Only in ospfd1.5/linux: core
diff -abur --exclude-from=exclude_files ospfd1.5/src/ifcfsm.C ospfd1.6/src/ifcfsm.C
--- ospfd1.5/src/ifcfsm.C	Wed May 24 11:00:30 2000
+++ ospfd1.6/src/ifcfsm.C	Tue May 30 17:00:51 2000
@@ -111,6 +111,10 @@
     int llevel;
     int	if_ostate;	// Previous interface state
 
+    // Don't process state transitions on loopback interfaces
+    if (type() == IFT_LOOPBK)
+        return;
+
     if_ostate = if_state;
     action = ospf->run_fsm(&IfcFsm[0], if_state, event);
 
diff -abur --exclude-from=exclude_files ospfd1.5/src/spfifc.C ospfd1.6/src/spfifc.C
--- ospfd1.5/src/spfifc.C	Wed May 24 11:00:30 2000
+++ ospfd1.6/src/spfifc.C	Tue May 30 17:00:51 2000
@@ -256,6 +256,15 @@
 	ospf->phy_detach(if_phyint, if_addr);
 }
 
+/* Return the physical interface type.
+ */
+
+int SpfIfc::type()
+
+{
+    return(if_type);
+}
+
 /* Return a printable string for each interface type
  */
 
@@ -322,10 +331,6 @@
 /* Trivial virtual functions for point-to-point interfaces.
  */
 
-int PPIfc::type()
-{
-    return(IFT_PP);
-}
 bool PPIfc::is_multi_access()
 {
     return(false);
@@ -334,10 +339,6 @@
 /* Trivial virtual functions for virtual links.
  */
 
-int VLIfc::type()
-{
-    return(IFT_VL);
-}
 SpfArea *VLIfc::transit_area()
 {
     return(if_tap);
@@ -364,18 +365,9 @@
 /* Trivial virtual functions for Broadcast interfaces.
  */
 
-int BroadcastIfc::type()
-{
-    return(IFT_BROADCAST);
-}
-
 /* Trivial virtual functions for NBMA interfaces.
  */
 
-int NBMAIfc::type()
-{
-    return(IFT_NBMA);
-}
 void NBMAIfc::if_send(Pkt *pdesc, InAddr addr)
 {
     nonbroadcast_send(pdesc, addr);
@@ -397,10 +389,6 @@
 /* Trivial virtual functions for Point-to-MultiPoint interfaces.
  */
 
-int P2mPIfc::type()
-{
-    return(IFT_P2MP);
-}
 void P2mPIfc::if_send(Pkt *pdesc, InAddr addr)
 {
     nonbroadcast_send(pdesc, addr);
@@ -424,32 +412,29 @@
 LoopIfc::LoopIfc(SpfArea *a, InAddr net, InMask mask) : SpfIfc(net, -1)
 
 {
+    if_type = IFT_LOOPBK;
     if_area = a;
     if_mask = mask;
     if_net = if_addr & if_mask;
     if_state = IFS_LOOP;
 }
 
-void LoopIfc::ifa_start()
-{
-}
+LoopIfc::~LoopIfc()
 
-RtrLink *LoopIfc::rl_insert(RTRhdr *, RtrLink *)
 {
-    return(0);
+    if_state = IFS_DOWN;
 }
 
-void LoopIfc::add_adj_to_cand(class PriQ &)
+void LoopIfc::ifa_start()
 {
 }
 
-int LoopIfc::type()
+RtrLink *LoopIfc::rl_insert(RTRhdr *, RtrLink *)
 {
-  return(IFT_LOOPBK);
+    return(0);
 }
 
-void LoopIfc::run_fsm(int)
-
+void LoopIfc::add_adj_to_cand(class PriQ &)
 {
 }
 
diff -abur --exclude-from=exclude_files ospfd1.5/src/spfifc.h ospfd1.6/src/spfifc.h
--- ospfd1.5/src/spfifc.h	Wed May 24 11:00:30 2000
+++ ospfd1.6/src/spfifc.h	Tue May 30 17:00:51 2000
@@ -111,6 +111,7 @@
     // Configurable parameters
     InMask if_mask;	// Interface address mask
     uns16 mtu;		// Max IP datagram in bytes
+    int if_type;	// Physical interface type
     int	if_IfIndex;	// MIB-II IfIndex
     uns16 if_cost;	// Cost
     byte if_rxmt;	// Retransmission interval
@@ -200,9 +201,10 @@
     void dump_stats(struct IfcRsp *irsp);
     bool mospf_enabled();
     void reorig_all_grplsas();
+    int type();
+    void run_fsm(int event);// Interface Finite state machine
 
