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, 359 insertions, 0 deletions

diff --git a/docs/configuration/protocols/segment-routing.md b/docs/configuration/protocols/segment-routing.md
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+(segment-routing)=
+
+# Segment Routing
+
+Segment Routing (SR) is a network architecture that is similar to source-routing
+. In this architecture, the ingress router adds a list of segments, known as
+SIDs, to the packet as it enters the network. These segments represent different
+portions of the network path that the packet will take.
+
+The SR segments are portions of the network path taken by the packet, and are
+called SIDs. At each node, the first SID of the list is read, executed as a
+forwarding function, and may be popped to let the next node read the next SID of
+the list. The SID list completely determines the path where the packet is
+forwarded.
+
+Segment Routing can be applied to an existing MPLS-based data plane and defines
+a control plane network architecture. In MPLS networks, segments are encoded as
+MPLS labels and are added at the ingress router. These MPLS labels are then
+exchanged and populated by Interior Gateway Protocols (IGPs) like IS-IS or OSPF
+which are running on most ISPs.
+
+:::{note}
+Segment routing defines a control plane network architecture and
+can be applied to an existing MPLS based dataplane. In the MPLS networks,
+segments are encoded as MPLS labels and are imposed at the ingress router.
+MPLS labels are exchanged and populated by IGPs like IS-IS.Segment Routing
+as per RFC8667 for MPLS dataplane. It supports IPv4, IPv6 and ECMP and has
+been tested against Cisco & Juniper routers.however,this deployment is still
+EXPERIMENTAL for FRR.
+:::
+
+## IS-IS SR Configuration
+
+Segment routing (SR) is used by the IGP protocols to interconnect network
+devices, below configuration shows how to enable SR on IS-IS:
+
+:::{note}
+``Known limitations:``
+
+No support for level redistribution (L1 to L2 or L2 to L1)
+
+No support for binding SID
+
+No support for SRLB
+
+Only one SRGB and default SPF Algorithm is supported
+:::
+
+```{cfgcmd} set protocols isis segment-routing global-block high-label-value \<label-value\>
+
+Set the Segment Routing Global Block i.e. the label range used by MPLS to
+store label in the MPLS FIB for Prefix SID. Note that the block size may
+not exceed 65535.
+```
+
+
+```{cfgcmd} set protocols isis segment-routing global-block low-label-value \<label-value\>
+
+Set the Segment Routing Global Block i.e. the low label range used by MPLS to
+store label in the MPLS FIB for Prefix SID. Note that the block size may
+not exceed 65535.
+```
+
+
+```{cfgcmd} set protocols isis segment-routing local-block high-label-value \<label-value\>
+
+Set the Segment Routing Local Block i.e. the label range used by MPLS to
+store label in the MPLS FIB for Prefix SID. Note that the block size may
+not exceed 65535.Segment Routing Local Block, The negative command always
+unsets both.
+```
+
+
+```{cfgcmd} set protocols isis segment-routing local-block \<low-label-value \<label-value\>
+
+Set the Segment Routing Local Block i.e. the low label range used by MPLS to
+store label in the MPLS FIB for Prefix SID. Note that the block size may
+not exceed 65535.Segment Routing Local Block, The negative command always
+unsets both.
+```
+
+
+```{cfgcmd} set protocols isis segment-routing maximum-label-depth \<1-16\>
+
+Set the Maximum Stack Depth supported by the router. The value depend of
+the MPLS dataplane.
+```
+
+
+```{cfgcmd} set protocols isis segment-routing prefix \<address\> index value \<0-65535\>
+
+A segment ID that contains an IP address prefix calculated by an IGP in the
+service provider core network. Prefix SIDs are globally unique, this value
+identify it
+```
+
+
+```{cfgcmd} set protocols isis segment-routing prefix \<address\> index \<no-php-flag | explicit-null| n-flag-clear\>
+
+this option allows to configure prefix-sid on SR. The ‘no-php-flag’ means NO
+Penultimate Hop Popping that allows SR node to request to its neighbor to
+not pop the label. The ‘explicit-null’ flag allows SR node to request to its
+neighbor to send IP packet with the EXPLICIT-NULL label. The ‘n-flag-clear’
+option can be used to explicitly clear the Node flag that is set by default
+for Prefix-SIDs associated to loopback addresses. This option is necessary
+to configure Anycast-SIDs.
