diff --git a/src/include/lwip/opt.h b/src/include/lwip/opt.h
index 4c29ec5f..75b33c54 100644
--- a/src/include/lwip/opt.h
+++ b/src/include/lwip/opt.h
@@ -1780,12 +1780,41 @@
 #endif
 
 /**
- * LWIP_PPP_API==1: Support PPP API (in pppapi.c)
+ * PRINTPKT_SUPPORT==1: Enable PPP print packet support
+ *
+ * Mandatory for debugging, it displays exchanged packet content in debug trace.
+ */
+#ifndef PRINTPKT_SUPPORT
+#define PRINTPKT_SUPPORT                0
+#endif
+
+/**
+ * PPP_IPV6_SUPPORT==1: Enable PPP IPv6 support
+ */
+#ifndef PPP_IPV6_SUPPORT
+#define PPP_IPV6_SUPPORT                0
+#endif
+
+/**
+ * LWIP_PPP_API==1: Enable PPP API (in pppapi.c)
  */
 #ifndef LWIP_PPP_API
 #define LWIP_PPP_API                    0
 #endif
 
+/**
+ * PPP_NOTIFY_PHASE==1: Support PPP notify phase support
+ *
+ * PPP notify phase support allows you to set a callback which is
+ * called on change of the internal PPP state machine.
+ *
+ * This can be used for example to set a LED pattern depending on the
+ * current phase of the PPP session.
+ */
+#ifndef PPP_NOTIFY_PHASE
+#define PPP_NOTIFY_PHASE                0
+#endif
+
 /**
  * pbuf_type PPP is using for LCP, PAP, CHAP, EAP, IPCP and IP6CP packets.
  *
@@ -1832,6 +1861,13 @@
 #define CHAP_SUPPORT                    1 /* MSCHAP requires CHAP support */
 #endif /* MSCHAP_SUPPORT */
 
+/**
+ * EAP_SUPPORT==1: Support EAP.
+ */
+#ifndef EAP_SUPPORT
+#define EAP_SUPPORT                     0
+#endif
+
 /**
  * CBCP_SUPPORT==1: Support CBCP. CURRENTLY NOT SUPPORTED! DO NOT SET!
  */
@@ -1860,6 +1896,13 @@
 #define LQR_SUPPORT                     0
 #endif
 
+/**
+ * PPP_SERVER==1: Enable PPP server support (waiting for incoming PPP session). CURRENTLY NOT SUPPORTED! DO NOT SET!
+ */
+#ifndef PPP_SERVER
+#define PPP_SERVER                      0
+#endif
+
 /**
  * VJ_SUPPORT==1: Support VJ header compression.
  */
diff --git a/src/include/netif/ppp/ppp.h b/src/include/netif/ppp/ppp.h
index cda32ba0..97ab3cde 100644
--- a/src/include/netif/ppp/ppp.h
+++ b/src/include/netif/ppp/ppp.h
@@ -48,6 +48,42 @@
 #include "lwip/ip6_addr.h"
 #endif /* PPP_IPV6_SUPPORT */
 
+/* Disable non-working or rarely used PPP feature, so rarely that we don't want to bloat opt.h with them */
+#ifndef PPP_OPTIONS
+#define PPP_OPTIONS         0
+#endif
+
+#ifndef PPP_REMOTENAME
+#define PPP_REMOTENAME      0
+#endif
+
+#ifndef PPP_IDLETIMELIMIT
+#define PPP_IDLETIMELIMIT   0
+#endif
+
+#ifndef PPP_LCP_ADAPTIVE
+#define PPP_LCP_ADAPTIVE    0
+#endif
+
+#ifndef PPP_MAXCONNECT
+#define PPP_MAXCONNECT      0
+#endif
+
+#ifndef DEMAND_SUPPORT
+#define DEMAND_SUPPORT      0
+#endif
+
+#ifndef PPP_ALLOWED_ADDRS
+#define PPP_ALLOWED_ADDRS   0
+#endif
+
+#ifndef PPP_PROTOCOLNAME
+#define PPP_PROTOCOLNAME    0
+#endif
+
+#ifndef PPP_STATS_SUPPORT
+#define PPP_STATS_SUPPORT   0
+#endif
 
 
 /*************************
diff --git a/src/netif/ppp/auth.c b/src/netif/ppp/auth.c
index 4cbf0afb..830e21fd 100644
--- a/src/netif/ppp/auth.c
+++ b/src/netif/ppp/auth.c
@@ -546,6 +546,7 @@ set_permitted_number(argv)
  * An Open on LCP has requested a change from Dead to Establish phase.
  */
 void link_required(ppp_pcb *pcb) {
+    LWIP_UNUSED_ARG(pcb);
 }
 
