diff --git a/src/core/snmp/asn1_enc.c b/src/core/snmp/asn1_enc.c
index c1667e79..0c3ead94 100644
--- a/src/core/snmp/asn1_enc.c
+++ b/src/core/snmp/asn1_enc.c
@@ -559,7 +559,7 @@ snmp_asn1_enc_oid(struct pbuf *p, u16_t ofs, u8_t ident_len, const s32_t *ident)
  * @return ERR_OK if successful, ERR_ARG if we can't (or won't) encode
  */
 err_t
-snmp_asn1_enc_raw(struct pbuf *p, u16_t ofs, u16_t raw_len, u8_t *raw)
+snmp_asn1_enc_raw(struct pbuf *p, u16_t ofs, u16_t raw_len, const u8_t *raw)
 {
   u16_t plen, base;
   u8_t *msg_ptr;
diff --git a/src/core/snmp/mib2.c b/src/core/snmp/mib2.c
index 5428a05a..b7dfd009 100644
--- a/src/core/snmp/mib2.c
+++ b/src/core/snmp/mib2.c
@@ -134,21 +134,21 @@ const s32_t snmp_ids[28] = {
   1, 2, 3, 4, 5, 6, 8, 9, 10, 11, 12, 13, 14, 15, 16,
   17, 18, 19, 20, 21, 22, 24, 25, 26, 27, 28, 29, 30
 };
-struct mib_node* const snmp_nodes[28] = {
-  (struct mib_node*)&snmp_scalar, (struct mib_node*)&snmp_scalar,
-  (struct mib_node*)&snmp_scalar, (struct mib_node*)&snmp_scalar,
-  (struct mib_node*)&snmp_scalar, (struct mib_node*)&snmp_scalar,
-  (struct mib_node*)&snmp_scalar, (struct mib_node*)&snmp_scalar,
-  (struct mib_node*)&snmp_scalar, (struct mib_node*)&snmp_scalar,
-  (struct mib_node*)&snmp_scalar, (struct mib_node*)&snmp_scalar,
-  (struct mib_node*)&snmp_scalar, (struct mib_node*)&snmp_scalar,
-  (struct mib_node*)&snmp_scalar, (struct mib_node*)&snmp_scalar,
-  (struct mib_node*)&snmp_scalar, (struct mib_node*)&snmp_scalar,
-  (struct mib_node*)&snmp_scalar, (struct mib_node*)&snmp_scalar,
-  (struct mib_node*)&snmp_scalar, (struct mib_node*)&snmp_scalar,
-  (struct mib_node*)&snmp_scalar, (struct mib_node*)&snmp_scalar,
-  (struct mib_node*)&snmp_scalar, (struct mib_node*)&snmp_scalar,
-  (struct mib_node*)&snmp_scalar, (struct mib_node*)&snmp_scalar
+const struct mib_node* const snmp_nodes[28] = {
+  (const struct mib_node*)&snmp_scalar, (const struct mib_node*)&snmp_scalar,
+  (const struct mib_node*)&snmp_scalar, (const struct mib_node*)&snmp_scalar,
+  (const struct mib_node*)&snmp_scalar, (const struct mib_node*)&snmp_scalar,
+  (const struct mib_node*)&snmp_scalar, (const struct mib_node*)&snmp_scalar,
+  (const struct mib_node*)&snmp_scalar, (const struct mib_node*)&snmp_scalar,
+  (const struct mib_node*)&snmp_scalar, (const struct mib_node*)&snmp_scalar,
+  (const struct mib_node*)&snmp_scalar, (const struct mib_node*)&snmp_scalar,
+  (const struct mib_node*)&snmp_scalar, (const struct mib_node*)&snmp_scalar,
+  (const struct mib_node*)&snmp_scalar, (const struct mib_node*)&snmp_scalar,
+  (const struct mib_node*)&snmp_scalar, (const struct mib_node*)&snmp_scalar,
+  (const struct mib_node*)&snmp_scalar, (const struct mib_node*)&snmp_scalar,
+  (const struct mib_node*)&snmp_scalar, (const struct mib_node*)&snmp_scalar,
+  (const struct mib_node*)&snmp_scalar, (const struct mib_node*)&snmp_scalar,
+  (const struct mib_node*)&snmp_scalar, (const struct mib_node*)&snmp_scalar
 };
 const struct mib_array_node snmp = {
   &noleafs_get_object_def,
@@ -179,10 +179,10 @@ struct mib_list_rootnode udp_root = {
   0
 };
 const s32_t udpentry_ids[2] = { 1, 2 };
-struct mib_node* const udpentry_nodes[2] = {
-  (struct mib_node*)&udp_root, (struct mib_node*)&udp_root,
+const struct mib_node* const udpentry_nodes[2] = {
+  (const struct mib_node*)&udp_root, (const struct mib_node*)&udp_root,
 };
-const struct mib_array_node udpentry = {
+struct mib_array_node udpentry = {
   &noleafs_get_object_def,
   &noleafs_get_value,
   &noleafs_set_test,
@@ -215,10 +215,10 @@ const mib_scalar_node udp_scalar = {
   0
 };
 const s32_t udp_ids[5] = { 1, 2, 3, 4, 5 };
-struct mib_node* const udp_nodes[5] = {
-  (struct mib_node*)&udp_scalar, (struct mib_node*)&udp_scalar,
-  (struct mib_node*)&udp_scalar, (struct mib_node*)&udp_scalar,
-  (struct mib_node*)&udptable
+const struct mib_node* const udp_nodes[5] = {
+  (const struct mib_node*)&udp_scalar, (const struct mib_node*)&udp_scalar,
+  (const struct mib_node*)&udp_scalar, (const struct mib_node*)&udp_scalar,
+  (const struct mib_node*)&udptable
 };
 const struct mib_array_node udp = {
   &noleafs_get_object_def,
@@ -247,12 +247,12 @@ struct mib_list_rootnode tcpconntree_root = {
   0
 };
 const s32_t tcpconnentry_ids[5] = { 1, 2, 3, 4, 5 };
-struct mib_node* const tcpconnentry_nodes[5] = {
+const struct mib_node* const tcpconnentry_nodes[5] = {
   (struct mib_node*)&tcpconntree_root, (struct mib_node*)&tcpconntree_root,
   (struct mib_node*)&tcpconntree_root, (struct mib_node*)&tcpconntree_root,
   (struct mib_node*)&tcpconntree_root
 };
-const struct mib_array_node tcpconnentry = {
+struct mib_array_node tcpconnentry = {
   &noleafs_get_object_def,
   &noleafs_get_value,
   &noleafs_set_test,
@@ -287,15 +287,15 @@ const mib_scalar_node tcp_scalar = {
   0
 };
 const s32_t tcp_ids[15] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 };
-struct mib_node* const tcp_nodes[15] = {
-  (struct mib_node*)&tcp_scalar, (struct mib_node*)&tcp_scalar,
-  (struct mib_node*)&tcp_scalar, (struct mib_node*)&tcp_scalar,
-  (struct mib_node*)&tcp_scalar, (struct mib_node*)&tcp_scalar,
-  (struct mib_node*)&tcp_scalar, (struct mib_node*)&tcp_scalar,
-  (struct mib_node*)&tcp_scalar, (struct mib_node*)&tcp_scalar,
-  (struct mib_node*)&tcp_scalar, (struct mib_node*)&tcp_scalar,
-  (struct mib_node*)&tcpconntable, (struct mib_node*)&tcp_scalar,
-  (struct mib_node*)&tcp_scalar
+const struct mib_node* const tcp_nodes[15] = {
+  (const struct mib_node*)&tcp_scalar, (const struct mib_node*)&tcp_scalar,
+  (const struct mib_node*)&tcp_scalar, (const struct mib_node*)&tcp_scalar,
+  (const struct mib_node*)&tcp_scalar, (const struct mib_node*)&tcp_scalar,
+  (const struct mib_node*)&tcp_scalar, (const struct mib_node*)&tcp_scalar,
+  (const struct mib_node*)&tcp_scalar, (const struct mib_node*)&tcp_scalar,
+  (const struct mib_node*)&tcp_scalar, (const struct mib_node*)&tcp_scalar,
+  (const struct mib_node*)&tcpconntable, (const struct mib_node*)&tcp_scalar,
+  (const struct mib_node*)&tcp_scalar
 };
 const struct mib_array_node tcp = {
   &noleafs_get_object_def,
@@ -319,20 +319,20 @@ const mib_scalar_node icmp_scalar = {
   0
 };
 const s32_t icmp_ids[26] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26 };
-struct mib_node* const icmp_nodes[26] = {
-  (struct mib_node*)&icmp_scalar, (struct mib_node*)&icmp_scalar,
-  (struct mib_node*)&icmp_scalar, (struct mib_node*)&icmp_scalar,
-  (struct mib_node*)&icmp_scalar, (struct mib_node*)&icmp_scalar,
