diff --git a/src/include/lwip/opt.h b/src/include/lwip/opt.h
index 26d4a800..9efcc50c 100644
--- a/src/include/lwip/opt.h
+++ b/src/include/lwip/opt.h
@@ -1927,6 +1927,13 @@
 #define ECP_SUPPORT                     0
 #endif
 
+/**
+ * DEMAND_SUPPORT==1: Support dial on demand. CURRENTLY NOT SUPPORTED! DO NOT SET!
+ */
+#ifndef DEMAND_SUPPORT
+#define DEMAND_SUPPORT                  0
+#endif
+
 /**
  * LQR_SUPPORT==1: Support Link Quality Report. Do nothing except exchanging some LCP packets.
  */
diff --git a/src/include/netif/ppp/fsm.h b/src/include/netif/ppp/fsm.h
index cd12075f..fda2d6e1 100644
--- a/src/include/netif/ppp/fsm.h
+++ b/src/include/netif/ppp/fsm.h
@@ -74,7 +74,7 @@
 typedef struct fsm {
     ppp_pcb *pcb;		/* PPP Interface */
     const struct fsm_callbacks *callbacks;	/* Callback routines */
-    char *term_reason;		/* Reason for closing protocol */
+    const char *term_reason;	/* Reason for closing protocol */
     u8_t seen_ack;		/* Have received valid Ack/Nak/Rej to Req */
 				  /* -- This is our only flag, we might use u_int :1 if we have more flags */
     u16_t protocol;		/* Data Link Layer Protocol field value */
@@ -120,7 +120,7 @@ typedef struct fsm_callbacks {
 		(fsm *);
     int  (*extcode)		/* Called when unknown code received */
 		(fsm *, int, int, u_char *, int);
-    char *proto_name;		/* String name for protocol (for messages) */
+    const char *proto_name;	/* String name for protocol (for messages) */
 } fsm_callbacks;
 
 
@@ -165,7 +165,7 @@ void fsm_init(fsm *f);
 void fsm_lowerup(fsm *f);
 void fsm_lowerdown(fsm *f);
 void fsm_open(fsm *f);
-void fsm_close(fsm *f, char *reason);
+void fsm_close(fsm *f, const char *reason);
 void fsm_input(fsm *f, u_char *inpacket, int l);
 void fsm_protreject(fsm *f);
 void fsm_sdata(fsm *f, u_char code, u_char id, u_char *data, int datalen);
diff --git a/src/include/netif/ppp/lcp.h b/src/include/netif/ppp/lcp.h
index 8162e257..d7fa7c46 100644
--- a/src/include/netif/ppp/lcp.h
+++ b/src/include/netif/ppp/lcp.h
@@ -159,7 +159,7 @@ typedef struct lcp_options {
 } lcp_options;
 
 void lcp_open(ppp_pcb *pcb);
-void lcp_close(ppp_pcb *pcb, char *reason);
+void lcp_close(ppp_pcb *pcb, const char *reason);
 void lcp_lowerup(ppp_pcb *pcb);
 void lcp_lowerdown(ppp_pcb *pcb);
 void lcp_sprotrej(ppp_pcb *pcb, u_char *p, int len);    /* send protocol reject */
diff --git a/src/include/netif/ppp/ppp.h b/src/include/netif/ppp/ppp.h
index 97ab3cde..49a45867 100644
--- a/src/include/netif/ppp/ppp.h
+++ b/src/include/netif/ppp/ppp.h
@@ -53,6 +53,10 @@
 #define PPP_OPTIONS         0
 #endif
 
+#ifndef PPP_NOTIFY
+#define PPP_NOTIFY          0
+#endif
+
 #ifndef PPP_REMOTENAME
 #define PPP_REMOTENAME      0
 #endif
@@ -69,10 +73,6 @@
 #define PPP_MAXCONNECT      0
 #endif
 
-#ifndef DEMAND_SUPPORT
-#define DEMAND_SUPPORT      0
-#endif
-
 #ifndef PPP_ALLOWED_ADDRS
 #define PPP_ALLOWED_ADDRS   0
 #endif
diff --git a/src/include/netif/ppp/ppp_impl.h b/src/include/netif/ppp/ppp_impl.h
index 595ba3a6..1030eb85 100644
--- a/src/include/netif/ppp/ppp_impl.h
+++ b/src/include/netif/ppp/ppp_impl.h
@@ -277,11 +277,11 @@ struct protent {
     /* Open the protocol */
     void (*open) (ppp_pcb *pcb);
     /* Close the protocol */
-    void (*close) (ppp_pcb *pcb, char *reason);
+    void (*close) (ppp_pcb *pcb, const char *reason);
 #if PRINTPKT_SUPPORT
     /* Print a packet in readable form */
     int  (*printpkt) (u_char *pkt, int len,
-			  void (*printer) (void *, char *, ...),
+			  void (*printer) (void *, const char *, ...),
 			  void *arg);
 #endif /* PRINTPKT_SUPPORT */
     /* FIXME: data input is only used by CCP, which is not supported at this time,
@@ -291,8 +291,8 @@ struct protent {
     void (*datainput) (ppp_pcb *pcb, u_char *pkt, int len);
     u8_t enabled_flag;		/* 0 if protocol is disabled */
 #if PRINTPKT_SUPPORT
-    char *name;			/* Text name of protocol */
-    char *data_name;		/* Text name of corresponding data protocol */
+    const char *name;		/* Text name of protocol */
+    const char *data_name;	/* Text name of corresponding data protocol */
 #endif /* PRINTPKT_SUPPORT */
 #if PPP_OPTIONS
     option_t *options;		/* List of command-line options */
@@ -552,17 +552,17 @@ int  str_to_epdisc (struct epdisc *, char *); /* endpt disc. from str */
 #endif
 
 /* Procedures exported from utils.c. */
-void ppp_print_string(char *p, int len, void (*printer) (void *, char *, ...), void *arg);   /* Format a string for output */
-int ppp_slprintf(char *buf, int buflen, char *fmt, ...);            /* sprintf++ */
-int ppp_vslprintf(char *buf, int buflen, char *fmt, va_list args);  /* vsprintf++ */
+void ppp_print_string(char *p, int len, void (*printer) (void *, const char *, ...), void *arg);   /* Format a string for output */
+int ppp_slprintf(char *buf, int buflen, const char *fmt, ...);            /* sprintf++ */
+int ppp_vslprintf(char *buf, int buflen, const char *fmt, va_list args);  /* vsprintf++ */
 size_t ppp_strlcpy(char *dest, const char *src, size_t len);        /* safe strcpy */
 size_t ppp_strlcat(char *dest, const char *src, size_t len);        /* safe strncpy */
-void ppp_dbglog(char *fmt, ...);    /* log a debug message */
-void ppp_info(char *fmt, ...);      /* log an informational message */
-void ppp_notice(char *fmt, ...);    /* log a notice-level message */
-void ppp_warn(char *fmt, ...);      /* log a warning message */
-void ppp_error(char *fmt, ...);     /* log an error message */
-void ppp_fatal(char *fmt, ...);     /* log an error message and die(1) */
+void ppp_dbglog(const char *fmt, ...);    /* log a debug message */
+void ppp_info(const char *fmt, ...);      /* log an informational message */
+void ppp_notice(const char *fmt, ...);    /* log a notice-level message */
+void ppp_warn(const char *fmt, ...);      /* log a warning message */
+void ppp_error(const char *fmt, ...);     /* log an error message */
+void ppp_fatal(const char *fmt, ...);     /* log an error message and die(1) */
 #if PRINTPKT_SUPPORT
 void ppp_dump_packet(const char *tag, unsigned char *p, int len);
                                 /* dump packet to debug log if interesting */
diff --git a/src/netif/ppp/auth.c b/src/netif/ppp/auth.c
index 830e21fd..bc16270a 100644
--- a/src/netif/ppp/auth.c
+++ b/src/netif/ppp/auth.c
@@ -1037,6 +1037,8 @@ void auth_peer_success(ppp_pcb *pcb, int protocol, int prot_flavor, char *name,
 	    bit |= CHAP_MS2_PEER;
 	    break;
 #endif /* MSCHAP_SUPPORT */
+	default:
+	    break;
 	}
 	break;
 #endif /* CHAP_SUPPORT */
@@ -1123,6 +1125,8 @@ void auth_withpeer_success(ppp_pcb *pcb, int protocol, int prot_flavor) {
 	    bit |= CHAP_MS2_WITHPEER;
 	    break;
 #endif /* MSCHAP_SUPPORT */
+	default:
+	    break;
 	}
 	break;
 #endif /* CHAP_SUPPORT */
diff --git a/src/netif/ppp/ccp.c b/src/netif/ppp/ccp.c
index 860374bc..0af35482 100644
--- a/src/netif/ppp/ccp.c
+++ b/src/netif/ppp/ccp.c
@@ -168,7 +168,7 @@ static option_t ccp_option_list[] = {
  */
 static void ccp_init (int unit);
 static void ccp_open (int unit);
-static void ccp_close (int unit, char *);
+static void ccp_close (int unit, const char *);
 static void ccp_lowerup (int unit);
 static void ccp_lowerdown (int);
 static void ccp_input (int unit, u_char *pkt, int len);
@@ -421,7 +421,7 @@ ccp_open(unit)
 static void
 ccp_close(unit, reason)
     int unit;
-    char *reason;
+    const char *reason;
 {
     ccp_flags_set(unit, 0, 0);
     fsm_close(&ccp_fsm[unit], reason);
diff --git a/src/netif/ppp/chap-md5.c b/src/netif/ppp/chap-md5.c
index f7965490..22fdc81d 100644
--- a/src/netif/ppp/chap-md5.c
+++ b/src/netif/ppp/chap-md5.c
@@ -95,12 +95,12 @@ static int chap_md5_verify_response(int id, char *name,
 
