POST['range_to'])) {
+					$input_errors[] = sprintf(gettext("The subnet range cannot overlap with virtual IP address %s."), $vip['subnet']);
 				}
 			}
 		}
+	}
 
-		$noip = false;
-		if (is_array($a_maps)) {
-			foreach ($a_maps as $map) {
-				if (empty($map['ipaddr'])) {
-					$noip = true;
-				}
+	$noip = false;
+	if (is_array($a_maps)) {
+		foreach ($a_maps as $map) {
+			if (empty($map['ipaddr'])) {
+				$noip = true;
 			}
 		}
+	}
 
-		if ($_POST['staticarp'] && $noip) {
-			$input_errors[] = gettext("Cannot enable static ARP when there are static map entries without IP addresses. Ensure all static maps have IP addresses and try again.");
-		}
+	if ($_POST['staticarp'] && $noip) {
+		$input_errors[] = gettext("Cannot enable static ARP when there are static map entries without IP addresses. Ensure all static maps have IP addresses and try again.");
+	}
 
-		if (is_array($pconfig['numberoptions']['item'])) {
-			foreach ($pconfig['numberoptions']['item'] as $numberoption) {
-				$numberoption_value = base64_decode($numberoption['value']);
-				if ($numberoption['type'] == 'text' && strstr($numberoption_value, '"')) {
-					$input_errors[] = gettext("Text type cannot include quotation marks.");
-				} else if ($numberoption['type'] == 'string' && !preg_match('/^"[^"]*"$/', $numberoption_value) && !preg_match('/^[0-9a-f]{2}(?:\:[0-9a-f]{2})*$/i', $numberoption_value)) {
-					$input_errors[] = gettext("String type must be enclosed in quotes like \"this\" or must be a series of octets specified in hexadecimal, separated by colons, like 01:23:45:67:89:ab:cd:ef");
-				} else if ($numberoption['type'] == 'boolean' && $numberoption_value != 'true' && $numberoption_value != 'false' && $numberoption_value != 'on' && $numberoption_value != 'off') {
-					$input_errors[] = gettext("Boolean type must be true, false, on, or off.");
-				} else if ($numberoption['type'] == 'unsigned integer 8' && (!is_numeric($numberoption_value) || $numberoption_value < 0 || $numberoption_value > 255)) {
-					$input_errors[] = gettext("Unsigned 8-bit integer type must be a number in the range 0 to 255.");
-				} else if ($numberoption['type'] == 'unsigned integer 16' && (!is_numeric($numberoption_value) || $numberoption_value < 0 || $numberoption_value > 65535)) {
-					$input_errors[] = gettext("Unsigned 16-bit integer type must be a number in the range 0 to 65535.");
-				} else if ($numberoption['type'] == 'unsigned integer 32' && (!is_numeric($numberoption_value) || $numberoption_value < 0 || $numberoption_value > 4294967295)) {
-					$input_errors[] = gettext("Unsigned 32-bit integer type must be a number in the range 0 to 4294967295.");
-				} else if ($numberoption['type'] == 'signed integer 8' && (!is_numeric($numberoption_value) || $numberoption_value < -128 || $numberoption_value > 127)) {
-					$input_errors[] = gettext("Signed 8-bit integer type must be a number in the range -128 to 127.");
-				} else if ($numberoption['type'] == 'signed integer 16' && (!is_numeric($numberoption_value) || $numberoption_value < -32768 || $numberoption_value > 32767)) {
-					$input_errors[] = gettext("Signed 16-bit integer type must be a number in the range -32768 to 32767.");
-				} else if ($numberoption['type'] == 'signed integer 32' && (!is_numeric($numberoption_value) || $numberoption_value < -2147483648 || $numberoption_value > 2147483647)) {
-					$input_errors[] = gettext("Signed 32-bit integer type must be a number in the range -2147483648 to 2147483647.");
-				} else if ($numberoption['type'] == 'ip-address' && !is_ipaddrv4($numberoption_value) && !is_hostname($numberoption_value)) {
-					$input_errors[] = gettext("IP address or host type must be an IP address or host name.");
-				}
+	if (is_array($pconfig['numberoptions']['item'])) {
+		foreach ($pconfig['numberoptions']['item'] as $numberoption) {
+			$numberoption_value = base64_decode($numberoption['value']);
+			if ($numberoption['type'] == 'text' && strstr($numberoption_value, '"')) {
+				$input_errors[] = gettext("Text type cannot include quotation marks.");
+			} else if ($numberoption['type'] == 'string' && !preg_match('/^"[^"]*"$/', $numberoption_value) && !preg_match('/^[0-9a-f]{2}(?:\:[0-9a-f]{2})*$/i', $numberoption_value)) {
+				$input_errors[] = gettext("String type must be enclosed in quotes like \"this\" or must be a series of octets specified in hexadecimal, separated by colons, like 01:23:45:67:89:ab:cd:ef");
+			} else if ($numberoption['type'] == 'boolean' && $numberoption_value != 'true' && $numberoption_value != 'false' && $numberoption_value != 'on' && $numberoption_value != 'off') {
+				$input_errors[] = gettext("Boolean type must be true, false, on, or off.");
+			} else if ($numberoption['type'] == 'unsigned integer 8' && (!is_numeric($numberoption_value) || $numberoption_value < 0 || $numberoption_value > 255)) {
+				$input_errors[] = gettext("Unsigned 8-bit integer type must be a number in the range 0 to 255.");
+			} else if ($numberoption['type'] == 'unsigned integer 16' && (!is_numeric($numberoption_value) || $numberoption_value < 0 || $numberoption_value > 65535)) {
+				$input_errors[] = gettext("Unsigned 16-bit integer type must be a number in the range 0 to 65535.");
+			} else if ($numberoption['type'] == 'unsigned integer 32' && (!is_numeric($numberoption_value) || $numberoption_value < 0 || $numberoption_value > 4294967295)) {
+				$input_errors[] = gettext("Unsigned 32-bit integer type must be a number in the range 0 to 4294967295.");
+			} else if ($numberoption['type'] == 'signed integer 8' && (!is_numeric($numberoption_value) || $numberoption_value < -128 || $numberoption_value > 127)) {
+				$input_errors[] = gettext("Signed 8-bit integer type must be a number in the range -128 to 127.");
+			} else if ($numberoption['type'] == 'signed integer 16' && (!is_numeric($numberoption_value) || $numberoption_value < -32768 || $numberoption_value > 32767)) {
+				$input_errors[] = gettext("Signed 16-bit integer type must be a number in the range -32768 to 32767.");
+			} else if ($numberoption['type'] == 'signed integer 32' && (!is_numeric($numberoption_value) || $numberoption_value < -2147483648 || $numberoption_value > 2147483647)) {
+				$input_errors[] = gettext("Signed 32-bit integer type must be a number in the range -2147483648 to 2147483647.");
+			} else if ($numberoption['type'] == 'ip-address' && !is_ipaddrv4($numberoption_value) && !is_hostname($numberoption_value)) {
+				$input_errors[] = gettext("IP address or host type must be an IP address or host name.");
 			}
 		}
+	}
+
+	/* If enabling DHCP Server, make sure that the DHCP Relay isn't enabled on this interface */
+	if ($_POST['enable'] && isset($config['dhcrelay']['enable']) && (stristr($config['dhcrelay']['interface'], $if) !== false)) {
+		$input_errors[] = sprintf(gettext("The DHCP relay on the %s interface must be disabled before enabling the DHCP server."), $iflist[$if]);
+	}
+
+	// If nothing is wrong so far, and we have range from and to, then check conditions related to the values of range from and to.
+	if (!$input_errors && $_POST['range_from'] && $_POST['range_to']) {
+		/* make sure the range lies within the current subnet */
+		if (ip_greater_than($_POST['range_from'], $_POST['range_to'])) {
+			$input_errors[] = gettext("The range is invalid (first element higher than second element).");
+		}
 
