diff --git a/perl-xCAT/xCAT/DHCP/Backend.pm b/perl-xCAT/xCAT/DHCP/Backend.pm
index 7ba20339b..581c10347 100644
--- a/perl-xCAT/xCAT/DHCP/Backend.pm
+++ b/perl-xCAT/xCAT/DHCP/Backend.pm
@@ -33,6 +33,20 @@ sub choose {
     my $selected = $normalized eq 'auto' ? $class->default_backend(%args) : $normalized;
 
     if ( $args{check_available} && !$class->available( $selected, %args ) ) {
+        # Ubuntu's metapackage guarantees isc-dhcp-server but only Recommends kea, so a
+        # --no-install-recommends install has auto preferring a kea that is not there. Fall
+        # back to whatever is installed; an explicitly forced backend still fails hard. #7710
+        if ( $normalized eq 'auto' ) {
+            for my $alt (qw(kea isc)) {
+                next if $alt eq $selected;
+                next unless $class->available( $alt, %args );
+                return {
+                    requested     => $normalized,
+                    name          => $alt,
+                    fallback_from => $selected,
+                };
+            }
+        }
         return {
             requested => $normalized,
             name      => $selected,
diff --git a/perl-xCAT/xCAT/DHCP/Backend/ISC.pm b/perl-xCAT/xCAT/DHCP/Backend/ISC.pm
index 13f008c49..3379dc69d 100644
--- a/perl-xCAT/xCAT/DHCP/Backend/ISC.pm
+++ b/perl-xCAT/xCAT/DHCP/Backend/ISC.pm
@@ -12,6 +12,12 @@ sub name {
     return 'isc';
 }
 
+# The backend auto-selection preferred, and undef when it did not fall back. #7710
+sub fallback_from {
+    my $self = shift;
+    return ref($self) ? $self->{selection}{fallback_from} : undef;
+}
+
 sub implemented {
     return 1;
 }
diff --git a/perl-xCAT/xCAT/DHCP/Backend/Kea.pm b/perl-xCAT/xCAT/DHCP/Backend/Kea.pm
index d4a54ba9d..0e478a349 100644
--- a/perl-xCAT/xCAT/DHCP/Backend/Kea.pm
+++ b/perl-xCAT/xCAT/DHCP/Backend/Kea.pm
@@ -22,6 +22,12 @@ sub name {
     return 'kea';
 }
 
+# The backend auto-selection preferred, and undef when it did not fall back. #7710
+sub fallback_from {
+    my $self = shift;
+    return ref($self) ? $self->{selection}{fallback_from} : undef;
+}
+
 sub implemented {
     return 1;
 }
diff --git a/xCAT-server/lib/xcat/plugins/dhcp.pm b/xCAT-server/lib/xcat/plugins/dhcp.pm
index 0c7babdf1..3dce823fe 100644
--- a/xCAT-server/lib/xcat/plugins/dhcp.pm
+++ b/xCAT-server/lib/xcat/plugins/dhcp.pm
@@ -230,17 +230,34 @@ sub _isc_static_host_fallback
     return _ubuntu_isc_omapi_limited() && !$::XCATSITEVALS{externaldhcpservers};
 }
 
+# Match the whole marker _add_isc_static_host writes: a looser /\Q$node\E\b/ ends at a
+# hyphen, so node "compute" would match "compute-01" and act on the wrong block. An older
+# xCAT wrote the end marker on the closing-brace line, so that brace stays optional.
+sub _isc_host_start_re
+{
+    my ($node, $hostname) = @_;
+
+    return defined($hostname)
+      ? qr/^#xCAT host declaration for \Q$node\E aka host \Q$hostname\E start$/
+      : qr/^#xCAT host declaration for \Q$node\E aka host .* start$/;
+}
+
+sub _isc_host_end_re
+{
+    my ($node, $hostname) = @_;
+
+    return defined($hostname)
+      ? qr/^(?:\}\s*)?#xCAT host declaration for \Q$node\E aka host \Q$hostname\E end$/
+      : qr/^(?:\}\s*)?#xCAT host declaration for \Q$node\E aka host .* end$/;
+}
+
 sub _delete_isc_static_host
 {
     my ($node, $config, $hostname) = @_;
     $config ||= \@dhcpconf;
 
