Index: configure.ac
===================================================================
--- configure.ac	(revision 11554)
+++ configure.ac	(working copy)
@@ -642,6 +642,12 @@
 #include <netinet/in.h>
 #endif])
 
+# Do we have IPv6 support?
+AC_CHECK_TYPES([struct sockaddr_in6], [], [], [AC_INCLUDES_DEFAULT
+#ifdef HAVE_NETINET_IN_H
+#include <netinet/in.h>
+#endif])
+
 # SA_RESTART in signal.h
 AC_MSG_CHECKING([if SA_RESTART defined in signal.h])
 AC_EGREP_CPP(yes, [
Index: config/ompi_configure_options.m4
===================================================================
--- config/ompi_configure_options.m4	(revision 11554)
+++ config/ompi_configure_options.m4	(working copy)
@@ -499,4 +499,20 @@
         [Build and install binaries required for Open MPI, such as the wrapper compilers.   Useful for multi-lib installations.  (default: enabled)])])
 AM_CONDITIONAL([OMPI_INSTALL_BINARIES], [test "$enable_binaries" != "no"])
 
+#
+# Do we want to disable IPv6 support?
+#
+AC_MSG_CHECKING([if want IPv6 support])
+AC_ARG_ENABLE([ipv6],
+    [AC_HELP_STRING([--disable-ipv6],
+        [Disable IPv6 support (default: enabled, but only if the underlying system supports it)])])
+if test "$enable_ipv6" = "no"; then
+    AC_MSG_RESULT([no])
+    ompi_want_ipv6=0
+else
+    AC_MSG_RESULT([yes (if underlying system supports it)])
+    ompi_want_ipv6=1
+fi
+AC_DEFINE_UNQUOTED([OMPI_ENABLE_IPV6], [$ompi_want_ipv6],
+                   [Enable IPv6 support, but only if the underlying system supports it])
 ])
Index: opal/include/opal_config_bottom.h
===================================================================
--- opal/include/opal_config_bottom.h	(revision 11554)
+++ opal/include/opal_config_bottom.h	(working copy)
@@ -341,4 +341,15 @@
 #  define OPAL_INT_TO_BOOL(VALUE)  (bool)(VALUE)
 #endif  /* defined(__WINDOWS__) */
 
+/**
+ * Top level define to check 2 things: a) if we want ipv6 support, and
+ * b) the underlying system supports ipv6.  Having one #define for
+ * this makes it simpler to check throughout the code base.
+ */
+#if OMPI_ENABLE_IPV6 && defined(HAVE_STRUCT_SOCKADDR_IN6)
+#define OMPI_WANT_IPV6 1
+#else
+#define OMPI_WANT_IPV6 0
+#endif
+
 #endif /* OMPI_BUILDING */