 #if 0
@@ -1003,6 +1004,7 @@ void continue_networks(ppp_pcb *pcb) {
  */
 void auth_peer_fail(ppp_pcb *pcb, int protocol) {
     int errcode = PPPERR_AUTHFAIL;
+    LWIP_UNUSED_ARG(protocol);
     /*
      * Authentication failure: take the link down
      */
@@ -1057,8 +1059,8 @@ void auth_peer_success(ppp_pcb *pcb, int protocol, int prot_flavor, char *name,
      * Save the authenticated name of the peer for later.
      */
     /* FIXME: do we need that ? */
-    if (namelen > sizeof(pcb->peer_authname) - 1)
-	namelen = sizeof(pcb->peer_authname) - 1;
+    if (namelen > (int)sizeof(pcb->peer_authname) - 1)
+	namelen = (int)sizeof(pcb->peer_authname) - 1;
     MEMCPY(pcb->peer_authname, name, namelen);
     pcb->peer_authname[namelen] = 0;
 #if 0 /* UNUSED */
@@ -1082,6 +1084,7 @@ void auth_peer_success(ppp_pcb *pcb, int protocol, int prot_flavor, char *name,
  */
 void auth_withpeer_fail(ppp_pcb *pcb, int protocol) {
     int errcode = PPPERR_AUTHFAIL;
+    LWIP_UNUSED_ARG(protocol);
     /*
      * We've failed to authenticate ourselves to our peer.
      *
@@ -1162,6 +1165,7 @@ void np_up(ppp_pcb *pcb, int proto) {
 #if PPP_IDLETIMELIMIT
     int tlim;
 #endif /* PPP_IDLETIMELIMIT */
+    LWIP_UNUSED_ARG(proto);
 
     if (pcb->num_np_up == 0) {
 	/*
@@ -1209,6 +1213,7 @@ void np_up(ppp_pcb *pcb, int proto) {
  * np_down - a network protocol has gone down.
  */
 void np_down(ppp_pcb *pcb, int proto) {
+    LWIP_UNUSED_ARG(proto);
     if (--pcb->num_np_up == 0) {
 #if PPP_IDLETIMELIMIT
 	UNTIMEOUT(check_idle, (void*)pcb);
@@ -1227,6 +1232,7 @@ void np_down(ppp_pcb *pcb, int proto) {
  * np_finished - a network protocol has finished using the link.
  */
 void np_finished(ppp_pcb *pcb, int proto) {
+    LWIP_UNUSED_ARG(proto);
     if (--pcb->num_np_open <= 0) {
 	/* no further use for the link: shut up shop. */
 	lcp_close(pcb, "No network protocols running");
diff --git a/src/netif/ppp/chap-md5.c b/src/netif/ppp/chap-md5.c
index f6361314..f7965490 100644
--- a/src/netif/ppp/chap-md5.c
+++ b/src/netif/ppp/chap-md5.c
@@ -70,6 +70,7 @@ static int chap_md5_verify_response(int id, char *name,
 	unsigned char idbyte = id;
 	unsigned char hash[MD5_HASH_SIZE];
 	int challenge_len, response_len;
+	LWIP_UNUSED_ARG(name);
 
 	challenge_len = *challenge++;
 	response_len = *response++;
@@ -98,6 +99,8 @@ static void chap_md5_make_response(unsigned char *response, int id, char *our_na
 	md5_context ctx;
 	unsigned char idbyte = id;
 	int challenge_len = *challenge++;
+	LWIP_UNUSED_ARG(our_name);
+	LWIP_UNUSED_ARG(private);
 
 	md5_starts(&ctx);
 	md5_update(&ctx, &idbyte, 1);
diff --git a/src/netif/ppp/chap-new.c b/src/netif/ppp/chap-new.c
index 052b4095..d4dbd7cc 100644
--- a/src/netif/ppp/chap-new.c
+++ b/src/netif/ppp/chap-new.c
@@ -106,7 +106,7 @@ static int chap_print_pkt(unsigned char *p, int plen,
 #endif /* PRINTPKT_SUPPORT */
 
 /* List of digest types that we know about */
-const static struct chap_digest_type* const chap_digests[] = {
+static const struct chap_digest_type* const chap_digests[] = {
     &md5_digest,
 #if MSCHAP_SUPPORT
     &chapms_digest,
@@ -409,7 +409,11 @@ static int chap_verify_response(char *name, char *ourname, int id,
 		ppp_error("No CHAP secret found for authenticating %q", name);
 		return 0;
 	}
-#endif
+#else
+	/* only here to clean compiler warnings */
+	LWIP_UNUSED_ARG(ourname);
+	secret_len = 0;
+#endif /* 0 */
 	ok = digest->verify_response(id, name, secret, secret_len, challenge,
 				     response, message, message_space);
 	memset(secret, 0, sizeof(secret));
@@ -486,6 +490,7 @@ static void chap_respond(ppp_pcb *pcb, int id,
 static void chap_handle_status(ppp_pcb *pcb, int code, int id,
 		   unsigned char *pkt, int len) {
 	const char *msg = NULL;
+	LWIP_UNUSED_ARG(id);
 
 	if ((pcb->chap_client.flags & (AUTH_DONE|AUTH_STARTED|LOWERUP))
 	    != (AUTH_STARTED|LOWERUP))
@@ -590,7 +595,7 @@ static int chap_print_pkt(unsigned char *p, int plen,
 	if (len < CHAP_HDRLEN || len > plen)
 		return 0;
 