+```
+
+```{opcmd} show isis segment-routing node
+
+   Show detailed information about all learned Segment Routing Nodes
+```
+
+
+```{opcmd} show isis route prefix-sid
+
+Show detailed information about prefix-sid and label learned
+```
+
+:::{note}
+more information related IGP - {ref}`routing-isis`
+:::
+
+
+## OSPF SR Configuration
+
+
+Segment routing (SR) is used by the IGP protocols to interconnect network
+devices, below configuration shows how to enable SR on OSPF:
+
+```{cfgcmd} set protocols ospf parameters opaque-lsa
+
+Enable the Opaque-LSA capability (rfc2370), necessary to transport label
+on IGP
+```
+
+```{cfgcmd} set protocols ospf segment-routing global-block high-label-value \<label-value\>
+
+Set the Segment Routing Global Block i.e. the label range used by MPLS to
+store label in the MPLS FIB for Prefix SID. Note that the block size may
+not exceed 65535.
+```
+
+```{cfgcmd} set protocols ospf segment-routing global-block low-label-value \<label-value\>
+
+Set the Segment Routing Global Block i.e. the low label range used by MPLS to
+store label in the MPLS FIB for Prefix SID. Note that the block size may
+not exceed 65535.
+```
+
+```{cfgcmd} set protocols ospf segment-routing local-block high-label-value \<label-value\>
+
+Set the Segment Routing Local Block i.e. the label range used by MPLS to
+store label in the MPLS FIB for Prefix SID. Note that the block size may
+not exceed 65535.Segment Routing Local Block, The negative command always
+unsets both.
+```
+
+```{cfgcmd} set protocols ospf segment-routing local-block \<low-label-value \<label-value\>
+
+Set the Segment Routing Local Block i.e. the low label range used by MPLS to
+store label in the MPLS FIB for Prefix SID. Note that the block size may
+not exceed 65535.Segment Routing Local Block, The negative command always
+unsets both.
+```
+
+```{cfgcmd} set protocols ospf segment-routing maximum-label-depth \<1-16\>
+
+Set the Maximum Stack Depth supported by the router. The value depend of
+the MPLS dataplane.
+```
+
+```{cfgcmd} set protocols ospf segment-routing prefix \<address\> index value \<0-65535\>
+
+A segment ID that contains an IP address prefix calculated by an IGP in the
+service provider core network. Prefix SIDs are globally unique, this value
+identify it
+```
+
+```{cfgcmd} set protocols ospf segment-routing prefix \<address\> index \<no-php-flag | explicit-null| n-flag-clear\>
+
+this option allows to configure prefix-sid on SR. The ‘no-php-flag’ means NO
+Penultimate Hop Popping that allows SR node to request to its neighbor to
+not pop the label. The ‘explicit-null’ flag allows SR node to request to its
+neighbor to send IP packet with the EXPLICIT-NULL label. The ‘n-flag-clear’
+option can be used to explicitly clear the Node flag that is set by default
+for Prefix-SIDs associated to loopback addresses. This option is necessary
+to configure Anycast-SIDs.
+```
+
+:::{note}
+more information related IGP - {ref}`routing-ospf`
+:::
+
+## Configuration Example
+
+we described the configuration SR ISIS / SR OSPF using 2 connected with them to
+share label information.
