diff --git a/xCAT-server/lib/xcat/plugins/mknb.pm b/xCAT-server/lib/xcat/plugins/mknb.pm
index 94702fe66..b9f01b633 100644
--- a/xCAT-server/lib/xcat/plugins/mknb.pm
+++ b/xCAT-server/lib/xcat/plugins/mknb.pm
@@ -841,11 +841,12 @@ sub process_request {
                 hexnet         => $_,
                 xcatd_address  => $xcatd_address,
                 xcatdport      => $xcatdport,
+                httpport       => $httpport,
                 consolecmdline => $consolecmdline,
             );
         }
     }
-    if (exists $GRUB2_DISCOVERY_ARCHES{$arch} and !-e "$tftpdir/boot/grub2/grub2.$arch") {
+    if (exists $GRUB2_DISCOVERY_ARCHES{$arch} && !-e "$tftpdir/boot/grub2/grub2.$arch") {
         # The discovery configurations are only reached through this boot loader, which
         # xCAT does not build: say so instead of letting the nodes time out in firmware.
         $callback->({ data => ["Note: $tftpdir/boot/grub2/grub2.$arch is missing; $arch nodes need it to reach these configurations (it is installed by grub2-xcat, or copied from the EL $arch installation media)"] });
@@ -879,7 +880,8 @@ sub _grub2_discovery_arches {
 # then grub.cfg-<8 hex digit ip>, then ever shorter prefixes of that ip, and
 # finally grub.cfg. nodeset writes the per-node files (full ip and mac), so a
 # per-network prefix is only reached by clients without a node configuration:
-# discovery. The file is rebuilt from the Genesis artifacts present under
+# discovery. The payload is fetched over HTTP, with a TFTP entry behind it.
+# The file is rebuilt from the Genesis artifacts present under
 # $tftpdir/xcat and removed when none are left. Returns the path written.
 sub _write_grub2_discovery_config {
     my (%args) = @_;
@@ -895,14 +897,33 @@ sub _write_grub2_discovery_config {
     if (defined($args{consolecmdline}) and $args{consolecmdline} ne '') {
         $cmdline .= " $args{consolecmdline}";
     }
+    # The Genesis initramfs is large and a TFTP server hands it to one client at a
+    # time, so the default entry fetches it over HTTP, the same way nodeset does for
+    # netboot=grub2-http. The TFTP entry stays as the second choice for a management
+    # node that does not serve the TFTP root over HTTP.
+    my $httpport = $args{httpport} || '80';
+    my $httproot = 'http,' . $args{xcatd_address} . ($httpport eq '80' ? '' : ":$httpport");
+    my $tftproot = 'tftp,' . $args{xcatd_address};
     my $content = "# xCAT Genesis discovery for network $hexnet - generated by mknb, do not edit\n";
     $content .= "set default=0\n";
+    # Every architecture branch defines the HTTP entry first and the TFTP entry
+    # second, so a payload GRUB cannot fetch over HTTP is retried over TFTP.
+    $content .= "set fallback=1\n";
     $content .= "set timeout=5\n";
     my $keyword = 'if';
     foreach my $entry (@arches) {
         my ($arch, $grub_cpu, $kernel, $initrd) = @{$entry};
         $content .= "$keyword [ \"\$grub_cpu\" = \"$grub_cpu\" ]; then\n";
         $content .= "menuentry \"xCAT Genesis $arch\" {\n";
+        $content .= "    insmod http\n";
+        $content .= "    insmod tftp\n";
+        $content .= "    set root=$httproot\n";
+        $content .= "    linux $tftpdir/$kernel $cmdline BOOTIF=\$net_default_mac\n";
+        $content .= "    initrd $tftpdir/$initrd\n";
+        $content .= "}\n";
+        $content .= "menuentry \"xCAT Genesis $arch (TFTP)\" {\n";
+        $content .= "    insmod tftp\n";
+        $content .= "    set root=$tftproot\n";
         $content .= "    linux /$kernel $cmdline BOOTIF=\$net_default_mac\n";
         $content .= "    initrd /$initrd\n";
         $content .= "}\n";
@@ -912,8 +933,7 @@ sub _write_grub2_discovery_config {
     # nodeset hard-links grub.cfg-<8 hex digit ip> to the node file; on a /32 network that is
     # this file's name, so replace the name instead of truncating a shared inode.
     unlink($cfgpath);
-    my $cfg;
-    open($cfg, ">", $cfgpath) or return;
+    open(my $cfg, ">", $cfgpath) or return;
     print $cfg $content;
     close($cfg);
     chmod(0644, $cfgpath);