Get PLAT prefix from systemd-networkd, if possible

Makes clatd check if systemd-networkd is aware of any PLAT prefix (which
it may have learned from the PREF64 Router Advertisement option, cf. RFC
8781).

If a prefix is obtained from systemd-network, DNS64-based PLAT prefix
discovery is skipped, as mandated by
https://datatracker.ietf.org/doc/draft-ietf-v6ops-prefer8781/.

However, if the dns64-servers config option is set, clatd will use
DNS64-based PLAT prefix discovery towards the specified servers, and it
will not query systemd-networkd at all.

Closes #32

Makefile

@@ -7,11 +7,9 @@ DNF_OR_YUM:=$(shell which dnf || which yum)
 SYSTEMCTL:=$(shell which systemctl)
 TAYGA:=$(shell which tayga)
 
-all:
-
 install:
 	# Install the main script
-	install -D -m0755 clatd $(DESTDIR)$(PREFIX)/sbin/clatd
+	install -m0755 clatd $(DESTDIR)$(PREFIX)/sbin/clatd
 	# Install manual page if pod2man is installed
 	pod2man --name clatd --center "clatd - a CLAT implementation for Linux" --section 8 README.pod $(DESTDIR)$(PREFIX)/share/man/man8/clatd.8 && gzip -f9 $(DESTDIR)$(PREFIX)/share/man/man8/clatd.8 || echo "pod2man is required to generate manual page"
 	# Install systemd service file if applicable for this system

clatd

@@ -27,7 +27,7 @@ use strict;
 use IPC::Cmd qw(can_run);
 use Net::IP;
 
-my $VERSION = "2.1.0";
+my $VERSION = "2.0.0";
 
 #
 # Populate the global config hash with the default values
@@ -42,7 +42,6 @@ $CFG{"clat-v4-addr"} = "192.0.0.1";	# from RFC 7335
 $CFG{"clat-v6-addr"} = "shared";	# re-use primary address from host OS
 $CFG{"dns64-servers"} = undef;		# use system resolver by default
 $CFG{"cmd-ip"} = "ip";			# assume in $PATH
-$CFG{"cmd-ipxlat-ctl"} = "ipxlat-ctl";	# assume in $PATH
 $CFG{"cmd-networkctl"} = "networkctl";	# assume in $PATH
 $CFG{"cmd-nft"} = "nft";		# assume in $PATH
 $CFG{"cmd-tayga"} = "tayga";		# assume in $PATH
@@ -63,7 +62,6 @@ $CFG{"v4-defaultroute-replace"} = 0;	# replace existing v4 defaultroute?
 $CFG{"v4-defaultroute-metric"} = 2048;	# metric for the IPv4 defaultroute
 $CFG{"v4-defaultroute-mtu"} = 1260;	# MTU for the IPv4 defaultroute
 $CFG{"v4-defaultroute-advmss"} = 0;	# TCP MSS for the IPv4 defaultroute
-$CFG{"xlat-engine"} = undef;		# which translation engine to use
 
 
 #
@@ -359,8 +357,7 @@ sub get_plat_prefix_from_dns64 {
     $res->nameservers(map {
       Net::IP->new($_)->version() == 4 ? "::ffff:$_" : $_;
     } $res->nameservers);
-    d2("Nameservers after Net::DNS bug workaround: ",
+    d2("Nameservers after Net::DNS bug workaround: ", $res->nameservers);
-       join(" ", $res->nameservers));
 
