Add incremental RST-to-MyST swap mechanism (#1857)

* feat: add swap_sources.py for incremental RST-to-MyST migration

Pre-build swap/restore script that renames md-{name}.md → {name}.md
before Sphinx builds and restores after. Includes state tracking,
exclude file generation, collision detection, and partial-failure
rollback. 10 tests cover all specified behaviors plus rollback path.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* feat: add import_myst.py for importing MyST files from myst/* branches

Adds scripts/import_myst.py with import_page, git_show, list_myst_files,
list_rst_files, and do_import. Imported files are written as md-{name}.md
alongside existing RST files; importing is decoupled from swap activation.

Adds tests/test_import_myst.py covering single-page write, identical-skip,
warn-on-different-without-force, force-overwrite, and nested-path creation.
All 5 tests pass on Python 3.9.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* feat: add MyST swap exclude patterns and directive config to conf.py

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* feat: add swap-wrapped rendering targets to Makefile

🤖 Generated by [robots](https://vyos.io)

* feat: add swap pre/post build hooks for ReadTheDocs

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* feat: add empty _swap.txt, remove atexit from swap script

The atexit handler in --swap mode caused immediate restore on process
exit, breaking standalone usage. Makefile trap and RTD post_build
handle restore reliably.

🤖 Generated by [robots](https://vyos.io)

* feat: activate quick-start as MyST canary via swap mechanism

Imports docs/md-quick-start.md from origin/myst/current and adds
quick-start to docs/_swap.txt. Validates the swap pipeline end-to-end
on one page: import_myst pulls the MD via git show, swap_sources
renames md-quick-start.md to quick-start.md, sphinx-build renders
quick-start.html with zero MD-specific warnings, and restore reverses
the rename cleanly.

🤖 Generated by [robots](https://vyos.io)

* feat: activate 106 visual-validated canaries via swap

Imports 105 MD files (plus quick-start already present) from
origin/myst/current and adds them to docs/_swap.txt. The selection
is the BackstopJS visual-passers cohort: pages with <5% rendered
diff vs the live RST docs at docs.vyos.io/en/latest/, filtered to
those with an RST counterpart on current and no cmdincludemd usage
(template-format reconciliation pending).

Local sphinx-build with all 106 swapped: succeeded with 100
warnings (vs 95 baseline). The 5 new warnings are all undefined
cross-reference labels, not build failures:
- contributing/development.md (missing 'coding-guidelines')
- operation/upgrade-recovery.md (3 missing 'how_it_works' /
  'cancelling_recovery')
- vpp/configuration/dataplane/{buffers,memory,unix}.md (missing
  'vpp_config_dataplane_*' labels)

Source list: ~/.claude/projects/-Users-vybot-GitHub-vyos-documentation/docs/2026-04-29-myst-conversion-audit/visual-passers-under-5pct.txt
BackstopJS report: claude/gifted-hertz-74b9f9 worktree
(visual-compare/), 2026-04-23 vs vyos--1838.org.readthedocs.build.

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* fix: re-import 4 canary md-*.md files with xref label fixes

Re-imports the dash-form-corrected versions of:
- contributing/md-development.md (added (coding-guidelines)= anchor)
- operation/md-upgrade-recovery.md (3 ref renames: how_it_works /
  cancelling_recovery -> dash form)
- vpp/configuration/dataplane/md-buffers.md (vpp_config_dataplane_physmem
  -> vpp-config-dataplane-physmem)
- vpp/configuration/dataplane/md-unix.md
  (vpp_config_dataplane_interface_rx_mode
  -> vpp-config-dataplane-interface-rx-mode)

Source: origin/myst/current commit 59fbe3ea. Verified locally: clean
swap-build no longer reports any of the 5 target labels (1 of 6 —
vpp-config-hugepages — remains because system.md isn't in the canary
swap list; that anchor lives there).

🤖 Generated by [robots](https://vyos.io)

* fix: re-add 4 canary md-*.md files deleted by 242b334a

Commit 242b334a accidentally staged deletions instead of modifications
because the working tree had unprefixed *.md files left over from an
incomplete swap-restore cycle. Re-imports the same 4 files from
origin/myst/current with the xref label fixes applied:

- contributing/md-development.md       — (coding-guidelines)= anchor
- operation/md-upgrade-recovery.md     — how_it_works → how-it-works,
                                         cancelling_recovery → cancelling-recovery
- vpp/configuration/dataplane/md-buffers.md — vpp_config_dataplane_physmem
                                              → vpp-config-dataplane-physmem
- vpp/configuration/dataplane/md-unix.md   — vpp_config_dataplane_interface_rx_mode
                                              → vpp-config-dataplane-interface-rx-mode

Source: origin/myst/current commit 59fbe3ea.

🤖 Generated by [robots](https://vyos.io)

* fix: resolve remaining xref label gaps in swap-active build

Three small additions clear the cross-reference warnings tied to
underscore-vs-dash label form mismatches and the vpp-config-hugepages
reference that previously needed system.md in the canary set.

- system.rst: add .. _vpp-config-hugepages: alongside the existing
  underscore label so memory.md references resolve regardless of
  whether system.md is swap-active.
- md-lcp.md: add (vpp_config_dataplane_lcp_ignore-kernel-routes)=
  alongside dash form (carries upstream from myst/current 079fa786).
- md-memory.md: add (vpp_config_dataplane_memory)= alongside dash
  form (also from myst/current 079fa786).

Local clean swap-build with 106 canaries:
  before: 305 warnings, 8 undefined-label entries in our scope
  after:  300 warnings, 0 undefined-label entries in our scope

Remaining undefined-label warnings (release-notes, prepare_commit)
are in documentation.rst and unrelated to the canary swap mechanism.

🤖 Generated by [robots](https://vyos.io)

* fix: re-add md-lcp.md and md-memory.md (deleted by 870c9e7e)

Same disaster pattern as 242b334a: a swap-restore cycle left
unprefixed *.md files in the working tree, and the subsequent
git add staged deletions instead of modifications. Restoring the
two affected md-*.md files from origin/myst/current 079fa786
(which has the dual underscore+dash anchors needed for the
swap-active build).