 static void chap_md5_make_response(unsigned char *response, int id, char *our_name,
 		       unsigned char *challenge, char *secret, int secret_len,
-		       unsigned char *private) {
+		       unsigned char *private_) {
 	md5_context ctx;
 	unsigned char idbyte = id;
 	int challenge_len = *challenge++;
 	LWIP_UNUSED_ARG(our_name);
-	LWIP_UNUSED_ARG(private);
+	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 d4dbd7cc..8d339506 100644
--- a/src/netif/ppp/chap-new.c
+++ b/src/netif/ppp/chap-new.c
@@ -102,7 +102,7 @@ static void chap_protrej(ppp_pcb *pcb);
 static void chap_input(ppp_pcb *pcb, unsigned char *pkt, int pktlen);
 #if PRINTPKT_SUPPORT
 static int chap_print_pkt(unsigned char *p, int plen,
-		void (*printer) (void *, char *, ...), void *arg);
+		void (*printer) (void *, const char *, ...), void *arg);
 #endif /* PRINTPKT_SUPPORT */
 
 /* List of digest types that we know about */
@@ -339,7 +339,7 @@ static void  chap_handle_response(ppp_pcb *pcb, int id,
 		return;
 	}
 
-	outp = p->payload;
+	outp = (unsigned char *)p->payload;
 	MAKEHEADER(outp, PPP_CHAP);
 
 	outp[0] = (pcb->chap_server.flags & AUTH_FAILED)? CHAP_FAILURE: CHAP_SUCCESS;
@@ -464,7 +464,7 @@ static void chap_respond(ppp_pcb *pcb, int id,
 		ppp_warn("No CHAP secret found for authenticating us to %q", rname);
 	}
 
-	outp = p->payload;
+	outp = (u_char*)p->payload;
 	MAKEHEADER(outp, PPP_CHAP);
 	outp += CHAP_HDRLEN;
 
@@ -551,6 +551,8 @@ static void chap_input(ppp_pcb *pcb, unsigned char *pkt, int pktlen) {
 	case CHAP_SUCCESS:
 		chap_handle_status(pcb, code, id, pkt, len);
 		break;
+	default:
+		break;
 	}
 }
 
@@ -577,12 +579,12 @@ static void chap_protrej(ppp_pcb *pcb) {
 /*
  * chap_print_pkt - print the contents of a CHAP packet.
  */
-static char *chap_code_names[] = {
+static const char *chap_code_names[] = {
 	"Challenge", "Response", "Success", "Failure"
 };
 
 static int chap_print_pkt(unsigned char *p, int plen,
-	       void (*printer) (void *, char *, ...), void *arg) {
+	       void (*printer) (void *, const char *, ...), void *arg) {
 	int code, id, len;
 	int clen, nlen;
 	unsigned char x;
diff --git a/src/netif/ppp/chap_ms.c b/src/netif/ppp/chap_ms.c
index 7935de65..e921b1e5 100644
--- a/src/netif/ppp/chap_ms.c
+++ b/src/netif/ppp/chap_ms.c
@@ -328,10 +328,10 @@ 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) {
+		     unsigned char *private_) {
 	LWIP_UNUSED_ARG(id);
 	LWIP_UNUSED_ARG(our_name);
-	LWIP_UNUSED_ARG(private);
+	LWIP_UNUSED_ARG(private_);
 	challenge++;	/* skip length, should be 8 */
 	*response++ = MS_CHAP_RESPONSE_LEN;
 	ChapMS(challenge, secret, secret_len, response);
@@ -339,7 +339,7 @@ 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) {
+		      unsigned char *private_) {
 	LWIP_UNUSED_ARG(id);
 	challenge++;	/* skip length, should be 16 */
 	*response++ = MS_CHAP2_RESPONSE_LEN;
@@ -349,11 +349,11 @@ static void chapms2_make_response(unsigned char *response, int id, char *our_nam
 #else
 		NULL,
 #endif
-		our_name, secret, secret_len, response, private,
+		our_name, secret, secret_len, response, private_,
 		MS_CHAP2_AUTHENTICATEE);
 }
 
-static int chapms2_check_success(unsigned char *msg, int len, unsigned char *private) {
+static int chapms2_check_success(unsigned char *msg, int len, unsigned char *private_) {
 	if ((len < MS_AUTH_RESPONSE_LENGTH + 2) ||
 	    strncmp((char *)msg, "S=", 2) != 0) {
 		/* Packet does not start with "S=" */
@@ -363,7 +363,7 @@ static int chapms2_check_success(unsigned char *msg, int len, unsigned char *pri
 	msg += 2;
 	len -= 2;
 	if (len < MS_AUTH_RESPONSE_LENGTH
-	    || memcmp(msg, private, MS_AUTH_RESPONSE_LENGTH)) {
+	    || memcmp(msg, private_, MS_AUTH_RESPONSE_LENGTH)) {
 		/* Authenticator Response did not match expected. */
 		ppp_error("MS-CHAPv2 mutual authentication failed.");
 		return 0;
@@ -383,7 +383,8 @@ static int chapms2_check_success(unsigned char *msg, int len, unsigned char *pri
 
 static void chapms_handle_failure(unsigned char *inp, int len) {
 	int err;
-	char *p, msg[64];
+	const char *p;
+	char msg[64];
 
 	/* We want a null-terminated string for strxxx(). */
 	len = LWIP_MIN(len, 63);
diff --git a/src/netif/ppp/eap.c b/src/netif/ppp/eap.c
index 2bb0c5e8..1c7013f5 100644
--- a/src/netif/ppp/eap.c
+++ b/src/netif/ppp/eap.c
@@ -108,7 +108,7 @@ static void eap_lowerup(ppp_pcb *pcb);
 static void eap_lowerdown(ppp_pcb *pcb);
 #if PRINTPKT_SUPPORT
 static int  eap_printpkt(u_char *inp, int inlen,
-    void (*)(void *arg, char *fmt, ...), void *arg);
+    void (*)(void *arg, const char *fmt, ...), void *arg);
 #endif /* PRINTPKT_SUPPORT */
 
 const struct protent eap_protent = {
@@ -187,9 +187,7 @@ static void eap_server_timeout(void *arg);
 /*
  * Convert EAP state code to printable string for debug.
  */
-static const char *
-eap_state_name(esc)
-enum eap_state_code esc;
+static const char * eap_state_name(enum eap_state_code esc)
 {
 	static const char *state_names[] = { EAP_STATES };
 
@@ -266,7 +264,7 @@ static void eap_send_failure(ppp_pcb *pcb) {
 		return;
 	}
 
-	outp = p->payload;
+	outp = (u_char*)p->payload;
 
 	MAKEHEADER(outp, PPP_EAP);
 
@@ -297,7 +295,7 @@ static void eap_send_success(ppp_pcb *pcb) {
 		return;
 	}
 
-	outp = p->payload;
+	outp = (u_char*)p->payload;
     
 	MAKEHEADER(outp, PPP_EAP);
 
@@ -649,7 +647,7 @@ static void eap_send_request(ppp_pcb *pcb) {
 	u_char *ptr;
 	int outlen;
 	int challen;
-	char *str;
+	const char *str;
 #ifdef USE_SRP
 	struct t_server *ts;
 	u_char clear[8], cipher[8], dig[SHA_DIGESTSIZE], *optr, *cp;
@@ -694,7 +692,7 @@ static void eap_send_request(ppp_pcb *pcb) {
 		return;
 	}
 
-	outp = p->payload;
+	outp = (u_char*)p->payload;
     
 	MAKEHEADER(outp, PPP_EAP);
 
@@ -1056,7 +1054,7 @@ static void eap_send_response(ppp_pcb *pcb, u_char id, u_char typenum, u_char *s
 		return;
 	}
 
-	outp = p->payload;
+	outp = (u_char*)p->payload;
 
 	MAKEHEADER(outp, PPP_EAP);
 
@@ -1090,7 +1088,7 @@ static void eap_chap_response(ppp_pcb *pcb, u_char id, u_char *hash, char *name,
 		return;
 	}
 
-	outp = p->payload;
+	outp = (u_char*)p->payload;
     
 	MAKEHEADER(outp, PPP_EAP);
 
@@ -1208,7 +1206,7 @@ static void eap_send_nak(ppp_pcb *pcb, u_char id, u_char type) {
 		return;
 	}
 
-	outp = p->payload;
+	outp = (u_char*)p->payload;
 
