diff --git a/lib/in46_addr.c b/lib/in46_addr.c
index 844e318..a220583 100644
--- a/lib/in46_addr.c
+++ b/lib/in46_addr.c
@@ -74,6 +74,23 @@
 		return 0;
 }
 
+/*! Determine if two in46_addr prefix are equal or not
+ *  The prefix length is determined by the shortest of the prefixes of a and b
+ *  \returns 1 in case the common prefix are equal; 0 otherwise */
+int in46a_prefix_equal(const struct in46_addr *a, const struct in46_addr *b)
+{
+	unsigned int len;
+	if (a->len > b->len)
+		len = b->len;
+	else
+		len = a->len;
+
+	if (!memcmp(&a->v6, &b->v6, len))
+		return 1;
+	else
+		return 0;
+}
+
 /*! Match if IPv6 addr1 + addr2 are within same \a mask */
 static int ipv6_within_mask(const struct in6_addr *addr1, const struct in6_addr *addr2,
 			    const struct in6_addr *mask)
diff --git a/lib/in46_addr.h b/lib/in46_addr.h
index a0ad6e1..0afd2b4 100644
--- a/lib/in46_addr.h
+++ b/lib/in46_addr.h
@@ -18,6 +18,7 @@
 extern int in46a_to_sas(struct sockaddr_storage *out, const struct in46_addr *in);
 extern const char *in46a_ntop(const struct in46_addr *in, char *dst, socklen_t dst_size);
 extern int in46a_equal(const struct in46_addr *a, const struct in46_addr *b);
+extern int in46a_prefix_equal(const struct in46_addr *a, const struct in46_addr *b);
 extern int in46a_within_mask(const struct in46_addr *addr, const struct in46_addr *net, size_t prefixlen);
 
 int in46a_to_eua(const struct in46_addr *src, struct ul66_t *eua);