path: root/package/network/services/dnsmasq/patches/0046-Add-shared-network-DHCP-configuration.patch

From ae5b7e04a1025167f1b80840e61432a3cea9625c Mon Sep 17 00:00:00 2001
From: Simon Kelley <simon@thekelleys.org.uk>
Date: Wed, 27 Mar 2019 22:33:28 +0000
Subject: [PATCH 46/57] Add --shared-network DHCP configuration.

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
---
 CHANGELOG     |   5 ++
 man/dnsmasq.8 |  21 ++++++
 src/dhcp.c    |  76 ++++++++++++++++++----
 src/dhcp6.c   | 175 ++++++++++++++++++++++++++++----------------------
 src/dnsmasq.h |  11 ++++
 src/option.c  |  41 ++++++++++++
 src/rfc2131.c |  97 +++++++++++++++++-----------
 src/rfc3315.c |  40 +++++++++---
 8 files changed, 332 insertions(+), 134 deletions(-)

--- a/CHANGELOG
+++ b/CHANGELOG
@@ -34,6 +34,11 @@ version 2.81
 	tries not to request capabilities not required by its
 	configuration.
 
+	Add --shared-network config. This enables allocation of addresses
+	the DHCP server in subnets where the server (or relay) doesn't
+	have an interface on the network in that subnet. Many thanks to
+	plank.de for sponsoring this feature.
+
 	
 version 2.80
 	Add support for RFC 4039 DHCP rapid commit. Thanks to Ashram Method
--- a/man/dnsmasq.8
+++ b/man/dnsmasq.8
@@ -1741,6 +1741,27 @@ It is permissible to add more than one a
 \fB--bridge-interface=int1,alias1,alias2\fP is exactly equivalent to
 \fB--bridge-interface=int1,alias1 --bridge-interface=int1,alias2\fP
 .TP
+.B --shared-network=<interface>|<addr>,<addr>
+The DHCP server determines which dhcp ranges are useable for allocating and
+address to a DHCP client based on the network from which the DHCP request arrives,
+and the IP configuration of the server's interface on that network. The shared-network
+option extends the available subnets (and therefore dhcp ranges) beyond the
+subnets configured on the arrival interface. The first argument is either the
+name of an interface or an address which is configured on a local interface, and the
+second argument is an address which defines another subnet on which addresses can be allocated.
+To be useful, there must be suitable dhcp-range which allows address allocation on this subnet
+and this dhcp-range MUST include the netmask. Use shared-network also needs extra
+consideration of routing. Dnsmasq doesn't have the usual information which it uses to
+determine the default route, so the default route option (or other routing) MUST be
+manually configured. The client must have a route to the server: if the two-address form
+of shared-network is used, this will be to the first specified address. If the interface,address
+form is used, there must be a route to all of the addresses configured on the interface.
+
+The two-address form of shared-network is also usable with a DHCP relay: the first address
+is the address of the relay and the second, as before, specifies an extra subnet which
+may be allocated.
+
+.TP
 .B \-s, --domain=<domain>[,<address range>[,local]]
 Specifies DNS domains for the DHCP server. Domains may be be given 
 unconditionally (without the IP range) or for limited IP ranges. This has two effects;
--- a/src/dhcp.c
+++ b/src/dhcp.c
@@ -507,33 +507,83 @@ static int check_listen_addrs(struct in_
 
    Note that the current chain may be superseded later for configured hosts or those coming via gateways. */
 
-static int complete_context(struct in_addr local, int if_index, char *label,
-			    struct in_addr netmask, struct in_addr broadcast, void *vparam)
+static void guess_range_netmask(struct in_addr addr, struct in_addr netmask)
 {
   struct dhcp_context *context;
-  struct dhcp_relay *relay;
-  struct iface_param *param = vparam;
 