-  (struct mib_node*)&icmp_scalar, (struct mib_node*)&icmp_scalar,
-  (struct mib_node*)&icmp_scalar, (struct mib_node*)&icmp_scalar,
-  (struct mib_node*)&icmp_scalar, (struct mib_node*)&icmp_scalar,
-  (struct mib_node*)&icmp_scalar, (struct mib_node*)&icmp_scalar,
-  (struct mib_node*)&icmp_scalar, (struct mib_node*)&icmp_scalar,
-  (struct mib_node*)&icmp_scalar, (struct mib_node*)&icmp_scalar,
-  (struct mib_node*)&icmp_scalar, (struct mib_node*)&icmp_scalar,
-  (struct mib_node*)&icmp_scalar, (struct mib_node*)&icmp_scalar,
-  (struct mib_node*)&icmp_scalar, (struct mib_node*)&icmp_scalar,
-  (struct mib_node*)&icmp_scalar, (struct mib_node*)&icmp_scalar
+const struct mib_node* const icmp_nodes[26] = {
+  (const struct mib_node*)&icmp_scalar, (const struct mib_node*)&icmp_scalar,
+  (const struct mib_node*)&icmp_scalar, (const struct mib_node*)&icmp_scalar,
+  (const struct mib_node*)&icmp_scalar, (const struct mib_node*)&icmp_scalar,
+  (const struct mib_node*)&icmp_scalar, (const struct mib_node*)&icmp_scalar,
+  (const struct mib_node*)&icmp_scalar, (const struct mib_node*)&icmp_scalar,
+  (const struct mib_node*)&icmp_scalar, (const struct mib_node*)&icmp_scalar,
+  (const struct mib_node*)&icmp_scalar, (const struct mib_node*)&icmp_scalar,
+  (const struct mib_node*)&icmp_scalar, (const struct mib_node*)&icmp_scalar,
+  (const struct mib_node*)&icmp_scalar, (const struct mib_node*)&icmp_scalar,
+  (const struct mib_node*)&icmp_scalar, (const struct mib_node*)&icmp_scalar,
+  (const struct mib_node*)&icmp_scalar, (const struct mib_node*)&icmp_scalar,
+  (const struct mib_node*)&icmp_scalar, (const struct mib_node*)&icmp_scalar,
+  (const struct mib_node*)&icmp_scalar, (const struct mib_node*)&icmp_scalar
 };
 const struct mib_array_node icmp = {
   &noleafs_get_object_def,
@@ -358,11 +358,11 @@ struct mib_list_rootnode ipntomtree_root = {
   0
 };
 const s32_t ipntomentry_ids[4] = { 1, 2, 3, 4 };
-struct mib_node* const ipntomentry_nodes[4] = {
+const struct mib_node* const ipntomentry_nodes[4] = {
   (struct mib_node*)&ipntomtree_root, (struct mib_node*)&ipntomtree_root,
   (struct mib_node*)&ipntomtree_root, (struct mib_node*)&ipntomtree_root
 };
-const struct mib_array_node ipntomentry = {
+struct mib_array_node ipntomentry = {
   &noleafs_get_object_def,
   &noleafs_get_value,
   &noleafs_set_test,
@@ -399,7 +399,7 @@ struct mib_list_rootnode iprtetree_root = {
   0
 };
 const s32_t iprteentry_ids[13] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 };
-struct mib_node* const iprteentry_nodes[13] = {
+const struct mib_node* const iprteentry_nodes[13] = {
   (struct mib_node*)&iprtetree_root, (struct mib_node*)&iprtetree_root,
   (struct mib_node*)&iprtetree_root, (struct mib_node*)&iprtetree_root,
   (struct mib_node*)&iprtetree_root, (struct mib_node*)&iprtetree_root,
@@ -408,7 +408,7 @@ struct mib_node* const iprteentry_nodes[13] = {
   (struct mib_node*)&iprtetree_root, (struct mib_node*)&iprtetree_root,
   (struct mib_node*)&iprtetree_root
 };
-const struct mib_array_node iprteentry = {
+struct mib_array_node iprteentry = {
   &noleafs_get_object_def,
   &noleafs_get_value,
   &noleafs_set_test,
@@ -445,14 +445,14 @@ struct mib_list_rootnode ipaddrtree_root = {
   0
 };
 const s32_t ipaddrentry_ids[5] = { 1, 2, 3, 4, 5 };
-struct mib_node* const ipaddrentry_nodes[5] = {
-  (struct mib_node*)&ipaddrtree_root,
-  (struct mib_node*)&ipaddrtree_root,
-  (struct mib_node*)&ipaddrtree_root,
-  (struct mib_node*)&ipaddrtree_root,
-  (struct mib_node*)&ipaddrtree_root
+const struct mib_node* const ipaddrentry_nodes[5] = {
+  (const struct mib_node*)&ipaddrtree_root,
+  (const struct mib_node*)&ipaddrtree_root,
+  (const struct mib_node*)&ipaddrtree_root,
+  (const struct mib_node*)&ipaddrtree_root,
+  (const struct mib_node*)&ipaddrtree_root
 };
-const struct mib_array_node ipaddrentry = {
+struct mib_array_node ipaddrentry = {
   &noleafs_get_object_def,
   &noleafs_get_value,
   &noleafs_set_test,
@@ -486,19 +486,19 @@ const mib_scalar_node ip_scalar = {
   0
 };
 const s32_t ip_ids[23] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 };
-struct mib_node* const ip_nodes[23] = {
-  (struct mib_node*)&ip_scalar, (struct mib_node*)&ip_scalar,
-  (struct mib_node*)&ip_scalar, (struct mib_node*)&ip_scalar,
-  (struct mib_node*)&ip_scalar, (struct mib_node*)&ip_scalar,
-  (struct mib_node*)&ip_scalar, (struct mib_node*)&ip_scalar,
-  (struct mib_node*)&ip_scalar, (struct mib_node*)&ip_scalar,
-  (struct mib_node*)&ip_scalar, (struct mib_node*)&ip_scalar,
-  (struct mib_node*)&ip_scalar, (struct mib_node*)&ip_scalar,
-  (struct mib_node*)&ip_scalar, (struct mib_node*)&ip_scalar,
-  (struct mib_node*)&ip_scalar, (struct mib_node*)&ip_scalar,
-  (struct mib_node*)&ip_scalar, (struct mib_node*)&ipaddrtable,
-  (struct mib_node*)&iprtetable, (struct mib_node*)&ipntomtable,
-  (struct mib_node*)&ip_scalar
+const struct mib_node* const ip_nodes[23] = {
+  (const struct mib_node*)&ip_scalar, (const struct mib_node*)&ip_scalar,
+  (const struct mib_node*)&ip_scalar, (const struct mib_node*)&ip_scalar,
+  (const struct mib_node*)&ip_scalar, (const struct mib_node*)&ip_scalar,
+  (const struct mib_node*)&ip_scalar, (const struct mib_node*)&ip_scalar,
+  (const struct mib_node*)&ip_scalar, (const struct mib_node*)&ip_scalar,
+  (const struct mib_node*)&ip_scalar, (const struct mib_node*)&ip_scalar,
+  (const struct mib_node*)&ip_scalar, (const struct mib_node*)&ip_scalar,
+  (const struct mib_node*)&ip_scalar, (const struct mib_node*)&ip_scalar,
+  (const struct mib_node*)&ip_scalar, (const struct mib_node*)&ip_scalar,
+  (const struct mib_node*)&ip_scalar, (const struct mib_node*)&ipaddrtable,
+  (const struct mib_node*)&iprtetable, (const struct mib_node*)&ipntomtable,
+  (const struct mib_node*)&ip_scalar
 };
 const struct mib_array_node mib2_ip = {
   &noleafs_get_object_def,
@@ -524,10 +524,10 @@ struct mib_list_rootnode arptree_root = {
   0
 };
 const s32_t atentry_ids[3] = { 1, 2, 3 };
-struct mib_node* const atentry_nodes[3] = {
-  (struct mib_node*)&arptree_root,
-  (struct mib_node*)&arptree_root,
-  (struct mib_node*)&arptree_root
+const struct mib_node* const atentry_nodes[3] = {
+  (const struct mib_node*)&arptree_root,
+  (const struct mib_node*)&arptree_root,
+  (const struct mib_node*)&arptree_root
 };
 const struct mib_array_node atentry = {
   &noleafs_get_object_def,
@@ -541,8 +541,8 @@ const struct mib_array_node atentry = {
 };
 