-	if (code >= 1 && code <= sizeof(chap_code_names) / sizeof(char *))
+	if (code >= 1 && code <= (int)sizeof(chap_code_names) / (int)sizeof(char *))
 		printer(arg, " %s", chap_code_names[code-1]);
 	else
 		printer(arg, " code=0x%x", code);
diff --git a/src/netif/ppp/chap_ms.c b/src/netif/ppp/chap_ms.c
index 2467aa54..7935de65 100644
--- a/src/netif/ppp/chap_ms.c
+++ b/src/netif/ppp/chap_ms.c
@@ -208,6 +208,8 @@ static int chapms_verify_response(int id, char *name,
 	unsigned char md[MS_CHAP_RESPONSE_LEN];
 	int diff;
 	int challenge_len, response_len;
+	LWIP_UNUSED_ARG(id);
+	LWIP_UNUSED_ARG(name);
 
 	challenge_len = *challenge++;	/* skip length, is 8 */
 	response_len = *response++;
@@ -254,6 +256,7 @@ static int chapms2_verify_response(int id, char *name,
 	unsigned char md[MS_CHAP2_RESPONSE_LEN];
 	char saresponse[MS_AUTH_RESPONSE_LENGTH+1];
 	int challenge_len, response_len;
+	LWIP_UNUSED_ARG(id);
 
 	challenge_len = *challenge++;	/* skip length, is 16 */
 	response_len = *response++;
@@ -326,6 +329,9 @@ static int chapms2_verify_response(int id, char *name,
 static void chapms_make_response(unsigned char *response, int id, char *our_name,
 		     unsigned char *challenge, char *secret, int secret_len,
 		     unsigned char *private) {
+	LWIP_UNUSED_ARG(id);
+	LWIP_UNUSED_ARG(our_name);
+	LWIP_UNUSED_ARG(private);
 	challenge++;	/* skip length, should be 8 */
 	*response++ = MS_CHAP_RESPONSE_LEN;
 	ChapMS(challenge, secret, secret_len, response);
@@ -334,6 +340,7 @@ static void chapms_make_response(unsigned char *response, int id, char *our_name
 static void chapms2_make_response(unsigned char *response, int id, char *our_name,
 		      unsigned char *challenge, char *secret, int secret_len,
 		      unsigned char *private) {
+	LWIP_UNUSED_ARG(id);
 	challenge++;	/* skip length, should be 16 */
 	*response++ = MS_CHAP2_RESPONSE_LEN;
 	ChapMS2(challenge,
@@ -608,7 +615,7 @@ void GenerateAuthenticatorResponse(u_char PasswordHashHash[MD4_SIGNATURE_SIZE],
     sha1_finish(&sha1Context, Digest);
 
     /* Convert to ASCII hex string. */
-    for (i = 0; i < LWIP_MAX((MS_AUTH_RESPONSE_LENGTH / 2), sizeof(Digest)); i++)
+    for (i = 0; i < LWIP_MAX((MS_AUTH_RESPONSE_LENGTH / 2), (int)sizeof(Digest)); i++)
 	sprintf((char *)&authResponse[i * 2], "%02X", Digest[i]);
 }
 
@@ -821,6 +828,7 @@ void ChapMS2(u_char *rchallenge, u_char *PeerChallenge,
     /* ARGSUSED */
     u_char *p = &response[MS_CHAP2_PEER_CHALLENGE];
     int i;
+    LWIP_UNUSED_ARG(authenticator);
 
     BZERO(response, MS_CHAP2_RESPONSE_LEN);
 
diff --git a/src/netif/ppp/eap.c b/src/netif/ppp/eap.c
index 4c385d6f..2bb0c5e8 100644
--- a/src/netif/ppp/eap.c
+++ b/src/netif/ppp/eap.c
@@ -2046,6 +2046,8 @@ static void eap_response(ppp_pcb *pcb, u_char *inp, int id, int len) {
  * eap_success - Receive EAP Success message (client mode).
  */
 static void eap_success(ppp_pcb *pcb, u_char *inp, int id, int len) {
+	LWIP_UNUSED_ARG(id);
+
 	if (pcb->eap.es_client.ea_state != eapOpen && !eap_client_active(pcb)) {
 		ppp_dbglog("EAP unexpected success message in state %s (%d)",
 		    eap_state_name(pcb->eap.es_client.ea_state),
@@ -2070,6 +2072,8 @@ static void eap_success(ppp_pcb *pcb, u_char *inp, int id, int len) {
  * eap_failure - Receive EAP Failure message (client mode).
  */
 static void eap_failure(ppp_pcb *pcb, u_char *inp, int id, int len) {
+	LWIP_UNUSED_ARG(id);
+
 	if (!eap_client_active(pcb)) {
 		ppp_dbglog("EAP unexpected failure message in state %s (%d)",
 		    eap_state_name(pcb->eap.es_client.ea_state),
@@ -2173,7 +2177,7 @@ static int eap_printpkt(u_char *inp, int inlen, void (*printer) (void *, char *,
 	if (len < EAP_HEADERLEN || len > inlen)
 		return (0);
 
