nat: T2947: add many-many translation

Support a 1:1 or 1:n prefix translation. The following configuration will NAT
source addresses from the 10.2.0.0/16 range to an address from 192.0.2.0/29.

For this feature to work a Linux Kernel 5.8 or higher is required!

vyos@vyos# show nat
 source {
     rule 100 {
         outbound-interface eth1
         source {
             address 10.2.0.0/16
         }
         translation {
             address 192.0.2.0/29
         }
     }
 }

This results in the nftables configuration:

chain POSTROUTING {
    type nat hook postrouting priority srcnat; policy accept;
    oifname "eth1" counter packets 0 bytes 0 snat ip prefix to ip saddr map
        { 10.2.0.0/16 : 192.0.2.0/29 } comment "SRC-NAT-100"
}

1 files changed, 5 insertions, 4 deletions

diff --git a/src/conf_mode/nat.py b/src/conf_mode/nat.py
index 2d98cb11b..dae958774 100755
--- a/src/conf_mode/nat.py
+++ b/src/conf_mode/nat.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python3
 #
-# Copyright (C) 2020 VyOS maintainers and contributors
+# Copyright (C) 2020-2021 VyOS maintainers and contributors
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License version 2 or later as
@@ -26,6 +26,7 @@ from netifaces import interfaces
 from vyos.config import Config
 from vyos.configdict import dict_merge
 from vyos.template import render
+from vyos.template import is_ip_network
 from vyos.util import cmd
 from vyos.util import check_kmod
 from vyos.util import dict_search
@@ -68,9 +69,9 @@ def verify_rule(config, err_msg):
                               'ports can only be specified when protocol is '\
                               'either tcp, udp or tcp_udp!')
 
-        if '/' in (dict_search('translation.address', config) or []):
+        if is_ip_network(dict_search('translation.address', config)):
             raise ConfigError(f'{err_msg}\n' \
-                             'Cannot use ports with an IPv4net type translation address as it\n' \
+                             'Cannot use ports with an IPv4 network as translation address as it\n' \
                              'statically maps a whole network of addresses onto another\n' \
                              'network of addresses')
 
@@ -147,7 +148,7 @@ def verify(nat):
 
             addr = dict_search('translation.address', config)
             if addr != None:
-                if addr != 'masquerade':
+                if addr != 'masquerade' and not is_ip_network(addr):
                     for ip in addr.split('-'):
                         if not is_addr_assigned(ip):
                             print(f'WARNING: IP address {ip} does not exist on the system!')