     my $pkt = $res->query('ipv4only.arpa', 'AAAA');
     if(!$pkt) {
@@ -394,7 +391,7 @@ sub get_plat_prefix_from_dns64 {
     p("No PLAT prefix could be discovered, using fallback");
     return $CFG{"plat-fallback-prefix"};
   } else {
-    p("No PLAT prefix could be discovered. Your connection probably doesn't provide",
+    p("No PLAT prefix could be discovered. Your ISP probably doesn't provide",
       " NAT64/DNS64 PLAT service. Exiting.");
     cleanup_and_exit(0);
   }
@@ -668,7 +665,6 @@ sub get_clat_v6_addr {
 #
 my $cleanup_remove_tayga_clat_dev;	# true if having created it
 my $cleanup_remove_nat46_clat_dev;	# true if having created it
-my $cleanup_remove_ipxlat_clat_dev;	# true if having created it
 my $cleanup_delete_taygaconf;		# true if having made a temp confile
 my $cleanup_zero_forwarding_sysctl;	# zero forwarding sysctl if set
 my @cleanup_accept_ra_sysctls;		# accept_ra sysctls to be reset to '1'
@@ -700,9 +696,6 @@ sub cleanup_and_exit {
     print $nat46_control_fh "del ", cfg("clat-dev"), "\n";
     close($nat46_control_fh) or err("close($nat46_control_fh: $!");
   }
-  if(defined($cleanup_remove_ipxlat_clat_dev)) {
-    cmd(\&w, cfg("cmd-ip"), qw(link delete dev), cfg("clat-dev"));
-  }
   if(defined($cleanup_zero_forwarding_sysctl)) {
     d("Cleanup: Resetting forwarding sysctl to 0");
     sysctl("net/ipv6/conf/all/forwarding", 0);
@@ -740,11 +733,11 @@ sub cleanup_and_exit {
   }
   if(defined($cleanup_remove_ufw_rules)) {
     cmd(\&w, cfg("cmd-ufw"), qw(route delete allow in on), cfg("clat-dev"),
-        "from", cfg("internal-clat-v6-addr"), qw(out on), cfg("plat-dev"), "to",
+        "from", cfg("clat-v6-addr"), qw(out on), cfg("plat-dev"), "to",
         cfg("plat-prefix"));
     cmd(\&w, cfg("cmd-ufw"), qw(route delete allow in on), cfg("plat-dev"),
         "from", cfg("plat-prefix"), qw(out on), cfg("clat-dev"), "to",
-        cfg("internal-clat-v6-addr"));
+        cfg("clat-v6-addr"));
   }
 
   exit($exitcode);
@@ -851,7 +844,6 @@ if(!$CFG{"plat-prefix"}) {
      $ip->prefixlen() != 64 and
      $ip->prefixlen() != 56 and
      $ip->prefixlen() != 48 and
-     $ip->prefixlen() != 40 and
      $ip->prefixlen() != 32) {
     err("PLAT prefix $CFG{'plat-prefix'} has an invalid prefix length ",
         "(see RFC 6052 section 2.2)");
@@ -878,16 +870,6 @@ if($CFG{"clat-v6-addr"} eq "shared") {
   $CFG{"clat-v6-addr"} = get_clat_v6_addr();
 }
 
-# Since ipxlat does not support EAM, we'll need to do SNAT66 from the RFC 6052
-# representaion of the CLAT IPv4 address used internally. It is sometimes
-# necessary to refer to this address instead of the CLAT IPv6 address, so
-# create a separate entry in the config hash for that. The other engines (tayga
-# and nat46) supports using EAM to map directly between the CLAT IPv4 address
-# and CLAT IPv6 address without any going via any intermediate RFC6052 address,
-# so default to having the two addresses identical (if using ipxlat, the
-# internal one will be overridden later).
-$CFG{"internal-clat-v6-addr"} = $CFG{"clat-v6-addr"};
-
 # Fill defaults for proxynd-enable and ctmark for clat-v6-addr!=shared
 if(!defined($CFG{"proxynd-enable"})) {
   $CFG{"proxynd-enable"} = 1;
@@ -924,49 +906,17 @@ if(cfgbool("v4-conncheck-enable") and !cfgbool("v4-defaultroute-replace")) {
   d("Skipping IPv4 connectivity check at user request");
 }
 
-
+# Let's figure out if there's nat46 kernel module loaded
 my $nat46_controlfile = "/proc/net/nat46/control";
+my $use_nat46 = (-e $nat46_controlfile);
 
-#
-# Auto-detect which translation engine to use if not specified in config
-if(!cfg("xlat-engine") and (-e $nat46_controlfile)) {
-  p("Using translation engine: nat46");
-  $CFG{"xlat-engine"} = "nat46";
-} elsif(!cfg("xlat-engine") and can_run(cfg("cmd-ipxlat-ctl"))) {
-  p("Using translation engine: ipxlat");
-  $CFG{"xlat-engine"} = "ipxlat";
-  my $pfx = Net::IP->new($CFG{"plat-prefix"});
-  my $fmt = $pfx->ip;
-  if($pfx->prefixlen == 96) {
-    $fmt =~ s/0000:0000$/%02x%02x:%02x%02x/;
-  } elsif($pfx->prefixlen == 64) {
-    $fmt =~ s/00:0000:0000:0000$/%02x:%02x%02x:%02x00:0000/;
-  } elsif($pfx->prefixlen == 56) {
-    $fmt =~ s/00:0000:0000:0000:0000$/%02x:00%02x:%02x%02x:0000:0000/;
-  } elsif($pfx->prefixlen == 48) {
-    $fmt =~ s/0000:0000:0000:0000:0000$/%02x%02x:00%02x:%02x00:0000:0000/;
-  } elsif($pfx->prefixlen == 40) {
-    $fmt =~ s/00:0000:0000:0000:0000:0000$/%02x:%02x%02x:00%02x:0000:0000:0000/;
-  } elsif($pfx->prefixlen == 32) {
-    $fmt =~ s/0000:0000:0000:0000:0000:0000$/%02x%02x:%02x%02x:0000:0000:0000:0000/;
-  }
-  my $ip = sprintf($fmt, split(/\./, $CFG{"clat-v4-addr"}));
-  $CFG{"internal-clat-v6-addr"} = Net::IP->new($ip)->short;
-  p("Using internal CLAT IPv6 address: ", $CFG{"internal-clat-v6-addr"});
-} elsif(!cfg("xlat-engine") and can_run(cfg("cmd-tayga"))) {
-  p("Using translation engine: TAYGA");
-  $CFG{"xlat-engine"} = "tayga";
-} elsif(!cfg("xlat-engine")) {
-  err("No supported translation engine available. Please install TAYGA or ensure ",
-      "either the nat46 or ipxlat kernel modules is loaded.");
-}
 