 	MAKEHEADER(outp, PPP_EAP);
 
@@ -1791,7 +1789,7 @@ static void eap_response(ppp_pcb *pcb, u_char *inp, int id, int len) {
 #endif /* PPP_REMOTENAME */
 		    )
 			free(pcb->eap.es_server.ea_peer);
-		pcb->eap.es_server.ea_peer = malloc(len + 1);
+		pcb->eap.es_server.ea_peer = (char*)malloc(len + 1);
 		if (pcb->eap.es_server.ea_peer == NULL) {
 			pcb->eap.es_server.ea_peerlen = 0;
 			eap_figure_next_state(pcb, 1);
@@ -2151,11 +2149,11 @@ static void eap_input(ppp_pcb *pcb, u_char *inp, int inlen) {
 /*
  * eap_printpkt - print the contents of an EAP packet.
  */
-static char *eap_codenames[] = {
+static const char *eap_codenames[] = {
 	"Request", "Response", "Success", "Failure"
 };
 
-static char *eap_typenames[] = {
+static const char *eap_typenames[] = {
 	"Identity", "Notification", "Nak", "MD5-Challenge",
 	"OTP", "Generic-Token", NULL, NULL,
 	"RSA", "DSS", "KEA", "KEA-Validate",
@@ -2163,7 +2161,7 @@ static char *eap_typenames[] = {
 	"Cisco", "Nokia", "SRP"
 };
 
-static int eap_printpkt(u_char *inp, int inlen, void (*printer) (void *, char *, ...), void *arg) {
+static int eap_printpkt(u_char *inp, int inlen, void (*printer) (void *, const char *, ...), void *arg) {
 	int code, id, len, rtype, vallen;
 	u_char *pstart;
 	u32_t uval;
@@ -2316,8 +2314,12 @@ static int eap_printpkt(u_char *inp, int inlen, void (*printer) (void *, char *,
 				INCPTR(len, inp);
 				len = 0;
 				break;
+			default:
+				break;
 			}
 			break;
+		default:
+			break;
 		}
 		break;
 
@@ -2421,13 +2423,18 @@ static int eap_printpkt(u_char *inp, int inlen, void (*printer) (void *, char *,
 				INCPTR(vallen, inp);
 				len -= vallen;
 				break;
+			default:
+				break;
 			}
 			break;
+		default:
+			break;
 		}
 		break;
 
 	case EAP_SUCCESS:	/* No payload expected for these! */
 	case EAP_FAILURE:
+	default:
 		break;
 
 	truncated:
diff --git a/src/netif/ppp/fsm.c b/src/netif/ppp/fsm.c
index 79077444..71f2c959 100644
--- a/src/netif/ppp/fsm.c
+++ b/src/netif/ppp/fsm.c
@@ -186,6 +186,8 @@ void fsm_open(fsm *f) {
 	    fsm_lowerup(f);
 	}
 	break;
+    default:
+	break;
     }
 }
 
@@ -232,7 +234,7 @@ static void terminate_layer(fsm *f, int nextstate) {
  * Cancel timeouts and either initiate close or possibly go directly to
  * the PPP_FSM_CLOSED state.
  */
-void fsm_close(fsm *f, char *reason) {
+void fsm_close(fsm *f, const char *reason) {
     f->term_reason = reason;
     f->term_reason_len = (reason == NULL? 0: LWIP_MIN(strlen(reason), 0xFF) );
     switch( f->state ){
@@ -252,6 +254,8 @@ void fsm_close(fsm *f, char *reason) {
     case PPP_FSM_OPENED:
 	terminate_layer(f, PPP_FSM_CLOSING);
 	break;
+    default:
+	break;
     }
 }
 
@@ -410,6 +414,8 @@ static void fsm_rconfreq(fsm *f, u_char id, u_char *inp, int len) {
 	fsm_sconfreq(f, 0);		/* Send initial Configure-Request */
 	f->state = PPP_FSM_REQSENT;
 	break;
+    default:
+	break;
     }
 
     /*
@@ -497,6 +503,8 @@ static void fsm_rconfack(fsm *f, int id, u_char *inp, int len) {
 	fsm_sconfreq(f, 0);		/* Send initial Configure-Request */
 	f->state = PPP_FSM_REQSENT;
 	break;
+    default:
+	break;
     }
 }
 
@@ -560,6 +568,8 @@ static void fsm_rconfnakrej(fsm *f, int code, int id, u_char *inp, int len) {
 	fsm_sconfreq(f, 0);		/* Send initial Configure-Request */
 	f->state = PPP_FSM_REQSENT;
 	break;
+    default:
+	break;
     }
 }
 
@@ -587,6 +597,8 @@ static void fsm_rtermreq(fsm *f, int id, u_char *p, int len) {
 	    (*f->callbacks->down)(f);	/* Inform upper layers */
 	TIMEOUT(fsm_timeout, f, pcb->settings.fsm_timeout_time);
 	break;
+    default:
+	break;
     }
 
     fsm_sdata(f, TERMACK, id, NULL, 0);
@@ -621,6 +633,8 @@ static void fsm_rtermack(fsm *f) {
 	fsm_sconfreq(f, 0);
 	f->state = PPP_FSM_REQSENT;
 	break;
+    default:
+	break;
     }
 }
 
@@ -730,7 +744,7 @@ static void fsm_sconfreq(fsm *f, int retransmit) {
     }
 
     /* send the request to our peer */
-    outp = p->payload;
+    outp = (u_char*)p->payload;
     MAKEHEADER(outp, f->protocol);
     PUTCHAR(CONFREQ, outp);
     PUTCHAR(f->reqid, outp);
@@ -771,7 +785,7 @@ void fsm_sdata(fsm *f, u_char code, u_char id, u_char *data, int datalen) {
         return;
     }
 
-    outp = p->payload;
+    outp = (u_char*)p->payload;
 /*  if (datalen && data != outp + PPP_HDRLEN + HEADERLEN)  -- was only for fsm_sconfreq() */
 	MEMCPY(outp + PPP_HDRLEN + HEADERLEN, data, datalen);
     MAKEHEADER(outp, f->protocol);
diff --git a/src/netif/ppp/ipcp.c b/src/netif/ppp/ipcp.c
index d6ef0fdc..b594d885 100644
--- a/src/netif/ppp/ipcp.c
+++ b/src/netif/ppp/ipcp.c
@@ -258,14 +258,14 @@ static option_t ipcp_option_list[] = {
  */
 static void ipcp_init(ppp_pcb *pcb);
 static void ipcp_open(ppp_pcb *pcb);
-static void ipcp_close(ppp_pcb *pcb, char *reason);
+static void ipcp_close(ppp_pcb *pcb, const char *reason);
 static void ipcp_lowerup(ppp_pcb *pcb);
 static void ipcp_lowerdown(ppp_pcb *pcb);
 static void ipcp_input(ppp_pcb *pcb, u_char *p, int len);
 static void ipcp_protrej(ppp_pcb *pcb);
 #if PRINTPKT_SUPPORT
 static int ipcp_printpkt(u_char *p, int plen,
-		void (*printer) (void *, char *, ...), void *arg);
+		void (*printer) (void *, const char *, ...), void *arg);
 #endif /* PRINTPKT_SUPPORT */
 #if PPP_OPTIONS
 static void ip_check_options (void);
@@ -657,7 +657,7 @@ static void ipcp_open(ppp_pcb *pcb) {
 /*
  * ipcp_close - Take IPCP down.
  */
-static void ipcp_close(ppp_pcb *pcb, char *reason) {
+static void ipcp_close(ppp_pcb *pcb, const char *reason) {
     fsm *f = &pcb->ipcp_fsm;
     fsm_close(f, reason);
 }
@@ -1031,10 +1031,10 @@ static int ipcp_nakci(fsm *f, u_char *p, int len, int treat_as_reject) {
     u_short cishort;
     u32_t ciaddr1, ciaddr2, l, cidnsaddr;
     ipcp_options no;		/* options we've seen Naks for */
-    ipcp_options try;		/* options to request next time */
+    ipcp_options try_;		/* options to request next time */
 
     BZERO(&no, sizeof(no));
-    try = *go;
+    try_ = *go;
 