+
+### Enable IS-IS with Segment Routing (Experimental)
+
+**Node 1:**
+
+```none
+set interfaces loopback lo address '192.168.255.255/32'
+set interfaces ethernet eth1 address '192.0.2.1/24'
+
+set protocols isis interface eth1
+set protocols isis interface lo
+set protocols isis net '49.0001.1921.6825.5255.00'
+set protocols isis segment-routing global-block high-label-value '599'
+set protocols isis segment-routing global-block low-label-value '550'
+set protocols isis segment-routing prefix 192.168.255.255/32 index value '1'
+set protocols isis segment-routing prefix 192.168.255.255/32 index explicit-null
+set protocols mpls interface 'eth1'
+```
+
+**Node 2:**
+
+```none
+set interfaces loopback lo address '192.168.255.254/32'
+set interfaces ethernet eth1 address '192.0.2.2/24'
+
+set protocols isis interface eth1
+set protocols isis interface lo
+set protocols isis net '49.0001.1921.6825.5254.00'
+set protocols isis segment-routing global-block high-label-value '599'
+set protocols isis segment-routing global-block low-label-value '550'
+set protocols isis segment-routing prefix 192.168.255.254/32 index value '2'
+set protocols isis segment-routing prefix 192.168.255.254/32 index explicit-null
+set protocols mpls interface 'eth1'
+```
+
+This gives us MPLS segment routing enabled and labels for far end loopbacks:
+
+```none
+Node-1@vyos:~$ show mpls table
+ Inbound Label  Type        Nexthop                Outbound Label
+ ----------------------------------------------------------------------
+ 552            SR (IS-IS)  192.0.2.2              IPv4 Explicit Null <-- Node-2 loopback learned on Node-1
+ 15000          SR (IS-IS)  192.0.2.2              implicit-null
+ 15001          SR (IS-IS)  fe80::e87:6cff:fe09:1  implicit-null
+ 15002          SR (IS-IS)  192.0.2.2              implicit-null
+ 15003          SR (IS-IS)  fe80::e87:6cff:fe09:1  implicit-null
+
+Node-2@vyos:~$ show mpls table
+ Inbound Label  Type        Nexthop               Outbound Label
+ ---------------------------------------------------------------------
+ 551            SR (IS-IS)  192.0.2.1             IPv4 Explicit Null <-- Node-1 loopback learned on Node-2
+ 15000          SR (IS-IS)  192.0.2.1             implicit-null
+ 15001          SR (IS-IS)  fe80::e33:2ff:fe80:1  implicit-null
+ 15002          SR (IS-IS)  192.0.2.1             implicit-null
+ 15003          SR (IS-IS)  fe80::e33:2ff:fe80:1  implicit-null
+```
+
+Here is the routing tables showing the MPLS segment routing label operations:
+
+```none
+Node-1@vyos:~$ show ip route isis
+Codes: K - kernel route, C - connected, S - static, R - RIP,
+       O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
+       T - Table, v - VNC, V - VNC-Direct, A - Babel, F - PBR,
+       f - OpenFabric,
+       > - selected route, * - FIB route, q - queued, r - rejected, b - backup
+       t - trapped, o - offload failure
+
+I   192.0.2.0/24 [115/20] via 192.0.2.2, eth1 inactive, weight 1, 00:07:48
+I>* 192.168.255.254/32 [115/20] via 192.0.2.2, eth1, label IPv4 Explicit Null, weight 1, 00:03:39
+
+Node-2@vyos:~$ show ip route isis
+Codes: K - kernel route, C - connected, S - static, R - RIP,
+       O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
+       T - Table, v - VNC, V - VNC-Direct, A - Babel, F - PBR,
+       f - OpenFabric,
+       > - selected route, * - FIB route, q - queued, r - rejected, b - backup
+       t - trapped, o - offload failure
+
+I   192.0.2.0/24 [115/20] via 192.0.2.1, eth1 inactive, weight 1, 00:07:46
