diff --git a/conf/confbase.Y b/conf/confbase.Y
index 06698833..9b4f54e9 100644
--- a/conf/confbase.Y
+++ b/conf/confbase.Y
@@ -178,7 +178,7 @@ pxlen4:
    }
  | ':' IP4 {
      $$ = ip4_masklen($2);
-     if ($$ == 255) cf_error("Invalid netmask %I", $2); /* XXXX */
+     if ($$ == 255) cf_error("Invalid netmask %I4", $2);
    }
  ;
 
diff --git a/lib/net.c b/lib/net.c
index 76ecd460..a78111ab 100644
--- a/lib/net.c
+++ b/lib/net.c
@@ -31,17 +31,16 @@ net_format(const net_addr *N, char *buf, int buflen)
 {
   net_addr_union *n = (void *) N;
 
-  /* XXXX fix %I vs %R */
   switch (n->n.type)
   {
   case NET_IP4:
-    return bsnprintf(buf, buflen, "%R/%d", n->ip4.prefix, n->ip4.pxlen);
+    return bsnprintf(buf, buflen, "%I4/%d", n->ip4.prefix, n->ip4.pxlen);
   case NET_IP6:
-    return bsnprintf(buf, buflen, "%I/%d", n->ip6.prefix, n->ip6.pxlen);
+    return bsnprintf(buf, buflen, "%I6/%d", n->ip6.prefix, n->ip6.pxlen);
   case NET_VPN4:
-    return bsnprintf(buf, buflen, "%u:%u %R/%d", (u32) (n->vpn4.rd >> 32), (u32) n->vpn4.rd, n->vpn4.prefix, n->vpn4.pxlen);
+    return bsnprintf(buf, buflen, "%u:%u %I4/%d", (u32) (n->vpn4.rd >> 32), (u32) n->vpn4.rd, n->vpn4.prefix, n->vpn4.pxlen);
   case NET_VPN6:
-    return bsnprintf(buf, buflen, "%u:%u %I/%d", (u32) (n->vpn6.rd >> 32), (u32) n->vpn6.rd, n->vpn6.prefix, n->vpn6.pxlen);
+    return bsnprintf(buf, buflen, "%u:%u %I6/%d", (u32) (n->vpn6.rd >> 32), (u32) n->vpn6.rd, n->vpn6.prefix, n->vpn6.pxlen);
   }
 
   return 0;
diff --git a/lib/printf.c b/lib/printf.c
index 071fc953..ce12202c 100644
--- a/lib/printf.c
+++ b/lib/printf.c
@@ -118,15 +118,15 @@ static char * number(char * str, long num, int base, int size, int precision,
  * @fmt: format string
  * @args: a list of arguments to be formatted
  *
- * This functions acts like ordinary sprintf() except that it checks
- * available space to avoid buffer overflows and it allows some more
- * format specifiers: |%I| for formatting of IP addresses (any non-zero
- * width is automatically replaced by standard IP address width which
- * depends on whether we use IPv4 or IPv6; |%#I| gives hexadecimal format),
- * |%R| for Router / Network ID (u32 value printed as IPv4 address)
- * and |%m| resp. |%M| for error messages (uses strerror() to translate @errno code to
- * message text). On the other hand, it doesn't support floating
- * point numbers.
+ * This functions acts like ordinary sprintf() except that it checks available
+ * space to avoid buffer overflows and it allows some more format specifiers:
+ * |%I| for formatting of IP addresses (width of 1 is automatically replaced by
+ * standard IP address width which depends on whether we use IPv4 or IPv6; |%I4|
+ * or |%I6| can be used for explicit ip4_addr / ip6_addr arguments, |%N| for
+ * generic network addresses (net_addr *), |%R| for Router / Network ID (u32
+ * value printed as IPv4 address) and |%m| resp. |%M| for error messages (uses
+ * strerror() to translate @errno code to message text). On the other hand, it
+ * doesn't support floating point numbers.
  *
  * Result: number of characters of the output string or -1 if
  * the buffer space was insufficient.
@@ -168,7 +168,7 @@ int bvsnprintf(char *buf, int size, const char *fmt, va_list args)
 				case '#': flags |= SPECIAL; goto repeat;
 				case '0': flags |= ZEROPAD; goto repeat;
 				}
-		
+
 		/* get field width */
 		field_width = -1;
 		if (is_digit(*fmt))
@@ -186,7 +186,7 @@ int bvsnprintf(char *buf, int size, const char *fmt, va_list args)
 		/* get the precision */
 		precision = -1;
 		if (*fmt == '.') {
-			++fmt;	
+			++fmt;
 			if (is_digit(*fmt))
 				precision = skip_atoi(&fmt);
 			else if (*fmt == '*') {
@@ -289,22 +289,36 @@ int bvsnprintf(char *buf, int size, const char *fmt, va_list args)
 			continue;
 
 		/* IP address */
-		case 'I': {
-			ip_addr a = va_arg(args, ip_addr);
-			if (flags & SPECIAL)
-				ip6_ntox(ipa_to_ip6(a), ipbuf);
-			else {
-				// XXXX better IPv4 / IPv6 distinction
-				if (ipa_is_ip4(a))
+		case 'I':
+			if (fmt[1] == '4') {
+				/* Explicit IPv4 address */
+				ip4_addr a = va_arg(args, ip4_addr);
+				ip4_ntop(a, ipbuf);
+				i = IP4_MAX_TEXT_LENGTH;
+			} else if (fmt[1] == '6') {
+				/* Explicit IPv6 address */
+				ip6_addr a = va_arg(args, ip6_addr);
+				ip6_ntop(a, ipbuf);
+				i = IP6_MAX_TEXT_LENGTH;
+			} else {
+				/* Just IP address */
+				ip_addr a = va_arg(args, ip_addr);
+
+				if (ipa_is_ip4(a)) {
 					ip4_ntop(ipa_to_ip4(a), ipbuf);
-				else
+					i = IP4_MAX_TEXT_LENGTH;
+				} else {
 					ip6_ntop(ipa_to_ip6(a), ipbuf);
-				if (field_width == 1)
-					field_width = (ipa_is_ip4(a) ? IP4_MAX_TEXT_LENGTH : IP6_MAX_TEXT_LENGTH);
+					i = IP6_MAX_TEXT_LENGTH;
+				}
 			}
+
 			s = ipbuf;
+			if (field_width == 1)
+				field_width = i;
+
 			goto str;
-			}
+
 		/* Interface scope after link-local IP address */
 		case 'J':
 			iface = va_arg(args, struct iface *);
diff --git a/sysdep/linux/netlink.c b/sysdep/linux/netlink.c
index be790c29..530cb240 100644
--- a/sysdep/linux/netlink.c
+++ b/sysdep/linux/netlink.c
@@ -691,7 +691,7 @@ nl_parse_addr4(struct ifaddrmsg *i, int scan, int new)
 	    ifa.brd = ipa_from_ip4(xbrd);
 	  else if (ifi->flags & IF_TMP_DOWN) /* Complain only during the first scan */
 	    {
-	      log(L_ERR "KIF: Invalid broadcast address %I for %s", xbrd, ifi->name);
+	      log(L_ERR "KIF: Invalid broadcast address %I4 for %s", xbrd, ifi->name);
 	      ifa.brd = ipa_from_ip4(ybrd);
 	    }
 	}