-  (void)label;
-  
   for (context = daemon->dhcp; context; context = context->next)
-    {
-      if (!(context->flags & CONTEXT_NETMASK) &&
-	  (is_same_net(local, context->start, netmask) ||
-	   is_same_net(local, context->end, netmask)))
+    if (!(context->flags & CONTEXT_NETMASK) &&
+	(is_same_net(addr, context->start, netmask) ||
+	 is_same_net(addr, context->end, netmask)))
       { 
 	if (context->netmask.s_addr != netmask.s_addr &&
-	    !(is_same_net(local, context->start, netmask) &&
-	      is_same_net(local, context->end, netmask)))
+	    !(is_same_net(addr, context->start, netmask) &&
+	      is_same_net(addr, context->end, netmask)))
 	  {
 	    strcpy(daemon->dhcp_buff, inet_ntoa(context->start));
 	    strcpy(daemon->dhcp_buff2, inet_ntoa(context->end));
 	    my_syslog(MS_DHCP | LOG_WARNING, _("DHCP range %s -- %s is not consistent with netmask %s"),
 		      daemon->dhcp_buff, daemon->dhcp_buff2, inet_ntoa(netmask));
 	  }	
- 	context->netmask = netmask;
+	context->netmask = netmask;
       }
+}
+
+static int complete_context(struct in_addr local, int if_index, char *label,
+			    struct in_addr netmask, struct in_addr broadcast, void *vparam)
+{
+  struct dhcp_context *context;
+  struct dhcp_relay *relay;
+  struct iface_param *param = vparam;
+  struct shared_network *share;
+  
+  (void)label;
+
+  for (share = daemon->shared_networks; share; share = share->next)
+    {
       
+#ifdef HAVE_DHCP6
+      if (share->shared_addr.s_addr == 0)
+	continue;
+#endif
+      
+      if (share->if_index != 0)
+	{
+	  if (share->if_index != if_index)
+	    continue;
+	}
+      else
+	{
+	  if (share->match_addr.s_addr != local.s_addr)
+	    continue;
+	}
+
+      for (context = daemon->dhcp; context; context = context->next)
+	{
+	  if (context->netmask.s_addr != 0 &&
+	      is_same_net(share->shared_addr, context->start, context->netmask) &&
+	      is_same_net(share->shared_addr, context->end, context->netmask))
+	    {
+	      /* link it onto the current chain if we've not seen it before */
+	      if (context->current == context)
+		{
+		  /* For a shared network, we have no way to guess what the default route should be. */
+		  context->router.s_addr = 0;
+		  context->local = local; /* Use configured address for Server Identifier */
+		  context->current = param->current;
+		  param->current = context;
+		}
+	      
+	      if (!(context->flags & CONTEXT_BRDCAST))
+		context->broadcast.s_addr  = context->start.s_addr | ~context->netmask.s_addr;
+	    }		
+	}
+    }
+
+  guess_range_netmask(local, netmask);
+  
+  for (context = daemon->dhcp; context; context = context->next)
+    {
       if (context->netmask.s_addr != 0 &&
 	  is_same_net(local, context->start, context->netmask) &&
 	  is_same_net(local, context->end, context->netmask))
--- a/src/dhcp6.c
+++ b/src/dhcp6.c
@@ -299,89 +299,114 @@ static int complete_context6(struct in6_
 			     unsigned int valid, void *vparam)
 {
   struct dhcp_context *context;
+  struct shared_network *share;
   struct dhcp_relay *relay;
   struct iface_param *param = vparam;
   struct iname *tmp;
  
