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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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