+I>* 192.168.255.255/32 [115/20] via 192.0.2.1, eth1, label IPv4 Explicit Null, weight 1, 00:03:43
+```
+
+
+### Enable OSPF with Segment Routing (Experimental):
+
+**Node 1**
+
+```none
+set interfaces loopback lo address 10.1.1.1/32
+set interfaces ethernet eth0 address 192.168.0.1/24
+set protocols ospf area 0 network '192.168.0.0/24'
+set protocols ospf area 0 network '10.1.1.1/32'
+set protocols ospf parameters opaque-lsa
+set protocols ospf parameters router-id '10.1.1.1'
+set protocols ospf segment-routing global-block high-label-value '1100'
+set protocols ospf segment-routing global-block low-label-value '1000'
+set protocols ospf segment-routing prefix 10.1.1.1/32 index explicit-null
+set protocols ospf segment-routing prefix 10.1.1.1/32 index value '1'
+```
+
+**Node 2**
+
+```none
+set interfaces loopback lo address 10.1.1.2/32
+set interfaces ethernet eth0 address 192.168.0.2/24
+set protocols ospf area 0 network '192.168.0.0/24'
+set protocols ospf area 0 network '10.1.1.2/32'
+set protocols ospf parameters opaque-lsa
+set protocols ospf parameters router-id '10.1.1.2'
+set protocols ospf segment-routing global-block high-label-value '1100'
+set protocols ospf segment-routing global-block low-label-value '1000'
+set protocols ospf segment-routing prefix 10.1.1.2/32 index explicit-null
+set protocols ospf segment-routing prefix 10.1.1.2/32 index value '2'
+```
+
+This gives us MPLS segment routing enabled and labels for far end loopbacks:
+
+```none
+Node-1@vyos:~$ show mpls table
+ Inbound Label  Type       Nexthop      Outbound Label
+ -----------------------------------------------------------
+ 1002           SR (OSPF)  192.168.0.2  IPv4 Explicit Null  <-- Node-2 loopback learned on Node-1
+ 15000          SR (OSPF)  192.168.0.2  implicit-null
+ 15001          SR (OSPF)  192.168.0.2  implicit-null
+
+Node-2@vyos:~$ show mpls table
+ Inbound Label  Type       Nexthop      Outbound Label
+ -----------------------------------------------------------
+ 1001           SR (OSPF)  192.168.0.1  IPv4 Explicit Null  <-- Node-1 loopback learned on Node-2
+ 15000          SR (OSPF)  192.168.0.1  implicit-null
+ 15001          SR (OSPF)  192.168.0.1  implicit-null
+```
+
+Here is the routing tables showing the MPLS segment routing label operations:
+
+```none
+Node-1@vyos:~$ show ip route ospf
+Codes: K - kernel route, C - connected, S - static, R - RIP,
+       O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
+       T - Table, v - VNC, V - VNC-Direct, A - Babel, F - PBR,
+       f - OpenFabric,
+       > - selected route, * - FIB route, q - queued, r - rejected, b - backup
+       t - trapped, o - offload failure
+
+O   10.1.1.1/32 [110/0] is directly connected, lo, weight 1, 00:03:43
+O>* 10.1.1.2/32 [110/1] via 192.168.0.2, eth0, label IPv4 Explicit Null, weight 1, 00:03:32
+O   192.168.0.0/24 [110/1] is directly connected, eth0, weight 1, 00:03:43
+
+Node-2@vyos:~$ show ip route ospf
+Codes: K - kernel route, C - connected, S - static, R - RIP,
+       O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
+       T - Table, v - VNC, V - VNC-Direct, A - Babel, F - PBR,
+       f - OpenFabric,
+       > - selected route, * - FIB route, q - queued, r - rejected, b - backup
+       t - trapped, o - offload failure
+
+O>* 10.1.1.1/32 [110/1] via 192.168.0.1, eth0, label IPv4 Explicit Null, weight 1, 00:03:36
+O   10.1.1.2/32 [110/0] is directly connected, lo, weight 1, 00:03:51
+O   192.168.0.0/24 [110/1] is directly connected, eth0, weight 1, 00:03:51
+```