 const s32_t attable_id = 1;
-struct mib_node* const attable_node = (struct mib_node*)&atentry;
-const struct mib_array_node attable = {
+const struct mib_node* const attable_node = (const struct mib_node*)&atentry;
+struct mib_array_node attable = {
   &noleafs_get_object_def,
   &noleafs_get_value,
   &noleafs_set_test,
@@ -585,20 +585,20 @@ struct mib_list_rootnode iflist_root = {
   0
 };
 const s32_t ifentry_ids[22] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22 };
-struct mib_node* const ifentry_nodes[22] = {
-  (struct mib_node*)&iflist_root, (struct mib_node*)&iflist_root,
-  (struct mib_node*)&iflist_root, (struct mib_node*)&iflist_root,
-  (struct mib_node*)&iflist_root, (struct mib_node*)&iflist_root,
-  (struct mib_node*)&iflist_root, (struct mib_node*)&iflist_root,
-  (struct mib_node*)&iflist_root, (struct mib_node*)&iflist_root,
-  (struct mib_node*)&iflist_root, (struct mib_node*)&iflist_root,
-  (struct mib_node*)&iflist_root, (struct mib_node*)&iflist_root,
-  (struct mib_node*)&iflist_root, (struct mib_node*)&iflist_root,
-  (struct mib_node*)&iflist_root, (struct mib_node*)&iflist_root,
-  (struct mib_node*)&iflist_root, (struct mib_node*)&iflist_root,
-  (struct mib_node*)&iflist_root, (struct mib_node*)&iflist_root
+const struct mib_node* const ifentry_nodes[22] = {
+  (const struct mib_node*)&iflist_root, (const struct mib_node*)&iflist_root,
+  (const struct mib_node*)&iflist_root, (const struct mib_node*)&iflist_root,
+  (const struct mib_node*)&iflist_root, (const struct mib_node*)&iflist_root,
+  (const struct mib_node*)&iflist_root, (const struct mib_node*)&iflist_root,
+  (const struct mib_node*)&iflist_root, (const struct mib_node*)&iflist_root,
+  (const struct mib_node*)&iflist_root, (const struct mib_node*)&iflist_root,
+  (const struct mib_node*)&iflist_root, (const struct mib_node*)&iflist_root,
+  (const struct mib_node*)&iflist_root, (const struct mib_node*)&iflist_root,
+  (const struct mib_node*)&iflist_root, (const struct mib_node*)&iflist_root,
+  (const struct mib_node*)&iflist_root, (const struct mib_node*)&iflist_root,
+  (const struct mib_node*)&iflist_root, (const struct mib_node*)&iflist_root
 };
-const struct mib_array_node ifentry = {
+struct mib_array_node ifentry = {
   &noleafs_get_object_def,
   &noleafs_get_value,
   &noleafs_set_test,
@@ -632,8 +632,8 @@ const mib_scalar_node interfaces_scalar = {
   0
 };
 const s32_t interfaces_ids[2] = { 1, 2 };
-struct mib_node* const interfaces_nodes[2] = {
-  (struct mib_node*)&interfaces_scalar, (struct mib_node*)&iftable
+const struct mib_node* const interfaces_nodes[2] = {
+  (const struct mib_node*)&interfaces_scalar, (const struct mib_node*)&iftable
 };
 const struct mib_array_node interfaces = {
   &noleafs_get_object_def,
@@ -658,11 +658,11 @@ const mib_scalar_node sys_tem_scalar = {
   0
 };
 const s32_t sys_tem_ids[7] = { 1, 2, 3, 4, 5, 6, 7 };
-struct mib_node* const sys_tem_nodes[7] = {
-  (struct mib_node*)&sys_tem_scalar, (struct mib_node*)&sys_tem_scalar,
-  (struct mib_node*)&sys_tem_scalar, (struct mib_node*)&sys_tem_scalar,
-  (struct mib_node*)&sys_tem_scalar, (struct mib_node*)&sys_tem_scalar,
-  (struct mib_node*)&sys_tem_scalar
+const struct mib_node* const sys_tem_nodes[7] = {
+  (const struct mib_node*)&sys_tem_scalar, (const struct mib_node*)&sys_tem_scalar,
+  (const struct mib_node*)&sys_tem_scalar, (const struct mib_node*)&sys_tem_scalar,
+  (const struct mib_node*)&sys_tem_scalar, (const struct mib_node*)&sys_tem_scalar,
+  (const struct mib_node*)&sys_tem_scalar
 };
 /* work around name issue with 'sys_tem', some compiler(s?) seem to reserve 'system' */
 const struct mib_array_node sys_tem = {
@@ -695,17 +695,17 @@ const s32_t mib2_ids[MIB2_GROUPS] =
   7,
   11
 };
-struct mib_node* const mib2_nodes[MIB2_GROUPS] = {
-  (struct mib_node*)&sys_tem,
-  (struct mib_node*)&interfaces,
-  (struct mib_node*)&at,
-  (struct mib_node*)&mib2_ip,
-  (struct mib_node*)&icmp,
+const struct mib_node* const mib2_nodes[MIB2_GROUPS] = {
+  (const struct mib_node*)&sys_tem,
+  (const struct mib_node*)&interfaces,
+  (const struct mib_node*)&at,
+  (const struct mib_node*)&mib2_ip,
+  (const struct mib_node*)&icmp,
 #if LWIP_TCP
-  (struct mib_node*)&tcp,
+  (const struct mib_node*)&tcp,
 #endif
-  (struct mib_node*)&udp,
-  (struct mib_node*)&snmp
+  (const struct mib_node*)&udp,
+  (const struct mib_node*)&snmp
 };
 
