diff --git a/scheme/lib/dns.scm b/scheme/lib/dns.scm
index 283a97d..e3469aa 100644
--- a/scheme/lib/dns.scm
+++ b/scheme/lib/dns.scm
@@ -264,7 +264,8 @@
   (if *debug* (display "name->octets\n"))
   (let loop ((s s))
     (cond
-     ((regexp-search (posix-string->regexp "^([^.]*)\\.(.*)") s)
+     ((regexp-search (rx (: bos (submatch (* (~ "."))) "." (submatch (* any))))
+		     s)
       => (lambda (match)
 	   (append
 	    (encode-portion (match:substring match 1))
@@ -276,6 +277,7 @@
 	   (encode-portion s)
 	   (list *nul*)))))))
 
+
 ;; for tcp: message has to be tagged with its length
 (define (add-size-tag m)
   (if *debug* (display "add-size-tag\n"))
@@ -322,17 +324,25 @@
 	  (char->ascii (list-ref s 2))
 	  (char->ascii (list-ref s 3))))
 
+(define ip-string-regexp (rx (: bos 
+			  (submatch (** 1 3 digit)) "." 
+			  (submatch (** 1 3 digit)) "." 
+			  (submatch (** 1 3 digit)) "." 
+			  (submatch (** 1 3 digit)) 
+			  eos)))
+
 ;; converts an ip-string to octets
 (define (string->octet-ip s)
-  (if *debug* (display "string->octet-ip\n"))
-  (let loop ((s s)
-	     (result '()))
-    (cond
-     ((regexp-search (posix-string->regexp "^([^.]*)\\.(.*)") s)
-      => (lambda (match)
-	   (loop (match:substring match 2) (append result (list (ascii->char (string->number (match:substring match 1))))))))
-     (else
-      (append result (list (ascii->char (string->number s))))))))
+  (cond
+   ((regexp-search ip-string-regexp  s)
+    => (lambda (match)
+	 (list
+	  (ascii->char (string->number (match:substring match 1)))
+	  (ascii->char (string->number (match:substring match 2)))
+	  (ascii->char (string->number (match:substring match 3)))
+	  (ascii->char (string->number (match:substring match 4))))))
+   (else
+    (error "invalid ip-string" s))))
 
 ;; calculates a "random" number, needed for message-ids
 (define random
@@ -344,24 +354,21 @@
 
 ;; checks if a string is a ip
 (define (ip-string? s)
-  (if *debug* (display "ip-string->in-addr\n"))
-  (let loop ((s s)
-	     (count 0))
-    (cond
-     ((regexp-search (posix-string->regexp "^([^.]*)\\.(.*)") s)
-      => (lambda (match)
-	   (let* ((portion (match:substring match 1))
-		  (number (string->number portion)))
-	     (if (and number (< number 256))
-		 (loop (match:substring match 2) (+ count 1))
-		 #f))))
-     (else
-      (let ((number (string->number s)))
-	(and number 
-	     (< number 256) 
-	     (= count 3)
-	     #t))))))
+  (define (byte-as-string? string) 
+    (let ((number (string->number string)))
+      (and number
+	   (>= number 0)
+	   (< number 256))))
+  (cond
+   ((regexp-search ip-string-regexp  s)
+    => (lambda (match)
+	 (and (byte-as-string? (match:substring match 1))
+	      (byte-as-string? (match:substring match 2))
+	      (byte-as-string? (match:substring match 3))
+	      (byte-as-string? (match:substring match 4)))))
+   (else #f)))
 
+    
 ;; checks if v is a address32
 (define (address32? v)
   (and (number? v)
@@ -369,25 +376,17 @@
 
 ;; returns a in-addr.arpa name-string or #f (needed to resolve hostname by ip)
 (define (ip-string->in-addr s)
-  (if *debug* (display "ip-string->in-addr\n"))
-  (let loop ((s s)
-	     (count 0)
-	     (result ""))
-    (cond
-     ((regexp-search (posix-string->regexp "^([^.]*)\\.(.*)") s)
-      => (lambda (match)
-	   (let* ((portion (match:substring match 1))
-		  (number (string->number portion)))
-	     (if (and number (< number 256))
-		 (loop (match:substring match 2) (+ count 1) (string-append portion "." result))
-		 #f))))
-     (else
-      (let ((number (string->number s)))
-	(and number 
-	     (< number 256) 
-	     (= count 3)
-	     (string-append s "." result "in-addr.arpa")))))))
-
+  (cond
+   ((regexp-search ip-string-regexp s)
+    => (lambda (match)
+	 (string-append
+	  (match:substring match 4) "."
+	  (match:substring match 3) "."
+	  (match:substring match 2) "."
+	  (match:substring match 1) "."
+	  "in-addr.arpa")))
+   (else #f)))
+      
 ;; filters types in a list of rrs 
 (define (filter-type list type)
   (if *debug* (display "ip-string->in-addr\n"))
@@ -1045,9 +1044,11 @@
 	    (if (null? ns)
 		(dns-error 'no-nameservers)
 		ns))
-	   ((regexp-search 
-	     (posix-string->regexp 
-	      "nameserver[ 	]+([0-9]+\\.[0-9]+\\.[0-9]+\\.[0-9]+)") l)
+	   ((regexp-search
+	     (rx (: "nameserver" (+ (| " " "\t") 
+				    (submatch (** 1 3 digit) 
+					      (= 3 (: "." (** 1 3 digit)))))))
+	     l)
 	    => (lambda (match)
 		 (loop (append ns (list (ip-string->address32 (match:substring match 1)))))))
 	   (else