Segment Routing

Segment Routing (SR) replaces traditional MPLS LDP signaling with a source-routed forwarding paradigm where the ingress router encodes the full path as an ordered list of segment identifiers. The Segment Routing Global Block (SRGB) and Local Block (SRLB) reserve label ranges in the Label Switching Database for prefix-SIDs and local segments such as adjacency-SIDs and binding-SIDs. The mapping server advertises prefix-to-SID mappings via IGP, enabling SR-capable nodes to interwork with LDP nodes in brownfield deployments. SRv6 with Micro-SID (uSID) extends this model over IPv6 by encoding up to six segment instructions within a single 128-bit SID carrier, minimizing MTU overhead while preserving full network programmability.

Diagram

Classes

configuration (iosxr.devices)

Name	Type	Constraint	Mandatory	Default Value
segment_routing	Class	[segment_routing]	No

segment_routing (iosxr.devices.configuration)

Name	Type	Constraint	Mandatory	Default Value
enable	Boolean	true, false	No
global_block_from	Integer	min: 16000, max: 1048574	No
global_block_to	Integer	min: 16001, max: 1048575	No
local_block_from	Integer	min: 15000, max: 1048574	No
local_block_to	Integer	min: 15001, max: 1048575	No
mapping_server	List	[mapping_server]	No
srv6	Class	[srv6]	No
traffic_engineering	Class	[traffic_engineering]	No

mapping_server (iosxr.devices.configuration.segment_routing)

Name	Type	Constraint	Mandatory	Default Value
address_family	Choice	ipv4, ipv6	Yes
prefix_sid_maps	List	[prefix_sid_maps]	No

srv6 (iosxr.devices.configuration.segment_routing)

Name	Type	Constraint	Mandatory	Default Value
enable	Boolean	true, false	No
encapsulation	Class	[encapsulation]	No
formats	List	[formats]	No
locators	List	[locators]	No
logging_locator_status	Boolean	true, false	No
sid_holdtime	Integer	min: 0, max: 60	No

traffic_engineering (iosxr.devices.configuration.segment_routing)

Name	Type	Constraint	Mandatory	Default Value
affinity_maps	List	[affinity_maps]	No
bfd_session_bringup	Integer	min: 10, max: 3600	No
binding_sids	Class	[binding_sids]	No
candidate_paths	List	[candidate_paths]	No
cspf_cache_size	Integer	min: 100, max: 100000	No
distribute_link_state	Class	[distribute_link_state]	No
effective_metric	Class	[effective_metric]	No
interfaces	List	[interfaces]	No
kshortest_paths	Integer	min: 1, max: 200	No
logging	Class	[logging]	No
max_install_standby_paths	Integer	min: 1, max: 3	No
maximum_sid_depth	Integer	min: 1, max: 255	No
path_disable_algo_checks	Class	[path_disable_algo_checks]	No
pcc	Class	[pcc]	No
resource_lists	List	[resource_lists]	No
segment_lists	Class	[segment_lists]	No
separate_next_hop	Boolean	true, false	No
srv6	Class	[srv6]	No
steering	Class	[steering]	No
te_latency	Boolean	true, false	No
timers	Class	[timers]	No
on_demand	List	[on_demand]	No
policies	List	[policies]	No
traces	List	[traces]	No

prefix_sid_maps (iosxr.devices.configuration.segment_routing.mapping_server)

Name	Type	Constraint	Mandatory	Default Value
prefix	IP		Yes
length	Integer	min: 1, max: 128	Yes
sid_index	Integer	min: 0, max: 1048575	Yes
range	Integer	min: 0, max: 65535	No
attached	Boolean	true, false	No

encapsulation (iosxr.devices.configuration.segment_routing.srv6)

Name	Type	Constraint	Mandatory	Default Value
hop_limit	Any	Integer[min: 0, max: 255] or Choice[propagate, propagate-disable] or String[Regex: ^.*[\$\%]\{.*$]	No
source_address	IP		No
traffic_class	Any	Integer[min: 0, max: 255] or Choice[propagate, propagate-disable] or String[Regex: ^.*[\$\%]\{.*$]	No

formats (iosxr.devices.configuration.segment_routing.srv6)

