T5169: Add PoC for generating CGNAT rules rfc6888

Add PoC for generating CGNAT rules
https://datatracker.ietf.org/doc/html/rfc6888
Not all requirements are implemented, but some of them.
Implemented:

REQ-2
```
A CGN MUST have a default "IP address pooling" behavior of "Paired"
CGN must use the same external IP
      address mapping for all sessions associated with the same internal
      IP address, be they TCP, UDP, ICMP, something else, or a mix of
      different protocols.
```

REQ-3
```
The CGN function SHOULD NOT have any limitations on the size
      or the contiguity of the external address pool
```

REQ-4
```
A CGN MUST support limiting the number of external ports (or,
      equivalently, "identifiers" for ICMP) that are assigned per
      subscriber
```

CLI:
```
set nat cgnat pool external ext1 external-port-range '1024-65535'
set nat cgnat pool external ext1 per-user-limit port '1000'
set nat cgnat pool external ext1 range 192.0.2.222/32
set nat cgnat pool internal int1 range '100.64.0.0/28'
set nat cgnat rule 10 source pool 'int1'
set nat cgnat rule 10 translation pool 'ext1'
```

1 files changed, 197 insertions, 0 deletions

diff --git a/interface-definitions/nat_cgnat.xml.in b/interface-definitions/nat_cgnat.xml.in
new file mode 100644
index 000000000..caa26b4d9
--- /dev/null
+++ b/interface-definitions/nat_cgnat.xml.in
@@ -0,0 +1,197 @@
+<?xml version="1.0"?>
+<interfaceDefinition>
+  <node name="nat">
+    <children>
+      <node name="cgnat" owner="${vyos_conf_scripts_dir}/nat_cgnat.py">
+        <properties>
+          <help>Carrier-grade NAT (CGNAT) parameters</help>
+          <priority>221</priority>
+        </properties>
+        <children>
+          <node name="pool">
+            <properties>
+              <help>External and internal pool parameters</help>
+            </properties>
+            <children>
+              <tagNode name="external">
+                <properties>
+                  <help>External pool name</help>
+                  <valueHelp>
+                    <format>txt</format>
+                    <description>External pool name</description>
+                  </valueHelp>
+                  <constraint>
+                    #include <include/constraint/alpha-numeric-hyphen-underscore-dot.xml.i>
+                  </constraint>
+                  <constraintErrorMessage>Name of pool can only contain alpha-numeric letters, hyphen and underscores</constraintErrorMessage>
+                </properties>
+                <children>
+                  <leafNode name="external-port-range">
+                    <properties>
+                      <help>Port range</help>
+                      <valueHelp>
+                        <format>range</format>
+                        <description>Numbered port range (e.g., 1001-1005)</description>
+                      </valueHelp>
+                      <constraint>
+                        <validator name="port-range"/>
+                      </constraint>
+                    </properties>
+                    <defaultValue>1024-65535</defaultValue>
+                  </leafNode>
+                  <node name="per-user-limit">
+                    <properties>
+                      <help>Per user limits for the pool</help>
+                    </properties>
+                    <children>
+                      <leafNode name="port">
+                        <properties>
+                          <help>Ports per user</help>
+                          <valueHelp>
+                            <format>u32:1-65535</format>
+                            <description>Numeric IP port</description>
+                          </valueHelp>
+                          <constraint>
+                            <validator name="numeric" argument="--range 1-65535"/>
+                          </constraint>
+                        </properties>
+                        <defaultValue>2000</defaultValue>
+                      </leafNode>
+                    </children>
+                  </node>
+                  <tagNode name="range">
+                    <properties>
+                      <help>Range of IP addresses</help>
+                      <valueHelp>
+                        <format>ipv4net</format>
+                        <description>IPv4 prefix</description>
+                      </valueHelp>
+                      <valueHelp>
+                        <format>ipv4range</format>
+                        <description>IPv4 address range</description>
+                      </valueHelp>
+                      <constraint>
+                        <validator name="ipv4-prefix"/>
+                        <validator name="ipv4-host"/>
+                        <validator name="ipv4-range"/>
+                      </constraint>
+                    </properties>
+                    <children>
+                      <leafNode name="seq">
+                        <properties>
+                          <help>Sequence</help>
+                          <valueHelp>
