diff -ur orig/ppp-2.3.10/pppd/auth.c ppp-2.3.10/pppd/auth.c
--- orig/ppp-2.3.10/pppd/auth.c	1999/11/15 21:02:00
+++ ppp-2.3.10/pppd/auth.c	1999/12/08 15:31:10
@@ -96,6 +96,9 @@
 /* List of addresses which the peer may use. */
 static struct permitted_ip *addresses[NUM_PPP];
 
+/* List of locked addreses. */
+static u_int32_t locked_addresses[NUM_PPP];
+
 /* Wordlist giving addresses which the peer may use
    without authenticating itself. */
 static struct wordlist *noauth_addrs;
@@ -151,6 +154,7 @@
 bool allow_any_ip = 0;		/* Allow peer to use any IP address */
 bool explicit_remote = 0;	/* User specified explicit remote name */
 char remote_name[MAXNAMELEN];	/* Peer's name for authentication */
+char pool_dir[MAXDIRNAMELEN];
 
 /* Bits in auth_pending[] */
 #define PAP_WITHPEER	1
@@ -172,6 +176,7 @@
 static int  have_pap_secret __P((int *));
 static int  have_chap_secret __P((char *, char *, int, int *));
 static int  ip_addr_check __P((u_int32_t, struct permitted_ip *));
+static int  lock_ip_addr __P((int, u_int32_t));
 static int  scan_authfile __P((FILE *, char *, char *, char *,
 			       struct wordlist **, struct wordlist **,
 			       char *));
@@ -233,6 +238,9 @@
     { "allow-ip", o_special, set_noauth_addr,
       "Set IP address(es) which can be used without authentication",
       OPT_PRIV },
+    { "pool-dir", o_string, pool_dir,
+      "Set the address pool directory",
+      OPT_PRIV|OPT_STATIC, NULL, MAXDIRNAMELEN },
     { NULL }
 };
 
@@ -1514,7 +1522,8 @@
 	ip[n].base = a & ip[n].mask;
 	++n;
 	if (~mask == 0 && suggested_ip == 0)
-	    suggested_ip = a;
+	    if ( lock_ip_addr(unit,a) )
+		suggested_ip = a;
     }
 
     ip[n].permit = 0;		/* make the last entry forbid all addresses */
@@ -1551,11 +1560,13 @@
     if (addresses[unit] != NULL) {
 	ok = ip_addr_check(addr, addresses[unit]);
-	if (ok >= 0)
-	    return ok;
+	if (ok > 0)
+	    return lock_ip_addr(unit, addr);
     }
     if (auth_required)
 	return 0;		/* no addresses authorized */
-    return allow_any_ip || !have_route_to(addr);
+    if ( !allow_any_ip && have_route_to(addr) )
+	return 0;
+    return lock_ip_addr(unit, addr);
 }
 
 static int
@@ -1597,6 +1608,73 @@
 	    return 1;		/* some IP address is allowed */
     }
     return 0;
+}
+
+/*
+ * lock_ip_addr - if pool_dir is present try to lock the given address
+ * (and release old lock, if present)
+ */
+static int
+lock_ip_addr(unit, addr)
+    int unit;
+    u_int32_t addr;
+{
+    int pool_dir_len = strlen(pool_dir);
+
+    if ( !pool_dir_len )
+	return 1;
+
+    if ( locked_addresses[unit]!=addr ) {
+	int lockfd;
+	FILE* lockf;
+	char fname[MAXDIRNAMELEN];
+	struct in_addr in;
+
+	memcpy(fname,pool_dir,pool_dir_len);
+
+	if ( locked_addresses[unit] ) {
+	    in.s_addr = locked_addresses[unit];
+	    strcpy(fname+pool_dir_len, inet_ntoa(in));
+	    unlink(fname);
+	    locked_addresses[unit] = 0;
+	}
+
+	in.s_addr = addr;
+	strcpy(fname+pool_dir_len, inet_ntoa(in));
+	lockfd = open(fname,O_WRONLY|O_CREAT|O_EXCL,S_IRUSR|S_IWUSR);
+	if ( lockfd == -1 )
+	    return 0;
+	lockf = fdopen(lockfd,"w");
+	fprintf(lockf,"%d\n",getpid());
+	fclose(lockf);
+	locked_addresses[unit] = addr;
+    }
+    return 1;
+}
+
+/*
+ * unlock_ip_addrs - remove all locks created by lock_ip_addr
+ */
+void
+unlock_ip_addrs()
+{
+    int unit;
+    char fname[MAXDIRNAMELEN];
+    int pool_dir_len = strlen(pool_dir);
+
+    if ( !pool_dir_len )
+	return;
+
+    memcpy(fname,pool_dir,pool_dir_len);
+
+    for (unit=0;unit<NUM_PPP;unit++)
+	if ( locked_addresses[unit] ) {
+	    struct in_addr in;
+	    in.s_addr = locked_addresses[unit];
+	    strcpy(fname+pool_dir_len, inet_ntoa(in));
+	    unlink(fname);
+	    locked_addresses[unit] = 0;
+	}
 }
 
 /*
diff -ur orig/ppp-2.3.10/pppd/main.c ppp-2.3.10/pppd/main.c
--- orig/ppp-2.3.10/pppd/main.c	1999/11/15 22:22:21
+++ ppp-2.3.10/pppd/main.c	1999/11/15 22:26:57
@@ -1172,6 +1172,8 @@
 	warn("unable to delete pid file %s: %m", linkpidfile);
     linkpidfile[0] = 0;
 
+    unlock_ip_addrs();
+
     if (locked)
 	unlock();
 }
diff -ur orig/ppp-2.3.10/pppd/pppd.h ppp-2.3.10/pppd/pppd.h
--- orig/ppp-2.3.10/pppd/pppd.h	1999/11/15 21:20:43
+++ ppp-2.3.10/pppd/pppd.h	1999/11/15 22:26:52
@@ -57,6 +57,8 @@
 #define MAXNAMELEN	256	/* max length of hostname or name for auth */
 #define MAXSECRETLEN	256	/* max length of password or secret */
 
+#define MAXDIRNAMELEN	256
+
 /*
  * Option descriptor structure.
  */
@@ -346,6 +348,7 @@
 				/* check if IP address is authorized */
 int  bad_ip_adrs __P((u_int32_t));
 				/* check if IP address is unreasonable */
+void unlock_ip_addrs();
 
 /* Procedures exported from demand.c */
 void demand_conf __P((void));	/* config interface(s) for demand-dial */