diff --git a/isisd/isis_pdu.h b/isisd/isis_pdu.h
index 95c1ee4..9e21553 100644
--- a/isisd/isis_pdu.h
+++ b/isisd/isis_pdu.h
@@ -95,7 +95,7 @@
   u_char version2;
   u_char reserved;
   u_char max_area_addrs;
-};
+} __attribute__ ((packed));
 
 #define ISIS_FIXED_HDR_LEN 8
 
@@ -186,6 +186,17 @@
 } __attribute__ ((packed));
 #define ISIS_LSP_HDR_LEN 19
 
+/*
+ * Since the length field of LSP Entries TLV is one byte long, and each LSP
+ * entry is LSP_ENTRIES_LEN (16) bytes long, the maximum number of LSP entries
+ * can be accomodated in a TLV is
+ * 255 / 16 = 15.
+ * 
+ * Therefore, the maximum length of the LSP Entries TLV is
+ * 16 * 15 + 2 (header) = 242 bytes.
+ */
+#define MAX_LSP_ENTRIES_TLV_SIZE 242
+
 #define L1_COMPLETE_SEQ_NUM  24
 #define L2_COMPLETE_SEQ_NUM  25
 /*
@@ -241,6 +252,8 @@
 #define ISIS_SNP_PSNP_FLAG 0
 #define ISIS_SNP_CSNP_FLAG 1
 
+#define ISIS_AUTH_MD5_SIZE       16U
+
 /*
  * Sending functions
  */
@@ -258,8 +271,4 @@
 void fill_fixed_hdr (struct isis_fixed_hdr *hdr, u_char pdu_type);
 int send_hello (struct isis_circuit *circuit, int level);
 
-
-int authentication_check (struct isis_passwd *one,
-			  struct isis_passwd *theother);
-
 #endif /* _ZEBRA_ISIS_PDU_H */