-		if (!$input_errors) {
-			/* make sure the range lies within the current subnet */
-			if (ip_greater_than($_POST['range_from'], $_POST['range_to'])) {
-				$input_errors[] = gettext("The range is invalid (first element higher than second element).");
+		if (!is_inrange_v4($_POST['range_from'], $subnet_start, $subnet_end) ||
+			!is_inrange_v4($_POST['range_to'], $subnet_start, $subnet_end)) {
+			$input_errors[] = gettext("The specified range lies outside of the current subnet.");
+		}
+
+		if (is_numeric($pool) || ($act == "newpool")) {
+			if (is_inrange_v4($_POST['range_from'],
+				$config['dhcpd'][$if]['range']['from'],
+				$config['dhcpd'][$if]['range']['to']) ||
+				is_inrange_v4($_POST['range_to'],
+				$config['dhcpd'][$if]['range']['from'],
+				$config['dhcpd'][$if]['range']['to'])) {
+				$input_errors[] = gettext("The specified range must not be within the DHCP range for this interface.");
 			}
+		}
 
-			if (!is_inrange_v4($_POST['range_from'], $subnet_start, $subnet_end) ||
-			    !is_inrange_v4($_POST['range_to'], $subnet_start, $subnet_end)) {
-				$input_errors[] = gettext("The specified range lies outside of the current subnet.");
+		foreach ($a_pools as $id => $p) {
+			if (is_numeric($pool) && ($id == $pool)) {
+				continue;
 			}
 