🤖 Generated by [robots](https://vyos.io)

* feat: expand canaries to 114; refresh 3 with cfgcmd body fix

Adds 8 new visual-validated canaries from the post-cfgcmd-fix
BackstopJS run (2026-04-29):

- configuration/policy/as-path-list
- configuration/policy/community-list
- configuration/policy/extcommunity-list
- configuration/policy/large-community-list
- configuration/policy/local-route
- configuration/policy/prefix-list
- configuration/service/salt-minion
- configuration/system/updates

Refreshes 3 existing canaries whose MD content changed via the
cfgcmd/opcmd single-line body fix on myst/current fc19ab5c:

- configuration/firewall/global-options
- configuration/firewall/groups
- configuration/policy/route

All 11 sourced from origin/myst/current. Net: 106 -> 114 canaries.

🤖 Generated by [robots](https://vyos.io)

* fix: re-import md-cloud-init.md (block 3 fix from myst/current)

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* feat(swap): import .md files and webp transition from myst/current

Selective import from origin/myst/current (cf9c9b34):
- Add/update 255 .md files (full MyST conversion plus webp ref updates)
- Delete 175 PNG/JPG from docs/_static/images (webp twins already present)
- Delete 5 autotest topology.png (webp twins already present)

Preserved on swap (untouched):
- All .rst files (incremental swap pattern)
- conf.py, _ext/, _include/*.txt, .gitignore
- 115 canary md-*.md files
- 7 superpowers/specs/*.md design docs
- Logos vyos-logo.png / vyos-logo-icon.png (referenced by conf.py)

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* chore(swap): remove canary md-*.md files and docs/superpowers

- Remove 115 canary md-*.md files (incremental swap helpers no longer needed)
- Remove 8 files under docs/superpowers (project planning/design docs that
  shouldn't ship in the documentation tree)

🤖 Generated by [robots](https://vyos.io)

* docs: address Copilot review feedback on imported MyST pages

Fix issues flagged by Copilot review on PR #1857 (the same content lives
in myst/current as the canonical source):

Real bugs:
- site-2-site-cisco.md: replace curly quote (U+2019) with ASCII apostrophe
- rsa-keys.md: fix typo "key-pair nam>>" → "key-pair name>"
- vmware.md: lowercase admonition directive (:::{NOTE} → :::{note})
- vpp/configuration/nat/index.md: remove blank line inside {include} fence

Grammar:
- vpp/configuration/interfaces/loopback.md: "bounded" → "bound"
- vpp/configuration/sflow.md: "VyOS support" → "VyOS supports"
- vpp/requirements.md: "bypass" → "bypasses"
- vpp/configuration/dataplane/interface.md: "configures" → "configure"

CI linter (IP addresses):
- nmp.md: wrap 8.8.8.8 example with stop/start_vyoslinter
- lac-lns.md: wrap LNS config block (contains 8.8.8.8)
- wan-load-balancing.md: wrap whole file (illustrative non-RFC IPs)
- policy/examples.md: replace 192.0.1.1 with RFC 5737 192.0.2.1

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* fix(swap): address Copilot review feedback on swap infrastructure

Category D — drop obsolete canary mechanism settings:
- conf.py: remove '**/md-*.md' from exclude_patterns (no canaries left)
- Makefile: replace malformed '*/_build/*' with '$(BUILDDIR)/**' and drop
  the '*/md-*' ignore (canary files no longer exist)

Category C — script robustness:
- import_myst.py:
  * list_myst_files() now raises SystemExit on git ls-tree failure instead
    of silently returning [] (would have masked typo'd --source refs)
  * list_rst_files() skips _build/ when scanning for .rst stems
  * import_page() rejects stems containing '..' or absolute paths and
    re-checks that the resolved destination stays under docs_dir
  * --dry-run uses a separate "would_import" counter; summary line now
    distinguishes dry-run from actual imports
- swap_sources.py:
  * parse_swap_list() reads with explicit encoding='utf-8'
  * do_restore() validates state file version + entry shape before
    renaming files; raises with actionable message on corruption
  * State file reads/writes use explicit encoding='utf-8' throughout

_swap.txt:
- Wrap long comment line to satisfy 80-character doc-linter limit

🤖 Generated by [robots](https://vyos.io)

* refactor(swap): rename imported .md files to md- prefix for swap mechanism

Restore the canary file naming convention that swap_sources.py expects:
the imported MyST pages now live as docs/<dir>/md-<name>.md alongside
the existing docs/<dir>/<name>.rst, so swap_sources.py --swap can rename
them into place at build time.

- 254 .md files renamed (every page with a matching .rst counterpart)
- 2 MyST-only pages left at their final names (no .rst exists, no swap
  needed): docs/copyright.md, docs/automation/terraform/terraformvyos.md

All 114 stems listed in docs/_swap.txt now have a corresponding
md-<name>.md source file ready to swap in.

🤖 Generated by [robots](https://vyos.io)

* docs: address CodeRabbit review feedback on imported MyST pages

Fix issues flagged by CodeRabbit on PR #1857. All issues are pre-existing
in the upstream RST docs and inherited by the MyST conversion.

Real bugs:
- inter-vrf-routing-vrf-lite.md: invalid IPv6 next-hop "2001:db8::*" →
  "2001:db8::1"
- ipsec-pa-route-based.md: vendor mislabel "Cisco" → "Palo Alto"
  (header on line 39 and "Monitoring on Cisco side" section heading)
- bgp-ipv6-unnumbered.md: AS number mismatch between configuration and
  verification output for both routers (Router A: 65020 → 64496;
  Router B: 65021 → 64499)
- qos.md: class 30 used "match ADDRESS20" instead of ADDRESS30 — broke
  the documented pattern (classes 10/20/30 → ADDRESS10/20/30)

Security:
- OpenVPN_with_LDAP.md: redact full PEM private key material from the
  three "set pki ... private key '...'" lines and from the embedded
  OpenVPN client <key> block; replace with <REDACTED> / ...REDACTED...
  placeholders. Public certificates retained.

🤖 Generated by [robots](https://vyos.io)

* feat(swap): default to serving MyST for all swapped pages

Replace the previously-curated 114-stem _swap.txt with the full set of
254 imported md-prefixed pages, so MD is served by default at build
time. To revert any specific page back to RST, remove its stem from
_swap.txt (or comment it out).

