diff --git a/lib/ChangeLog b/lib/ChangeLog
index 514f47a..7c372df 100644
--- a/lib/ChangeLog
+++ b/lib/ChangeLog
@@ -1,3 +1,8 @@
+2004-08-26  Greg Troxel  <gdt@fnord.ir.bbn.com>
+
+	* sockopt.h: Define method-independent macro for callers of
+	get_ifindex to use for cmsg length.
+
 2004-08-19 Paul Jakma <paul@dishone.st>
 
 	* zebra.h: add MAX and MIN defines (eg for ospf6d)
diff --git a/lib/sockopt.h b/lib/sockopt.h
index b7aa1b3..cd79718 100644
--- a/lib/sockopt.h
+++ b/lib/sockopt.h
@@ -31,25 +31,46 @@
 int setsockopt_ipv6_multicast_loop (int, int);
 #endif /* HAVE_IPV6 */
 
-#if defined (IP_PKTINFO)
+/*
+ * It is OK to reference in6_pktinfo here without a protecting #if
+ * because this macro will only be used #if HAVE_IPV6, and in6_pktinfo
+ * is not optional for HAVE_IPV6.
+ */
+#define SOPT_SIZE_CMSG_PKTINFO_IPV6() (sizeof (struct in6_pktinfo));
 
+/*
+ * Size defines for control messages used to get ifindex.  We define
+ * values for each method, and define a macro that can be used by code
+ * that is unaware of which method is in use.
+ * XXX Needs to use CMSG_DATA and CMSG_ALIGN.
+ */
+#if defined (IP_PKTINFO)
+/* Linux in_pktinfo. */
 #define SOPT_SIZE_CMSG_PKTINFO_IPV4()  (sizeof (struct in_pktinfo))
-#define SOPT_SIZE_CMSG_IFINDEX_IPV4 SOPT_SIZE_CMSG_PKTINFO_IPV4
+
+/* XXX This should perhaps be defined even if IP_PKTINFO is not. */
 #define SOPT_SIZE_CMSG_PKTINFO(af) \
   ((af == AF_INET) ? SOPT_SIZE_CMSG_PKTINFO_IPV4() \
                    : SOPT_SIZE_CMSG_PKTINFO_IPV6()
 
+#define SOPT_SIZE_CMSG_IFINDEX_IPV4()	SOPT_SIZE_CMSG_PKTINFO_IPV4
+
 #elif defined (IP_RECVIF)
+/* BSD/Solaris.  Arguably these should say RECVIF rather than IFINDEX. */
+
 #if defined (SUNOS_5)
 #define SOPT_SIZE_CMSG_IFINDEX_IPV4()  (sizeof (uint_t))
 #else
-#define SOPT_SIZE_CMSG_IFINDEX_IPV4()  (sizeof (struct sockaddr_dl))
+#define SOPT_SIZE_CMSG_IFINDEX_IPV4()	\
+	__CMSG_ALIGN((sizeof (struct sockaddr_dl)))
 #endif /* SUNOS_5 */
 
 #endif
 
-#define SOPT_SIZE_CMSG_PKTINFO_IPV6() (sizeof (struct in6_pktinfo));
-
+/*
+ * AF-parameterized message size.
+ * XXX Why is this here?  Is it used?  The v6 case is not defined. 
+ */
 #define SOPT_SIZE_CMSG_IFINDEX(af) \
   ((af == AF_INET) ? SOPT_SIZE_CMSG_IFINDEX_IPV4() \
                    : SOPT_SIZE_CMSG_IFINDEX_IPV6()
@@ -60,9 +81,13 @@
 			     unsigned int mcast_addr,
 			     unsigned int ifindex);
 
-#if defined (IP_PKTINFO)
+/*
+ * XXX Exactly what is this an interface to?  Specifically, what calls
+ * can be made after calling it?
+ */
 int setsockopt_pktinfo (int, int, int);
-#endif
+
+/* Ask for, and get, ifindex, by whatever method is supported. */
 int setsockopt_ifindex (int, int, int);
 int getsockopt_ifindex (int, struct msghdr *);
 #endif /*_ZEBRA_SOCKOPT_H */