--- src/fsm.h.orig	2018-06-23 17:52:14.984221000 +0700
+++ src/fsm.h	2018-06-23 17:51:37.007775000 +0700
@@ -43,6 +43,7 @@
   #define MODE_NAK	1
   #define MODE_REJ	2
   #define MODE_NOP	3
+  #define MODE_ACK	4
 
   /* Codes */
   #define CODE_VENDOR		0
--- src/ccp.c.orig	2016-01-06 22:42:06.000000000 +0700
+++ src/ccp.c	2018-06-23 17:39:25.144177000 +0700
@@ -938,6 +938,7 @@ CcpDecodeConfig(Fsm fp, FsmOption list, 
 	CCP_PEER_REJ(ccp, index);
 	break;
 
+      case MODE_ACK:
       case MODE_NAK:
       case MODE_NOP:
 	(*ct->DecodeConfig)(fp, opt, mode);
--- src/ecp.c.orig	2016-01-06 22:42:06.000000000 +0700
+++ src/ecp.c	2018-06-23 17:38:52.920025000 +0700
@@ -793,6 +793,7 @@ EcpDecodeConfig(Fsm fp, FsmOption list, 
 	ECP_PEER_REJ(ecp, index);
 	break;
 
+      case MODE_ACK:
       case MODE_NOP:
 	(*et->DecodeConfig)(fp, opt, mode);
 	break;
--- src/fsm.c.orig	2016-01-06 22:42:06.000000000 +0700
+++ src/fsm.c	2018-06-23 17:40:37.112129000 +0700
@@ -664,7 +664,7 @@ FsmRecvConfigAck(Fsm fp, FsmHeader lhp, 
   /* XXX We should verify the contents are equal to our last sent config-req */
 
   /* Decode packet */
-  FsmDecodeBuffer(fp, MBDATA(bp), MBLEN(bp), MODE_NOP);
+  FsmDecodeBuffer(fp, MBDATA(bp), MBLEN(bp), MODE_ACK);
 
   /* Do whatever */
   switch (fp->state) {
--- src/lcp.c.orig	2016-01-06 22:42:06.000000000 +0700
+++ src/lcp.c	2018-06-23 17:48:20.968167000 +0700
@@ -843,6 +843,10 @@ LcpDecodeConfig(Fsm fp, FsmOption list, 
 	  mru = ntohs(mru);
 	  Log(LG_LCP, ("[%s]   %s %d", l->name, oi->name, mru));
 	  switch (mode) {
+	    case MODE_ACK:
+	      if (mru == lcp->want_mru)
+		lcp->peer_mru = mru;
+	      break;
 	    case MODE_REQ:
 	      if (mru < LCP_MIN_MRU) {
 		mru = htons(LCP_MIN_MRU);