-	if (code >= 1 && code <= sizeof(eap_codenames) / sizeof(char *))
+	if (code >= 1 && code <= (int)sizeof(eap_codenames) / (int)sizeof(char *))
 		printer(arg, " %s", eap_codenames[code-1]);
 	else
 		printer(arg, " code=0x%x", code);
@@ -2188,7 +2192,7 @@ static int eap_printpkt(u_char *inp, int inlen, void (*printer) (void *, char *,
 		GETCHAR(rtype, inp);
 		len--;
 		if (rtype >= 1 &&
-		    rtype <= sizeof (eap_typenames) / sizeof (char *))
+		    rtype <= (int)sizeof (eap_typenames) / (int)sizeof (char *))
 			printer(arg, " %s", eap_typenames[rtype-1]);
 		else
 			printer(arg, " type=0x%x", rtype);
@@ -2283,7 +2287,7 @@ static int eap_printpkt(u_char *inp, int inlen, void (*printer) (void *, char *,
 				break;
 
 			case EAPSRP_SVALIDATOR:
-				if (len < sizeof (u32_t))
+				if (len < (int)sizeof (u32_t))
 					break;
 				GETLONG(uval, inp);
 				len -= sizeof (u32_t);
@@ -2323,7 +2327,7 @@ static int eap_printpkt(u_char *inp, int inlen, void (*printer) (void *, char *,
 		GETCHAR(rtype, inp);
 		len--;
 		if (rtype >= 1 &&
-		    rtype <= sizeof (eap_typenames) / sizeof (char *))
+		    rtype <= (int)sizeof (eap_typenames) / (int)sizeof (char *))
 			printer(arg, " %s", eap_typenames[rtype-1]);
 		else
 			printer(arg, " type=0x%x", rtype);
@@ -2347,7 +2351,7 @@ static int eap_printpkt(u_char *inp, int inlen, void (*printer) (void *, char *,
 			len--;
 			printer(arg, " <Suggested-type %02X", rtype);
 			if (rtype >= 1 &&
-			    rtype < sizeof (eap_typenames) / sizeof (char *))
+			    rtype < (int)sizeof (eap_typenames) / (int)sizeof (char *))
 				printer(arg, " (%s)", eap_typenames[rtype-1]);
 			printer(arg, ">");
 			break;
@@ -2389,7 +2393,7 @@ static int eap_printpkt(u_char *inp, int inlen, void (*printer) (void *, char *,
 				break;
 
 			case EAPSRP_CVALIDATOR:
-				if (len < sizeof (u32_t))
+				if (len < (int)sizeof (u32_t))
 					break;
 				GETLONG(uval, inp);
 				len -= sizeof (u32_t);
diff --git a/src/netif/ppp/ipcp.c b/src/netif/ppp/ipcp.c
index 1944fc86..8a0c87ac 100644
--- a/src/netif/ppp/ipcp.c
+++ b/src/netif/ppp/ipcp.c
@@ -2041,6 +2041,7 @@ static void ipcp_down(fsm *f) {
  * proxy arp entries, etc.
  */
 static void ipcp_clear_addrs(ppp_pcb *pcb, u32_t ouraddr, u32_t hisaddr, u8_t replacedefaultroute) {
+    LWIP_UNUSED_ARG(replacedefaultroute);
 
     if (pcb->proxy_arp_set) {
 	cifproxyarp(pcb, hisaddr);
@@ -2113,7 +2114,7 @@ static int ipcp_printpkt(u_char *p, int plen,
     if (len < HEADERLEN || len > plen)
 	return 0;
 
-    if (code >= 1 && code <= sizeof(ipcp_codenames) / sizeof(char *))
+    if (code >= 1 && code <= (int)sizeof(ipcp_codenames) / (int)sizeof(char *))
 	printer(arg, " %s", ipcp_codenames[code-1]);
     else
 	printer(arg, " code=0x%x", code);
diff --git a/src/netif/ppp/ipv6cp.c b/src/netif/ppp/ipv6cp.c
index 8fb01ada..bb472445 100644
--- a/src/netif/ppp/ipv6cp.c
+++ b/src/netif/ppp/ipv6cp.c
@@ -44,30 +44,30 @@
     Alain.Durand@imag.fr, IMAG,
     Jean-Luc.Richier@imag.fr, IMAG-LSR.
 
-    Ce travail a été fait au sein du GIE DYADE (Groupement d'Intérêt
-    Économique ayant pour membres BULL S.A. et l'INRIA).
+    Ce travail a �t� fait au sein du GIE DYADE (Groupement d'Int�r�t
+    �conomique ayant pour membres BULL S.A. et l'INRIA).
 