 
 #
 # Write out the TAYGA config file, either to the user-specified location,
 # or to a temporary file (which we'll delete later)
 #
-if(cfg("xlat-engine") eq "tayga") {
+unless($use_nat46) {
   my $tayga_conffile = cfg("tayga-conffile");
   my $tayga_conffile_fh;
   if(!$tayga_conffile) {
@@ -1025,11 +975,11 @@ if(can_run(cfg("cmd-ufw"))) {
     if(/^Status: active$/) {
       p("UFW local firewall framework active, allowing CLAT-PLAT traffic");
       cmd(\&err, cfg("cmd-ufw"), qw(route allow in on), cfg("clat-dev"),
-          "from", cfg("internal-clat-v6-addr"), qw(out on), cfg("plat-dev"), "to",
+          "from", cfg("clat-v6-addr"), qw(out on), cfg("plat-dev"), "to",
           cfg("plat-prefix"));
       cmd(\&err, cfg("cmd-ufw"), qw(route allow in on), cfg("plat-dev"),
           "from", cfg("plat-prefix"), qw(out on), cfg("clat-dev"), "to",
-          cfg("internal-clat-v6-addr"));
+          cfg("clat-v6-addr"));
       $cleanup_remove_ufw_rules = 1;
     }
   }
@@ -1076,17 +1026,14 @@ close($fd) or err("'ip -6 rule show prio 0 table local' failed");
 # route to the corresponding IPv6 address, and possibly an IPv4 default route
 #
 p("Creating and configuring up CLAT device '", cfg("clat-dev"), "'");
-if(cfg("xlat-engine") eq "nat46") {
+if($use_nat46) {
   my $nat46_control_fh;
   open($nat46_control_fh, ">$nat46_controlfile") or
       err("Could not open nat46 control socket for writing");
   print $nat46_control_fh "add ", cfg("clat-dev"), "\n";
   close($nat46_control_fh) or err("close($nat46_control_fh: $!");
   $cleanup_remove_nat46_clat_dev = 1;
-} elsif(cfg("xlat-engine") eq "ipxlat") {
+} else {
-  cmd(\&err, cfg("cmd-ip"), qw(link add name), cfg("clat-dev"), qw(type ipxlat));
-  $cleanup_remove_ipxlat_clat_dev = 1;
-} elsif(cfg("xlat-engine") eq "tayga") {
   cmd(\&err, cfg("cmd-tayga"), "--config", cfg("tayga-conffile"), "--mktun",
       cfgint("debug") ? "-d" : "");
   $cleanup_remove_tayga_clat_dev = 1;
@@ -1094,10 +1041,10 @@ if(cfg("xlat-engine") eq "nat46") {
 cmd(\&err, cfg("cmd-ip"), qw(link set up dev), cfg("clat-dev"));
 cmd(\&err, cfg("cmd-ip"), qw(-4 address add), cfg("clat-v4-addr"),
     "dev", cfg("clat-dev"));
-cmd(\&err, cfg("cmd-ip"), qw(-6 route add), cfg("internal-clat-v6-addr"),
+cmd(\&err, cfg("cmd-ip"), qw(-6 route add), cfg("clat-v6-addr"),
     "dev", cfg("clat-dev"), "table", cfgint("route-table"));
 cmd(\&err, cfg("cmd-ip"), qw(-6 rule add prio 0 from),
-    cfg("plat-prefix"), "to", cfg("internal-clat-v6-addr"),
+    cfg("plat-prefix"), "to", cfg("clat-v6-addr"),
     cfgint("ctmark") ? ("fwmark", cfgint("ctmark")) : (),
     "table", cfg("route-table"));
 $cleanup_remove_clat_iprule = 1;
@@ -1108,13 +1055,13 @@ if(cfgint("ctmark")) {
     or err("'nft -f-' failed to execute");
   print $fd "add table ip6 clatd\n";
   print $fd "add chain ip6 clatd prerouting ",
-            "{ type filter hook prerouting priority mangle; }\n";
+            "{ type filter hook prerouting priority 0; }\n";