   (void)scope; /* warning */
   
-  if (if_index == param->ind)
-    {
-      if (IN6_IS_ADDR_LINKLOCAL(local))
-	param->ll_addr = *local;
-      else if (IN6_IS_ADDR_ULA(local))
-	param->ula_addr = *local;
-
-      if (!IN6_IS_ADDR_LOOPBACK(local) &&
-	  !IN6_IS_ADDR_LINKLOCAL(local) &&
-	  !IN6_IS_ADDR_MULTICAST(local))
-	{
-	  /* if we have --listen-address config, see if the 
-	     arrival interface has a matching address. */
-	  for (tmp = daemon->if_addrs; tmp; tmp = tmp->next)
-	    if (tmp->addr.sa.sa_family == AF_INET6 &&
-		IN6_ARE_ADDR_EQUAL(&tmp->addr.in6.sin6_addr, local))
-	      param->addr_match = 1;
-	  
-	  /* Determine a globally address on the arrival interface, even
-	     if we have no matching dhcp-context, because we're only
-	     allocating on remote subnets via relays. This
-	     is used as a default for the DNS server option. */
-	  param->fallback = *local;
-	  
-	  for (context = daemon->dhcp6; context; context = context->next)
-	    {
-	      if ((context->flags & CONTEXT_DHCP) &&
-		  !(context->flags & (CONTEXT_TEMPLATE | CONTEXT_OLD)) &&
-		  prefix <= context->prefix &&
-		  is_same_net6(local, &context->start6, context->prefix) &&
-		  is_same_net6(local, &context->end6, context->prefix))
-		{
-		  
-		  
-		  /* link it onto the current chain if we've not seen it before */
-		  if (context->current == context)
-		    {
-		      struct dhcp_context *tmp, **up;
-		      
-		      /* use interface values only for constructed contexts */
-		      if (!(context->flags & CONTEXT_CONSTRUCTED))
-			preferred = valid = 0xffffffff;
-		      else if (flags & IFACE_DEPRECATED)
-			preferred = 0;
-		      
-		      if (context->flags & CONTEXT_DEPRECATE)
-			preferred = 0;
-		      
-		      /* order chain, longest preferred time first */
-		      for (up = &param->current, tmp = param->current; tmp; tmp = tmp->current)
-			if (tmp->preferred <= preferred)
-			  break;
-			else
-			  up = &tmp->current;
-		      
-		      context->current = *up;
-		      *up = context;
-		      context->local6 = *local;
-		      context->preferred = preferred;
-		      context->valid = valid;
-		    }
-		}
-	    }
-	}
-
-      for (relay = daemon->relay6; relay; relay = relay->next)
-	if (IN6_ARE_ADDR_EQUAL(local, &relay->local.addr6) && relay->current == relay &&
-	    (IN6_IS_ADDR_UNSPECIFIED(&param->relay_local) || IN6_ARE_ADDR_EQUAL(local, &param->relay_local)))
+  if (if_index != param->ind)
+    return 1;
+  
+  if (IN6_IS_ADDR_LINKLOCAL(local))
+    param->ll_addr = *local;
+  else if (IN6_IS_ADDR_ULA(local))
+    param->ula_addr = *local;
+      
+  if (IN6_IS_ADDR_LOOPBACK(local) ||
+      IN6_IS_ADDR_LINKLOCAL(local) ||
+      IN6_IS_ADDR_MULTICAST(local))
+    return 1;
+  
+  /* if we have --listen-address config, see if the 
+     arrival interface has a matching address. */
+  for (tmp = daemon->if_addrs; tmp; tmp = tmp->next)
+    if (tmp->addr.sa.sa_family == AF_INET6 &&
+	IN6_ARE_ADDR_EQUAL(&tmp->addr.in6.sin6_addr, local))
+      param->addr_match = 1;
+  
+  /* Determine a globally address on the arrival interface, even
+     if we have no matching dhcp-context, because we're only
+     allocating on remote subnets via relays. This
+     is used as a default for the DNS server option. */
+  param->fallback = *local;
+  
+  for (context = daemon->dhcp6; context; context = context->next)
+    if ((context->flags & CONTEXT_DHCP) &&
+	!(context->flags & (CONTEXT_TEMPLATE | CONTEXT_OLD)) &&
+	prefix <= context->prefix &&
+	context->current == context)
+      {
+	if (is_same_net6(local, &context->start6, context->prefix) &&
+	    is_same_net6(local, &context->end6, context->prefix))
 	  {
-	    relay->current = param->relay;
-	    param->relay = relay;
-	    param->relay_local = *local;
+	    struct dhcp_context *tmp, **up;
+	    
+	    /* use interface values only for constructed contexts */
+	    if (!(context->flags & CONTEXT_CONSTRUCTED))
+	      preferred = valid = 0xffffffff;
+	    else if (flags & IFACE_DEPRECATED)
+	      preferred = 0;
+		    
+	    if (context->flags & CONTEXT_DEPRECATE)
+	      preferred = 0;
+	    
+	    /* order chain, longest preferred time first */
+	    for (up = &param->current, tmp = param->current; tmp; tmp = tmp->current)
+	      if (tmp->preferred <= preferred)
+		break;
+	      else
+		up = &tmp->current;
+	    
+	    context->current = *up;
+	    *up = context;
+	    context->local6 = *local;
+	    context->preferred = preferred;
+	    context->valid = valid;
 	  }
-      
-    }          
- 
- return 1;
+	else
+	  {
+	    for (share = daemon->shared_networks; share; share = share->next)
+	      {
+		/* IPv4 shared_address - ignore */
+		if (share->shared_addr.s_addr != 0)
+		  continue;
+			
+		if (share->if_index != 0)
+		  {
+		    if (share->if_index != if_index)
+		      continue;
+		  }
+		else
+		  {
+		    if (!IN6_ARE_ADDR_EQUAL(&share->match_addr6, local))
+		      continue;
+		  }
+		
+		if (is_same_net6(&share->shared_addr6, &context->start6, context->prefix) &&
+		    is_same_net6(&share->shared_addr6, &context->end6, context->prefix))
+		  {
+		    context->current = param->current;
+		    param->current = context;
+		    context->local6 = *local;
+		    context->preferred = context->flags & CONTEXT_DEPRECATE ? 0 :0xffffffff;
+		    context->valid = 0xffffffff;
+		  }
+	      }
+	  }      
+      }
+
+  for (relay = daemon->relay6; relay; relay = relay->next)
+    if (IN6_ARE_ADDR_EQUAL(local, &relay->local.addr6) && relay->current == relay &&
+	(IN6_IS_ADDR_UNSPECIFIED(&param->relay_local) || IN6_ARE_ADDR_EQUAL(local, &param->relay_local)))
+      {
+	relay->current = param->relay;
+	param->relay = relay;
+	param->relay_local = *local;
+      }
+     
+  return 1;
 }
 