-    my $start_marker = defined($hostname)
-      ? qr/^#xCAT host declaration for \Q$node\E aka host \Q$hostname\E start$/
-      : qr/^#xCAT host declaration for \Q$node\E aka host .* start$/;
-    my $end_marker = defined($hostname)
-      ? qr/^(?:\}\s*)?#xCAT host declaration for \Q$node\E aka host \Q$hostname\E end$/
-      : qr/^(?:\}\s*)?#xCAT host declaration for \Q$node\E aka host .* end$/;
+    my $start_marker = _isc_host_start_re($node, $hostname);
+    my $end_marker   = _isc_host_end_re($node, $hostname);
 
     my @updated;
     my $skip = 0;
@@ -329,6 +346,45 @@ sub _add_isc_static_host
     $restartdhcp = 1;
 }
 
+# Answer `makedhcp -q <node>` from dhcpd.conf rather than omshell, which on Ubuntu's ISC
+# 4.4 can wedge at 100% CPU and never be reaped -- the same reason the write paths avoid it.
+# Returns the shape _parse_omshell_host_output does, so listnode prints it unchanged.
+sub _query_isc_static_host
+{
+    my $node  = shift;
+    my @lines = @_ ? @_ : @dhcpconf;
+
+    # Only the reconfigure paths populate @dhcpconf, so a bare query reads the file itself.
+    if (!@lines && $dhcpconffile && -r $dhcpconffile) {
+        if (open(my $dhfh, '<', $dhcpconffile)) {
+            @lines = <$dhfh>;
+            close($dhfh);
+        }
+    }
+
+    my $start_re = _isc_host_start_re($node);
+    my $end_re   = _isc_host_end_re($node);
+
+    my ($nname, $ipaddr, $hwaddr);
+    my $skip = 0;
+    foreach my $line (@lines) {
+        if ($line =~ $start_re) {
+            $skip  = 1;
+            $nname = $node;
+            next;
+        }
+        last if $skip && $line =~ $end_re;
+        next unless $skip;
+        if ($line =~ /^\s*hardware\s+ethernet\s+(.+?)\s*;/) {
+            $hwaddr = "hardware-address = $1";
+        } elsif ($line =~ /^\s*fixed-address\s+(.+?)\s*;/) {
+            $ipaddr = "ip-address = $1";
+        }
+    }
+
+    return ($nname, $ipaddr, $hwaddr);
+}
+
 sub _open_omshell_writer
 {
     my $settings = shift;
@@ -489,6 +545,21 @@ sub listnode
     my $callback = shift;
     my $rsp;
 
+    # On Ubuntu's ISC-limited releases the omshell host query can wedge at 100% CPU and never
+    # be reaped, so answer from the static host block xCAT already wrote into dhcpd.conf and
+    # never spawn omshell. This runs before the omapi key lookup below, which is moot here.
+    if (_isc_static_host_fallback()) {
+        my ($sname, $sip, $shw) = _query_isc_static_host($node);
+        if ($sip) {
+            push @{ $rsp->{data} }, "$sname: $sip, $shw";
+            xCAT::MsgUtils->message("I", $rsp, $callback);
+        } else {
+            $rsp->{data}->[0] = "$node: no DHCP reservation found in $dhcpconffile";
+            xCAT::MsgUtils->message("I", $rsp, $callback);
+        }
+        return;
+    }
+
     my $settings = _omapi_settings($callback);
     return unless $settings;
 
@@ -1803,6 +1874,14 @@ sub process_request
         xCAT::MsgUtils->message("E", $rsp, $callback, 1);
         return;
     }
+    if ( $backend->can('fallback_from') && ( my $from = $backend->fallback_from ) ) {
+        my $rsp = {};
+        $rsp->{data}->[0] =
+            "DHCP backend '$from' auto-selected for this OS is not installed; "
+          . "falling back to the available '" . $backend->name . "' backend. "
+          . "Install '$from' or set site.dhcpbackend to silence this.";
+        xCAT::MsgUtils->message("W", $rsp, $callback);
+    }
     if ( $backend->name eq 'kea' && $statements ) {
         my $rsp = {};
         $rsp->{data}->[0] = "The -s option contains ISC DHCP statement text and is not supported with the Kea DHCP backend.";