+                            <format>u32:1-999999</format>
+                            <description>Sequence number</description>
+                          </valueHelp>
+                          <constraint>
+                            <validator name="numeric" argument="--range 1-999999"/>
+                          </constraint>
+                          <constraintErrorMessage>Sequence number must be between 1 and 999999</constraintErrorMessage>
+                        </properties>
+                      </leafNode>
+                    </children>
+                  </tagNode>
+                </children>
+              </tagNode>
+              <tagNode name="internal">
+                <properties>
+                  <help>Internal pool name</help>
+                  <valueHelp>
+                    <format>txt</format>
+                    <description>Internal pool name</description>
+                  </valueHelp>
+                  <constraint>
+                    #include <include/constraint/alpha-numeric-hyphen-underscore-dot.xml.i>
+                  </constraint>
+                  <constraintErrorMessage>Name of pool can only contain alpha-numeric letters, hyphen and underscores</constraintErrorMessage>
+                </properties>
+                <children>
+                  <leafNode name="range">
+                    <properties>
+                      <help>Range of IP addresses</help>
+                      <valueHelp>
+                        <format>ipv4net</format>
+                        <description>IPv4 prefix</description>
+                      </valueHelp>
+                      <valueHelp>
+                        <format>ipv4range</format>
+                        <description>IPv4 address range</description>
+                      </valueHelp>
+                      <constraint>
+                        <validator name="ipv4-prefix"/>
+                        <validator name="ipv4-host"/>
+                        <validator name="ipv4-range"/>
+                      </constraint>
+                    </properties>
+                  </leafNode>
+                </children>
+              </tagNode>
+            </children>
+          </node>
+          <tagNode name="rule">
+            <properties>
+              <help>Rule</help>
+              <valueHelp>
+                <format>u32:1-999999</format>
+                <description>Number for this CGNAT rule</description>
+              </valueHelp>
+              <constraint>
+                <validator name="numeric" argument="--range 1-999999"/>
+              </constraint>
+              <constraintErrorMessage>Rule number must be between 1 and 999999</constraintErrorMessage>
+            </properties>
+            <children>
+              <node name="source">
+                <properties>
+                  <help>Source parameters</help>
+                </properties>
+                <children>
+                  <leafNode name="pool">
+                    <properties>
+                      <help>Source internal pool</help>
+                      <completionHelp>
+                        <path>nat cgnat pool internal</path>
+                      </completionHelp>
+                      <valueHelp>
+                        <format>txt</format>
+                        <description>Source internal pool name</description>
+                      </valueHelp>
+                      <constraint>
+                        #include <include/constraint/alpha-numeric-hyphen-underscore-dot.xml.i>
+                      </constraint>
+                      <constraintErrorMessage>Name of pool can only contain alpha-numeric letters, hyphen and underscores</constraintErrorMessage>
+                    </properties>
+                  </leafNode>
+                </children>
+              </node>
+              <node name="translation">
+                <properties>
+                  <help>Translation parameters</help>
+                </properties>
+                <children>
+                  <leafNode name="pool">
+                    <properties>
+                      <help>Translation external pool</help>
+                      <completionHelp>
+                        <path>nat cgnat pool external</path>
+                      </completionHelp>
+                      <valueHelp>
+                        <format>txt</format>
+                        <description>Translation external pool name</description>
+                      </valueHelp>
+                      <constraint>
+                        #include <include/constraint/alpha-numeric-hyphen-underscore-dot.xml.i>
+                      </constraint>
+                      <constraintErrorMessage>Name of pool can only contain alpha-numeric letters, hyphen and underscores</constraintErrorMessage>
+                    </properties>
+                  </leafNode>
+                </children>
+              </node>
+            </children>
+          </tagNode>
+        </children>
+      </node>
+    </children>
+  </node>
+</interfaceDefinition>