diff --git a/isisd/isis_adjacency.c b/isisd/isis_adjacency.c
index fb14a21f0d..d492eafa42 100644
--- a/isisd/isis_adjacency.c
+++ b/isisd/isis_adjacency.c
@@ -52,7 +52,7 @@
 extern struct isis *isis;
 
 static struct isis_adjacency *
-adj_alloc (u_char * id)
+adj_alloc (const u_char *id)
 {
   struct isis_adjacency *adj;
 
@@ -63,7 +63,7 @@ adj_alloc (u_char * id)
 }
 
 struct isis_adjacency *
-isis_new_adj (u_char * id, u_char * snpa, int level,
+isis_new_adj (const u_char * id, const u_char * snpa, int level,
 	      struct isis_circuit *circuit)
 {
   struct isis_adjacency *adj;
@@ -104,7 +104,7 @@ isis_new_adj (u_char * id, u_char * snpa, int level,
 }
 
 struct isis_adjacency *
-isis_adj_lookup (u_char * sysid, struct list *adjdb)
+isis_adj_lookup (const u_char * sysid, struct list *adjdb)
 {
   struct isis_adjacency *adj;
   struct listnode *node;
@@ -117,7 +117,7 @@ isis_adj_lookup (u_char * sysid, struct list *adjdb)
 }
 
 struct isis_adjacency *
-isis_adj_lookup_snpa (u_char * ssnpa, struct list *adjdb)
+isis_adj_lookup_snpa (const u_char * ssnpa, struct list *adjdb)
 {
   struct listnode *node;
   struct isis_adjacency *adj;
diff --git a/isisd/isis_adjacency.h b/isisd/isis_adjacency.h
index caa3107db2..99d0c493ba 100644
--- a/isisd/isis_adjacency.h
+++ b/isisd/isis_adjacency.h
@@ -101,10 +101,10 @@ struct isis_adjacency
   struct isis_circuit *circuit;	/* back pointer */
 };
 
-struct isis_adjacency *isis_adj_lookup (u_char * sysid, struct list *adjdb);
-struct isis_adjacency *isis_adj_lookup_snpa (u_char * ssnpa,
+struct isis_adjacency *isis_adj_lookup (const u_char * sysid, struct list *adjdb);
+struct isis_adjacency *isis_adj_lookup_snpa (const u_char * ssnpa,
 					     struct list *adjdb);
-struct isis_adjacency *isis_new_adj (u_char * id, u_char * snpa, int level,
+struct isis_adjacency *isis_new_adj (const u_char * id, const u_char * snpa, int level,
 				     struct isis_circuit *circuit);
 void isis_delete_adj (void *adj);
 void isis_adj_state_change (struct isis_adjacency *adj,
diff --git a/isisd/isis_dynhn.c b/isisd/isis_dynhn.c
index ffb0d503fb..412f098a1b 100644
--- a/isisd/isis_dynhn.c
+++ b/isisd/isis_dynhn.c
@@ -78,7 +78,7 @@ dyn_cache_cleanup (struct thread *thread)
 }
 
 struct isis_dynhn *
-dynhn_find_by_id (u_char * id)
+dynhn_find_by_id (const u_char * id)
 {
   struct listnode *node = NULL;
   struct isis_dynhn *dyn = NULL;
@@ -104,7 +104,7 @@ dynhn_find_by_name (const char *hostname)
 }
 
 void
-isis_dynhn_insert (u_char * id, struct hostname *hostname, int level)
+isis_dynhn_insert (const u_char * id, struct hostname *hostname, int level)
 {
   struct isis_dynhn *dyn;
 
@@ -135,7 +135,7 @@ isis_dynhn_insert (u_char * id, struct hostname *hostname, int level)
 }
 
 void
-isis_dynhn_remove (u_char * id)
+isis_dynhn_remove (const u_char * id)
 {
   struct isis_dynhn *dyn;
 
diff --git a/isisd/isis_dynhn.h b/isisd/isis_dynhn.h
index 379c454fc5..f06a067be1 100644
--- a/isisd/isis_dynhn.h
+++ b/isisd/isis_dynhn.h
@@ -32,9 +32,9 @@ struct isis_dynhn
 };
 
 void dyn_cache_init (void);
-void isis_dynhn_insert (u_char * id, struct hostname *hostname, int level);
-void isis_dynhn_remove (u_char * id);
-struct isis_dynhn *dynhn_find_by_id (u_char * id);
+void isis_dynhn_insert (const u_char * id, struct hostname *hostname, int level);
+void isis_dynhn_remove (const u_char * id);
+struct isis_dynhn *dynhn_find_by_id (const u_char * id);
 struct isis_dynhn *dynhn_find_by_name (const char *hostname);
 void dynhn_print_all (struct vty *vty);
 