 const struct mib_array_node mib2 = {
@@ -721,7 +721,7 @@ const struct mib_array_node mib2 = {
 
 /* mgmt .1.3.6.1.2 */
 const s32_t mgmt_ids[1] = { 1 };
-struct mib_node* const mgmt_nodes[1] = { (struct mib_node*)&mib2 };
+const struct mib_node* const mgmt_nodes[1] = { (const struct mib_node*)&mib2 };
 const struct mib_array_node mgmt = {
   &noleafs_get_object_def,
   &noleafs_get_value,
@@ -751,7 +751,7 @@ const struct mib_array_node internet = {
 };
 #else
 const s32_t internet_ids[1] = { 2 };
-struct mib_node* const internet_nodes[1] = { (struct mib_node*)&mgmt };
+const struct mib_node* const internet_nodes[1] = { (const struct mib_node*)&mgmt };
 const struct mib_array_node internet = {
   &noleafs_get_object_def,
   &noleafs_get_value,
@@ -777,24 +777,24 @@ static const u8_t sysdescr_len_default = 4;
 static const u8_t sysdescr_default[] = "lwIP";
 static const u8_t* sysdescr_len_ptr = &sysdescr_len_default;
 static const u8_t* sysdescr_ptr = &sysdescr_default[0];
-/** mib-2.system.sysContact */
-static const u8_t syscontact_len_default = 0;
-static const u8_t syscontact_default[] = "";
-static u8_t* syscontact_len_ptr = (u8_t*)&syscontact_len_default;
-static u8_t* syscontact_ptr = (u8_t*)&syscontact_default[0];
-/** mib-2.system.sysName */
-static const u8_t sysname_len_default = 8;
-static const u8_t sysname_default[] = "FQDN-unk";
-static u8_t* sysname_len_ptr = (u8_t*)&sysname_len_default;
-static u8_t* sysname_ptr = (u8_t*)&sysname_default[0];
-/** mib-2.system.sysLocation */
-static const u8_t syslocation_len_default = 0;
-static const u8_t syslocation_default[] = "";
-static u8_t* syslocation_len_ptr = (u8_t*)&syslocation_len_default;
-static u8_t* syslocation_ptr = (u8_t*)&syslocation_default[0];
-/** mib-2.snmp.snmpEnableAuthenTraps */
-static const u8_t snmpenableauthentraps_default = 2; /* disabled */
-static u8_t* snmpenableauthentraps_ptr = (u8_t*)&snmpenableauthentraps_default;
+/** mib-2.system.sysContact @todo: this design is broken (SNMP-set writes without known buffer size) */
+static u8_t syscontact_len_default = 0;
+static u8_t syscontact_default[] = "";
+static u8_t* syscontact_len_ptr = &syscontact_len_default;
+static u8_t* syscontact_ptr = &syscontact_default[0];
+/** mib-2.system.sysName @todo: this design is broken (SNMP-set writes without known buffer size) */
+static u8_t sysname_len_default = 8;
+static u8_t sysname_default[] = "FQDN-unk";
+static u8_t* sysname_len_ptr = &sysname_len_default;
+static u8_t* sysname_ptr = &sysname_default[0];
+/** mib-2.system.sysLocation @todo: this design is broken (SNMP-set writes without known buffer size) */
+static u8_t syslocation_len_default = 0;
+static u8_t syslocation_default[] = "";
+static u8_t* syslocation_len_ptr = &syslocation_len_default;
+static u8_t* syslocation_ptr = &syslocation_default[0];
+/** mib-2.snmp.snmpEnableAuthenTraps @todo: this design is broken (SNMP-set writes without known buffer size) */
+static u8_t snmpenableauthentraps_default = 2; /* disabled */
+static u8_t* snmpenableauthentraps_ptr = &snmpenableauthentraps_default;
 