     // Virtual functions
-    virtual void run_fsm(int event);// Interface Finite state machine
     virtual void clear_config();
     virtual void if_send(Pkt *, InAddr);
     virtual void nbr_send(Pkt *, SpfNbr *); // send OSPF packet to neighbor
@@ -212,7 +214,6 @@
     virtual int rl_size();
     virtual void add_adj_to_cand(class PriQ &cand) = 0;
     virtual int adjacency_wanted(class SpfNbr *np);
-    virtual int type() = 0;
     virtual void send_hello_response(SpfNbr *np);
     virtual bool is_virtual();
     virtual bool is_multi_access();
@@ -308,7 +309,6 @@
 class PPIfc : public SpfIfc {
   public:
     inline PPIfc(InAddr addr, int phyint);
-    int type();
     bool is_multi_access();
     virtual void ifa_start();
     virtual class SpfNbr *find_nbr(InAddr, rtid_t);
@@ -322,6 +322,7 @@
 
 inline PPIfc::PPIfc(InAddr addr, int phyint) : SpfIfc(addr, phyint)
 {
+    if_type = IFT_PP;
 }
 
 /* A virtual link. These send a single copy of each multicast packet
@@ -337,7 +338,6 @@
   public:
     VLIfc(SpfArea *, class RTRrte *);
     ~VLIfc();
-    virtual int type();
     virtual SpfArea *transit_area();
     virtual rtid_t *vl_endpt();
     virtual bool is_virtual();
@@ -375,12 +375,12 @@
 class BroadcastIfc : public DRIfc {
   public:
     inline BroadcastIfc(InAddr addr, int phyint);
-    virtual int type();
 };
 
 inline BroadcastIfc::BroadcastIfc(InAddr addr, int phyint)
 : DRIfc(addr, phyint)
 {
+    if_type = IFT_BROADCAST;
 }
 
 /* The NBMA interface, such full mesh-connected Frame relay subnets.
@@ -391,7 +391,6 @@
 class NBMAIfc : public DRIfc {
   public:
     inline NBMAIfc(InAddr addr, int phyint);
-    virtual int type();
     virtual void if_send(Pkt *pdesc, InAddr addr);
     virtual void start_hellos();
     virtual void restart_hellos();
@@ -402,6 +401,7 @@
 
 inline NBMAIfc::NBMAIfc(InAddr addr, int phyint) : DRIfc(addr, phyint)
 {
+    if_type = IFT_NBMA;
 }
 
 /* The point-to-Multipoint interface, such as non-full-mesh connected
@@ -413,7 +413,6 @@
 class P2mPIfc : public SpfIfc {
   public:
     inline P2mPIfc(InAddr addr, int phyint);
-    virtual int type();
     virtual void if_send(Pkt *pdesc, InAddr addr);
     virtual void start_hellos();
     virtual void restart_hellos();
@@ -427,6 +426,7 @@
 
 inline P2mPIfc::P2mPIfc(InAddr addr, int phyint) : SpfIfc(addr, phyint)
 {
+    if_type = IFT_P2MP;
 }
 
 /* The loopback interface. One allocated for each loopback
@@ -439,9 +439,8 @@
 class LoopIfc : public SpfIfc {
   public:
     LoopIfc(SpfArea *, InAddr net, InMask mask);
+    ~LoopIfc();
     virtual void ifa_start();
     virtual RtrLink *rl_insert(RTRhdr *, RtrLink *);
     virtual void add_adj_to_cand(class PriQ &cand);
-    virtual int type();
-    virtual void run_fsm(int event);// Interface Finite state machine
 };
diff -abur --exclude-from=exclude_files ospfd1.5/src/spfvl.C ospfd1.6/src/spfvl.C
--- ospfd1.5/src/spfvl.C	Wed May 24 11:00:30 2000
+++ ospfd1.6/src/spfvl.C	Tue May 30 17:00:51 2000
@@ -91,6 +91,7 @@
 {
     SpfArea *bb;
 
+    if_type = IFT_VL;
     if_tap = tap;	// Transit area
     if_nbrid = endpt->rtrid();// Configured neighbor ID
     if_rmtaddr = 0;	// IP address of other end (learned dynamically)

.