🤖 Generated by [robots](https://vyos.io)

* fix(ext): handle RST fallback in CmdInclude when _renderer absent

`cmdincludemd` is in `myst_fence_as_directive`, so MyST routes
fence blocks through `render_fence → render_restructuredtext →
MockRSTParser`. In that path `self.state` is a plain docutils Body
with no `_renderer`, crashing the build.

Fall back to `nested_parse` when `_renderer` is unavailable so the
directive works in both MyST and RST/MockRSTParser contexts.

🤖 Generated by [robots](https://vyos.io)

* feat(conf): copy .md sources into HTML output for plain-text serving

Adds a build-finished hook that mirrors every .md file from the Sphinx
source tree into the HTML output directory verbatim, making unrendered
MyST sources accessible alongside HTML renders at the same URL path.

🤖 Generated by [robots](https://vyos.io)

* docs: address review feedback from PR #1857

Fix conversion artifacts, typos, grammar errors, and technical
inaccuracies flagged by automated code review (Copilot + CodeRabbit).

Infrastructure: add root-level md-*.md exclusion to conf.py,
fix sphinx-autobuild ignore globs in Makefile.

Content: fix curly quotes, invalid Go panic() calls, shell quoting
in cURL examples, incorrect firewall command paths, typos across
22 documentation files, remove duplicate sections.

🤖 Generated by [robots](https://vyos.io)