 /** mib-2.interfaces.ifTable.ifEntry.ifSpecific (zeroDotZero) */
 static const struct snmp_obj_id ifspecific = {2, {0, 0}};
diff --git a/src/core/snmp/mib_structs.c b/src/core/snmp/mib_structs.c
index 8084cced..e137b7bf 100644
--- a/src/core/snmp/mib_structs.c
+++ b/src/core/snmp/mib_structs.c
@@ -48,7 +48,7 @@ const s32_t prefix[4] = {1, 3, 6, 1};
 struct nse
 {
   /** right child */
-  struct mib_node* r_ptr;
+  const struct mib_node* r_ptr;
   /** right child identifier */
   s32_t r_id;
   /** right child next level */
@@ -65,7 +65,7 @@ static void
 push_node(const struct nse* node)
 {
   LWIP_ASSERT("node_stack_cnt < NODE_STACK_SIZE",node_stack_cnt < NODE_STACK_SIZE);
-  LWIP_DEBUGF(SNMP_MIB_DEBUG,("push_node() node=%p id=%"S32_F"\n",(void*)(node->r_ptr),node->r_id));
+  LWIP_DEBUGF(SNMP_MIB_DEBUG,("push_node() node=%p id=%"S32_F"\n",(const void*)(node->r_ptr),node->r_id));
   if (node_stack_cnt < NODE_STACK_SIZE)
   {
     node_stack[node_stack_cnt] = *node;
@@ -84,7 +84,7 @@ pop_node(struct nse* node)
     node_stack_cnt--;
     *node = node_stack[node_stack_cnt];
   }
-  LWIP_DEBUGF(SNMP_MIB_DEBUG,("pop_node() node=%p id=%"S32_F"\n",(void *)(node->r_ptr),node->r_id));
+  LWIP_DEBUGF(SNMP_MIB_DEBUG,("pop_node() node=%p id=%"S32_F"\n",(const void *)(node->r_ptr),node->r_id));
 }
 
 /**
@@ -449,25 +449,25 @@ snmp_mib_node_delete(struct mib_list_rootnode *rn, struct mib_list_node *n)
  * @param np points to the found object instance (return)
  * @return pointer to the requested parent (!) node if success, NULL otherwise
  */
-struct mib_node *
-snmp_search_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snmp_name_ptr *np)
+const struct mib_node *
+snmp_search_tree(const struct mib_node *node, u8_t ident_len, s32_t *ident, struct snmp_name_ptr *np)
 {
   u8_t node_type, ext_level;
 
   ext_level = 0;
-  LWIP_DEBUGF(SNMP_MIB_DEBUG,("node==%p *ident==%"S32_F"\n",(void*)node,*ident));
+  LWIP_DEBUGF(SNMP_MIB_DEBUG,("node==%p *ident==%"S32_F"\n",(const void*)node,*ident));
   while (node != NULL)
   {
     node_type = node->node_type;
     if ((node_type == MIB_NODE_AR) || (node_type == MIB_NODE_RA))
     {
-      struct mib_array_node *an;
+      const struct mib_array_node *an;
       u16_t i;
 
       if (ident_len > 0)
       {
         /* array node (internal ROM or RAM, fixed length) */
-        an = (struct mib_array_node *)node;
+        an = (const struct mib_array_node *)node;
         i = 0;
         while ((i < an->maxlength) && (an->objid[i] != *ident))
         {
@@ -483,7 +483,7 @@ snmp_search_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
                inspect remaining instance number / table index */
             np->ident_len = ident_len;
             np->ident = ident;
-            return (struct mib_node*)an;
+            return (const struct mib_node*)an;
           }
           else
           {
@@ -509,13 +509,13 @@ snmp_search_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
     }
     else if(node_type == MIB_NODE_LR)
     {
-      struct mib_list_rootnode *lrn;
+      const struct mib_list_rootnode *lrn;
       struct mib_list_node *ln;
 
       if (ident_len > 0)
       {
         /* list root node (internal 'RAM', variable length) */
-        lrn = (struct mib_list_rootnode *)node;
+        lrn = (const struct mib_list_rootnode *)node;
         ln = lrn->head;
         /* iterate over list, head to tail */
         while ((ln != NULL) && (ln->objid != *ident))
@@ -530,7 +530,7 @@ snmp_search_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
           {
             np->ident_len = ident_len;
             np->ident = ident;
-            return (struct mib_node*)lrn;
+            return (const struct mib_node*)lrn;
           }
           else
           {
@@ -556,13 +556,13 @@ snmp_search_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
     }
     else if(node_type == MIB_NODE_EX)
     {
-      struct mib_external_node *en;
+      const struct mib_external_node *en;
       u16_t i, len;
 
       if (ident_len > 0)
       {
         /* external node (addressing and access via functions) */
-        en = (struct mib_external_node *)node;
+        en = (const struct mib_external_node *)node;
 
         i = 0;
         len = en->level_length(en->addr_inf,ext_level);
@@ -580,7 +580,7 @@ snmp_search_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
           {
             np->ident_len = ident_len;
             np->ident = ident;
-            return (struct mib_node*)en;
+            return (const struct mib_node*)en;
           }
           else
           {
@@ -606,14 +606,14 @@ snmp_search_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
     }
     else if (node_type == MIB_NODE_SC)
     {
-      mib_scalar_node *sn;
+      const mib_scalar_node *sn;
 
-      sn = (mib_scalar_node *)node;
+      sn = (const mib_scalar_node *)node;
       if ((ident_len == 1) && (*ident == 0))
       {
         np->ident_len = ident_len;
         np->ident = ident;
-        return (struct mib_node*)sn;
+        return (const struct mib_node*)sn;
       }
       else
       {
@@ -630,7 +630,7 @@ snmp_search_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
     }
   }
   /* done, found nothing */
-  LWIP_DEBUGF(SNMP_MIB_DEBUG,("search failed node==%p\n",(void*)node));
+  LWIP_DEBUGF(SNMP_MIB_DEBUG,("search failed node==%p\n",(const void*)node));
   return NULL;
 }
 
@@ -638,7 +638,7 @@ snmp_search_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
  * Test table for presence of at least one table entry.
  */
 static u8_t
-empty_table(struct mib_node *node)
+empty_table(const struct mib_node *node)
 {
   u8_t node_type;
   u8_t empty = 0;
@@ -648,8 +648,8 @@ empty_table(struct mib_node *node)
     node_type = node->node_type;
     if (node_type == MIB_NODE_LR)
     {
-      struct mib_list_rootnode *lrn;
-      lrn = (struct mib_list_rootnode *)node;
+      const struct mib_list_rootnode *lrn;
+      lrn = (const struct mib_list_rootnode *)node;
       if ((lrn->count == 0) || (lrn->head == NULL))
       {
         empty = 1;
@@ -657,8 +657,8 @@ empty_table(struct mib_node *node)
     }
     else if ((node_type == MIB_NODE_AR) || (node_type == MIB_NODE_RA))
     {
-      struct mib_array_node *an;
-      an = (struct mib_array_node *)node;
+      const struct mib_array_node *an;
+      an = (const struct mib_array_node *)node;
       if ((an->maxlength == 0) || (an->nptr == NULL))
       {
         empty = 1;
@@ -666,8 +666,8 @@ empty_table(struct mib_node *node)
     }
     else if (node_type == MIB_NODE_EX)
     {
-      struct mib_external_node *en;
-      en = (struct mib_external_node *)node;
+      const struct mib_external_node *en;
+      en = (const struct mib_external_node *)node;
       if (en->tree_levels == 0)
       {
         empty = 1;
@@ -680,8 +680,8 @@ empty_table(struct mib_node *node)
 /**
  * Tree expansion.
  */
-struct mib_node *
-snmp_expand_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snmp_obj_id *oidret)
+const struct mib_node *
+snmp_expand_tree(const struct mib_node *node, u8_t ident_len, s32_t *ident, struct snmp_obj_id *oidret)
 {
   u8_t node_type, ext_level, climb_tree;
 
