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, 67 insertions, 0 deletions

diff --git a/docs/configuration/interfaces/loopback.md b/docs/configuration/interfaces/loopback.md
new file mode 100644
index 00000000..72f14c16
--- /dev/null
+++ b/docs/configuration/interfaces/loopback.md
@@ -0,0 +1,67 @@
+---
+lastproofread: '2026-01-23'
+---
+
+(loopback-interface)=
+
+# Loopback
+
+The loopback interface is a virtual, software-based network interface. All
+traffic sent to it loops back and only targets services on the local host.
+
+:::{note}
+Only one loopback `lo` interface is allowed per operating system.
+If you require multiple virtual interfaces, use the {ref}`dummy-interface`
+interface type.
+:::
+
+## Configuration
+
+### Common interface configuration
+
+```{cmdincludemd} /_include/interface-address.txt
+:var0: loopback
+:var1: lo
+```
+
+```{cmdincludemd} /_include/interface-description.txt
+:var0: loopback
+:var1: lo
+```
+
+
+## Operation
+
+```{opcmd} show interfaces loopback
+
+Show brief interface information.
+
+:::{code-block} none
+vyos@vyos:~$ show interfaces loopback
+Codes: S - State, L - Link, u - Up, D - Down, A - Admin Down
+Interface        IP Address                        S/L  Description
+---------        ----------                        ---  -----------
+lo               127.0.0.1/8                       u/u
+                 ::1/128
+:::
+```
+
+```{opcmd} show interfaces loopback lo
+
+Show detailed interface information.
+
+:::{code-block} none
+vyos@vyos:~$ show interfaces loopback lo
+lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
+  link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
+  inet 127.0.0.1/8 scope host lo
+       valid_lft forever preferred_lft forever
+  inet6 ::1/128 scope host
+       valid_lft forever preferred_lft forever
+
+  RX:  bytes    packets     errors    dropped    overrun      mcast
+           300          6          0          0          0          0
+  TX:  bytes    packets     errors    dropped    carrier collisions
+           300          6          0          0          0          0
+:::
+```
\ No newline at end of file