-			if (is_numeric($pool) || ($act == "newpool")) {
-				if (is_inrange_v4($_POST['range_from'],
-				    $config['dhcpd'][$if]['range']['from'],
-				    $config['dhcpd'][$if]['range']['to']) ||
-				    is_inrange_v4($_POST['range_to'],
-				    $config['dhcpd'][$if]['range']['from'],
-				    $config['dhcpd'][$if]['range']['to'])) {
-					$input_errors[] = gettext("The specified range must not be within the DHCP range for this interface.");
-				}
+			if (is_inrange_v4($_POST['range_from'],
+				$p['range']['from'], $p['range']['to']) ||
+				is_inrange_v4($_POST['range_to'],
+				$p['range']['from'], $p['range']['to'])) {
+				$input_errors[] = gettext("The specified range must not be within the range configured on a DHCP pool for this interface.");
+				break;
 			}
+		}
 
-			foreach ($a_pools as $id => $p) {
-				if (is_numeric($pool) && ($id == $pool)) {
+		if (is_array($a_maps)) {
+			foreach ($a_maps as $map) {
+				if (empty($map['ipaddr'])) {
 					continue;
 				}
-
-				if (is_inrange_v4($_POST['range_from'],
-				    $p['range']['from'], $p['range']['to']) ||
-				    is_inrange_v4($_POST['range_to'],
-				    $p['range']['from'], $p['range']['to'])) {
-					$input_errors[] = gettext("The specified range must not be within the range configured on a DHCP pool for this interface.");
+				if (is_inrange_v4($map['ipaddr'], $_POST['range_from'], $_POST['range_to'])) {
+					$input_errors[] = sprintf(gettext("The DHCP range cannot overlap any static DHCP mappings."));
 					break;
 				}
 			}
-
-			/* make sure that the DHCP Relay isn't enabled on this interface */
-			if (isset($config['dhcrelay']['enable']) && (stristr($config['dhcrelay']['interface'], $if) !== false)) {
-				$input_errors[] = sprintf(gettext("The DHCP relay on the %s interface must be disabled before enabling the DHCP server."), $iflist[$if]);
-			}
-
-			if (is_array($a_maps)) {
-				foreach ($a_maps as $map) {
-					if (empty($map['ipaddr'])) {
-						continue;
-					}
-					if (is_inrange_v4($map['ipaddr'], $_POST['range_from'], $_POST['range_to'])) {
-						$input_errors[] = sprintf(gettext("The DHCP range cannot overlap any static DHCP mappings."));
-						break;
-					}
-				}
-			}
 		}
 	}
 
@@ -700,7 +706,7 @@ function build_pooltable() {
 
 $pgtitle = array(gettext("Services"), gettext("DHCP Server"));
 
-if (!empty($if) && !isset($config['dhcrelay']['enable']) && isset($iflist[$if])) {
+if (!empty($if) && isset($iflist[$if])) {
 	$pgtitle[] = $iflist[$if];
 }
 $shortcut_section = "dhcp";
@@ -715,12 +721,6 @@ if ($savemsg) {
 	print_info_box($savemsg, 'success');
 }
 
-if (isset($config['dhcrelay']['enable'])) {
-	print_info_box(gettext("DHCP Relay is currently enabled. Cannot enable the DHCP Server service while the DHCP Relay is enabled on any interface."));
-	include("foot.inc");
-	exit;
-}
-
 if (is_subsystem_dirty('staticmaps')) {
 	print_apply_box(gettext("The static mapping configuration has been changed.") . "<br />" . gettext("The changes must be applied for them to take effect."));
 }
@@ -760,12 +760,21 @@ $form = new Form();
 $section = new Form_Section('General Options');
 
 if (!is_numeric($pool) && !($act == "newpool")) {
-	$section->addInput(new Form_Checkbox(
-		'enable',
-		'Enable',
-		sprintf(gettext("Enable DHCP server on %s interface"), htmlspecialchars($iflist[$if])),
-		$pconfig['enable']
-	));
+	if (isset($config['dhcrelay']['enable'])) {
+		$section->addInput(new Form_Checkbox(
+			'enable',
+			'Enable',
+			gettext("DHCP Relay is currently enabled. DHCP Server canot be enabled while the DHCP Relay is enabled on any interface."),
+			$pconfig['enable']
+		))->setAttribute('disabled', true);
+	} else {
+		$section->addInput(new Form_Checkbox(
+			'enable',
+			'Enable',
+			sprintf(gettext("Enable DHCP server on %s interface"), htmlspecialchars($iflist[$if])),
+			$pconfig['enable']
+		));
+	}
 } else {
 	print_info_box(gettext('Editing pool-specific options. To return to the Interface, click its tab above.'), 'info', false);
 }