@@ -694,11 +694,11 @@ snmp_expand_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
     node_type = node->node_type;
     if ((node_type == MIB_NODE_AR) || (node_type == MIB_NODE_RA))
     {
-      struct mib_array_node *an;
+      const struct mib_array_node *an;
       u16_t i;
 
       /* array node (internal ROM or RAM, fixed length) */
-      an = (struct mib_array_node *)node;
+      an = (const struct mib_array_node *)node;
       if (ident_len > 0)
       {
         i = 0;
@@ -719,7 +719,7 @@ snmp_expand_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
             /* leaf node (e.g. in a fixed size table) */
             if (an->objid[i] > *ident)
             {
-              return (struct mib_node*)an;
+              return (const struct mib_node*)an;
             }
             else if ((i + 1) < an->maxlength)
             {
@@ -727,7 +727,7 @@ snmp_expand_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
               (oidret->len)--;
               oidret->id[oidret->len] = an->objid[i + 1];
               (oidret->len)++;
-              return (struct mib_node*)an;
+              return (const struct mib_node*)an;
             }
             else
             {
@@ -797,7 +797,7 @@ snmp_expand_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
           if (an->nptr[j] == NULL)
           {
             /* leaf node */
-            return (struct mib_node*)an;
+            return (const struct mib_node*)an;
           }
           else
           {
@@ -814,11 +814,11 @@ snmp_expand_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
     }
     else if(node_type == MIB_NODE_LR)
     {
-      struct mib_list_rootnode *lrn;
+      const struct mib_list_rootnode *lrn;
       struct mib_list_node *ln;
 
       /* list root node (internal 'RAM', variable length) */
-      lrn = (struct mib_list_rootnode *)node;
+      lrn = (const struct mib_list_rootnode *)node;
       if (ident_len > 0)
       {
         ln = lrn->head;
@@ -837,7 +837,7 @@ snmp_expand_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
             /* leaf node */
             if (ln->objid > *ident)
             {
-              return (struct mib_node*)lrn;
+              return (const struct mib_node*)lrn;
             }
             else if (ln->next != NULL)
             {
@@ -845,7 +845,7 @@ snmp_expand_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
               (oidret->len)--;
               oidret->id[oidret->len] = ln->next->objid;
               (oidret->len)++;
-              return (struct mib_node*)lrn;
+              return (const struct mib_node*)lrn;
             }
             else
             {
@@ -915,7 +915,7 @@ snmp_expand_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
           {
             /* leaf node */
             LWIP_DEBUGF(SNMP_MIB_DEBUG,("jn->nptr == NULL\n"));
-            return (struct mib_node*)lrn;
+            return (const struct mib_node*)lrn;
           }
           else
           {
@@ -932,11 +932,11 @@ snmp_expand_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
     }
     else if(node_type == MIB_NODE_EX)
     {
-      struct mib_external_node *en;
+      const struct mib_external_node *en;
       s32_t ex_id;
 
       /* external node (addressing and access via functions) */
-      en = (struct mib_external_node *)node;
+      en = (const struct mib_external_node *)node;
       if (ident_len > 0)
       {
         u16_t i, len;
@@ -961,7 +961,7 @@ snmp_expand_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
             /* leaf node */
             if (ex_id > *ident)
             {
-              return (struct mib_node*)en;
+              return (const struct mib_node*)en;
             }
             else if ((i + 1) < len)
             {
@@ -970,7 +970,7 @@ snmp_expand_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
               (oidret->len)--;
               oidret->id[oidret->len] = ex_id;
               (oidret->len)++;
-              return (struct mib_node*)en;
+              return (const struct mib_node*)en;
             }
             else
             {
@@ -1031,7 +1031,7 @@ snmp_expand_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
         {
           /* leaf node */
           LWIP_DEBUGF(SNMP_MIB_DEBUG,("(ext_level + 1) == en->tree_levels\n"));
-          return (struct mib_node*)en;
+          return (const struct mib_node*)en;
         }
         else
         {
@@ -1042,10 +1042,10 @@ snmp_expand_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
     }
     else if(node_type == MIB_NODE_SC)
     {
-      mib_scalar_node *sn;
+      const mib_scalar_node *sn;
 
       /* scalar node  */
-      sn = (mib_scalar_node *)node;
+      sn = (const mib_scalar_node *)node;
       if (ident_len > 0)
       {
         /* at .0 */
@@ -1058,7 +1058,7 @@ snmp_expand_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
         (oidret->len)++;
         /* leaf node */
         LWIP_DEBUGF(SNMP_MIB_DEBUG,("completed scalar leaf\n"));
-        return (struct mib_node*)sn;
+        return (const struct mib_node*)sn;
       }
     }
     else
@@ -1100,7 +1100,7 @@ snmp_expand_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snm
     }
   }
   /* done, found nothing */
-  LWIP_DEBUGF(SNMP_MIB_DEBUG,("expand failed node==%p\n",(void*)node));
+  LWIP_DEBUGF(SNMP_MIB_DEBUG,("expand failed node==%p\n",(const void*)node));
   return NULL;
 }
 
diff --git a/src/core/snmp/msg_in.c b/src/core/snmp/msg_in.c
index 57457b51..64d38b56 100644
--- a/src/core/snmp/msg_in.c
+++ b/src/core/snmp/msg_in.c
@@ -249,7 +249,7 @@ snmp_msg_get_event(u8_t request_id, struct snmp_msg_pstat *msg_ps)
 
   if (msg_ps->state == SNMP_MSG_EXTERNAL_GET_OBJDEF)
   {
-    struct mib_external_node *en;
+    const struct mib_external_node *en;
     struct snmp_name_ptr np;
 
     /* get_object_def() answer*/
@@ -272,7 +272,7 @@ snmp_msg_get_event(u8_t request_id, struct snmp_msg_pstat *msg_ps)
   }
   else if (msg_ps->state == SNMP_MSG_EXTERNAL_GET_VALUE)
   {
-    struct mib_external_node *en;
+    const struct mib_external_node *en;
     struct snmp_varbind *vb;
 