     /*
      * Any Nak'd CIs must be in exactly the same order that we sent.
@@ -1100,15 +1100,15 @@ static int ipcp_nakci(fsm *f, u_char *p, int len, int treat_as_reject) {
      */
     NAKCIADDRS(CI_ADDRS, !go->neg_addr && go->old_addrs,
 	       if (treat_as_reject) {
-		   try.old_addrs = 0;
+		   try_.old_addrs = 0;
 	       } else {
 		   if (go->accept_local && ciaddr1) {
 		       /* take his idea of our address */
-		       try.ouraddr = ciaddr1;
+		       try_.ouraddr = ciaddr1;
 		   }
 		   if (go->accept_remote && ciaddr2) {
 		       /* take his idea of his address */
-		       try.hisaddr = ciaddr2;
+		       try_.hisaddr = ciaddr2;
 		   }
 	       }
 	);
@@ -1121,52 +1121,52 @@ static int ipcp_nakci(fsm *f, u_char *p, int len, int treat_as_reject) {
      */
     NAKCIVJ(CI_COMPRESSTYPE, neg_vj,
 	    if (treat_as_reject) {
-		try.neg_vj = 0;
+		try_.neg_vj = 0;
 	    } else if (cilen == CILEN_VJ) {
 		GETCHAR(cimaxslotindex, p);
 		GETCHAR(cicflag, p);
 		if (cishort == IPCP_VJ_COMP) {
-		    try.old_vj = 0;
+		    try_.old_vj = 0;
 		    if (cimaxslotindex < go->maxslotindex)
-			try.maxslotindex = cimaxslotindex;
+			try_.maxslotindex = cimaxslotindex;
 		    if (!cicflag)
-			try.cflag = 0;
+			try_.cflag = 0;
 		} else {
-		    try.neg_vj = 0;
+		    try_.neg_vj = 0;
 		}
 	    } else {
 		if (cishort == IPCP_VJ_COMP || cishort == IPCP_VJ_COMP_OLD) {
-		    try.old_vj = 1;
-		    try.vj_protocol = cishort;
+		    try_.old_vj = 1;
+		    try_.vj_protocol = cishort;
 		} else {
-		    try.neg_vj = 0;
+		    try_.neg_vj = 0;
 		}
 	    }
 	    );
 
     NAKCIADDR(CI_ADDR, neg_addr,
 	      if (treat_as_reject) {
-		  try.neg_addr = 0;
-		  try.old_addrs = 0;
+		  try_.neg_addr = 0;
+		  try_.old_addrs = 0;
 	      } else if (go->accept_local && ciaddr1) {
 		  /* take his idea of our address */
-		  try.ouraddr = ciaddr1;
+		  try_.ouraddr = ciaddr1;
 	      }
 	      );
 
     NAKCIDNS(CI_MS_DNS1, req_dns1,
 	     if (treat_as_reject) {
-		 try.req_dns1 = 0;
+		 try_.req_dns1 = 0;
 	     } else {
-		 try.dnsaddr[0] = cidnsaddr;
+		 try_.dnsaddr[0] = cidnsaddr;
 	     }
 	     );
 
     NAKCIDNS(CI_MS_DNS2, req_dns2,
 	     if (treat_as_reject) {
-		 try.req_dns2 = 0;
+		 try_.req_dns2 = 0;
 	     } else {
-		 try.dnsaddr[1] = cidnsaddr;
+		 try_.dnsaddr[1] = cidnsaddr;
 	     }
 	     );
 
@@ -1196,43 +1196,43 @@ static int ipcp_nakci(fsm *f, u_char *p, int len, int treat_as_reject) {
 	    if ((!go->neg_addr && go->old_addrs) || no.old_addrs
 		|| cilen != CILEN_ADDRS)
 		goto bad;
-	    try.neg_addr = 0;
+	    try_.neg_addr = 0;
 	    GETLONG(l, p);
 	    ciaddr1 = htonl(l);
 	    if (ciaddr1 && go->accept_local)
-		try.ouraddr = ciaddr1;
+		try_.ouraddr = ciaddr1;
 	    GETLONG(l, p);
 	    ciaddr2 = htonl(l);
 	    if (ciaddr2 && go->accept_remote)
-		try.hisaddr = ciaddr2;
+		try_.hisaddr = ciaddr2;
 	    no.old_addrs = 1;
 	    break;
 	case CI_ADDR:
 	    if (go->neg_addr || no.neg_addr || cilen != CILEN_ADDR)
 		goto bad;
-	    try.old_addrs = 0;
+	    try_.old_addrs = 0;
 	    GETLONG(l, p);
 	    ciaddr1 = htonl(l);
 	    if (ciaddr1 && go->accept_local)
-		try.ouraddr = ciaddr1;
-	    if (try.ouraddr != 0)
-		try.neg_addr = 1;
+		try_.ouraddr = ciaddr1;
+	    if (try_.ouraddr != 0)
+		try_.neg_addr = 1;
 	    no.neg_addr = 1;
 	    break;
 	case CI_MS_DNS1:
 	    if (go->req_dns1 || no.req_dns1 || cilen != CILEN_ADDR)
 		goto bad;
 	    GETLONG(l, p);
-	    try.dnsaddr[0] = htonl(l);
-	    try.req_dns1 = 1;
+	    try_.dnsaddr[0] = htonl(l);
+	    try_.req_dns1 = 1;
 	    no.req_dns1 = 1;
 	    break;
 	case CI_MS_DNS2:
 	    if (go->req_dns2 || no.req_dns2 || cilen != CILEN_ADDR)
 		goto bad;
 	    GETLONG(l, p);
-	    try.dnsaddr[1] = htonl(l);
-	    try.req_dns2 = 1;
+	    try_.dnsaddr[1] = htonl(l);
+	    try_.req_dns2 = 1;
 	    no.req_dns2 = 1;
 	    break;
 	case CI_MS_WINS1:
@@ -1242,7 +1242,9 @@ static int ipcp_nakci(fsm *f, u_char *p, int len, int treat_as_reject) {
 	    GETLONG(l, p);
 	    ciaddr1 = htonl(l);
 	    if (ciaddr1)
-		try.winsaddr[citype == CI_MS_WINS2] = ciaddr1;
+		try_.winsaddr[citype == CI_MS_WINS2] = ciaddr1;
+	    break;
+	default:
 	    break;
 	}
 	p = next;
@@ -1253,7 +1255,7 @@ static int ipcp_nakci(fsm *f, u_char *p, int len, int treat_as_reject) {
      * If there are any remaining options, we ignore them.
      */
     if (f->state != PPP_FSM_OPENED)
-	*go = try;
+	*go = try_;
 
     return 1;
 
@@ -1273,9 +1275,9 @@ static int ipcp_rejci(fsm *f, u_char *p, int len) {
     u_char cimaxslotindex, ciflag, cilen;
     u_short cishort;
     u32_t cilong;
-    ipcp_options try;		/* options to request next time */
+    ipcp_options try_;		/* options to request next time */
 
-    try = *go;
+    try_ = *go;
     /*
      * Any Rejected CIs must be in exactly the same order that we sent.
      * Check packet length and CI length at each step.
@@ -1299,7 +1301,7 @@ static int ipcp_rejci(fsm *f, u_char *p, int len) {
 	/* Check rejected value. */ \
 	if (cilong != val2) \
 	    goto bad; \
-	try.old_addrs = 0; \
+	try_.old_addrs = 0; \
     }
 
 #define REJCIVJ(opt, neg, val, old, maxslot, cflag) \
@@ -1321,7 +1323,7 @@ static int ipcp_rejci(fsm *f, u_char *p, int len) {
 	   if (ciflag != cflag) \
 	     goto bad; \
         } \
-	try.neg = 0; \
+	try_.neg = 0; \
      }
 
 #define REJCIADDR(opt, neg, val) \
@@ -1337,7 +1339,7 @@ static int ipcp_rejci(fsm *f, u_char *p, int len) {
 	/* Check rejected value. */ \
 	if (cilong != val) \
 	    goto bad; \
-	try.neg = 0; \
+	try_.neg = 0; \
     }
 
 #define REJCIDNS(opt, neg, dnsaddr) \
@@ -1353,7 +1355,7 @@ static int ipcp_rejci(fsm *f, u_char *p, int len) {
 	/* Check rejected value. */ \
 	if (cilong != dnsaddr) \
 	    goto bad; \
-	try.neg = 0; \
+	try_.neg = 0; \
     }
 
 #define REJCIWINS(opt, addr) \
@@ -1369,7 +1371,7 @@ static int ipcp_rejci(fsm *f, u_char *p, int len) {
 	/* Check rejected value. */ \
 	if (cilong != addr) \
 	    goto bad; \
-	try.winsaddr[opt == CI_MS_WINS2] = 0; \
+	try_.winsaddr[opt == CI_MS_WINS2] = 0; \
     }
 
     REJCIADDRS(CI_ADDRS, !go->neg_addr && go->old_addrs,
@@ -1397,7 +1399,7 @@ static int ipcp_rejci(fsm *f, u_char *p, int len) {
      * Now we can update state.
      */
     if (f->state != PPP_FSM_OPENED)
-	*go = try;
+	*go = try_;
     return 1;
 
 bad:
@@ -2093,13 +2095,13 @@ create_resolv(peerdns1, peerdns2)
 /*
  * ipcp_printpkt - print the contents of an IPCP packet.
  */
-static char *ipcp_codenames[] = {
+static const char *ipcp_codenames[] = {
     "ConfReq", "ConfAck", "ConfNak", "ConfRej",
     "TermReq", "TermAck", "CodeRej"
 };
 
 static int ipcp_printpkt(u_char *p, int plen,
-		void (*printer) (void *, char *, ...), void *arg) {
+		void (*printer) (void *, const char *, ...), void *arg) {
     int code, id, len, olen;
     u_char *pstart, *optend;
     u_short cishort;
@@ -2183,6 +2185,8 @@ static int ipcp_printpkt(u_char *p, int plen,
 		GETLONG(cilong, p);
 		printer(arg, "ms-wins %I", htonl(cilong));
 		break;
+	    default:
+		break;
 	    }
 	    while (p < optend) {
 		GETCHAR(code, p);
@@ -2201,6 +2205,8 @@ static int ipcp_printpkt(u_char *p, int plen,
 	    len = 0;
 	}
 	break;
+    default:
+	break;
     }
 