diff --git a/isisd/isis_misc.c b/isisd/isis_misc.c
index 968fa05fe3..230fe24387 100644
--- a/isisd/isis_misc.c
+++ b/isisd/isis_misc.c
@@ -63,7 +63,7 @@ char nlpidstring[30];
  * This converts the isonet to its printable format
  */
 const char *
-isonet_print (u_char * from, int len)
+isonet_print (const u_char * from, int len)
 {
   int i = 0;
   char *pos = isonet;
@@ -370,7 +370,7 @@ syst2string (int type)
  * Print functions - we print to static vars
  */
 const char *
-snpa_print (u_char * from)
+snpa_print (const u_char * from)
 {
   int i = 0;
   u_char *pos = (u_char *)snpa;
@@ -402,7 +402,7 @@ snpa_print (u_char * from)
 }
 
 const char *
-sysid_print (u_char * from)
+sysid_print (const u_char * from)
 {
   int i = 0;
   char *pos = sysid;
@@ -434,7 +434,7 @@ sysid_print (u_char * from)
 }
 
 const char *
-rawlspid_print (u_char * from)
+rawlspid_print (const u_char * from)
 {
   char *pos = lspid;
   if (!from)
@@ -553,7 +553,7 @@ unix_hostname (void)
  * If no dynamic hostname found then returns formatted system ID.
  */
 const char *
-print_sys_hostname (u_char *sysid)
+print_sys_hostname (const u_char *sysid)
 {
   struct isis_dynhn *dyn;
 
diff --git a/isisd/isis_misc.h b/isisd/isis_misc.h
index 0cd65a66ae..37eaea1549 100644
--- a/isisd/isis_misc.h
+++ b/isisd/isis_misc.h
@@ -41,14 +41,14 @@ int sysid2buff (u_char *, const char *);
 /*
  * Printing functions
  */
-const char *isonet_print (u_char *, int len);
-const char *sysid_print (u_char *);
-const char *snpa_print (u_char *);
-const char *rawlspid_print (u_char *);
+const char *isonet_print (const u_char *, int len);
+const char *sysid_print (const u_char *);
+const char *snpa_print (const u_char *);
+const char *rawlspid_print (const u_char *);
 const char *time2string (u_int32_t);
 /* typedef struct nlpids nlpids; */
 char *nlpid2string (struct nlpids *);
-const char *print_sys_hostname (u_char *sysid);
+const char *print_sys_hostname (const u_char *sysid);
 void zlog_dump_data (void *data, int len);
 
 /*
diff --git a/isisd/isis_pdu.c b/isisd/isis_pdu.c
index b47a8646ea..2b1d43f3c3 100644
--- a/isisd/isis_pdu.c
+++ b/isisd/isis_pdu.c
@@ -884,7 +884,7 @@ process_p2p_hello (struct isis_circuit *circuit)
  * Process IS-IS LAN Level 1/2 Hello PDU
  */
 static int
-process_lan_hello (int level, struct isis_circuit *circuit, u_char * ssnpa)
+process_lan_hello (int level, struct isis_circuit *circuit, const u_char *ssnpa)
 {
   int retval = ISIS_OK;
   struct isis_lan_hello_hdr hdr;
@@ -1272,7 +1272,7 @@ out:
  * Section 7.3.15.1 - Action on receipt of a link state PDU
  */
 static int
-process_lsp (int level, struct isis_circuit *circuit, u_char * ssnpa)
+process_lsp (int level, struct isis_circuit *circuit, const u_char *ssnpa)
 {
   struct isis_link_state_hdr *hdr;
   struct isis_adjacency *adj = NULL;
@@ -1621,7 +1621,7 @@ dontcheckadj:
 
 static int
 process_snp (int snp_type, int level, struct isis_circuit *circuit,
-	     u_char * ssnpa)
+	     const u_char *ssnpa)
 {
   int retval = ISIS_OK;
   int cmp, own_lsp;
@@ -1917,7 +1917,7 @@ process_snp (int snp_type, int level, struct isis_circuit *circuit,
 }
 
 static int
-process_csnp (int level, struct isis_circuit *circuit, u_char * ssnpa)
+process_csnp (int level, struct isis_circuit *circuit, const u_char *ssnpa)
 {
   if (isis->debugs & DEBUG_SNP_PACKETS)
     {
@@ -1941,7 +1941,7 @@ process_csnp (int level, struct isis_circuit *circuit, u_char * ssnpa)
 }
 
 static int
-process_psnp (int level, struct isis_circuit *circuit, u_char * ssnpa)
+process_psnp (int level, struct isis_circuit *circuit, const u_char *ssnpa)
 {
   if (isis->debugs & DEBUG_SNP_PACKETS)
     {