     Ce logiciel informatique est disponible aux conditions
-    usuelles dans la recherche, c'est-à-dire qu'il peut
-    être utilisé, copié, modifié, distribué à l'unique
-    condition que ce texte soit conservé afin que
+    usuelles dans la recherche, c'est-�-dire qu'il peut
+    �tre utilis�, copi�, modifi�, distribu� � l'unique
+    condition que ce texte soit conserv� afin que
     l'origine de ce logiciel soit reconnue.
 
     Le nom de l'Institut National de Recherche en Informatique
     et en Automatique (INRIA), de l'IMAG, ou d'une personne morale
-    ou physique ayant participé à l'élaboration de ce logiciel ne peut
-    être utilisé sans son accord préalable explicite.
+    ou physique ayant particip� � l'�laboration de ce logiciel ne peut
+    �tre utilis� sans son accord pr�alable explicite.
 
     Ce logiciel est fourni tel quel sans aucune garantie,
-    support ou responsabilité d'aucune sorte.
-    Ce logiciel est dérivé de sources d'origine
+    support ou responsabilit� d'aucune sorte.
+    Ce logiciel est d�riv� de sources d'origine
     "University of California at Berkeley" et
     "Digital Equipment Corporation" couvertes par des copyrights.
 
-    L'Institut d'Informatique et de Mathématiques Appliquées de Grenoble (IMAG)
-    est une fédération d'unités mixtes de recherche du CNRS, de l'Institut National
-    Polytechnique de Grenoble et de l'Université Joseph Fourier regroupant
-    sept laboratoires dont le laboratoire Logiciels, Systèmes, Réseaux (LSR).
+    L'Institut d'Informatique et de Math�matiques Appliqu�es de Grenoble (IMAG)
+    est une f�d�ration d'unit�s mixtes de recherche du CNRS, de l'Institut National
+    Polytechnique de Grenoble et de l'Universit� Joseph Fourier regroupant
+    sept laboratoires dont le laboratoire Logiciels, Syst�mes, R�seaux (LSR).
 
     This work has been done in the context of GIE DYADE (joint R & D venture
     between BULL S.A. and INRIA).
@@ -270,9 +270,9 @@ static int  ipv6_demand_conf(int u);
 static int ipv6cp_printpkt(u_char *p, int plen,
 		void (*printer)(void *, char *, ...), void *arg);
 #endif /* PRINTPKT_SUPPORT */
-#if PPP_DEMAND
+#if DEMAND_SUPPORT
 static int ipv6_active_pkt(u_char *pkt, int len);
-#endif /* PPP_DEMAND */
+#endif /* DEMAND_SUPPORT */
 
 const struct protent ipv6cp_protent = {
     PPP_IPV6CP,
@@ -1035,7 +1035,7 @@ endswitch:
     return (rc);			/* Return final code */
 }
 
-#if PPP_OPTION
+#if PPP_OPTIONS
 /*
  * ipv6_check_options - check that any IP-related options are OK,
  * and assign appropriate defaults.
@@ -1092,7 +1092,7 @@ static void ipv6_check_options() {
 	exit(1);
     }
 }
-#endif /* PPP_OPTION */
+#endif /* PPP_OPTIONS */
 
 #if DEMAND_SUPPORT
 /*
@@ -1271,7 +1271,7 @@ static void ipv6cp_down(fsm *f) {
     sif6comp(f->unit, 0);
 #endif
 
-#if PPP_DEMAND
+#if DEMAND_SUPPORT
     /*
      * If we are doing dial-on-demand, set the interface
      * to queue up outgoing packets (for now).
@@ -1279,7 +1279,7 @@ static void ipv6cp_down(fsm *f) {
     if (demand) {
 	sifnpmode(f->pcb, PPP_IPV6, NPMODE_QUEUE);
     } else
-#endif /* PPP_DEMAND */
+#endif /* DEMAND_SUPPORT */
     {
 	sifnpmode(f->pcb, PPP_IPV6, NPMODE_DROP);
 	ipv6cp_clear_addrs(f->pcb,
@@ -1396,7 +1396,7 @@ static int ipv6cp_printpkt(u_char *p, int plen,
     if (len < HEADERLEN || len > plen)
 	return 0;
 
-    if (code >= 1 && code <= sizeof(ipv6cp_codenames) / sizeof(char *))
+    if (code >= 1 && code <= (int)sizeof(ipv6cp_codenames) / (int)sizeof(char *))
 	printer(arg, " %s", ipv6cp_codenames[code-1]);
     else
 	printer(arg, " code=0x%x", code);
@@ -1464,7 +1464,7 @@ static int ipv6cp_printpkt(u_char *p, int plen,
 }
 #endif /* PRINTPKT_SUPPORT */
 
-#if PPP_DEMAND
+#if DEMAND_SUPPORT
 /*
  * ipv6_active_pkt - see if this IP packet is worth bringing the link up for.
  * We don't bring the link up for IP fragments or for TCP FIN packets
@@ -1502,6 +1502,6 @@ static int ipv6_active_pkt(u_char *pkt, int len) {
 	return 0;
     return 1;
 }
-#endif /* PPP_DEMAND */
+#endif /* DEMAND_SUPPORT */
 