 struct dhcp_config *config_find_by_address6(struct dhcp_config *configs, struct in6_addr *net, int prefix, u64 addr)
--- a/src/dnsmasq.h
+++ b/src/dnsmasq.h
@@ -910,6 +910,16 @@ struct dhcp_context {
   struct dhcp_context *next, *current;
 };
 
+struct shared_network {
+  int if_index;
+  struct in_addr match_addr, shared_addr;
+#ifdef HAVE_DHCP6
+  /* shared_addr == 0 for IP6 entries. */
+  struct in6_addr match_addr6, shared_addr6;
+#endif
+  struct shared_network *next;
+};
+
 #define CONTEXT_STATIC         (1u<<0)
 #define CONTEXT_NETMASK        (1u<<1)
 #define CONTEXT_BRDCAST        (1u<<2)
@@ -1107,6 +1117,7 @@ extern struct daemon {
   struct ping_result *ping_results;
   FILE *lease_stream;
   struct dhcp_bridge *bridges;
+  struct shared_network *shared_networks;
 #ifdef HAVE_DHCP6
   int duid_len;
   unsigned char *duid;
--- a/src/option.c
+++ b/src/option.c
@@ -166,6 +166,7 @@ struct myoption {
 #define LOPT_UBUS          354
 #define LOPT_NAME_MATCH    355
 #define LOPT_CAA           356
+#define LOPT_SHARED_NET    357
  
 #ifdef HAVE_GETOPT_LONG
 static const struct option opts[] =  
@@ -259,6 +260,7 @@ static const struct myoption opts[] =
     { "ptr-record", 1, 0, LOPT_PTR },
     { "naptr-record", 1, 0, LOPT_NAPTR },
     { "bridge-interface", 1, 0 , LOPT_BRIDGE },
+    { "shared-network", 1, 0, LOPT_SHARED_NET },
     { "dhcp-option-force", 1, 0, LOPT_FORCE },
     { "tftp-no-blocksize", 0, 0, LOPT_NOBLOCK },
     { "log-dhcp", 0, 0, LOPT_LOG_OPTS },
@@ -431,6 +433,7 @@ static struct {
   { '3', ARG_DUP, "[=tag:<tag>]...", gettext_noop("Enable dynamic address allocation for bootp."), NULL },
   { '4', ARG_DUP, "set:<tag>,<mac address>", gettext_noop("Map MAC address (with wildcards) to option set."), NULL },
   { LOPT_BRIDGE, ARG_DUP, "<iface>,<alias>..", gettext_noop("Treat DHCP requests on aliases as arriving from interface."), NULL },
+  { LOPT_SHARED_NET, ARG_DUP, "<iface>|<addr>,<addr>", gettext_noop("Specify extra networks sharing a broadcast domain for DHCP"), NULL},
   { '5', OPT_NO_PING, NULL, gettext_noop("Disable ICMP echo address checking in the DHCP server."), NULL },
   { '6', ARG_ONE, "<path>", gettext_noop("Shell script to run on DHCP lease creation and destruction."), NULL },
   { LOPT_LUASCRIPT, ARG_DUP, "path", gettext_noop("Lua script to run on DHCP lease creation and destruction."), NULL },
@@ -2873,6 +2876,44 @@ static int one_opt(int option, char *arg
       }
 