     /* print the rest of the bytes in the packet */
diff --git a/src/netif/ppp/ipv6cp.c b/src/netif/ppp/ipv6cp.c
index bb472445..32964bc8 100644
--- a/src/netif/ppp/ipv6cp.c
+++ b/src/netif/ppp/ipv6cp.c
@@ -255,7 +255,7 @@ static option_t ipv6cp_option_list[] = {
  */
 static void ipv6cp_init(ppp_pcb *pcb);
 static void ipv6cp_open(ppp_pcb *pcb);
-static void ipv6cp_close(ppp_pcb *pcb, char *reason);
+static void ipv6cp_close(ppp_pcb *pcb, const char *reason);
 static void ipv6cp_lowerup(ppp_pcb *pcb);
 static void ipv6cp_lowerdown(ppp_pcb *pcb);
 static void ipv6cp_input(ppp_pcb *pcb, u_char *p, int len);
@@ -462,7 +462,7 @@ static void ipv6cp_open(ppp_pcb *pcb) {
 /*
  * ipv6cp_close - Take IPV6CP down.
  */
-static void ipv6cp_close(ppp_pcb *pcb, char *reason) {
+static void ipv6cp_close(ppp_pcb *pcb, const char *reason) {
     fsm_close(&pcb->ipv6cp_fsm, reason);
 }
 
diff --git a/src/netif/ppp/lcp.c b/src/netif/ppp/lcp.c
index bd616c40..5aa99da7 100644
--- a/src/netif/ppp/lcp.c
+++ b/src/netif/ppp/lcp.c
@@ -269,7 +269,7 @@ static void lcp_input(ppp_pcb *pcb, u_char *p, int len);
 static void lcp_protrej(ppp_pcb *pcb);
 #if PRINTPKT_SUPPORT
 static int lcp_printpkt(u_char *p, int plen,
-		void (*printer) (void *, char *, ...), void *arg);
+		void (*printer) (void *, const char *, ...), void *arg);
 #endif /* PRINTPKT_SUPPORT */
 
 const struct protent lcp_protent = {
@@ -436,7 +436,7 @@ void lcp_open(ppp_pcb *pcb) {
 /*
  * lcp_close - Take LCP down.
  */
-void lcp_close(ppp_pcb *pcb, char *reason) {
+void lcp_close(ppp_pcb *pcb, const char *reason) {
     fsm *f = &pcb->lcp_fsm;
     int oldstate;
 
@@ -525,7 +525,7 @@ void lcp_lowerdown(ppp_pcb *pcb) {
  * lcp_delayed_up - Bring the lower layer up now.
  */
 static void lcp_delayed_up(void *arg) {
-    fsm *f = arg;
+    fsm *f = (fsm*)arg;
 
     if (f->flags & DELAYED_UP) {
 	f->flags &= ~DELAYED_UP;
@@ -1487,6 +1487,8 @@ static int lcp_nakci(fsm *f, u_char *p, int len, int treat_as_reject) {
 	    if (go->neg_endpoint || no.neg_endpoint || cilen < CILEN_CHAR)
 		goto bad;
 	    break;
+	default:
+	    break;
 	}
 	p = next;
     }
@@ -1790,7 +1792,7 @@ static int lcp_reqci(fsm *f, u_char *inp, int *lenp, int reject_if_disagree) {
         return 0;
     }
 
-    nakoutp = nakp->payload;
+    nakoutp = (u_char*)nakp->payload;
     rejp = inp;
     while (l) {
 	orc = CONFACK;			/* Assume success */
@@ -2213,6 +2215,8 @@ endswitch:
     case CONFREJ:
 	*lenp = rejp - inp;
 	break;
+    default:
+	break;
     }
 
     pbuf_free(nakp);
@@ -2311,7 +2315,7 @@ static void lcp_finished(fsm *f) {
 /*
  * lcp_printpkt - print the contents of an LCP packet.
  */
-static char *lcp_codenames[] = {
+static const char *lcp_codenames[] = {
     "ConfReq", "ConfAck", "ConfNak", "ConfRej",
     "TermReq", "TermAck", "CodeRej", "ProtRej",
     "EchoReq", "EchoRep", "DiscReq", "Ident",
@@ -2319,7 +2323,7 @@ static char *lcp_codenames[] = {
 };
 
 static int lcp_printpkt(u_char *p, int plen,
-		void (*printer) (void *, char *, ...), void *arg) {
+		void (*printer) (void *, const char *, ...), void *arg) {
     int code, id, len, olen, i;
     u_char *pstart, *optend;
     u_short cishort;
@@ -2402,6 +2406,8 @@ static int lcp_printpkt(u_char *p, int plen,
 				++p;
 				break;
 #endif /* MSCHAP_SUPPORT */
+			    default:
+				break;
 			    }
 			}
 			break;
@@ -2497,6 +2503,8 @@ static int lcp_printpkt(u_char *p, int plen,
 		printer(arg, "endpoint");
 #endif
 		break;
+	    default:
+		break;
 	    }
 	    while (p < optend) {
 		GETCHAR(code, p);
@@ -2547,6 +2555,8 @@ static int lcp_printpkt(u_char *p, int plen,
 	    len = 0;
 	}
 	break;
+    default:
+	break;
     }
 
     /* print the rest of the bytes in the packet */
diff --git a/src/netif/ppp/magic.c b/src/netif/ppp/magic.c
index 86aef275..a6a55490 100644
--- a/src/netif/ppp/magic.c
+++ b/src/netif/ppp/magic.c
@@ -109,7 +109,7 @@ static long magic_randcount = 0;      /* Pseudo-random incrementer */
  *
  * Ref: Applied Cryptography 2nd Ed. by Bruce Schneier p. 427
  */
-void magic_churnrand(char *rand_data, u32_t rand_len) {
+static void magic_churnrand(char *rand_data, u32_t rand_len) {
   md5_context md5;
 
   /* LWIP_DEBUGF(LOG_INFO, ("magic_churnrand: %u@%P\n", rand_len, rand_data)); */
@@ -133,7 +133,7 @@ void magic_churnrand(char *rand_data, u32_t rand_len) {
 /*
  * Initialize the random number generator.
  */
-void magic_init() {
+void magic_init(void) {
   magic_churnrand(NULL, 0);
 }
 
@@ -183,7 +183,7 @@ void random_bytes(unsigned char *buf, u32_t buf_len) {
 /*
  * Return a new random number.
  */
-u32_t magic() {
+u32_t magic(void) {
   u32_t new_rand;
 
   random_bytes((unsigned char *)&new_rand, sizeof(new_rand));
diff --git a/src/netif/ppp/ppp.c b/src/netif/ppp/ppp.c
index d2cdf1f0..7693258d 100644
--- a/src/netif/ppp/ppp.c
+++ b/src/netif/ppp/ppp.c
@@ -674,7 +674,7 @@ void ppp_input(ppp_pcb *pcb, struct pbuf *pb) {
   protocol = (((u8_t *)pb->payload)[0] << 8) | ((u8_t*)pb->payload)[1];
 
 #if PRINTPKT_SUPPORT
-  ppp_dump_packet("rcvd", pb->payload, pb->len);
+  ppp_dump_packet("rcvd", (unsigned char *)pb->payload, pb->len);
 #endif /* PRINTPKT_SUPPORT */
 
   if(pbuf_header(pb, -(s16_t)sizeof(protocol))) {
@@ -774,7 +774,7 @@ void ppp_input(ppp_pcb *pcb, struct pbuf *pb) {
       for (i = 0; (protp = protocols[i]) != NULL; ++i) {
         if (protp->protocol == protocol && protp->enabled_flag) {
           pb = ppp_singlebuf(pb);
-          (*protp->input)(pcb, pb->payload, pb->len);
+          (*protp->input)(pcb, (u_char*)pb->payload, pb->len);
           goto out;
         }
 #if 0 /* UNUSED
@@ -807,7 +807,7 @@ void ppp_input(ppp_pcb *pcb, struct pbuf *pb) {
         LWIP_ASSERT("pbuf_header failed\n", 0);
         goto drop;
       }
-      lcp_sprotrej(pcb, pb->payload, pb->len);
+      lcp_sprotrej(pcb, (u_char*)pb->payload, pb->len);
     }
     break;
   }
@@ -948,7 +948,7 @@ pppos_put(ppp_pcb *pcb, struct pbuf *nb)
   int c;
 
   for(b = nb; b != NULL; b = b->next) {
-    c = sio_write(pcb->fd, b->payload, b->len);
+    c = sio_write(pcb->fd, (u8_t*)b->payload, b->len);
     if(c != b->len) {
       PPPDEBUG(LOG_WARNING,
                ("PPP pppos_put: incomplete sio_write(fd:%"SZT_F", len:%d, c: 0x%"X8_F") c = %d\n", (size_t)pcb->fd, b->len, c, c));
@@ -1187,7 +1187,9 @@ static err_t ppp_netif_output_over_serial(ppp_pcb *pcb, struct pbuf *pb, u_short
 static err_t ppp_netif_output_over_ethernet(ppp_pcb *pcb, struct pbuf *p, u_short protocol) {
   struct pbuf *pb;
   int i=0;
+#if LWIP_SNMP
   u16_t tot_len;
+#endif /* LWIP_SNMP */
   err_t err;
 