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

3 files changed, 1045 insertions, 0 deletions

diff --git a/docs/vpp/configuration/nat/md-cgnat.md b/docs/vpp/configuration/nat/md-cgnat.md
new file mode 100644
index 00000000..d3742b59
--- /dev/null
+++ b/docs/vpp/configuration/nat/md-cgnat.md
@@ -0,0 +1,249 @@
+---
+lastproofread: '2026-03-03'
+---
+
+(vpp_config_nat_cgnat)=
+
+```{include} /_include/need_improvement.txt
+```
+
+
+# VPP CGNAT Configuration
+
+Carrier-grade NAT (CGNAT) is a NAT type designed for Internet Service
+Providers (ISPs) to manage limited pools of public IP addresses. It
+solves two main problems:
+- Enables fair sharing of a limited number of public IP addresses among
+  multiple customers, ensuring all have internet access without interfering
+  with each other.
+- Enables tracking and logging of public IP address usage by different
+  customers, which is often a regulatory requirement.
+
+CGNAT configuration is straightforward. Define the inside and outside
+interfaces, then create rules to manage the translation of private IP
+addresses to public IP addresses.
+
+:::{warning}
+**Enabling CGNAT** on an interface (both inside and outside)
+**disables normal routing** on these interfaces and **blocks management
+access** to the VyOS router itself.
+
+Ensure you have an alternative management path to the router before applying
+your CGNAT configuration.
+:::
+
+## Interface Configuration
+
+Define the inside and outside interfaces. The inside interface connects
+to the private network, while the outside interface connects to the public
+network.
+
+```{cfgcmd} set vpp nat cgnat interface inside \<inside-interface\>
+```
+
+```{cfgcmd} set vpp nat cgnat interface outside \<outside-interface\>
+```
+
+This is a mandatory step, as the CGNAT needs to know on which interfaces it
+needs to apply rules and operate.
+
+## NAT Rules Configuration
+
+Next, you need to create the NAT rules.
+
+```{cfgcmd} set vpp nat cgnat rule \<rule-number\> description \<description\>
+```
+
+Add a description to the rule for easier identification.
+
+```{cfgcmd} set vpp nat cgnat rule \<rule-number\> inside-prefix \<inside-prefix\>
+```
+
+Specify the inside prefix (private IP range) to translate.
+
+```{cfgcmd} set vpp nat cgnat rule \<rule-number\> outside-prefix \<outside-prefix\>
+```
+
+Specify the outside prefix (public IP range) to use for translation.
+
+## Exclude Rules Configuration
+
+CGNAT exclude rules are implemented as DET44 identity mappings. Matching
+traffic is excluded from CGNAT translation and keeps its original
+address/port tuple.
+
+```{cfgcmd} set vpp nat cgnat exclude rule \<rule-number\> description \<description\>
+```
+
+Adds a description (stored as VPP identity-mapping tag) for easier
+identification.
+
+```{cfgcmd} set vpp nat cgnat exclude rule \<rule-number\> local-address \<local-address\>
+```
+
+Sets the local IPv4 address that should be excluded from translation. This
+option is mandatory for each exclude rule.
+
+```{cfgcmd} set vpp nat cgnat exclude rule \<rule-number\> protocol \<tcp|udp|icmp|all\>
+```
+
+Matches a specific protocol. Default is `all`.
+
+```{cfgcmd} set vpp nat cgnat exclude rule \<rule-number\> local-port \<1-65535\>
+```
+
+Matches a specific local port (or ICMP identifier in case of ICMP protocol).
+
+:::{important}
+Exclude-rule validation rules:
+- `local-address` must be specified.
+- `protocol` and `local-port` must either both be specified or both be
+  : omitted.
+- Duplicate identity mappings are not allowed (same local-address,
+  : protocol, local-port tuple).
+:::
+
+:::{note}
+A common use case for exclude rules is preserving management-plane access to
+the router itself (for example SSH) and local-originated services (for
+example DNS queries) when CGNAT is enabled.
+:::
+
+:::{important}
+**Memory Requirements**
+
+CGNAT memory usage scales with the number of internal customers.
+
+**Each 256 customers** (equivalent to a /24 subnet) requires
+approximately **4 MB of main heap memory**. This memory maintains
+customer-to-port mappings and session state information.
+
+Configure your VPP main heap size appropriately based on your expected
+customer count. See {ref}`VPP Memory Configuration <vpp_config_dataplane_memory>` for details on adjusting main heap size.
+:::
+
+## Session Limitations
+
+CGNAT has built-in session limitations to ensure fair resource allocation:
+
+Each customer (internal IP address) is limited to a maximum of 1000
+simultaneous sessions, even if more than 1000 ports are allocated to that
+customer. This limitation applies to all session types (TCP, UDP, ICMP).
+
+## Timeouts Configuration
+
+You can adjust NAT session timers to optimize address space usage by
+controlling how long sessions remain active and how long they occupy IP
+address and port combinations.
+
+Adjust these settings for different protocols individually:
+
+```
+set vpp nat cgnat timeout icmp <timeout-value>
+set vpp nat cgnat timeout tcp-established <timeout-value>
+set vpp nat cgnat timeout tcp-transitory <timeout-value>
+set vpp nat cgnat timeout udp <timeout-value>
+```
+
+## Example Configuration
+
+Here is an example CGNAT configuration with these assumptions:
+- Inside interface: `eth2`
+- Outside interface: `eth1`
+- Inside prefix: `100.64.0.0/16`
+- Outside prefix: `203.0.113.0/24`
+
+```
+set vpp nat cgnat interface inside eth2
+set vpp nat cgnat interface outside eth1
+set vpp nat cgnat rule 1 description "CGNAT Rule 1"
+set vpp nat cgnat rule 1 inside-prefix 100.64.0.0/16
+set vpp nat cgnat rule 1 outside-prefix 203.0.113.0/24
+set vpp nat cgnat exclude rule 10 description "Bypass management host"
+set vpp nat cgnat exclude rule 10 local-address 100.64.0.10
+set vpp nat cgnat exclude rule 20 description "Bypass subscriber DNS"
+set vpp nat cgnat exclude rule 20 local-address 100.64.0.20
+set vpp nat cgnat exclude rule 20 protocol udp
+set vpp nat cgnat exclude rule 20 local-port 53
+```
+
+### Operational Commands
+
+Once the CGNAT is configured, you can use the following commands to monitor
+its status and operation:
+
+```{opcmd} show vpp nat cgnat interfaces
+```
+
+Displays the configured inside and outside interfaces.
+
+```
+vyos@vyos:~$ show vpp nat cgnat interfaces
+CGNAT interfaces:
+  eth2 in
+  eth1 out
+```
+
+```{opcmd} show vpp nat cgnat sessions
+```
+
+Display active NAT sessions. This command may produce extensive output if
+many sessions are active.
+
+```{opcmd} show vpp nat cgnat mappings
+```
+
+Display current NAT mappings, including inside and outside address
+prefixes.
+
+```
+vyos@vyos:~$ show vpp nat cgnat mappings
+Inside         Outside           Sharing ratio    Ports per host    Sessions
+-------------  --------------  ---------------  ----------------  ----------
+100.64.0.0/16  203.0.113.0/24              256               252           0
+```
+
+```{opcmd} show vpp nat cgnat exclude-rules
+```
+
