diff --git a/xCAT-server/lib/xcat/plugins/debian.pm b/xCAT-server/lib/xcat/plugins/debian.pm
index b923c37c8..07fcbfb20 100644
--- a/xCAT-server/lib/xcat/plugins/debian.pm
+++ b/xCAT-server/lib/xcat/plugins/debian.pm
@@ -521,7 +521,7 @@ sub copycd
 
     Arguments:
         $instserver the install server name, address, or the '!myipfn!' placeholder
-        $resolver   optional coderef, for tests; defaults to NetworkUtils::getipaddr
+        $resolver   optional coderef, for tests; defaults to NetworkUtils::getipaddr, IPv4 only
     Returns:
         the value to put in nfsroot, or undef when a real name does not resolve
 
@@ -534,7 +534,9 @@ sub subiquity_nfsroot_server {
     return undef unless defined($instserver) && length($instserver);
     return $instserver if $instserver eq '!myipfn!';
 
-    $resolver ||= sub { xCAT::NetworkUtils->getipaddr($_[0]) };
+    # A dual-stack management node also has an AAAA record. casper takes everything after the
+    # first colon in nfsroot= as the path, so an IPv6 address there cannot be parsed.
+    $resolver ||= sub { xCAT::NetworkUtils->getipaddr($_[0], OnlyV4 => 1) };
     return $resolver->($instserver);
 }
 
diff --git a/xCAT-server/share/xcat/install/ubuntu/compute.subiquity.tmpl b/xCAT-server/share/xcat/install/ubuntu/compute.subiquity.tmpl
index 4ec7faf20..9da43e4c0 100644
--- a/xCAT-server/share/xcat/install/ubuntu/compute.subiquity.tmpl
+++ b/xCAT-server/share/xcat/install/ubuntu/compute.subiquity.tmpl
@@ -68,12 +68,17 @@ autoinstall:
       echo "=== DNS setup ==="
       # glibc's resolver discards a nameserver line naming a host, so writing the xcatmaster
       # *name* leaves the installer -- and the in-target apt that inherits this file -- with no
-      # DNS. Resolve it here, while the live installer's DHCP resolv.conf still works.
+      # DNS. Resolve it here, while the live installer's DHCP resolv.conf still works, and keep
+      # that file when the name does not resolve. A name written back is the case this step
+      # exists to prevent.
       xcatmaster_host="#TABLE:noderes:$NODE:xcatmaster#"
       xcatmaster_ip="$(getent ahostsv4 "$xcatmaster_host" | awk '{print $1; exit}')"
-      [ -n "$xcatmaster_ip" ] || xcatmaster_ip="$xcatmaster_host"
-      rm -f /etc/resolv.conf
-      echo "nameserver $xcatmaster_ip" >/etc/resolv.conf
+      if [ -n "$xcatmaster_ip" ]; then
+        rm -f /etc/resolv.conf
+        echo "nameserver $xcatmaster_ip" >/etc/resolv.conf
+      else
+        echo "xcat: $xcatmaster_host has no IPv4 address; keeping the resolver DHCP supplied"
+      fi
       echo "domain #TABLE:site:key=domain:value#" >>/etc/resolv.conf
       echo "=== early-commands complete ==="
   late-commands:
@@ -108,11 +113,13 @@ autoinstall:
     curtin in-target --target /target /root/post.script;
     } >>/target/var/log/xcat/xcat.log 2>&1'
     # Flip the node to local-disk boot, or it PXE-loops back into the installer on reboot.
-    # "next" is the request xcatd's install monitor answers with "nodeset <node> next". Send it
-    # from the live installer, retried, and log a failure rather than silently reinstalling. A
-    # monitor that died and never came back is a separate problem; see #7759 -- but one that
-    # accepts the connection and then never answers would block a bare read forever and hang the
-    # install here, so both reads are bounded.
-    - ['bash', '-c', 'xm=#XCATVAR:XCATMASTER#; ok=0; for i in 1 2 3 4 5; do if exec 3<>/dev/tcp/$xm/3002; then read -r -t 10 r <&3 || true; printf "next\n" >&3; if read -r -t 10 r <&3; then ok=1; fi; exec 3>&- 3<&-; [ "$ok" = 1 ] && break; fi; sleep 5; done; if [ "$ok" != 1 ]; then echo "xcat: FAILED to flip $(hostname) to local-disk boot via $xm:3002; the node will PXE back into the installer" >>/target/var/log/xcat/xcat.log; fi; exit 0']
+    # xcatd's install monitor greets with "ready", then answers "next" with "done" and runs
+    # "nodeset <node> next". Require both tokens: another service on that port is not a flipped
+    # node. The monitor listens on site.xcatiport; TABLEBLANKOKAY because an absent key fails a
+    # plain TABLE lookup, and with it the whole template.
+    # Retry, and log a failure rather than reinstall silently. Both reads are bounded: a monitor
+    # that accepts and never answers would block a bare read and hang the install here. A
+    # monitor that died and never came back is #7759.
+    - ['bash', '-c', 'xm=#XCATVAR:XCATMASTER#; port="#TABLEBLANKOKAY:site:key=xcatiport:value#"; [ -n "$port" ] || port=3002; ok=0; for i in 1 2 3 4 5; do if exec 3<>/dev/tcp/$xm/$port; then if read -r -t 10 hello <&3 && [ "$hello" = "ready" ]; then printf "next\n" >&3; if read -r -t 10 ack <&3 && [ "$ack" = "done" ]; then ok=1; fi; fi; exec 3>&- 3<&-; [ "$ok" = 1 ] && break; fi; sleep 5; done; if [ "$ok" != 1 ]; then echo "xcat: FAILED to flip $(hostname) to local-disk boot via $xm:$port; the node will PXE back into the installer" >>/target/var/log/xcat/xcat.log; fi; exit 0']
   error-commands:
     - tar -c --ignore-failed-read --transform='s/^/#HOSTNAME#-logs\//' /var/crash /var/log/installer /tmp/pre-install.log /autoinstall.yaml 2>/dev/null |nc -l 8080