   print $fd "add rule ip6 clatd prerouting",
             " iif ", cfg("clat-dev"),
-            " ip6 saddr ", cfg("internal-clat-v6-addr"),
+            " ip6 saddr ", cfg("clat-v6-addr"),
             " ip6 daddr ", cfg("plat-prefix"),
             " ct mark set ", cfgint("ctmark"),
-            # set meta mark as well, to placate firewalld's IPv6_rpfilter and NixOS' rpfilter rules
+            # set meta mark as well, to placate firewalld's IPv6_rpfilter
             " meta mark set ", cfgint("ctmark"), " counter\n";
   print $fd "add rule ip6 clatd prerouting",
             " iif ", cfg("plat-dev"),
@@ -1122,15 +1069,6 @@ if(cfgint("ctmark")) {
             " ip6 daddr ", cfg("clat-v6-addr"),
             " ct mark ", cfgint("ctmark"),
             " meta mark set ct mark counter\n";
-  if(cfg("clat-v6-addr") ne cfg("internal-clat-v6-addr")) {
-    print $fd "add chain ip6 clatd postrouting ",
-              "{ type nat hook postrouting priority srcnat; }\n";
-    print $fd "add rule ip6 clatd postrouting",
-              " iif ", cfg("clat-dev"),
-              " ip6 saddr ", cfg("internal-clat-v6-addr"),
-              " ip6 daddr ", cfg("plat-prefix"),
-              " snat to ", cfg("clat-v6-addr");
-  }
   close($fd) or err("'nft -f-' failed");
   $cleanup_remove_nftable = 1;
 }
@@ -1177,7 +1115,7 @@ if(cfg("script-up")) {
 # All preparation done! We can now start nat46 or TAYGA, which will handle the actual
 # translation of IP packets.
 #
-if(cfg("xlat-engine") eq "nat46") {
+if($use_nat46){
   p("Setting up nat46 kernel module");
   my $nat46_control_fh;
   open($nat46_control_fh, ">$nat46_controlfile") or
@@ -1193,13 +1131,7 @@ if(cfg("xlat-engine") eq "nat46") {
   $SIG{'INT'} = \&cleanup_handler;
   $SIG{'TERM'} = \&cleanup_handler;
   sleep();
-} elsif(cfg("xlat-engine") eq "ipxlat") {
+} else {
-  cmd(\&err, cfg("cmd-ipxlat-ctl"), cfg("clat-dev"), "pool6", cfg("plat-prefix"));
-  # Nothing more to do here, we just set up a cleanup handler and sleep forever.
-  $SIG{'INT'} = \&cleanup_handler;
-  $SIG{'TERM'} = \&cleanup_handler;
-  sleep();
-} elsif(cfg("xlat-engine") eq "tayga") {
   my $tayga_conffile = cfg("tayga-conffile");
   p("Starting up TAYGA, using config file '$tayga_conffile'");
 

ipxlat-ctl

@@ -1,18 +0,0 @@
-#!/bin/bash -e
-
-# This is a wrapper around the python ynl cli included with the kernel that
-# mimics the documented behaviour of the ipxlat-ctl tool available at
-# https://codeberg.org/IPv6-Monostack/ipxlat, but which I haven't been able to
-# make work. You'll need to ensure the tool is somewhere in $PATH.
-
-PATH=/usr/src/kernels/ipxlat-net-next/tools/net/ynl/pyynl:$PATH
-
-dev="$1"
-prefix="$3"
-
-IID=$(< /sys/class/net/$dev/ifindex)
-ADDR_HEX=$(python3 -c 'import ipaddress,sys; print(ipaddress.IPv6Address(sys.argv[1]).packed.hex())' ${prefix%/*})
-PREFIXLEN=${prefix#*/}
-JSON='{"ifindex": '"$IID"', "config": {"xlat-prefix6": { "prefix": "'$ADDR_HEX'", "prefix-len": '$PREFIXLEN'}}}'
-
-cli.py --family ipxlat --do dev-set --json "$JSON"