+Displays configured CGNAT exclude rules (identity mappings).
+
+```
+vyos@vyos:~$ show vpp nat cgnat exclude-rules
+Address      Protocol    Port    VRF  Description
+-----------  ----------  ------  -----  ---------------------
+100.64.0.10  all         any       0    Bypass management host
+100.64.0.20  udp         53        0    Bypass subscriber DNS
+```
+
+### Potential Issues and Troubleshooting
+
+Configuration fails to apply with an error similar to:
+
+```
+vpp_papi.vpp_papi.VPPIOError: [Errno 2] VPP API client: read failed
+```
+
+CGNAT utilizes main heap memory and if you are trying to configure big
+prefixes or a large number of NAT sessions, you may run into memory allocation
+issues. Try to {ref}`increase the main heap size in VPP configuration
+<vpp-config-dataplane-memory>`.
+
+## SSH/DNS Reachability After Enabling CGNAT
+
+If SSH access to the router (or local-originated DNS queries) stops working
+after enabling CGNAT, traffic may be dropped by DET44 when it does not match a
+translation mapping.
+
+In this case, add an exclude rule for the router local address that must
+bypass CGNAT translation.
+
+```
+set vpp nat cgnat exclude rule 100 local-address <router-ip>
+```
+
+Then verify:
+
+```
+show vpp nat cgnat exclude-rules
+```
diff --git a/docs/vpp/configuration/nat/md-index.md b/docs/vpp/configuration/nat/md-index.md
new file mode 100644
index 00000000..2591a791
--- /dev/null
+++ b/docs/vpp/configuration/nat/md-index.md
@@ -0,0 +1,41 @@
+---
+lastproofread: '2026-03-05'
+---
+
+(vpp-config-nat-index)=
+
+```{include} /_include/need_improvement.txt
+```
+
+# VPP NAT Configuration
+
+```{toctree}
+:includehidden: true
+:maxdepth: 1
+
+cgnat
+nat44
+```
+
+VPP Dataplane in VyOS supports two types of NAT:
+
+## NAT44
+
+This type is a classic NAT implementation where you can configure static
+and dynamic NAT rules. It supports both source and destination NAT. While the
+configuration may look a bit unusual compared to traditional NAT
+implementations, it provides flexibility in network configurations.
+
+## CGNAT
+
+CGNAT is a special type of NAT44, which is highly useful when you have
+multiple local customers and a limited number of public IP addresses. It
+shares the public IP address space fairly between customers by using a
+combination of IP address and port number to distinguish between them.
+
+ISPs often use this NAT type to provide internet access to customers.
+
+It supports only source NAT.
+
+CGNAT also supports exclude rules (identity mappings) to bypass translation
+for selected local addresses or protocol/port tuples.
diff --git a/docs/vpp/configuration/nat/md-nat44.md b/docs/vpp/configuration/nat/md-nat44.md
new file mode 100644
index 00000000..01b1cd3a
--- /dev/null
+++ b/docs/vpp/configuration/nat/md-nat44.md
@@ -0,0 +1,755 @@
+---
+lastproofread: '2026-03-05'
+---
+
+(vpp-config-nat-nat44)=
+
+```{include} /_include/need_improvement.txt
+```
+
+
+# VPP NAT44 Configuration
+
+NAT44 has two main use cases:
+- **Source NAT (SNAT)**: Enabling internet access for hosts in private
+  networks using dynamic or static address translation.
+- **Destination NAT (DNAT)**: Providing external access to internal services
+  through static port forwarding rules.
+
+VyOS supports both dynamic translation using address pools and static
+mappings for predictable address translation requirements.
+
+Configuring NAT44 involves a few steps:
+1. Define the inside and outside interfaces.
+2. Create NAT rules for SNAT or DNAT.
+
+## Dynamic and Static Operations
+
+NAT44 configuration can be done in one of two ways or in both ways
+simultaneously:
+1. Dynamically performing NAT using a pool of public IP addresses.
+2. Statically mapping private IP addresses to public IP addresses.
+
+To configure dynamic NAT, you need to define a pool of public IP
+addresses that will be used for translation. This offers an easy way to
+provide internet access to internal users.
+
+Static rules are suitable for scenarios where you need consistent and
+predictable mappings between private and public IP addresses. They are also
+the only way to configure DNAT.
+
+### NAT Rule Processing and Traffic Flow
+
+This section explains how different combinations of NAT rules affect
+traffic handling on a router. There are three possible combinations of NAT
+rule configurations:
+1. **Dynamic NAT Only**
+   - **All** traffic received on the "in" interface is processed by
+     dynamic NAT rules without exceptions.
+2. **Dynamic + Static NAT**
+   - **All** traffic received on the "in" interface is first matched
+     against static NAT rules.
+   - If no match is found, it is then processed against dynamic NAT rules.
+3. **Static NAT Only**
+   - **All** traffic on the "in" interface is checked against static NAT
+     rules.
+   - If no match is found, the traffic is routed **without NAT**.
+
+:::{important}
+- If **dynamic NAT rules** are present, **all** traffic received on
+  "in" interfaces is subject to NAT processing.
+- If **only static NAT rules** are configured, traffic that does not
+  match any static rule is routed unchanged.
+:::
+
+## Interfaces Configuration
+
+The first step in configuring NAT44 is defining which interfaces handle
+inside (private) and outside (public) traffic. VyOS uses these interface
+designations to determine the direction of translation.
+
+### Inside Interfaces
+
+Inside interfaces connect to private networks where hosts need source NAT
+to access external networks.
+
+```{cfgcmd} set vpp nat nat44 interface inside \<inside-interface\>
+```
+
+Traffic flowing **from** inside interfaces gets source NAT applied,
+translating private source addresses to public addresses from the
+translation pool.
+
+### Outside Interfaces
+
+Outside interfaces connect to public networks where external hosts may
+need to access internal services.
+
+```{cfgcmd} set vpp nat nat44 interface outside \<outside-interface\>
+```
+
+Traffic flowing **to** outside interfaces can trigger destination NAT
+based on static rules, allowing external access to internal services.
+
+### Interface Roles and Traffic Flow
+
+:::{note}
+While VyOS uses "inside" and "outside" as established conventions,
+the technical definitions are:
+- **Inside interface**: Interface where traffic originates that needs
+  source NAT (SNAT)
+- **Outside interface**: Interface where traffic originates that needs
+  destination NAT (DNAT)
+
+In complex network topologies, the same physical interface can be
+configured as both inside and outside to handle bidirectional NAT
+scenarios.
+:::
+
+**Traffic Processing:**
+1. **Inside → Outside** (SNAT): Private hosts accessing external networks
+2. **Outside → Inside** (DNAT): External hosts accessing internal services
+   via static rules
+3. **Dynamic NAT**: Created automatically for inside→outside traffic
+4. **Static NAT**: Requires explicit configuration for outside→inside
+   traffic
+
+### Multiple Interface Support