   /* @todo: try to use pbuf_header() here! */
@@ -1209,7 +1211,9 @@ static err_t ppp_netif_output_over_ethernet(ppp_pcb *pcb, struct pbuf *p, u_shor
   *((u_char*)pb->payload + i) = protocol & 0xFF;
 
   pbuf_chain(pb, p);
+#if LWIP_SNMP
   tot_len = pb->tot_len;
+#endif /* LWIP_SNMP */
 
   if( (err = pppoe_xmit(pcb->pppoe_sc, pb)) != ERR_OK) {
     LINK_STATS_INC(link.err);
@@ -1229,7 +1233,9 @@ static err_t ppp_netif_output_over_ethernet(ppp_pcb *pcb, struct pbuf *p, u_shor
 static err_t ppp_netif_output_over_l2tp(ppp_pcb *pcb, struct pbuf *p, u_short protocol) {
   struct pbuf *pb;
   int i=0;
+#if LWIP_SNMP
   u16_t tot_len;
+#endif /* LWIP_SNMP */
   err_t err;
 
   /* @todo: try to use pbuf_header() here! */
@@ -1251,7 +1257,9 @@ static err_t ppp_netif_output_over_l2tp(ppp_pcb *pcb, struct pbuf *p, u_short pr
   *((u_char*)pb->payload + i) = protocol & 0xFF;
 
   pbuf_chain(pb, p);
+#if LWIP_SNMP
   tot_len = pb->tot_len;
+#endif /* LWIP_SNMP */
 
   if( (err = pppol2tp_xmit(pcb->l2tp_pcb, pb)) != ERR_OK) {
     LINK_STATS_INC(link.err);
@@ -1309,6 +1317,9 @@ ppp_ioctl(ppp_pcb *pcb, int cmd, void *arg)
       return PPPERR_PARAM;
       break;
 #endif /* PPPOS_SUPPORT */
+
+    default:
+      break;
   }
 
   return PPPERR_PARAM;
@@ -1354,7 +1365,7 @@ int ppp_write(ppp_pcb *pcb, struct pbuf *p) {
 
 #if PPPOS_SUPPORT
 static int ppp_write_over_serial(ppp_pcb *pcb, struct pbuf *p) {
-  u_char *s = p->payload;
+  u_char *s = (u_char*)p->payload;
   int n = p->len;
   u_char c;
   u_int fcs_out;
@@ -1422,7 +1433,9 @@ static int ppp_write_over_serial(ppp_pcb *pcb, struct pbuf *p) {
 #if PPPOE_SUPPORT
 static int ppp_write_over_ethernet(ppp_pcb *pcb, struct pbuf *p) {
   struct pbuf *ph; /* Ethernet + PPPoE header */
+#if LWIP_SNMP
   u16_t tot_len;
+#endif /* LWIP_SNMP */
 
   /* skip address & flags */
   pbuf_header(p, -(s16_t)2);
@@ -1438,7 +1451,9 @@ static int ppp_write_over_ethernet(ppp_pcb *pcb, struct pbuf *p) {
 
   pbuf_header(ph, -(s16_t)PPPOE_HEADERLEN); /* hide PPPoE header */
   pbuf_cat(ph, p);
+#if LWIP_SNMP
   tot_len = ph->tot_len;
+#endif /* LWIP_SNMP */
 
   pcb->last_xmit = sys_jiffies();
 
@@ -1458,7 +1473,9 @@ static int ppp_write_over_ethernet(ppp_pcb *pcb, struct pbuf *p) {
 #if PPPOL2TP_SUPPORT
 static int ppp_write_over_l2tp(ppp_pcb *pcb, struct pbuf *p) {
   struct pbuf *ph; /* UDP + L2TP header */
+#if LWIP_SNMP
   u16_t tot_len;
+#endif /* LWIP_SNMP */
 
   ph = pbuf_alloc(PBUF_TRANSPORT, (u16_t)(PPPOL2TP_OUTPUT_DATA_HEADER_LEN), PBUF_RAM);
   if(!ph) {
@@ -1471,7 +1488,9 @@ static int ppp_write_over_l2tp(ppp_pcb *pcb, struct pbuf *p) {
 
   pbuf_header(ph, -(s16_t)PPPOL2TP_OUTPUT_DATA_HEADER_LEN); /* hide L2TP header */
   pbuf_cat(ph, p);
+#if LWIP_SNMP
   tot_len = ph->tot_len;
+#endif /* LWIP_SNMP */
 
   pcb->last_xmit = sys_jiffies();
 
@@ -1763,6 +1782,8 @@ pppos_input(ppp_pcb *pcb, u_char *s, int l)
           /* Load character into buffer. */
           ((u_char*)pcrx->in_tail->payload)[pcrx->in_tail->len++] = cur_char;
           break;
+        default:
+          break;
       }
 
       /* update the frame check sequence number. */
@@ -1814,7 +1835,7 @@ struct pbuf * ppp_singlebuf(struct pbuf *p) {
     return p; /* live dangerously */
   }
 
-  for(b = p, pl = q->payload; b != NULL; b = b->next) {
+  for(b = p, pl = (u_char*)q->payload; b != NULL; b = b->next) {
     MEMCPY(pl, b->payload, b->len);
     pl += b->len;
   }
@@ -1848,6 +1869,9 @@ static void ppp_over_ethernet_link_status_cb(ppp_pcb *pcb, int state) {
       pppoe_err_code = PPPERR_OPEN;
       new_phase(pcb, PPP_PHASE_DEAD);
       break;
+
+    default:
+      break;
   }
 
   pcb->link_status_cb(pcb, pcb->err_code ? pcb->err_code : pppoe_err_code, pcb->ctx_cb);
@@ -1898,6 +1922,9 @@ static void ppp_over_l2tp_link_status_cb(ppp_pcb *pcb, int state) {
       pppol2tp_err_code = PPPERR_OPEN;
       new_phase(pcb, PPP_PHASE_DEAD);
       break;
+
+    default:
+      break;
   }
 
   pcb->link_status_cb(pcb, pcb->err_code ? pcb->err_code : pppol2tp_err_code, pcb->ctx_cb);
@@ -1947,7 +1974,7 @@ void ppp_link_terminated(ppp_pcb *pcb) {
     /* We cannot call ppp_free_current_input_packet() here because
      * rx thread might still call pppos_input()
      */
-    PPPDEBUG(LOG_DEBUG, ("ppp_link_terminated: unit %d: link_status_cb=%p err_code=%d\n", pcb->num, pcb->link_status_cb, pcb->err_code));
+    PPPDEBUG(LOG_DEBUG, ("ppp_link_terminated: unit %d: err_code=%d\n", pcb->num, pcb->err_code));
     pcb->link_status_cb(pcb, pcb->err_code ? pcb->err_code : PPPERR_PROTOCOL, pcb->ctx_cb);
 #endif /* PPPOS_SUPPORT */
   }
diff --git a/src/netif/ppp/pppoe.c b/src/netif/ppp/pppoe.c
index 101ac90e..2aa819c3 100644
--- a/src/netif/ppp/pppoe.c
+++ b/src/netif/ppp/pppoe.c
@@ -384,6 +384,8 @@ pppoe_disc_input(struct netif *netif, struct pbuf *pb)
       case PPPOE_TAG_GENERIC_ERR:
         err_msg = "GENERIC ERROR";
         break;
+      default:
+        break;
     }
     if (NULL != err_msg) {
       if (len) {
diff --git a/src/netif/ppp/pppol2tp.c b/src/netif/ppp/pppol2tp.c
index 017223b4..b526410a 100644
--- a/src/netif/ppp/pppol2tp.c
+++ b/src/netif/ppp/pppol2tp.c
@@ -203,7 +203,7 @@ static void pppol2tp_input(void *arg, struct udp_pcb *pcb, struct pbuf *p, struc
     goto packet_too_short;
   }
 
-  inp = p->payload;
+  inp = (u8_t*)p->payload;
   GETSHORT(hflags, inp);
 
   if (hflags & PPPOL2TP_HEADERFLAG_CONTROL) {
@@ -321,7 +321,7 @@ static void pppol2tp_dispatch_control_packet(pppol2tp_pcb *l2tp, struct ip_addr
   u16_t avplen, avpflags, vendorid, attributetype, messagetype=0;
   err_t err;
 #if PPPOL2TP_AUTH_SUPPORT
-  md5_context md5_context;
+  md5_context md5_ctx;
   u8_t md5_hash[16];
   u8_t challenge_id = 0;
 #endif /* PPPOL2TP_AUTH_SUPPORT */
@@ -344,7 +344,7 @@ static void pppol2tp_dispatch_control_packet(pppol2tp_pcb *l2tp, struct ip_addr
     return;
   }
 