 #ifdef HAVE_DHCP
+    case LOPT_SHARED_NET: /* --shared-network */
+      {
+	struct shared_network *new = opt_malloc(sizeof(struct shared_network));
+
+#ifdef HAVE_DHCP6
+	new->shared_addr.s_addr = 0;
+#endif
+	new->if_index = 0;
+	
+	if (!(comma = split(arg)))
+	  {
+	  snerr:
+	    free(new);
+	    ret_err(_("bad shared-network"));
+	  }
+	
+	if (inet_pton(AF_INET, comma, &new->shared_addr))
+	  {
+	    if (!inet_pton(AF_INET, arg, &new->match_addr) &&
+		!(new->if_index = if_nametoindex(arg)))
+	      goto snerr;
+	  }
+#ifdef HAVE_DHCP6
+	else if (inet_pton(AF_INET6, comma, &new->shared_addr6))
+	  {
+	    if (!inet_pton(AF_INET6, arg, &new->match_addr6) &&
+		!(new->if_index = if_nametoindex(arg)))
+	      goto snerr;
+	  }
+#endif
+	else
+	  goto snerr;
+
+	new->next = daemon->shared_networks;
+	daemon->shared_networks = new;
+	break;
+      }
+	  
     case 'F':  /* --dhcp-range */
       {
 	int k, leasepos = 2;
--- a/src/rfc2131.c
+++ b/src/rfc2131.c
@@ -274,8 +274,9 @@ size_t dhcp_reply(struct dhcp_context *c
   if (mess->giaddr.s_addr || subnet_addr.s_addr || mess->ciaddr.s_addr)
     {
       struct dhcp_context *context_tmp, *context_new = NULL;
+      struct shared_network *share = NULL;
       struct in_addr addr;
-      int force = 0;
+      int force = 0, via_relay = 0;
       
       if (subnet_addr.s_addr)
 	{
@@ -286,6 +287,7 @@ size_t dhcp_reply(struct dhcp_context *c
 	{
 	  addr = mess->giaddr;
 	  force = 1;
+	  via_relay = 1;
 	}
       else
 	{
@@ -302,42 +304,65 @@ size_t dhcp_reply(struct dhcp_context *c
 	} 
 		
       if (!context_new)
-	for (context_tmp = daemon->dhcp; context_tmp; context_tmp = context_tmp->next)
-	  {
-	    struct in_addr netmask = context_tmp->netmask;
+	{
+	  for (context_tmp = daemon->dhcp; context_tmp; context_tmp = context_tmp->next)
+	    {
+	      struct in_addr netmask = context_tmp->netmask;
+	      
+	      /* guess the netmask for relayed networks */
+	      if (!(context_tmp->flags & CONTEXT_NETMASK) && context_tmp->netmask.s_addr == 0)
+		{
+		  if (IN_CLASSA(ntohl(context_tmp->start.s_addr)) && IN_CLASSA(ntohl(context_tmp->end.s_addr)))
+		    netmask.s_addr = htonl(0xff000000);
+		  else if (IN_CLASSB(ntohl(context_tmp->start.s_addr)) && IN_CLASSB(ntohl(context_tmp->end.s_addr)))
+		    netmask.s_addr = htonl(0xffff0000);
+		  else if (IN_CLASSC(ntohl(context_tmp->start.s_addr)) && IN_CLASSC(ntohl(context_tmp->end.s_addr)))
+		    netmask.s_addr = htonl(0xffffff00); 
+		}
 