+
+You can configure multiple interfaces as inside or outside to support
+complex network topologies:
+
+```none
+# Multiple inside interfaces (different private networks)
+set vpp nat nat44 interface inside eth0
+set vpp nat nat44 interface inside eth2
+
+# Multiple outside interfaces (redundancy or load balancing)  
+set vpp nat nat44 interface outside eth1
+set vpp nat nat44 interface outside eth3
+```
+
+## Address Pool Configuration
+
+Address pools define ranges of IP addresses that can be used for NAT
+translations. VyOS NAT44 supports two types of address pools, each serving
+different purposes.
+
+### Translation Pools
+
+Translation pools are used for dynamic source NAT (SNAT). They provide a
+range of public IP addresses that can be dynamically assigned to private
+hosts when they access external networks.
+
+```{cfgcmd} set vpp nat nat44 address-pool translation address \<ip-address | ip-address-range\>
+```
+
+```{cfgcmd} set vpp nat nat44 address-pool translation interface \<interface-name\>
+```
+
+**Examples:**
+
+```none
+# Single address pool
+set vpp nat nat44 address-pool translation address 203.0.113.10
+
+# Address range pool  
+set vpp nat nat44 address-pool translation address 203.0.113.10-203.0.113.20
+
+# Interface-based pool (use a first IP assigned to the interface)
+set vpp nat nat44 address-pool translation interface eth1
+```
+
+### Twice-NAT Pools
+
+Twice-NAT pools are used when performing both source and destination NAT on
+the same traffic flow. This is particularly useful in scenarios where you
+need to:
+- Translate both source and destination addresses
+- Provide access between networks with overlapping IP ranges
+- Implement advanced NAT scenarios like self-twice-nat
+
+```{cfgcmd} set vpp nat nat44 address-pool twice-nat address \<ip-address | ip-address-range\>
+```
+
+```{cfgcmd} set vpp nat nat44 address-pool twice-nat interface \<interface-name\>
+```
+
+**Examples:**
+
+```none
+# Twice-NAT pool for advanced scenarios
+set vpp nat nat44 address-pool twice-nat address 192.168.100.1-192.168.100.10
+
+# Interface-based twice-nat pool
+set vpp nat nat44 address-pool twice-nat interface eth2
+```
+
+### Pool Requirements
+
+:::{important}
+- For dynamic NAT to work, you must configure at least one
+  **translation** pool.
+- For static rules with twice-nat options, you must configure a
+  **twice-nat** pool.
+- Interface-based pools automatically include main (first) IP address
+  assigned to the specified interface.
+:::
+
+### Pool Selection Priority
+
+When multiple pools are configured, VyOS uses the following selection
+priority:
+1. **Static mappings**: Always use the specific external address defined in
+   the rule.
+2. **Dynamic NAT**: Use available addresses from translation pools in the
+   order they were configured.
+3. **Twice-NAT**: Use addresses from twice-nat pools for secondary
+   translation.
+
+:::{note}
+As soon as you have configured interfaces and pool, the NAT44 is
+operational.
+:::
+
+## Static Rules Configuration
+
+Static NAT rules provide predictable and consistent mappings between private
+and public IP addresses. They are essential for:
+- **Destination NAT (DNAT)**: Allowing external hosts to access services in
+  the private network.
+- **Server publishing**: Making internal services available from the
+  Internet.
+- **Consistent mappings**: Ensuring the same private IP always maps to the
+  same public IP.
+
+Unlike dynamic NAT that uses a pool of addresses, static rules create
+one-to-one mappings that persist until explicitly removed.
+
+### Basic Static Rule Configuration
+
+To create a static NAT rule, you need to define the local (internal) and
+external (public) address mappings:
+
+```{cfgcmd} set vpp nat nat44 static rule \<rule-number\> local address \<internal-ip\>
+```
+
+```{cfgcmd} set vpp nat nat44 static rule \<rule-number\> external address \<external-ip\>
+```
+
+Where:
+- `<rule-number>` is a unique identifier for the rule
+- `<internal-ip>` is the private IP address in your local network
+- `<external-ip>` is the public IP address that external hosts will use
+
+This basic configuration creates a static one-to-one mapping. Traffic from
+outside to the external IP will be translated to the internal IP, and vice
+versa.
+
+### Port-based Static Rules
+
+For more granular control, you can create port-specific static rules. This
+is useful when you want to publish specific services:
+
+```{cfgcmd} set vpp nat nat44 static rule \<rule-number\> local address \<internal-ip\>
+```
+
+```{cfgcmd} set vpp nat nat44 static rule \<rule-number\> local port \<internal-port\>
+```
+
+```{cfgcmd} set vpp nat nat44 static rule \<rule-number\> external address \<external-ip\>
+```
+
+```{cfgcmd} set vpp nat nat44 static rule \<rule-number\> external port \<external-port\>
+```
+
+```{cfgcmd} set vpp nat nat44 static rule \<rule-number\> protocol \<protocol\>
+```
+
+Where:
+- `<internal-port>` and `<external-port>` are the port numbers used by
+  the connection.
+- `<protocol>` specifies the protocol (tcp, udp, icmp).
+
+:::{important}
+If you do not specify ports and protocol, the rule will apply to *all*
+traffic between the specified internal and external addresses.
+
+Rules must contain either both ports and protocol, or neither.
+:::
+
+### Advanced Static Rule Options
+
+VyOS NAT44 supports several advanced options for static rules:
+
+#### Twice-NAT
+
+Twice-NAT performs both source and destination NAT. When an external host
+accesses an internal service, the source IP of such a connection is
+translated to an address from the twice-NAT address pool.
+
+This is practical in scenarios where internal services cannot connect to
+public networks, so they see such traffic as internal.
+
+The twice-NAT option can be enabled with the following command:
+
+```{cfgcmd} set vpp nat nat44 static rule \<rule-number\> options twice-nat
+```
+
+#### Self Twice-NAT
+
+Self Twice-NAT is used when a local host needs to access itself via the
+external address:
+
+```{cfgcmd} set vpp nat nat44 static rule \<rule-number\> options self-twice-nat
+```
+
+This option rewrites source IP addresses on packets sent only from a local
+address to an external address configured in a rule.
+
+:::{important}
+- Using `self-twice-nat` option requires you to set the interface
+  connected to the local network as both inside and outside, because
+  both source and destination NAT need to be applied.
+- External IP address used in static rules must belong to one of the
+  configured translation pools.
+:::
+
+#### Out-to-In Only
+
+Restricts the rule to only apply to traffic from outside to inside
+interfaces:
+
+```{cfgcmd} set vpp nat nat44 static rule \<rule-number\> options out-to-in-only
+```
+
+This prevents the creation of sessions from the inside interface, making it
+a purely DNAT rule.
+
+#### Force Twice-NAT Address
+
+When using twice-nat, you can force the use of a specific IP address from