     /* get_value() answer */
@@ -339,7 +339,7 @@ snmp_msg_get_event(u8_t request_id, struct snmp_msg_pstat *msg_ps)
   while ((msg_ps->state == SNMP_MSG_SEARCH_OBJ) &&
          (msg_ps->vb_idx < msg_ps->invb.count))
   {
-    struct mib_node *mn;
+    const struct mib_node *mn;
     struct snmp_name_ptr np;
 
     if (msg_ps->vb_idx == 0)
@@ -353,14 +353,14 @@ snmp_msg_get_event(u8_t request_id, struct snmp_msg_pstat *msg_ps)
     /** test object identifier for .iso.org.dod.internet prefix */
     if (snmp_iso_prefix_tst(msg_ps->vb_ptr->ident_len,  msg_ps->vb_ptr->ident))
     {
-      mn = snmp_search_tree((struct mib_node*)&internet, msg_ps->vb_ptr->ident_len - 4,
+      mn = snmp_search_tree((const struct mib_node*)&internet, msg_ps->vb_ptr->ident_len - 4,
                              msg_ps->vb_ptr->ident + 4, &np);
       if (mn != NULL)
       {
         if (mn->node_type == MIB_NODE_EX)
         {
           /* external object */
-          struct mib_external_node *en = (struct mib_external_node*)mn;
+          const struct mib_external_node *en = (const struct mib_external_node*)mn;
 
           msg_ps->state = SNMP_MSG_EXTERNAL_GET_OBJDEF;
           /* save en && args in msg_ps!! */
@@ -478,7 +478,7 @@ snmp_msg_getnext_event(u8_t request_id, struct snmp_msg_pstat *msg_ps)
 
   if (msg_ps->state == SNMP_MSG_EXTERNAL_GET_OBJDEF)
   {
-    struct mib_external_node *en;
+    const struct mib_external_node *en;
 
     /* get_object_def() answer*/
     en = msg_ps->ext_mib_node;
@@ -499,7 +499,7 @@ snmp_msg_getnext_event(u8_t request_id, struct snmp_msg_pstat *msg_ps)
   }
   else if (msg_ps->state == SNMP_MSG_EXTERNAL_GET_VALUE)
   {
-    struct mib_external_node *en;
+    const struct mib_external_node *en;
     struct snmp_varbind *vb;
 
     /* get_value() answer */
@@ -527,7 +527,7 @@ snmp_msg_getnext_event(u8_t request_id, struct snmp_msg_pstat *msg_ps)
   while ((msg_ps->state == SNMP_MSG_SEARCH_OBJ) &&
          (msg_ps->vb_idx < msg_ps->invb.count))
   {
-    struct mib_node *mn;
+    const struct mib_node *mn;
     struct snmp_obj_id oid;
 
     if (msg_ps->vb_idx == 0)
@@ -543,14 +543,14 @@ snmp_msg_getnext_event(u8_t request_id, struct snmp_msg_pstat *msg_ps)
       if (msg_ps->vb_ptr->ident_len > 3)
       {
         /* can offset ident_len and ident */
-        mn = snmp_expand_tree((struct mib_node*)&internet,
+        mn = snmp_expand_tree((const struct mib_node*)&internet,
                               msg_ps->vb_ptr->ident_len - 4,
                               msg_ps->vb_ptr->ident + 4, &oid);
       }
       else
       {
         /* can't offset ident_len -4, ident + 4 */
-        mn = snmp_expand_tree((struct mib_node*)&internet, 0, NULL, &oid);
+        mn = snmp_expand_tree((const struct mib_node*)&internet, 0, NULL, &oid);
       }
     }
     else
@@ -562,7 +562,7 @@ snmp_msg_getnext_event(u8_t request_id, struct snmp_msg_pstat *msg_ps)
       if (mn->node_type == MIB_NODE_EX)
       {
         /* external object */
-        struct mib_external_node *en = (struct mib_external_node*)mn;
+        const struct mib_external_node *en = (const struct mib_external_node*)mn;
 
         msg_ps->state = SNMP_MSG_EXTERNAL_GET_OBJDEF;
         /* save en && args in msg_ps!! */
@@ -623,7 +623,7 @@ snmp_msg_set_event(u8_t request_id, struct snmp_msg_pstat *msg_ps)
 
   if (msg_ps->state == SNMP_MSG_EXTERNAL_GET_OBJDEF)
   {
-    struct mib_external_node *en;
+    const struct mib_external_node *en;
     struct snmp_name_ptr np;
 
     /* get_object_def() answer*/
@@ -646,7 +646,7 @@ snmp_msg_set_event(u8_t request_id, struct snmp_msg_pstat *msg_ps)
   }
   else if (msg_ps->state == SNMP_MSG_EXTERNAL_SET_TEST)
   {
-    struct mib_external_node *en;
+    const struct mib_external_node *en;
 
     /* set_test() answer*/
     en = msg_ps->ext_mib_node;
@@ -676,7 +676,7 @@ snmp_msg_set_event(u8_t request_id, struct snmp_msg_pstat *msg_ps)
   }
   else if (msg_ps->state == SNMP_MSG_EXTERNAL_GET_OBJDEF_S)
   {
-    struct mib_external_node *en;
+    const struct mib_external_node *en;
     struct snmp_name_ptr np;
 
     /* get_object_def() answer*/
@@ -700,7 +700,7 @@ snmp_msg_set_event(u8_t request_id, struct snmp_msg_pstat *msg_ps)
   }
   else if (msg_ps->state == SNMP_MSG_EXTERNAL_SET_VALUE)
   {
-    struct mib_external_node *en;
+    const struct mib_external_node *en;
 
