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, 205 insertions, 0 deletions

diff --git a/docs/configuration/protocols/bfd.md b/docs/configuration/protocols/bfd.md
new file mode 100644
index 00000000..13623e03
--- /dev/null
+++ b/docs/configuration/protocols/bfd.md
@@ -0,0 +1,205 @@
+---
+lastproofread: '2023-01-27'
+---
+
+```{include} /_include/need_improvement.txt
+```
+
+(routing-bfd)=
+
+# BFD
+
+{abbr}`BFD (Bidirectional Forwarding Detection)` is described and extended by
+the following RFCs: {rfc}`5880`, {rfc}`5881` and {rfc}`5883`.
+
+In the age of very fast networks, a second of unreachability may equal millions of lost packets.
+The idea behind BFD is to detect very quickly when a peer is down and take action extremely fast.
+
+BFD sends lots of small UDP packets very quickly to ensures that the peer is still alive.
+
+This allows avoiding the timers defined in BGP and OSPF protocol to expires.
+
+## Configure BFD
+
+```{cfgcmd} set protocols bfd peer \<address\>
+
+Set BFD peer IPv4 address or IPv6 address
+```
+
+```{cfgcmd} set protocols bfd peer \<address\> echo-mode
+
+Enables the echo transmission mode
+```
+
+```{cfgcmd} set protocols bfd peer \<address\> multihop
+
+Allow this BFD peer to not be directly connected
+```
+
+```{cfgcmd} set protocols bfd peer \<address\> source [address \<address\> | interface \<interface\>]
+
+Bind listener to specific interface/address, mandatory for IPv6
+```
+
+```{cfgcmd} set protocols bfd peer \<address\> interval echo-interval \<10-60000\>
+
+The minimal echo receive transmission interval that this system is
+capable of handling
+```
+
+```{cfgcmd} set protocols bfd peer \<address\> interval multiplier \<2-255\>
+
+Remote transmission interval will be multiplied by this value
+```
+
+```{cfgcmd} set protocols bfd peer \<address\> interval [receive | transmit] \<10-60000\>
+
+Interval in milliseconds
+```
+
+```{cfgcmd} set protocols bfd peer \<address\> shutdown
+
+Disable a BFD peer
+```
+
+```{cfgcmd} set protocols bfd peer \<address\> minimum-ttl \<1-254\>
+
+For multi hop sessions only. Configure the minimum expected TTL for an
+incoming BFD control packet.
+
+This feature serves the purpose of thightening the packet validation
+requirements to avoid receiving BFD control packets from other sessions.
+```
+
+### Enable BFD in BGP
+
+```{cfgcmd} set protocols bgp neighbor \<neighbor\> bfd
+
+Enable BFD on a single BGP neighbor
+```
+
+```{cfgcmd} set protocols bgp peer-group \<neighbor\> bfd
+
+Enable BFD on a BGP peer group
+```
+
+### Enable BFD in OSPF
+
+```{cfgcmd} set protocols ospf interface \<interface\> bfd
+
+   Enable BFD for OSPF on an interface
+
+```
+
+```{cfgcmd} set protocols ospfv3 interface \<interface\> bfd
+
+Enable BFD for OSPFv3 on an interface
+```
+
+### Enable BFD in ISIS
+
+```{cfgcmd} set protocols isis \<name\> interface \<interface\> bfd
+
+Enable BFD for ISIS on an interface
+
+```
+
+## Operational Commands
+
+```{opcmd} show bfd peers
+
+   Show all BFD peers
+
+   :::{code-block} none
+   BFD Peers:
+        peer 198.51.100.33 vrf default interface eth4.100
+                ID: 4182341893
+                Remote ID: 12678929647
+                Status: up
+                Uptime: 1 month(s), 16 hour(s), 29 minute(s), 38 second(s)
+                Diagnostics: ok
+                Remote diagnostics: ok
+                Local timers:
+                        Receive interval: 300ms
+                        Transmission interval: 300ms
+                        Echo transmission interval: 50ms
+                Remote timers:
+                        Receive interval: 300ms
+                        Transmission interval: 300ms
+                        Echo transmission interval: 0ms
+
+        peer 198.51.100.55 vrf default interface eth4.101
+                ID: 4618932327
+                Remote ID: 3312345688
+                Status: up
+                Uptime: 20 hour(s), 16 minute(s), 19 second(s)
+                Diagnostics: ok
+                Remote diagnostics: ok
+                Local timers:
+                        Receive interval: 300ms
+                        Transmission interval: 300ms
+                        Echo transmission interval: 50ms
+                Remote timers:
+                        Receive interval: 300ms
+                        Transmission interval: 300ms
+                        Echo transmission interval: 0ms
+   :::
+```
+
+## BFD Static Route Monitoring
+
+
+A monitored static route conditions the installation to the RIB on the BFD
+session running state: when BFD session is up the route is installed to RIB,
+but when the BFD session is down it is removed from the RIB.
+
+
+### Configuration
+
+```{cfgcmd} set protocols static route \<subnet\> next-hop \<address\> bfd profile \<profile\>
+
+Configure a static route for \<subnet\> using gateway \<address\>
+and use the gateway address as BFD peer destination address.
+```
+
+```{cfgcmd} set protocols static route \<subnet\> next-hop \<address\> bfd multi-hop source \<address\> profile \<profile\>
+
+Configure a static route for \<subnet\> using gateway \<address\>,
+use source address to identify the peer when is multi-hop session
+and the gateway address as BFD peer destination address.
+```
+
+```{cfgcmd} set protocols static route6 \<subnet\> next-hop \<address\> bfd profile \<profile\>
+
+Configure a static route for \<subnet\> using gateway \<address\>
+and use the gateway address as BFD peer destination address.
+```
+
+```{cfgcmd} set protocols static route6 \<subnet\> next-hop \<address\> bfd multi-hop source \<address\> profile \<profile\>
+
+Configure a static route for \<subnet\> using gateway \<address\>,
+use source address to identify the peer when is multi-hop session
+and the gateway address as BFD peer destination address.
+```
+
+(bfd-operational-commands)=
+
+## Operational Commands
+
+```{opcmd} show bfd static routes
+
+Showing BFD monitored static routes
+
+:::{code-block} none
+Showing BFD monitored static routes:
+
+  Next hops:
+    VRF default IPv4 Unicast:
+        10.10.13.3/32 peer 192.168.2.3 (status: installed)
+        172.16.10.3/32 peer 192.168.10.1 (status: uninstalled)
+
+    VRF default IPv4 Multicast:
+
+    VRF default IPv6 Unicast:
+:::
+```
\ No newline at end of file