 #endif /* PPP_SUPPORT && PPP_IPV6_SUPPORT */
diff --git a/src/netif/ppp/lcp.c b/src/netif/ppp/lcp.c
index 52f7a50f..bd616c40 100644
--- a/src/netif/ppp/lcp.c
+++ b/src/netif/ppp/lcp.c
@@ -1382,6 +1382,8 @@ static int lcp_nakci(fsm *f, u_char *p, int len, int treat_as_reject) {
 		       try_.mrru = cishort;
 		   );
     }
+#else /* HAVE_MULTILINK */
+    LWIP_UNUSED_ARG(treat_as_reject);
 #endif /* HAVE_MULTILINK */
 
     /*
@@ -2332,7 +2334,7 @@ static int lcp_printpkt(u_char *p, int plen,
     if (len < HEADERLEN || len > plen)
 	return 0;
 
-    if (code >= 1 && code <= sizeof(lcp_codenames) / sizeof(char *))
+   if (code >= 1 && code <= (int)sizeof(lcp_codenames) / (int)sizeof(char *))
 	printer(arg, " %s", lcp_codenames[code-1]);
     else
 	printer(arg, " code=0x%x", code);
@@ -2617,6 +2619,7 @@ static void lcp_received_echo_reply(fsm *f, int id, u_char *inp, int len) {
     ppp_pcb *pcb = f->pcb;
     lcp_options *go = &pcb->lcp_gotoptions;
     u32_t magic;
+    LWIP_UNUSED_ARG(id);
 
     /* Check the magic number - don't count replies from ourselves. */
     if (len < 4) {
diff --git a/src/netif/ppp/multilink.c b/src/netif/ppp/multilink.c
index 9acbb567..3bea516a 100644
--- a/src/netif/ppp/multilink.c
+++ b/src/netif/ppp/multilink.c
@@ -29,7 +29,7 @@
  */
 
 #include "lwip/opt.h"
-#if PPP_SUPPORT && HAVE_MULTILINK /* don't build if not configured for use in lwipopts.h */
+#if PPP_SUPPORT && defined(HAVE_MULTILINK) /* don't build if not configured for use in lwipopts.h */
 
 /* Multilink support
  *
diff --git a/src/netif/ppp/ppp.c b/src/netif/ppp/ppp.c
index 12a57ebd..d2cdf1f0 100644
--- a/src/netif/ppp/ppp.c
+++ b/src/netif/ppp/ppp.c
@@ -602,7 +602,7 @@ static void ppp_clear(ppp_pcb *pcb) {
 
   LWIP_ASSERT("pcb->phase == PPP_PHASE_DEAD || pcb->phase == PPP_PHASE_HOLDOFF", pcb->phase == PPP_PHASE_DEAD || pcb->phase == PPP_PHASE_HOLDOFF);
 
-#if PPP_STATS_SUPPORTs
+#if PPP_STATS_SUPPORT
   link_stats_valid = 0;
 #endif /* PPP_STATS_SUPPORT */
 