+the twice-nat address pool:
+
+```{cfgcmd} set vpp nat nat44 static rule \<rule-number\> options twice-nat-address \<ip-address\>
+```
+
+#### Rule Description
+
+To document your rules, you can add a description:
+
+```{cfgcmd} set vpp nat nat44 static rule \<rule-number\> description \<description\>
+```
+
+### Static Rules Configuration Examples
+
+**Full one-to-one NAT mapping:**
+
+```none
+set vpp nat nat44 static rule 100 local address 192.168.1.10
+set vpp nat nat44 static rule 100 external address 203.0.113.10
+set vpp nat nat44 static rule 100 description "One-to-one mapping"
+```
+
+**Port-specific SSH access:**
+
+```none
+set vpp nat nat44 static rule 200 local address 192.168.1.20
+set vpp nat nat44 static rule 200 local port 22
+set vpp nat nat44 static rule 200 external address 203.0.113.10
+set vpp nat nat44 static rule 200 external port 2222
+set vpp nat nat44 static rule 200 protocol tcp
+set vpp nat nat44 static rule 200 description "SSH access to server"
+```
+
+**Twice-NAT for local service access:**
+
+```none
+set vpp nat nat44 static rule 300 local address 192.168.1.30
+set vpp nat nat44 static rule 300 local port 80
+set vpp nat nat44 static rule 300 external address 203.0.113.10
+set vpp nat nat44 static rule 300 external port 80
+set vpp nat nat44 static rule 300 protocol tcp
+set vpp nat nat44 static rule 300 options twice-nat
+set vpp nat nat44 static rule 300 description "Web service with twice-nat"
+```
+:::{note}
+When using twice-nat or self-twice-nat options, ensure you have
+configured a twice-nat address pool using:
+```none
+set vpp nat nat44 address-pool twice-nat address <twice-nat-ip-range>
+```
+:::
+
+## Exclude Rules Configuration
+
+Exclude rules allow you to prevent specific traffic from undergoing NAT
+translation. This is particularly useful for:
+- **Router management**: Allowing SSH access to the router itself from
+  external networks.
+- **Service bypass**: Excluding specific services from NAT processing
+- **Traffic forwarding**: Allowing forwarded traffic to bypass NAT with 1-to-1
+  mapping.
+
+Exclude rules take precedence over both dynamic and static NAT rules,
+ensuring that matching traffic bypasses NAT processing. For forwarded
+traffic, exclude rules create invisible 1-to-1 mappings that allow packets
+to pass through without NAT modifications.
+
+### Basic Exclude Rule Configuration
+
+To create an exclude rule, you need to specify the traffic characteristics
+that should bypass NAT. You can configure exclude rules in two ways:
+
+**Option 1: Using local address**
+
+```{cfgcmd} set vpp nat nat44 exclude rule \<rule-number\> local-address \<internal-ip\>
+```
+
+**Option 2: Using external interface**
+
+```{cfgcmd} set vpp nat nat44 exclude rule \<rule-number\> external-interface \<interface-name\>
+```
+
+Where:
+- `<rule-number>` is a unique identifier for the exclude rule.
+- `<internal-ip>` is the local IP address that should be excluded from
+  : NAT.
+- `<interface-name>` is the external interface where the traffic
+  : originates.
+
+:::{important}
+You must use either `local-address` OR `external-interface` in an
+exclude rule, but not both simultaneously. These options are mutually
+exclusive.
+:::
+
+### Port-specific Exclude Rules
+
+For more granular control, you can exclude only specific ports and protocols.
+You can combine port and protocol specifications with either `local-address` or
+`external-interface`:
+
+**With local address:**
+
+```{cfgcmd} set vpp nat nat44 exclude rule \<rule-number\> local-address \<internal-ip\>
+```
+
+```{cfgcmd} set vpp nat nat44 exclude rule \<rule-number\> local-port \<port-number\>
+```
+
+```{cfgcmd} set vpp nat nat44 exclude rule \<rule-number\> protocol \<protocol\>
+```
+
+**With external interface:**
+
+```{cfgcmd} set vpp nat nat44 exclude rule \<rule-number\> external-interface \<interface-name\>
+```
+
+```{cfgcmd} set vpp nat nat44 exclude rule \<rule-number\> local-port \<port-number\>
+```
+
+```{cfgcmd} set vpp nat nat44 exclude rule \<rule-number\> protocol \<protocol\>
+```
+
+Where:
+- `<port-number>` is the specific port to exclude (1-65535)
+- `<protocol>` can be `tcp`, `udp`, `icmp`, or `all` (default)
+
+### Rule Documentation
+
+Add descriptions to your exclude rules for better management:
+
+```{cfgcmd} set vpp nat nat44 exclude rule \<rule-number\> description \<description\>
+```
+
+### Exclude Rules Configuration Examples
+
+**Exclude SSH access to router:**
+
+```none
+# Allow external SSH access to router without NAT
+set vpp nat nat44 exclude rule 10 local-address 192.168.1.1
+set vpp nat nat44 exclude rule 10 local-port 22
+set vpp nat nat44 exclude rule 10 protocol tcp
+set vpp nat nat44 exclude rule 10 description "SSH access to router"
+```
+
+**Exclude SNMP monitoring:**
+
+```none
+# Allow SNMP monitoring without NAT translation
+set vpp nat nat44 exclude rule 20 local-port 161
+set vpp nat nat44 exclude rule 20 protocol udp
+set vpp nat nat44 exclude rule 20 external-interface eth1
+set vpp nat nat44 exclude rule 20 description "SNMP monitoring"
+```
+
+**Exclude all traffic to router management interface:**
+
+```none
+# Exclude all traffic to router's management IP
+set vpp nat nat44 exclude rule 30 local-address 192.168.100.1
+set vpp nat nat44 exclude rule 30 description "Management interface bypass"
+```
+
+**Exclude all traffic from external interface:**
+
+```none
+# Exclude all traffic from external interface (alternative approach)
+set vpp nat nat44 exclude rule 31 external-interface eth1
+set vpp nat nat44 exclude rule 31 description "External interface bypass"
+```
+
+**Exclude forwarded traffic for specific service:**
+
+```none
+# Allow external access to internal server without NAT translation
+set vpp nat nat44 exclude rule 40 local-address 192.168.1.50
+set vpp nat nat44 exclude rule 40 local-port 8080
+set vpp nat nat44 exclude rule 40 protocol tcp
+set vpp nat nat44 exclude rule 40 description "Direct access to internal service"
+```
+
+### Common Use Cases
+
+**Router Administration:**
+
+Exclude rules are essential when you need to manage the router from external
+networks. Without exclude rules, NAT would attempt to translate the router's
+own traffic, potentially breaking management connections.
+
+**Service Monitoring:**
+
+Network monitoring systems often need direct access to router services.
+Exclude rules ensure that monitoring traffic bypasses NAT translation.
+
+**Routing Protocols:**
+
+Some routing protocols or network services may require direct communication
+without NAT interference.
+
+**Traffic Forwarding:**
+
+Exclude rules also work for forwarded traffic between networks. Without
+exclude rules, traffic from external to local networks must either match a
+static rule or be dropped. With exclude rules, traffic can bypass NAT
+processing with invisible 1-to-1 mappings.
+
+:::{important}