Name	Type	Constraint	Mandatory	Default Value
name	Choice	usid-f3216	Yes
usid_local_id_block_explicit_from	Integer	min: 57344, max: 57344	No
usid_local_id_block_explicit_to	Integer	min: 57444, max: 65279	No
usid_wide_local_id_block_start	Integer	min: 65520, max: 65527	No

locators (iosxr.devices.configuration.segment_routing.srv6)

Name	Type	Constraint	Mandatory	Default Value
algorithm	Integer	min: 128, max: 255	No
anycast	Boolean	true, false	No
length	Integer	min: 32, max: 112	No
micro_segment_behavior_unode	Choice	psp-usd, shift-only	No
name	String		Yes
prefix	IP		No

affinity_maps (iosxr.devices.configuration.segment_routing.traffic_engineering)

Name	Type	Constraint	Mandatory	Default Value
name	String		Yes
bit_position	Integer	min: 0, max: 255	Yes

binding_sids (iosxr.devices.configuration.segment_routing.traffic_engineering)

Name	Type	Constraint	Mandatory	Default Value
dynamic	Choice	disable	No
explicit	Choice	enforce-srlb, fallback-dynamic	No

candidate_paths (iosxr.devices.configuration.segment_routing.traffic_engineering)

Name	Type	Constraint	Mandatory	Default Value
type	Choice	all, bgp-odn, bgp-srte, local, pcep	Yes
source_address	String		Yes

distribute_link_state (iosxr.devices.configuration.segment_routing.traffic_engineering)

Name	Type	Constraint	Mandatory	Default Value
enable	Boolean	true, false	No
report_candidate_path_inactive	Boolean	true, false	No
throttle	Integer	min: 1, max: 20	No

effective_metric (iosxr.devices.configuration.segment_routing.traffic_engineering)

Name	Type	Constraint	Mandatory	Default Value
admin_distances	List	[admin_distances]	No
flex_algos	List	[flex_algos]	No

interfaces (iosxr.devices.configuration.segment_routing.traffic_engineering)

Name	Type	Constraint	Mandatory	Default Value
name	String		Yes
affinities	List	[affinities]	No
metric	Integer	min: 0, max: 2147483647	No

logging (iosxr.devices.configuration.segment_routing.traffic_engineering)

Name	Type	Constraint	Mandatory	Default Value
pcep_peer_status	Boolean	true, false	No
policy_status	Boolean	true, false	No

path_disable_algo_checks (iosxr.devices.configuration.segment_routing.traffic_engineering)

Name	Type	Constraint	Mandatory	Default Value
strict_spf	Class	[strict_spf]	No

pcc (iosxr.devices.configuration.segment_routing.traffic_engineering)

Name	Type	Constraint	Mandatory	Default Value
dead_timer	Integer	min: 1, max: 255	No
delegation_timeout	Integer	min: 0, max: 1576800000	No
initiated_orphan	Integer	min: 0, max: 180	No
initiated_state	Integer	min: 0, max: 86400	No
keepalive_timer	Integer	min: 0, max: 255	No
pces	List	[pces]	No
profiles	List	[profiles]	No
redundancy	Choice	pcc_centric, pce_centric	No
report_all	Boolean	true, false	No
source_address_ipv4	String		No
source_address_ipv6	String		No

resource_lists (iosxr.devices.configuration.segment_routing.traffic_engineering)

Name	Type	Constraint	Mandatory	Default Value
name	String		Yes
entries	List	[entries]	No

segment_lists (iosxr.devices.configuration.segment_routing.traffic_engineering)

Name	Type	Constraint	Mandatory	Default Value
mpls	Class	[mpls]	No
srv6	Class	[srv6]	No

srv6 (iosxr.devices.configuration.segment_routing.traffic_engineering)

Name	Type	Constraint	Mandatory	Default Value
behavior	Choice	ub6-encaps-reduced, ub6-insert-reduced	No
binding_sid_type	Choice	srv6-dynamic	No
locator	String		No
maximum_sid_depth	Integer	min: 1, max: 255	No

steering (iosxr.devices.configuration.segment_routing.traffic_engineering)

Name	Type	Constraint	Mandatory	Default Value
labeled_services	Class	[labeled_services]	No

timers (iosxr.devices.configuration.segment_routing.traffic_engineering)

