feat: flip swap mechanism on sagitta — MD as primary, RST as override

Mirror of #1899 (current) and #1900 (circinus) for sagitta. Same logic,
same scripts, per-branch file set.

Changes:
- Rename docs/**/md-<stem>.md to docs/**/<stem>.md (drop md- prefix) for
  all 210 stems previously listed in docs/_swap.txt
- Rename docs/**/<stem>.rst to docs/**/rst-<stem>.rst (add rst- prefix)
  for the same 210 stems
- Repurpose docs/_swap.txt as docs/_rst_overrides.txt; initially empty
- conf.py exclude_patterns flipped: rst-*.rst excluded by default
- conf.py runtime-artifact references updated to _rst_override_state.json
  and _md_exclude.txt
- scripts/swap_sources.py imported from current (post-#1899 rewrite, with
  inverted rename direction)
- scripts/import_myst.py and tests/test_import_myst.py deleted (obsolete)
- tests/test_swap_sources.py imported from current (post-#1899 rewrite)

Side-effect: fixes the same 404 on /en/1.4/ View page source links that
#1899 fixed for /en/rolling/ and #1900 fixed for /en/1.5/.

Per-branch differences vs #1899:
- sagitta has 210 stems vs current's 254 (sagitta has no vpp pages and
  fewer current-only features; cli + installation/cloud/aws are still
  RST-only on sagitta pending the title-level fix follow-up)
- otherwise the script/conf.py/test changes are byte-identical with current

Generated by robots https://vyos.io

1 files changed, 80 insertions, 0 deletions

diff --git a/docs/configuration/interfaces/loopback.md b/docs/configuration/interfaces/loopback.md
new file mode 100644
index 00000000..37da5399
--- /dev/null
+++ b/docs/configuration/interfaces/loopback.md
@@ -0,0 +1,80 @@
+---
+lastproofread: '2023-01-20'
+---
+
+(loopback-interface)=
+
+# Loopback
+
+The loopback networking interface is a virtual network device implemented
+entirely in software. All traffic sent to it "loops back" and just targets
+services on your local machine.
+
+:::{note}
+There can only be one loopback `lo` interface on the system. If
+you need multiple interfaces, please use the {ref}`dummy-interface`
+interface type.
+:::
+
+:::{hint}
+A loopback interface is always up, thus it could be used for
+management traffic or as source/destination for and {abbr}`IGP (Interior
+Gateway Protocol)` like {ref}`routing-bgp` so your internal BGP link is not
+dependent on physical link states and multiple routes can be chosen to the
+destination. A {ref}`dummy-interface` Interface should always be preferred
+over a {ref}`loopback-interface` interface.
+:::
+
+## Configuration
+
+### Common interface configuration
+
+```{eval-rst}
+.. cmdincludemd:: /_include/interface-address.txt
+   :var0: loopback
+   :var1: lo
+```
+
+```{eval-rst}
+.. cmdincludemd:: /_include/interface-description.txt
+   :var0: loopback
+   :var1: lo
+```
+
+## Operation
+
+```{eval-rst}
+.. 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
+```
+
+```{eval-rst}
+.. opcmd:: show interfaces loopback lo
+
+   Show detailed information on the given loopback interface `lo`.
+
+   .. 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
+```