--- a/pppd/chap.c
+++ b/pppd/chap.c
@@ -42,6 +42,9 @@
 #include "chap.h"
 #include "chap-md5.h"
 
+#include <semaphore.h>
+#include "syncppp.h"
+
 #ifdef PPP_WITH_CHAPMS
 #include "chap_ms.h"
 #define MDTYPE_ALL (MDTYPE_MICROSOFT_V2 | MDTYPE_MICROSOFT | MDTYPE_MD5)
@@ -520,6 +523,18 @@ chap_respond(struct chap_client_state *c
 	p[2] = len >> 8;
 	p[3] = len;
 
+	if (npppd > 1) {
+		if (syncppp(npppd) < 0) {
+			error("syncppp sync fail");
+			sem_unlink(SEM_COUNT_NAME);
+			sem_unlink(SEM_BLOCK_NAME);
+		} else {
+			info("syncppp sync succeeded");
+		}
+	} else {
+		info("syncppp not active");
+	}
+
 	output(0, response, PPP_HDRLEN + len);
 }
 
--- a/pppd/Makefile.am
+++ b/pppd/Makefile.am
@@ -67,6 +67,7 @@ noinst_HEADERS = \
     peap.h \
     pppd-private.h \
     spinlock.h \
+    syncppp.h \
     tls.h \
     tdb.h
 
@@ -85,6 +86,7 @@ pppd_SOURCES = \
     main.c \
     options.c \
     session.c \
+    syncppp.c \
     tty.c \
     upap.c \
     utils.c
@@ -95,7 +97,7 @@ BUILT_SOURCE = \
 
 pppd_CPPFLAGS = -DSYSCONFDIR=\"${sysconfdir}\" -DPPPD_RUNTIME_DIR='"@PPPD_RUNTIME_DIR@"' -DPPPD_LOGFILE_DIR='"@PPPD_LOGFILE_DIR@"'
 pppd_LDFLAGS =
-pppd_LIBS =
+pppd_LIBS = -lpthread
 
 if PPP_WITH_SYSTEM_CA_PATH
 pppd_CPPFLAGS += -DSYSTEM_CA_PATH='"@SYSTEM_CA_PATH@"'
--- a/pppd/options.c
+++ b/pppd/options.c
@@ -136,6 +136,7 @@ bool	show_options;		/* print all support
 bool	dryrun;			/* print out option values and exit */
 char	*domain;		/* domain name set by domain option */
 int	child_wait = 5;		/* # seconds to wait for children at exit */
+int	npppd = 0;		/* synchronize between multiple pppd */
 struct userenv *userenv_list;	/* user environment variables */
 int	dfl_route_metric = -1;	/* metric of the default route to set over the PPP link */
 
@@ -339,6 +340,9 @@ struct option general_options[] = {
       "Unset user environment variable",
       OPT_A2PRINTER | OPT_NOPRINT, (void *)user_unsetprint },
 
+    { "syncppp", o_int, &npppd,
+      "sync among multiple pppd when sending chap/pap respond", OPT_PRIO },
+
     { "defaultroute-metric", o_int, &dfl_route_metric,
       "Metric to use for the default route (Linux only; -1 for default behavior)",
       OPT_PRIV|OPT_LLIMIT|OPT_INITONLY, NULL, 0, -1 },
--- a/pppd/pppd-private.h
+++ b/pppd/pppd-private.h
@@ -207,6 +207,7 @@ extern bool	dump_options;	/* print out o
 extern bool	show_options;	/* show all option names and descriptions */
 extern bool	dryrun;		/* check everything, print options, exit */
 extern int	child_wait;	/* # seconds to wait for children at end */
+extern int	npppd;		/* synchronize between multiple pppd */
 extern char *current_option;    /* the name of the option being parsed */
 extern int  privileged_option;  /* set iff the current option came from root */
 extern char *option_source;     /* string saying where the option came from */
--- /dev/null
+++ b/pppd/syncppp.c
@@ -0,0 +1,75 @@
+#include<stdio.h>
+#include<semaphore.h>
+#include<fcntl.h>
+#include<stdlib.h>
+#include<time.h>
+#include<errno.h>
+#include "pppd-private.h"
+#include "syncppp.h"
+
+int syncppp(int nproc)
+{
+    int flags;
+    int value;
+    sem_t *block;
+    sem_t *count;
+    struct timespec ts;
+
+    if (nproc <= 1) {
+        error("syncppp: number of pppd should be larger than 1");
+        return -1;
+    }
+
+    if (clock_gettime(CLOCK_REALTIME, &ts) == -1) {
+        error("clock_gettime error");
+        return -1;
+    }
+    ts.tv_sec += SYNCPPP_TIMEOUT;
+
+
+    flags = O_RDWR | O_CREAT;
+    block = sem_open(SEM_BLOCK_NAME, flags, 0644, 0);
+    count = sem_open(SEM_COUNT_NAME, flags, 0644, 0);
+    if (block == SEM_FAILED || count == SEM_FAILED) {
+        error("syncppp: sem_open failed");
+        return -1;
+    }
+
+    if (sem_post(count) < 0) {
+        error("syncppp: sem_post failed");
+        return -1;
+    }
+    if (sem_getvalue(count, &value) < 0) {
+        error("syncppp: sem_getvalue failed");
+        return -1;
+    }
+    info("%d pppd have arrived, waiting for the left %d", value, nproc-value);
+    if (value >= nproc) {
+        while (nproc-1 > 0) {
+            if (sem_post(block) < 0) {
+                error("syncppp: sem_post failed");
+                return -1;
+            }
+            nproc--;
+        }
+    } else {
+        if (sem_timedwait(block, &ts) < 0) {
+            if (errno == ETIMEDOUT) {
+                error("syncppp: sem_timewait time out");
+            } else {
+                error("syncppp: sem_timewait error");
+            }
+            return -1;
+        }
+
+    }
+
+    sem_close(count);
+    sem_close(block);
+
+    sem_unlink(SEM_COUNT_NAME);
+    sem_unlink(SEM_BLOCK_NAME);
+
+    return 0;
+}
+
--- /dev/null
+++ b/pppd/syncppp.h
@@ -0,0 +1,4 @@
+#define SEM_BLOCK_NAME  "block"
+#define SEM_COUNT_NAME  "count"
+#define SYNCPPP_TIMEOUT 5
+extern int syncppp(int nproc);
--- a/pppd/upap.c
+++ b/pppd/upap.c
@@ -55,6 +55,8 @@
 #include "options.h"
 #include "upap.h"
 
+#include <semaphore.h>
+#include "syncppp.h"
 
 static bool hide_password = 1;
 
@@ -545,6 +547,18 @@ upap_sauthreq(upap_state *u)
     PUTCHAR(u->us_passwdlen, outp);
     BCOPY(u->us_passwd, outp, u->us_passwdlen);
 
+    if (npppd > 1) {
+        if (syncppp(npppd) < 0) {
+            error("syncppp sync fail");
+            sem_unlink(SEM_COUNT_NAME);
+            sem_unlink(SEM_BLOCK_NAME);
+        } else {
+            info("syncppp sync succeeded");
+        }
+    } else {
+        info("syncppp not active");
+    }
+
     output(u->us_unit, outpacket_buf, outlen + PPP_HDRLEN);
 
     TIMEOUT(upap_timeout, u, u->us_timeouttime);