diff --git a/arp.rkt b/arp.rkt
index f3071a7..a6ab180 100644
--- a/arp.rkt
+++ b/arp.rkt
@@ -109,9 +109,10 @@
 	 (sender-protocol-address0 :: binary bytes plen)
 	 (target-hardware-address0 :: binary bytes hlen)
 	 (target-protocol-address0 :: binary bytes plen)
-	 (:: binary) ;; TODO: are the extra zeros coming from the
-		     ;; router real, or an artifact of my
-		     ;; packet-capture implementation?
+	 (:: binary) ;; The extra zeros exist because ethernet packets
+		     ;; have a minimum size. This is, in part, why
+		     ;; IPv4 headers have a total-length field, so
+		     ;; that the zero padding can be removed.
 	 ]
        (let ()
 	 (define sender-protocol-address (bit-string->bytes sender-protocol-address0))
diff --git a/ip.rkt b/ip.rkt
index 2f7d999..452662a 100644
--- a/ip.rkt
+++ b/ip.rkt
@@ -247,14 +247,16 @@
        (source-ip0 :: binary bits 32)
        (destination-ip0 :: binary bits 32)
        (rest :: binary) ]
-     (let ((source-ip (bit-string->bytes source-ip0))
-	   (destination-ip (bit-string->bytes destination-ip0))
-	   (options-length (* 4 (- header-length IP-MINIMUM-HEADER-LENGTH))))
+     (let* ((source-ip (bit-string->bytes source-ip0))
+	    (destination-ip (bit-string->bytes destination-ip0))
+	    (options-length (* 4 (- header-length IP-MINIMUM-HEADER-LENGTH)))
+	    (data-length (- total-length (* 4 header-length))))
        (if (and (>= header-length 5)
 		(>= (bit-string-byte-count body) (* header-length 4)))
 	   (bit-string-case rest
 	     ([ (opts :: binary bytes options-length)
-		(data :: binary) ]
+		(data :: binary bytes data-length)
+		(:: binary) ] ;; Very short ethernet packets have a trailer of zeros
 	      (ip-packet interface-name
 			 (bit-string->bytes source-ip)
 			 (bit-string->bytes destination-ip)