-  inp = p->payload;
+  inp = (u8_t*)p->payload;
   /* Decode AVPs */
   while (p->len > 0) {
     if (p->len < sizeof(avpflags) + sizeof(vendorid) + sizeof(attributetype) ) {
@@ -396,6 +396,8 @@ static void pppol2tp_dispatch_control_packet(pppol2tp_pcb *l2tp, struct ip_addr
              */
           }
           return;
+        default:
+          break;
       }
       goto nextavp;
     }
@@ -408,8 +410,8 @@ static void pppol2tp_dispatch_control_packet(pppol2tp_pcb *l2tp, struct ip_addr
     switch (messagetype) {
       /* Start Control Connection Reply */
       case PPPOL2TP_MESSAGETYPE_SCCRP:
-	switch (attributetype) {
-	  case PPPOL2TP_AVPTYPE_TUNNELID:
+       switch (attributetype) {
+          case PPPOL2TP_AVPTYPE_TUNNELID:
             if (avplen != sizeof(l2tp->source_tunnel_id) ) {
                PPPDEBUG(LOG_DEBUG, ("pppol2tp: AVP Assign tunnel ID length check failed\n"));
                return;
@@ -418,7 +420,7 @@ static void pppol2tp_dispatch_control_packet(pppol2tp_pcb *l2tp, struct ip_addr
             PPPDEBUG(LOG_DEBUG, ("pppol2tp: Assigned tunnel ID %"U16_F"\n", l2tp->source_tunnel_id));
             goto nextavp;
 #if PPPOL2TP_AUTH_SUPPORT
-	  case PPPOL2TP_AVPTYPE_CHALLENGE:
+          case PPPOL2TP_AVPTYPE_CHALLENGE:
             if (avplen == 0) {
                PPPDEBUG(LOG_DEBUG, ("pppol2tp: Challenge length check failed\n"));
                return;
@@ -429,26 +431,26 @@ static void pppol2tp_dispatch_control_packet(pppol2tp_pcb *l2tp, struct ip_addr
               return;
             }
             /* Generate hash of ID, secret, challenge */
-            md5_starts(&md5_context);
+            md5_starts(&md5_ctx);
             challenge_id = PPPOL2TP_MESSAGETYPE_SCCCN;
-            md5_update(&md5_context, &challenge_id, 1);
-            md5_update(&md5_context, l2tp->secret, l2tp->secret_len);
-            md5_update(&md5_context, inp, avplen);
-            md5_finish(&md5_context, l2tp->challenge_hash);
+            md5_update(&md5_ctx, &challenge_id, 1);
+            md5_update(&md5_ctx, l2tp->secret, l2tp->secret_len);
+            md5_update(&md5_ctx, inp, avplen);
+            md5_finish(&md5_ctx, l2tp->challenge_hash);
             l2tp->send_challenge = 1;
             goto skipavp;
-	  case PPPOL2TP_AVPTYPE_CHALLENGERESPONSE:
+          case PPPOL2TP_AVPTYPE_CHALLENGERESPONSE:
             if (avplen != PPPOL2TP_AVPTYPE_CHALLENGERESPONSE_SIZE) {
                PPPDEBUG(LOG_DEBUG, ("pppol2tp: AVP Challenge Response length check failed\n"));
                return;
             }
             /* Generate hash of ID, secret, challenge */
-            md5_starts(&md5_context);
+            md5_starts(&md5_ctx);
             challenge_id = PPPOL2TP_MESSAGETYPE_SCCRP;
-            md5_update(&md5_context, &challenge_id, 1);
-            md5_update(&md5_context, l2tp->secret, l2tp->secret_len);
-            md5_update(&md5_context, l2tp->secret_rv, sizeof(l2tp->secret_rv));
-            md5_finish(&md5_context, md5_hash);
+            md5_update(&md5_ctx, &challenge_id, 1);
+            md5_update(&md5_ctx, l2tp->secret, l2tp->secret_len);
+            md5_update(&md5_ctx, l2tp->secret_rv, sizeof(l2tp->secret_rv));
+            md5_finish(&md5_ctx, md5_hash);
             if ( memcmp(inp, md5_hash, sizeof(md5_hash)) ) {
               PPPDEBUG(LOG_DEBUG, ("pppol2tp: Received challenge response from peer and secret key do not match\n"));
               pppol2tp_abort_connect(l2tp);
@@ -456,12 +458,14 @@ static void pppol2tp_dispatch_control_packet(pppol2tp_pcb *l2tp, struct ip_addr
             }
             goto skipavp;
 #endif /* PPPOL2TP_AUTH_SUPPORT */
-	}
-	break;
+          default:
+            break;
+        }
+        break;
       /* Incoming Call Reply */
       case PPPOL2TP_MESSAGETYPE_ICRP:
-	switch (attributetype) {
-	  case PPPOL2TP_AVPTYPE_SESSIONID:
+        switch (attributetype) {
+         case PPPOL2TP_AVPTYPE_SESSIONID:
             if (avplen != sizeof(l2tp->source_session_id) ) {
                PPPDEBUG(LOG_DEBUG, ("pppol2tp: AVP Assign session ID length check failed\n"));
                return;
@@ -469,8 +473,12 @@ static void pppol2tp_dispatch_control_packet(pppol2tp_pcb *l2tp, struct ip_addr
             GETSHORT(l2tp->source_session_id, inp);
             PPPDEBUG(LOG_DEBUG, ("pppol2tp: Assigned session ID %"U16_F"\n", l2tp->source_session_id));
             goto nextavp;
-	}
-	break;
+          default:
+            break;
+        }
+        break;
+      default:
+        break;
     }
 
 skipavp:
@@ -991,7 +999,7 @@ err_t pppol2tp_xmit(pppol2tp_pcb *l2tp, struct pbuf *pb) {
     return ERR_BUF;
   }
 
-  p = pb->payload;
+  p = (u8_t*)pb->payload;
   PUTSHORT(PPPOL2TP_HEADERFLAG_DATA_MANDATORY, p);
   PUTSHORT(l2tp->source_tunnel_id, p); /* Tunnel Id */
   PUTSHORT(l2tp->source_session_id, p); /* Session Id */
diff --git a/src/netif/ppp/upap.c b/src/netif/ppp/upap.c
index 72931305..1bdbdefa 100644
--- a/src/netif/ppp/upap.c
+++ b/src/netif/ppp/upap.c
@@ -86,7 +86,7 @@ static void upap_lowerdown(ppp_pcb *pcb);
 static void upap_input(ppp_pcb *pcb, u_char *inpacket, int l);
 static void upap_protrej(ppp_pcb *pcb);
 #if PRINTPKT_SUPPORT
-static int upap_printpkt(u_char *p, int plen, void (*printer) (void *, char *, ...), void *arg);
+static int upap_printpkt(u_char *p, int plen, void (*printer) (void *, const char *, ...), void *arg);
 #endif /* PRINTPKT_SUPPORT */
 
 const struct protent pap_protent = {
@@ -126,7 +126,7 @@ 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);
 static void upap_sauthreq(ppp_pcb *pcb);
 #if PPP_SERVER
-static void upap_sresp(ppp_pcb *pcb, u_char code, u_char id, char *msg, int msglen);
+static void upap_sresp(ppp_pcb *pcb, u_char code, u_char id, const char *msg, int msglen);
 #endif /* PPP_SERVER */
 
 
@@ -363,7 +363,7 @@ static void upap_rauthreq(ppp_pcb *pcb, u_char *inp, int id, int len) {
 #endif
     char rhostname[256];
     int retcode;
-    char *msg;
+    const char *msg;
     int msglen;
 
     if (pcb->upap.us_serverstate < UPAPSS_LISTEN)
@@ -546,7 +546,7 @@ static void upap_sauthreq(ppp_pcb *pcb) {
         return;
     }
 
-    outp = p->payload;
+    outp = (u_char*)p->payload;
     MAKEHEADER(outp, PPP_PAP);
 
     PUTCHAR(UPAP_AUTHREQ, outp);
@@ -569,7 +569,7 @@ static void upap_sauthreq(ppp_pcb *pcb) {
 /*
  * upap_sresp - Send a response (ack or nak).
  */
-static void upap_sresp(ppp_pcb *pcb, u_char code, u_char id, char *msg, int msglen) {
+static void upap_sresp(ppp_pcb *pcb, u_char code, u_char id, const char *msg, int msglen) {
     struct pbuf *p;
     u_char *outp;
     int outlen;
@@ -583,7 +583,7 @@ static void upap_sresp(ppp_pcb *pcb, u_char code, u_char id, char *msg, int msgl
         return;
     }
 
-    outp = p->payload;
+    outp = (u_char*)p->payload;
     MAKEHEADER(outp, PPP_PAP);
 
     PUTCHAR(code, outp);
@@ -600,11 +600,11 @@ static void upap_sresp(ppp_pcb *pcb, u_char code, u_char id, char *msg, int msgl
 /*
  * upap_printpkt - print the contents of a PAP packet.
  */
-static char *upap_codenames[] = {
+static const char *upap_codenames[] = {
     "AuthReq", "AuthAck", "AuthNak"
 };
 