@@ -1622,6 +1622,10 @@ pppos_input(ppp_pcb *pcb, u_char *s, int l)
           /* Packet consumed, release our references. */
           pcrx->in_head = NULL;
           pcrx->in_tail = NULL;
+#if IP_FORWARD || LWIP_IPV6_FORWARD
+          /* hide the room for Ethernet forwarding header */
+          pbuf_header(inp, -(s16_t)PBUF_LINK_HLEN);
+#endif /* IP_FORWARD || LWIP_IPV6_FORWARD */
 #if PPP_INPROC_MULTITHREADED
           if(tcpip_callback_with_block(pppos_input_callback, inp, 0) != ERR_OK) {
             PPPDEBUG(LOG_ERR, ("pppos_input[%d]: tcpip_callback() failed, dropping packet\n", pcb->num));
@@ -1711,6 +1715,7 @@ pppos_input(ppp_pcb *pcb, u_char *s, int l)
         case PDDATA:                    /* Process data byte. */
           /* Make space to receive processed data. */
           if (pcrx->in_tail == NULL || pcrx->in_tail->len == PBUF_POOL_BUFSIZE) {
+            u16_t pbuf_alloc_len;
             if (pcrx->in_tail != NULL) {
               pcrx->in_tail->tot_len = pcrx->in_tail->len;
               if (pcrx->in_tail != pcrx->in_head) {
@@ -1720,45 +1725,35 @@ pppos_input(ppp_pcb *pcb, u_char *s, int l)
               }
             }
             /* If we haven't started a packet, we need a packet header. */
+            pbuf_alloc_len = 0;
 #if IP_FORWARD || LWIP_IPV6_FORWARD
-            /* If IP forwarding is enabled we are using a PBUF_LINK packet type so
+            /* If IP forwarding is enabled we are reserving PBUF_LINK_HLEN bytes so
              * the packet is being allocated with enough header space to be
              * forwarded (to Ethernet for example).
              */
-            next_pbuf = pbuf_alloc(PBUF_LINK, 0, PBUF_POOL);
-#else /* IP_FORWARD || LWIP_IPV6_FORWARD */
-            next_pbuf = pbuf_alloc(PBUF_RAW, 0, PBUF_POOL);
+            if (pcrx->in_head == NULL) {
+              pbuf_alloc_len = PBUF_LINK_HLEN;
+            }
 #endif /* IP_FORWARD || LWIP_IPV6_FORWARD */
+            next_pbuf = pbuf_alloc(PBUF_RAW, pbuf_alloc_len, PBUF_POOL);
             if (next_pbuf == NULL) {
               /* No free buffers.  Drop the input packet and let the
                * higher layers deal with it.  Continue processing
                * the received pbuf chain in case a new packet starts. */
-              PPPDEBUG(LOG_ERR, ("pppos_input[%d]: NO FREE MBUFS!\n", pcb->num));
+              PPPDEBUG(LOG_ERR, ("pppos_input[%d]: NO FREE PBUFS!\n", pcb->num));
               LINK_STATS_INC(link.memerr);
               ppp_drop(pcrx);
               pcrx->in_state = PDSTART;  /* Wait for flag sequence. */
               break;
             }
             if (pcrx->in_head == NULL) {
-              u8_t *payload;
-              /* pbuf_header() used below is only trying to put PPP headers
-               * before the current payload pointer if there is enough space
-               * in the pbuf to do so. Therefore we don't care if it fails,
-               * but if it fail we have to set len to the size used by PPP headers.
-               */
+              u8_t *payload = ((u8_t*)next_pbuf->payload) + pbuf_alloc_len;
 #if PPP_INPROC_MULTITHREADED
-              if (pbuf_header(next_pbuf, +sizeof(struct pppos_input_header) +sizeof(pcrx->in_protocol))) {
-                next_pbuf->len += sizeof(struct pppos_input_header) + sizeof(pcrx->in_protocol);
-              }
-              payload = next_pbuf->payload;
               ((struct pppos_input_header*)payload)->pcb = pcb;
               payload += sizeof(struct pppos_input_header);
-#else /* PPP_INPROC_MULTITHREADED */
-              if (pbuf_header(next_pbuf, +sizeof(pcrx->in_protocol))) {
-                next_pbuf->len += sizeof(pcrx->in_protocol);
-              }
-              payload = next_pbuf->payload;
+              next_pbuf->len += sizeof(struct pppos_input_header);
 #endif /* PPP_INPROC_MULTITHREADED */
+              next_pbuf->len += sizeof(pcrx->in_protocol);
               *(payload++) = pcrx->in_protocol >> 8;
               *(payload) = pcrx->in_protocol & 0xFF;
               pcrx->in_head = next_pbuf;
@@ -1930,6 +1925,7 @@ static void ppp_over_l2tp_open(ppp_pcb *pcb) {
 #endif /* PPPOL2TP_SUPPORT */
 
 void ppp_link_down(ppp_pcb *pcb) {
+  LWIP_UNUSED_ARG(pcb); /* necessary if PPPDEBUG is defined to an empty function */
   PPPDEBUG(LOG_DEBUG, ("ppp_link_down: unit %d\n", pcb->num));
 }
 
@@ -2014,6 +2010,7 @@ int ppp_send_config(ppp_pcb *pcb, int mtu, u32_t accm, int pcomp, int accomp) {
 #if PPPOS_SUPPORT
   int i;
 #endif /* PPPOS_SUPPORT */
+  LWIP_UNUSED_ARG(mtu);
 
   /* pcb->mtu = mtu; -- set correctly with netif_set_mtu */
   pcb->pcomp = pcomp;
diff --git a/src/netif/ppp/pppoe.c b/src/netif/ppp/pppoe.c
index a5f4bd30..101ac90e 100644
--- a/src/netif/ppp/pppoe.c
+++ b/src/netif/ppp/pppoe.c
@@ -313,7 +313,7 @@ pppoe_disc_input(struct netif *netif, struct pbuf *pb)
   hunique_len = 0;
 #endif
   session = 0;
-  if (pb->len - off < PPPOE_HEADERLEN) {
+  if (pb->len - off < (u16_t)PPPOE_HEADERLEN) {
     PPPDEBUG(LOG_DEBUG, ("pppoe: packet too short: %d\n", pb->len));
     goto done;
   }
diff --git a/src/netif/ppp/pppol2tp.c b/src/netif/ppp/pppol2tp.c
index dad340aa..017223b4 100644
--- a/src/netif/ppp/pppol2tp.c
+++ b/src/netif/ppp/pppol2tp.c
@@ -189,6 +189,7 @@ static void pppol2tp_input(void *arg, struct udp_pcb *pcb, struct pbuf *p, struc
   pppol2tp_pcb *l2tp = (pppol2tp_pcb*)arg;
   u16_t hflags, hlen, len=0, tunnel_id=0, session_id=0, ns=0, nr=0, offset=0;
   u8_t *inp;
+  LWIP_UNUSED_ARG(pcb);
 