-	    /* guess the netmask for relayed networks */
-	    if (!(context_tmp->flags & CONTEXT_NETMASK) && context_tmp->netmask.s_addr == 0)
-	      {
-		if (IN_CLASSA(ntohl(context_tmp->start.s_addr)) && IN_CLASSA(ntohl(context_tmp->end.s_addr)))
-		  netmask.s_addr = htonl(0xff000000);
-		else if (IN_CLASSB(ntohl(context_tmp->start.s_addr)) && IN_CLASSB(ntohl(context_tmp->end.s_addr)))
-		  netmask.s_addr = htonl(0xffff0000);
-		else if (IN_CLASSC(ntohl(context_tmp->start.s_addr)) && IN_CLASSC(ntohl(context_tmp->end.s_addr)))
-		  netmask.s_addr = htonl(0xffffff00); 
-	      }
-	    
-	    /* This section fills in context mainly when a client which is on a remote (relayed)
-	       network renews a lease without using the relay, after dnsmasq has restarted. */
-	    if (netmask.s_addr != 0  && 
-		is_same_net(addr, context_tmp->start, netmask) &&
-		is_same_net(addr, context_tmp->end, netmask))
-	      {
-		context_tmp->netmask = netmask;
-		if (context_tmp->local.s_addr == 0)
-		  context_tmp->local = fallback;
-		if (context_tmp->router.s_addr == 0)
-		  context_tmp->router = mess->giaddr;
-	   
-		/* fill in missing broadcast addresses for relayed ranges */
-		if (!(context_tmp->flags & CONTEXT_BRDCAST) && context_tmp->broadcast.s_addr == 0 )
-		  context_tmp->broadcast.s_addr = context_tmp->start.s_addr | ~context_tmp->netmask.s_addr;
-		
-		context_tmp->current = context_new;
-		context_new = context_tmp;
-	      }
-	  }
-      
+	      /* check to see is a context is OK because of a shared address on
+		 the relayed subnet. */
+	      if (via_relay)
+		for (share = daemon->shared_networks; share; share = share->next)
+		  {
+#ifdef HAVE_DHCP6
+		    if (share->shared_addr.s_addr == 0)
+		      continue;
+#endif
+		    if (share->if_index != 0 ||
+			share->match_addr.s_addr != mess->giaddr.s_addr)
+		      continue;
+		    
+		    if (netmask.s_addr != 0  && 
+			is_same_net(share->shared_addr, context_tmp->start, netmask) &&
+			is_same_net(share->shared_addr, context_tmp->end, netmask))
+		      break;
+		  }
+	      
+	      /* This section fills in context mainly when a client which is on a remote (relayed)
+		 network renews a lease without using the relay, after dnsmasq has restarted. */
+	      if (share ||
+		  (netmask.s_addr != 0  && 
+		   is_same_net(addr, context_tmp->start, netmask) &&
+		   is_same_net(addr, context_tmp->end, netmask)))
+		{
+		  context_tmp->netmask = netmask;
+		  if (context_tmp->local.s_addr == 0)
+		    context_tmp->local = fallback;
+		  if (context_tmp->router.s_addr == 0 && !share)
+		    context_tmp->router = mess->giaddr;
+		  
+		  /* fill in missing broadcast addresses for relayed ranges */
+		  if (!(context_tmp->flags & CONTEXT_BRDCAST) && context_tmp->broadcast.s_addr == 0 )
+		    context_tmp->broadcast.s_addr = context_tmp->start.s_addr | ~context_tmp->netmask.s_addr;
+		  
+		  context_tmp->current = context_new;
+		  context_new = context_tmp;
+		}
+	      
+	    }
+	}
+	  
       if (context_new || force)
 	context = context_new; 
     }
--- a/src/rfc3315.c
+++ b/src/rfc3315.c
@@ -134,21 +134,41 @@ static int dhcp6_maybe_relay(struct stat
       else
 	{
 	  struct dhcp_context *c;
+	  struct shared_network *share = NULL;
 	  state->context = NULL;
-	   
+
 	  if (!IN6_IS_ADDR_LOOPBACK(state->link_address) &&
 	      !IN6_IS_ADDR_LINKLOCAL(state->link_address) &&
 	      !IN6_IS_ADDR_MULTICAST(state->link_address))
 	    for (c = daemon->dhcp6; c; c = c->next)
-	      if ((c->flags & CONTEXT_DHCP) &&
-		  !(c->flags & (CONTEXT_TEMPLATE | CONTEXT_OLD)) &&
-		  is_same_net6(state->link_address, &c->start6, c->prefix) &&
-		  is_same_net6(state->link_address, &c->end6, c->prefix))
-		{
-		  c->preferred = c->valid = 0xffffffff;
-		  c->current = state->context;
-		  state->context = c;
-		}
+	      {
+		for (share = daemon->shared_networks; share; share = share->next)
+		  {
+		    if (share->shared_addr.s_addr != 0)
+		      continue;
+		    
+		    if (share->if_index != 0 ||
+			!IN6_ARE_ADDR_EQUAL(state->link_address, &share->match_addr6))
+		      continue;
+		    
+		    if ((c->flags & CONTEXT_DHCP) &&
+			!(c->flags & (CONTEXT_TEMPLATE | CONTEXT_OLD)) &&
+			is_same_net6(&share->shared_addr6, &c->start6, c->prefix) &&
+			is_same_net6(&share->shared_addr6, &c->end6, c->prefix))
+		      break;
+		  }
+		
+		if (share ||
+		    ((c->flags & CONTEXT_DHCP) &&
+		     !(c->flags & (CONTEXT_TEMPLATE | CONTEXT_OLD)) &&
+		     is_same_net6(state->link_address, &c->start6, c->prefix) &&
+		     is_same_net6(state->link_address, &c->end6, c->prefix)))
+		  {
+		    c->preferred = c->valid = 0xffffffff;
+		    c->current = state->context;
+		    state->context = c;
+		  }
+	      }
 	  
 	  if (!state->context)
 	    {