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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
+ indentify 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
+ indentify 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:**
+
+.. code-block:: 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:**
+
+.. code-block:: 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:
+
+.. code-block:: 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:
+
+.. code-block:: 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**
+
+.. code-block:: 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**
+
+.. code-block:: 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:
+
+.. code-block:: 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:
+
+.. code-block:: 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
+
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