-static int upap_printpkt(u_char *p, int plen, void (*printer) (void *, char *, ...), void *arg) {
+static int upap_printpkt(u_char *p, int plen, void (*printer) (void *, const char *, ...), void *arg) {
     int code, id, len;
     int mlen, ulen, wlen;
     char *user, *pwd, *msg;
@@ -665,6 +665,8 @@ static int upap_printpkt(u_char *p, int plen, void (*printer) (void *, char *, .
 	printer(arg, " ");
 	ppp_print_string(msg, mlen, printer, arg);
 	break;
+    default:
+	break;
     }
 
     /* print the rest of the bytes in the packet */
diff --git a/src/netif/ppp/utils.c b/src/netif/ppp/utils.c
index 60cf7f85..ecd305a0 100644
--- a/src/netif/ppp/utils.c
+++ b/src/netif/ppp/utils.c
@@ -69,12 +69,12 @@
 extern char *strerror();
 #endif
 
-static void ppp_logit(int level, char *fmt, va_list args);
+static void ppp_logit(int level, const char *fmt, va_list args);
 static void ppp_log_write(int level, char *buf);
 #if PRINTPKT_SUPPORT
-static void ppp_vslp_printer(void *arg, char *fmt, ...);
+static void ppp_vslp_printer(void *arg, const char *fmt, ...);
 static void ppp_format_packet(u_char *p, int len,
-		void (*printer) (void *, char *, ...), void *arg);
+		void (*printer) (void *, const char *, ...), void *arg);
 
 struct buffer_info {
     char *ptr;
@@ -119,7 +119,7 @@ size_t ppp_strlcat(char *dest, const char *src, size_t len) {
  * Doesn't do floating-point formats.
  * Returns the number of chars put into buf.
  */
-int ppp_slprintf(char *buf, int buflen, char *fmt, ...) {
+int ppp_slprintf(char *buf, int buflen, const char *fmt, ...) {
     va_list args;
     int n;
 
@@ -134,12 +134,13 @@ int ppp_slprintf(char *buf, int buflen, char *fmt, ...) {
  */
 #define OUTCHAR(c)	(buflen > 0? (--buflen, *buf++ = (c)): 0)
 
-int ppp_vslprintf(char *buf, int buflen, char *fmt, va_list args) {
+int ppp_vslprintf(char *buf, int buflen, const char *fmt, va_list args) {
     int c, i, n;
     int width, prec, fillch;
     int base, len, neg, quoted;
     unsigned long val = 0;
-    char *str, *f, *buf0;
+    const char *f;
+    char *str, *buf0;
     unsigned char *p;
     char num[32];
 #if 0 /* need port */
@@ -372,6 +373,8 @@ int ppp_vslprintf(char *buf, int buflen, char *fmt, va_list args) {
 		*--str = 'x';
 		*--str = '0';
 		break;
+	    default:
+		break;
 	    }
 	    len = num + sizeof(num) - 1 - str;
 	} else {
@@ -402,7 +405,7 @@ int ppp_vslprintf(char *buf, int buflen, char *fmt, va_list args) {
 /*
  * vslp_printer - used in processing a %P format
  */
-static void ppp_vslp_printer(void *arg, char *fmt, ...) {
+static void ppp_vslp_printer(void *arg, const char *fmt, ...) {
     int n;
     va_list pvar;
     struct buffer_info *bi;
@@ -441,7 +444,7 @@ log_packet(p, len, prefix, level)
  * calling `printer(arg, format, ...)' to output it.
  */
 static void ppp_format_packet(u_char *p, int len,
-		void (*printer) (void *, char *, ...), void *arg) {
+		void (*printer) (void *, const char *, ...), void *arg) {
     int i, n;
     u_short proto;
     const struct protent *protp;
@@ -516,7 +519,7 @@ end_pr_log()
  * pr_log - printer routine for outputting to log
  */
 void
-pr_log (void *arg, char *fmt, ...)
+pr_log (void *arg, const char *fmt, ...)
 {
 	int l, n;
 	va_list pvar;
@@ -566,7 +569,7 @@ pr_log (void *arg, char *fmt, ...)
  * ppp_print_string - print a readable representation of a string using
  * printer.
  */
-void ppp_print_string(char *p, int len, void (*printer) (void *, char *, ...), void *arg) {
+void ppp_print_string(char *p, int len, void (*printer) (void *, const char *, ...), void *arg) {
     int c;
 
     printer(arg, "\"");
@@ -599,7 +602,7 @@ void ppp_print_string(char *p, int len, void (*printer) (void *, char *, ...), v
 /*
  * ppp_logit - does the hard work for fatal et al.
  */
-static void ppp_logit(int level, char *fmt, va_list args) {
+static void ppp_logit(int level, const char *fmt, va_list args) {
     char buf[1024];
 
     ppp_vslprintf(buf, sizeof(buf), fmt, args);
@@ -626,7 +629,7 @@ static void ppp_log_write(int level, char *buf) {
 /*
  * ppp_fatal - log an error message and die horribly.
  */
-void ppp_fatal(char *fmt, ...) {
+void ppp_fatal(const char *fmt, ...) {
     va_list pvar;
 
     va_start(pvar, fmt);
@@ -642,7 +645,7 @@ void ppp_fatal(char *fmt, ...) {
 /*
  * ppp_error - log an error message.
  */
-void ppp_error(char *fmt, ...) {
+void ppp_error(const char *fmt, ...) {
     va_list pvar;
 
     va_start(pvar, fmt);
@@ -656,7 +659,7 @@ void ppp_error(char *fmt, ...) {
 /*
  * ppp_warn - log a warning message.
  */
-void ppp_warn(char *fmt, ...) {
+void ppp_warn(const char *fmt, ...) {
     va_list pvar;
 
     va_start(pvar, fmt);
@@ -667,7 +670,7 @@ void ppp_warn(char *fmt, ...) {
 /*
  * ppp_notice - log a notice-level message.
  */
-void ppp_notice(char *fmt, ...) {
+void ppp_notice(const char *fmt, ...) {
     va_list pvar;
 
     va_start(pvar, fmt);
@@ -678,7 +681,7 @@ void ppp_notice(char *fmt, ...) {
 /*
  * ppp_info - log an informational message.
  */
-void ppp_info(char *fmt, ...) {
+void ppp_info(const char *fmt, ...) {
     va_list pvar;
 
     va_start(pvar, fmt);
@@ -689,7 +692,7 @@ void ppp_info(char *fmt, ...) {
 /*
  * ppp_dbglog - log a debug message.
  */
-void ppp_dbglog(char *fmt, ...) {
+void ppp_dbglog(const char *fmt, ...) {
     va_list pvar;
 
     va_start(pvar, fmt);
diff --git a/src/netif/ppp/vj.c b/src/netif/ppp/vj.c
index 5c195909..dc805adb 100644
--- a/src/netif/ppp/vj.c
+++ b/src/netif/ppp/vj.c
@@ -95,23 +95,23 @@ vj_compress_init(struct vjcompress *comp)
 
 #define DECODEL(f) { \
   if (*cp == 0) {\
-    u32_t tmp = ntohl(f) + ((cp[1] << 8) | cp[2]); \
-    (f) = htonl(tmp); \
+    u32_t tmp_ = ntohl(f) + ((cp[1] << 8) | cp[2]); \
+    (f) = htonl(tmp_); \
     cp += 3; \
   } else { \
-    u32_t tmp = ntohl(f) + (u32_t)*cp++; \
-    (f) = htonl(tmp); \
+    u32_t tmp_ = ntohl(f) + (u32_t)*cp++; \
+    (f) = htonl(tmp_); \
   } \
 }
 
 #define DECODES(f) { \
   if (*cp == 0) {\
-    u_short tmp = ntohs(f) + (((u_short)cp[1] << 8) | cp[2]); \
-    (f) = htons(tmp); \
+    u_short tmp_ = ntohs(f) + (((u_short)cp[1] << 8) | cp[2]); \
+    (f) = htons(tmp_); \
     cp += 3; \
   } else { \
-    u_short tmp = ntohs(f) + (u_short)*cp++; \
-    (f) = htons(tmp); \
+    u_short tmp_ = ntohs(f) + (u_short)*cp++; \
+    (f) = htons(tmp_); \
   } \
 }
 
@@ -342,6 +342,8 @@ vj_compress_tcp(struct vjcompress *comp, struct pbuf *pb)
       cp = new_seq;
     }
     break;
+  default:
+     break;
   }
 
   deltaS = (u_short)(ntohs(IPH_ID(ip)) - ntohs(IPH_ID(&cs->cs_ip)));
@@ -613,7 +615,7 @@ vj_uncompress_tcp(struct pbuf **nb, struct vjcompress *comp)
       goto bad;
     }
 
-    bufptr = n0->payload;
+    bufptr = (u8_t*)n0->payload;
     for(q = np; q != NULL; q = q->next) {
       MEMCPY(q->payload, bufptr, q->len);
       bufptr += q->len;