+Exclude rules affect both traffic destined for the router itself and
+forwarded traffic flowing through the router. For forwarded traffic, exclude
+rules create transparent 1-to-1 mappings that allow packets to pass without
+NAT modifications, while from the outside perspective, the traffic appears to
+bypass NAT entirely.
+:::
+
+## Advanced NAT44 Settings
+
+VyOS provides additional NAT44 settings for fine-tuning performance and
+behavior.
+
+### Session Timeouts
+
+NAT44 maintains translation sessions with configurable timeout values for
+different protocols:
+
+```{cfgcmd} set vpp nat nat44 timeout icmp \<seconds\>
+
+Set the timeout for ICMP sessions (Default: 60 seconds).
+```
+
+```{cfgcmd} set vpp nat nat44 timeout tcp-established \<seconds\>
+
+Set the timeout for established TCP connections (Default: 7440 seconds
+or 2 hours 4 minutes).
+```
+
+```{cfgcmd} set vpp nat nat44 timeout tcp-transitory \<seconds\>
+
+Set the timeout for transitory TCP connections (setup/teardown) (Default:
+240 seconds or 4 minutes).
+```
+
+```{cfgcmd} set vpp nat nat44 timeout udp \<seconds\>
+
+Set the timeout for UDP sessions (Default: 300 seconds or 5 minutes).
+```
+
+**Example:**
+
+```none
+# Customize timeouts for high-traffic environment
+set vpp nat nat44 timeout tcp-established 3600
+set vpp nat nat44 timeout udp 600
+set vpp nat nat44 timeout icmp 30
+```
+
+### Session Limits
+
+Control the maximum number of concurrent NAT sessions:
+
+```{cfgcmd} set vpp nat nat44 session-limit \<number\>
+
+Set the maximum number of NAT sessions per worker thread (Default:
+64512).
+```
+
+This setting helps prevent memory exhaustion and ensures predictable
+performance under high load.
+
+**Example:**
+
+```none
+# Increase session limit for high-capacity deployment
+set vpp nat nat44 session-limit 100000
+```
+
+## Complete Configuration Example
+
+Here's a complete example showing how to configure VyOS NAT44 for a typical
+network setup:
+
+**Network Topology:**
+
+```none
+Internet (203.0.113.0/24)
+        |
+┌───────────────────┐
+│   eth1 (outside)  │ 203.0.113.1/24
+│     VyOS Router   │
+│   eth0 (inside)   │ 192.168.1.1/24  
+└───────────────────┘
+        |
+Internal Network (192.168.1.0/24)
+├── 192.168.1.10 (Web Server)
+├── 192.168.1.20 (SSH Server)  
+└── 192.168.1.30 (API Service)
+```
+
+**Configuration:**
+
+```none
+# Configure interfaces
+set vpp nat nat44 interface inside eth0
+set vpp nat nat44 interface outside eth1
+
+# Configure address pools
+set vpp nat nat44 address-pool translation address 203.0.113.10-203.0.113.50
+set vpp nat nat44 address-pool twice-nat address 203.0.113.100-203.0.113.110
+
+# Exclude rules for router management
+set vpp nat nat44 exclude rule 10 local-address 203.0.113.1
+set vpp nat nat44 exclude rule 10 local-port 22
+set vpp nat nat44 exclude rule 10 protocol tcp
+set vpp nat nat44 exclude rule 10 description "SSH access to router"
+
+set vpp nat nat44 exclude rule 11 local-address 203.0.113.1
+set vpp nat nat44 exclude rule 11 local-port 443
+set vpp nat nat44 exclude rule 11 protocol tcp
+set vpp nat nat44 exclude rule 11 description "HTTPS access to router web interface"
+
+# Static rule for web server (HTTP)
+set vpp nat nat44 static rule 100 local address 192.168.1.10
+set vpp nat nat44 static rule 100 local port 80
+set vpp nat nat44 static rule 100 external address 203.0.113.10
+set vpp nat nat44 static rule 100 external port 80
+set vpp nat nat44 static rule 100 protocol tcp
+set vpp nat nat44 static rule 100 description "Public web server"
+
+# Static rule for web server (HTTPS)
+set vpp nat nat44 static rule 101 local address 192.168.1.10
+set vpp nat nat44 static rule 101 local port 443
+set vpp nat nat44 static rule 101 external address 203.0.113.10
+set vpp nat nat44 static rule 101 external port 443
+set vpp nat nat44 static rule 101 protocol tcp
+set vpp nat nat44 static rule 101 description "Public web server HTTPS"
+
+# Static rule for SSH server with custom port
+set vpp nat nat44 static rule 200 local address 192.168.1.20
+set vpp nat nat44 static rule 200 local port 22
+set vpp nat nat44 static rule 200 external address 203.0.113.11
+set vpp nat nat44 static rule 200 external port 2222
+set vpp nat nat44 static rule 200 protocol tcp
+set vpp nat nat44 static rule 200 description "SSH access"
+
+# Static rule for API service (out-to-in only for security)
+set vpp nat nat44 static rule 300 local address 192.168.1.30
+set vpp nat nat44 static rule 300 local port 8080
+set vpp nat nat44 static rule 300 external address 203.0.113.12
+set vpp nat nat44 static rule 300 external port 8080
+set vpp nat nat44 static rule 300 protocol tcp
+set vpp nat nat44 static rule 300 options out-to-in-only
+set vpp nat nat44 static rule 300 description "API service (No Internet access for it)"
+```
+
+## Best Practices and Troubleshooting
+
+### Recommendations
+
+- **Use exclude rules** for router management services like SSH
+- **Use out-to-in-only** for services that do not need access to external
+  : networks.
+- **Limit port ranges** in static rules to only necessary ports.
+- **Document all rules** using descriptions for easier management.
+- **Use non-standard ports** for publishing SSH and other administrative
+  : services.
+- **Configure appropriate pool sizes** based on expected concurrent
+  : connections in your network.
+
+### Common Configuration Issues
+
+**Static rules not working:**
+
+1. Verify that the external IP address is included in an address pool
+2. Check that interfaces are correctly configured as inside or outside
+3. Ensure firewall rules allow the traffic
+
+**Twice-NAT not functioning:**
+
+1. Confirm twice-nat pool is configured
+2. Verify static rules have the correct twice-nat option
+3. Check that both translation and twice-nat pools are properly defined
+
+**Router management access issues:**
+
+1. Verify exclude rules are configured for management services
+2. Check that local-address matches the router's interface IP
+3. Ensure external-interface is correctly specified
+
+**Forwarded traffic from external networks not bypassing NAT:**
+
+1. Verify exclude rules are configured for the specific traffic flow
+2. Check that local-address matches the destination IP in the internal
+   network
+3. Ensure protocol and port specifications match the traffic requirements
+
+## Operational Commands
+
+Monitor NAT44 status and active connections using VyOS operational
+commands:
+
+```{opcmd} show vpp nat nat44 addresses
+
+Display configured NAT44 address pools.
+```
+
+```{opcmd} show vpp nat nat44 interfaces
+
+Show which interfaces are configured as inside or outside for NAT44.
+```
+
+```{opcmd} show vpp nat nat44 sessions
+
+Display active NAT44 translation sessions.
+```
+
+```{opcmd} show vpp nat nat44 static
+
+Show all configured static NAT mappings.
+```
+
+```{opcmd} show vpp nat nat44 summary
+
+Display a summary of NAT44 and statistics.
+```
\ No newline at end of file