feat: flip swap mechanism — MD as primary, RST as override (Phase 1)

This is the first of three phases inverting the per-page swap mechanism
so MD becomes the canonical primary and RST becomes the rare override.

Phase 1 — file renames + conf.py exclude_patterns flip only:
- Rename docs/**/md-<stem>.md to docs/**/<stem>.md (drop md- prefix)
  for all 254 stems previously listed in docs/_swap.txt
- Rename docs/**/<stem>.rst to docs/**/rst-<stem>.rst (add rst- prefix)
  for the same 254 stems
- Repurpose docs/_swap.txt as docs/_rst_overrides.txt; initially empty
  comment-only since no pages need the RST fallback right now
- conf.py exclude_patterns flipped: rst-*.rst is now excluded by default
  instead of md-*.md
- conf.py runtime-artifact references updated to _rst_override_state.json
  and _md_exclude.txt (Phase 2 will rewrite swap_sources.py to produce
  these names; for now no swap script runs because overrides list is empty)

Phase 2 (next commit on this branch) will rewrite scripts/swap_sources.py
with inverted rename direction, delete scripts/import_myst.py + tests, and
update tests/test_swap_sources.py for the new semantics.

Phase 3 will be the cleanup pass and ready-for-review flip.

Generated by robots https://vyos.io

1 files changed, 119 insertions, 0 deletions

diff --git a/docs/vpp/configuration/interfaces/ipip.md b/docs/vpp/configuration/interfaces/ipip.md
new file mode 100644
index 00000000..80a724b0
--- /dev/null
+++ b/docs/vpp/configuration/interfaces/ipip.md
@@ -0,0 +1,119 @@
+---
+lastproofread: '2026-03-13'
+---
+
+(vpp-config-interfaces-ipip)=
+
+```{include} /_include/need_improvement.txt
+```
+
+
+# VPP IPIP Configuration
+
+VPP IPIP interfaces provide IP-in-IP tunneling with high-performance
+packet processing. IPIP tunnels encapsulate IP packets within IP
+packets, creating point-to-point connections across Layer 3 networks.
+
+## Basic Configuration
+
+### Creating an IPIP Interface
+
+```{cfgcmd} set interfaces vpp ipip \<vppipipN\>
+
+Create an IPIP interface where ``<vppipipN>`` follows the naming
+convention ``vppipip1``, ``vppipip2``, etc.
+```
+
+```{cfgcmd} set interfaces vpp ipip \<vppipipN\> remote \<address\>
+
+Set the tunnel remote endpoint address. Supports both IPv4 and IPv6
+addresses.
+```
+
+```{cfgcmd} set interfaces vpp ipip \<vppipipN\> source-address \<address\>
+
+Set the tunnel source address. The source address must match an address
+configured on the local system.
+```
+
+**Basic Example:**
+
+```none
+set interfaces vpp ipip vppipip1
+set interfaces vpp ipip vppipip1 remote 203.0.113.2
+set interfaces vpp ipip vppipip1 source-address 192.168.1.1
+```
+
+## Interface Configuration
+### Description and Administrative Control
+
+```{cfgcmd} set interfaces vpp ipip \<vppipipN\> description \<description\>
+
+Set a descriptive name for the IPIP interface.
+```
+
+```{cfgcmd} set interfaces vpp ipip \<vppipipN\> disable
+
+Administratively disable the IPIP interface.
+```
+
+### Kernel Interface Integration
+
+Kernel interface is bound to the VPP IPIP interface for management and
+application compatibility.
+
+## IP Address Configuration
+
+```{cfgcmd} set interfaces vpp ipip \<vppipipN\> address \<ip-address/prefix\>
+
+Configure IPv4 or IPv6 addresses on the kernel interface. Multiple
+addresses can be assigned.
+```
+
+**Examples:**
+
+```none
+# IPv4 address
+set interfaces vpp ipip vppipip0 address 192.168.1.10/24
+
+# IPv6 address
+set interfaces vpp ipip vppipip0 address 2001:db8::10/64
+```
+
+## MTU Configuration
+
+```{cfgcmd} set interfaces vpp ipip \<vppipipN\> mtu \<size\>
+
+Set the Maximum Transmission Unit (MTU) for the kernel interface.
+The MTU must be compatible with the connected VPP interface.
+```
+
+## Configuration Examples
+### IPv4 IPIP Tunnel
+
+```none
+# Basic IPv4 IPIP tunnel
+set interfaces vpp ipip vppipip1
+set interfaces vpp ipip vppipip1 description "Site-to-site IPIP tunnel"
+set interfaces vpp ipip vppipip1 remote 203.0.113.10
+set interfaces vpp ipip vppipip1 source-address 192.168.1.1
+```
+
+### IPv6 IPIP Tunnel
+
+```none
+# IPv6 endpoints
+set interfaces vpp ipip vppipip2
+set interfaces vpp ipip vppipip2 remote 2001:db8::2
+set interfaces vpp ipip vppipip2 source-address 2001:db8::1
+```
+
+### IPIP with Kernel Interface
+
+```none
+# IPIP tunnel with management interface
+set interfaces vpp ipip vppipip3
+set interfaces vpp ipip vppipip3 remote 203.0.113.30
+set interfaces vpp ipip vppipip3 source-address 192.168.1.1
+set interfaces vpp ipip vppipip3 address 10.0.2.1/30
+```