     /** set_value_a() */
     en = msg_ps->ext_mib_node;
@@ -716,7 +716,7 @@ snmp_msg_set_event(u8_t request_id, struct snmp_msg_pstat *msg_ps)
   while ((msg_ps->state == SNMP_MSG_SEARCH_OBJ) &&
          (msg_ps->vb_idx < msg_ps->invb.count))
   {
-    struct mib_node *mn;
+    const struct mib_node *mn;
     struct snmp_name_ptr np;
 
     if (msg_ps->vb_idx == 0)
@@ -730,14 +730,14 @@ snmp_msg_set_event(u8_t request_id, struct snmp_msg_pstat *msg_ps)
     /** test object identifier for .iso.org.dod.internet prefix */
     if (snmp_iso_prefix_tst(msg_ps->vb_ptr->ident_len,  msg_ps->vb_ptr->ident))
     {
-      mn = snmp_search_tree((struct mib_node*)&internet, msg_ps->vb_ptr->ident_len - 4,
+      mn = snmp_search_tree((const struct mib_node*)&internet, msg_ps->vb_ptr->ident_len - 4,
                              msg_ps->vb_ptr->ident + 4, &np);
       if (mn != NULL)
       {
         if (mn->node_type == MIB_NODE_EX)
         {
           /* external object */
-          struct mib_external_node *en = (struct mib_external_node*)mn;
+          const struct mib_external_node *en = (const struct mib_external_node*)mn;
 
           msg_ps->state = SNMP_MSG_EXTERNAL_GET_OBJDEF;
           /* save en && args in msg_ps!! */
@@ -811,7 +811,7 @@ snmp_msg_set_event(u8_t request_id, struct snmp_msg_pstat *msg_ps)
   while ((msg_ps->state == SNMP_MSG_INTERNAL_SET_VALUE) &&
          (msg_ps->vb_idx < msg_ps->invb.count))
   {
-    struct mib_node *mn;
+    const struct mib_node *mn;
     struct snmp_name_ptr np;
 
     if (msg_ps->vb_idx == 0)
@@ -823,7 +823,7 @@ snmp_msg_set_event(u8_t request_id, struct snmp_msg_pstat *msg_ps)
       msg_ps->vb_ptr = msg_ps->vb_ptr->next;
     }
     /* skip iso prefix test, was done previously while settesting() */
-    mn = snmp_search_tree((struct mib_node*)&internet, msg_ps->vb_ptr->ident_len - 4,
+    mn = snmp_search_tree((const struct mib_node*)&internet, msg_ps->vb_ptr->ident_len - 4,
                            msg_ps->vb_ptr->ident + 4, &np);
     /* check if object is still available
        (e.g. external hot-plug thingy present?) */
@@ -832,7 +832,7 @@ snmp_msg_set_event(u8_t request_id, struct snmp_msg_pstat *msg_ps)
       if (mn->node_type == MIB_NODE_EX)
       {
         /* external object */
-        struct mib_external_node *en = (struct mib_external_node*)mn;
+        const struct mib_external_node *en = (const struct mib_external_node*)mn;
 
         msg_ps->state = SNMP_MSG_EXTERNAL_GET_OBJDEF_S;
         /* save en && args in msg_ps!! */
diff --git a/src/core/snmp/msg_out.c b/src/core/snmp/msg_out.c
index 1a915931..4e840481 100644
--- a/src/core/snmp/msg_out.c
+++ b/src/core/snmp/msg_out.c
@@ -571,7 +571,7 @@ snmp_trap_header_enc(struct snmp_msg_trap *m_trap, struct pbuf *p)
   ofs += 1;
   snmp_asn1_enc_length(p, ofs, m_trap->thl.comlen);
   ofs += m_trap->thl.comlenlen;
-  snmp_asn1_enc_raw(p, ofs, m_trap->thl.comlen, (u8_t *)&snmp_community_trap[0]);
+  snmp_asn1_enc_raw(p, ofs, m_trap->thl.comlen, (const u8_t *)&snmp_community_trap[0]);
   ofs += m_trap->thl.comlen;
 
   snmp_asn1_enc_type(p, ofs, (SNMP_ASN1_CONTXT | SNMP_ASN1_CONSTR | SNMP_ASN1_PDU_TRAP));
diff --git a/src/include/lwip/snmp_asn1.h b/src/include/lwip/snmp_asn1.h
index b05c8e72..147f5db9 100644
--- a/src/include/lwip/snmp_asn1.h
+++ b/src/include/lwip/snmp_asn1.h
@@ -90,7 +90,7 @@ err_t snmp_asn1_enc_length(struct pbuf *p, u16_t ofs, u16_t length);
 err_t snmp_asn1_enc_u32t(struct pbuf *p, u16_t ofs, u16_t octets_needed, u32_t value);
 err_t snmp_asn1_enc_s32t(struct pbuf *p, u16_t ofs, u16_t octets_needed, s32_t value);
 err_t snmp_asn1_enc_oid(struct pbuf *p, u16_t ofs, u8_t ident_len, const s32_t *ident);
-err_t snmp_asn1_enc_raw(struct pbuf *p, u16_t ofs, u16_t raw_len, u8_t *raw);
+err_t snmp_asn1_enc_raw(struct pbuf *p, u16_t ofs, u16_t raw_len, const u8_t *raw);
 
 #ifdef __cplusplus
 }
diff --git a/src/include/lwip/snmp_msg.h b/src/include/lwip/snmp_msg.h
index 81056abc..47b92ba8 100644
--- a/src/include/lwip/snmp_msg.h
+++ b/src/include/lwip/snmp_msg.h
@@ -241,7 +241,7 @@ struct snmp_msg_pstat
   /* one out of MSG_EMPTY, MSG_DEMUX, MSG_INTERNAL, MSG_EXTERNAL_x */
   u8_t state;
   /* saved arguments for MSG_EXTERNAL_x */
-  struct mib_external_node *ext_mib_node;
+  const struct mib_external_node *ext_mib_node;
   struct snmp_name_ptr ext_name_ptr;
   struct obj_def ext_object_def;
   struct snmp_obj_id ext_oid;
diff --git a/src/include/lwip/snmp_structs.h b/src/include/lwip/snmp_structs.h
index b735c71e..c8293459 100644
--- a/src/include/lwip/snmp_structs.h
+++ b/src/include/lwip/snmp_structs.h
@@ -138,7 +138,7 @@ struct mib_array_node
 
   /* additional struct members */
   const s32_t *objid;
-  struct mib_node* const *nptr;
+  const struct mib_node* const *nptr;
 };
 
 /** derived node, points to a fixed size mem_malloced array
@@ -254,8 +254,8 @@ s8_t snmp_mib_node_insert(struct mib_list_rootnode *rn, s32_t objid, struct mib_
 s8_t snmp_mib_node_find(struct mib_list_rootnode *rn, s32_t objid, struct mib_list_node **fn);
 struct mib_list_rootnode *snmp_mib_node_delete(struct mib_list_rootnode *rn, struct mib_list_node *n);
 
-struct mib_node* snmp_search_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snmp_name_ptr *np);
-struct mib_node* snmp_expand_tree(struct mib_node *node, u8_t ident_len, s32_t *ident, struct snmp_obj_id *oidret);
+const struct mib_node* snmp_search_tree(const struct mib_node *node, u8_t ident_len, s32_t *ident, struct snmp_name_ptr *np);
+const struct mib_node* snmp_expand_tree(const struct mib_node *node, u8_t ident_len, s32_t *ident, struct snmp_obj_id *oidret);
 u8_t snmp_iso_prefix_tst(u8_t ident_len, s32_t *ident);
 u8_t snmp_iso_prefix_expand(u8_t ident_len, s32_t *ident, struct snmp_obj_id *oidret);