   if (l2tp->phase < PPPOL2TP_STATE_SCCRQ_SENT) {
     goto free_and_return;
@@ -324,6 +325,10 @@ static void pppol2tp_dispatch_control_packet(pppol2tp_pcb *l2tp, struct ip_addr
   u8_t md5_hash[16];
   u8_t challenge_id = 0;
 #endif /* PPPOL2TP_AUTH_SUPPORT */
+  LWIP_UNUSED_ARG(addr);
+  LWIP_UNUSED_ARG(len);
+  LWIP_UNUSED_ARG(tunnel_id);
+  LWIP_UNUSED_ARG(session_id);
 
   l2tp->peer_nr = nr;
   l2tp->peer_ns = ns;
diff --git a/src/netif/ppp/upap.c b/src/netif/ppp/upap.c
index 11dddd3e..72931305 100644
--- a/src/netif/ppp/upap.c
+++ b/src/netif/ppp/upap.c
@@ -357,7 +357,10 @@ static void upap_input(ppp_pcb *pcb, u_char *inpacket, int l) {
  */
 static void upap_rauthreq(ppp_pcb *pcb, u_char *inp, int id, int len) {
     u_char ruserlen, rpasswdlen;
-    char *ruser, *rpasswd;
+    char *ruser;
+#if 0
+    char *rpasswd;
+#endif
     char rhostname[256];
     int retcode;
     char *msg;
@@ -401,12 +404,12 @@ static void upap_rauthreq(ppp_pcb *pcb, u_char *inp, int id, int len) {
     }
 
     /* FIXME: we need a way to check peer secret */
+#if 0
     rpasswd = (char *) inp;
 
     /*
      * Check the username and password given.
      */
-#if 0
     retcode = check_passwd(pcb->upap.us_unit, ruser, ruserlen, rpasswd,
 			   rpasswdlen, &msg);
     BZERO(rpasswd, rpasswdlen);
@@ -423,11 +426,17 @@ static void upap_rauthreq(ppp_pcb *pcb, u_char *inp, int id, int len) {
 	    warn("calling number %q is not authorized", remote_number);
 	}
     }
-#endif
 
     msglen = strlen(msg);
     if (msglen > 255)
 	msglen = 255;
+#else
+    /* only here to clean compiler warnings */
+    retcode = UPAP_AUTHNAK;
+    msg = NULL;
+    msglen = 0;
+#endif /* 0 */
+
     upap_sresp(pcb, retcode, id, msg, msglen);
 
     /* Null terminate and clean remote name. */
@@ -454,6 +463,7 @@ static void upap_rauthreq(ppp_pcb *pcb, u_char *inp, int id, int len) {
 static void upap_rauthack(ppp_pcb *pcb, u_char *inp, int id, int len) {
     u_char msglen;
     char *msg;
+    LWIP_UNUSED_ARG(id);
 
     if (pcb->upap.us_clientstate != UPAPCS_AUTHREQ) /* XXX */
 	return;
@@ -488,6 +498,7 @@ static void upap_rauthack(ppp_pcb *pcb, u_char *inp, int id, int len) {
 static void upap_rauthnak(ppp_pcb *pcb, u_char *inp, int id, int len) {
     u_char msglen;
     char *msg;
+    LWIP_UNUSED_ARG(id);
 
     if (pcb->upap.us_clientstate != UPAPCS_AUTHREQ) /* XXX */
 	return;
@@ -608,7 +619,7 @@ static int upap_printpkt(u_char *p, int plen, void (*printer) (void *, char *, .
     if (len < UPAP_HEADERLEN || len > plen)
 	return 0;
 
-    if (code >= 1 && code <= sizeof(upap_codenames) / sizeof(char *))
+    if (code >= 1 && code <= (int)sizeof(upap_codenames) / (int)sizeof(char *))
 	printer(arg, " %s", upap_codenames[code-1]);
     else
 	printer(arg, " code=0x%x", code);
diff --git a/src/netif/ppp/utils.c b/src/netif/ppp/utils.c
index d03f6c25..60cf7f85 100644
--- a/src/netif/ppp/utils.c
+++ b/src/netif/ppp/utils.c
@@ -209,7 +209,7 @@ int ppp_vslprintf(char *buf, int buflen, char *fmt, va_list args) {
 		val = va_arg(args, long);
 		if ((long)val < 0) {
 		    neg = 1;
-		    val = -val;
+		    val = (unsigned long)-val;
 		}
 		base = 10;
 		break;
@@ -607,6 +607,8 @@ static void ppp_logit(int level, char *fmt, va_list args) {
 }
 
 static void ppp_log_write(int level, char *buf) {
+    LWIP_UNUSED_ARG(level); /* necessary if PPPDEBUG is defined to an empty function */
+    LWIP_UNUSED_ARG(buf);
     PPPDEBUG(level, ("%s\n", buf) );
 #if 0
     if (log_to_fd >= 0 && (level != LOG_DEBUG || debug)) {