Name	Type	Constraint	Mandatory	Default Value
candidate_path_cleanup_delay	Integer	min: 0, max: 86400	No
cleanup_delay	Integer	min: 0, max: 300	No
delete_delay	Integer	min: 0, max: 3600	No
initial_verify_restart	Integer	min: 10, max: 10000	No
initial_verify_startup	Integer	min: 10, max: 10000	No
initial_verify_switchover	Integer	min: 10, max: 10000	No
install_delay	Integer	min: 0, max: 300	No
periodic_reoptimization	Integer	min: 0, max: 86400	No

on_demand (iosxr.devices.configuration.segment_routing.traffic_engineering)

Name	Type	Constraint	Mandatory	Default Value
bandwidth	Integer	min: 1, max: 4294967295	No
bfd	Class	[bfd]	No
color	Integer	min: 1, max: 4294967295	Yes
constraints	Class	[constraints]	No
dynamic	Class	[dynamic]	No
effective_metric	Class	[effective_metric]	No
max_install_standby_paths	Integer	min: 0, max: 3	No
maximum_sid_depth	Integer	min: 1, max: 255	No
pce_group	String		No
per_flow	Class	[per_flow]	No
performance_measurement	Class	[performance_measurement]	No
source_address	IP		No
srv6	Class	[srv6]	No
steering	Class	[steering]	No

policies (iosxr.devices.configuration.segment_routing.traffic_engineering)

Name	Type	Constraint	Mandatory	Default Value
auto_route	Class	[auto_route]	No
bandwidth	Integer	min: 1, max: 4294967295	No
bfd	Class	[bfd]	No
binding_sid_mpls_label	Integer	min: 16, max: 1048575	No
binding_sid_type	Choice	mpls	No
candidate_paths	List	[candidate_paths]	No
color	Integer	min: 1, max: 4294967295	Yes
effective_metric	Class	[effective_metric]	No
endpoint_address	IP		No
ipv6_disable	Boolean	true, false	No
max_install_standby_paths	Integer	min: 0, max: 3	No
name	String		Yes
path_protection	Boolean	true, false	No
pce_group	String		No
performance_measurement	Class	[performance_measurement]	No
shutdown	Boolean	true, false	No
source_address	IP		No
srv6	Class	[srv6]	No
steering	Class	[steering]	No
transit_eligible	Boolean	true, false	No

traces (iosxr.devices.configuration.segment_routing.traffic_engineering)

Name	Type	Constraint	Mandatory	Default Value
buffer	Choice	agent, all, bsid, chkpt, common, error, fib, fs, gen-error, im, init, lmrib, lsd, p-cpath, p-lsp, p-state, pcep, pfp, policy, rib, srv-api, timer, treesid, treesid-chkpt	Yes
count	Integer	min: 0, max: 1000000	Yes

admin_distances (iosxr.devices.configuration.segment_routing.traffic_engineering.effective_metric)

Name	Type	Constraint	Mandatory	Default Value
type	Choice	unknown, hopcount, igp, latency, te	Yes
distance	Integer	min: 1, max: 255	Yes

flex_algos (iosxr.devices.configuration.segment_routing.traffic_engineering.effective_metric)

Name	Type	Constraint	Mandatory	Default Value
type	Any	Choice[igp, latency, te, bandwidth] or Integer[min: 0, max: 255] or String[Regex: ^.*[\$\%]\{.*$]	Yes
distance	Integer	min: 1, max: 255	Yes

affinities (iosxr.devices.configuration.segment_routing.traffic_engineering.interfaces)

Name	Type	Constraint	Mandatory	Default Value
name	String		Yes

strict_spf (iosxr.devices.configuration.segment_routing.traffic_engineering.path_disable_algo_checks)

Name	Type	Constraint	Mandatory	Default Value
all_areas	Boolean	true, false	No
areas	List	[areas]	No

pces (iosxr.devices.configuration.segment_routing.traffic_engineering.pcc)

Name	Type	Constraint	Mandatory	Default Value
address	Any	IP or String or String[Regex: ^.*[\$\%]\{.*$]	Yes
password	String		No
password_type	Choice	7	No
pce_group	String		No
precedence	Integer	min: 0, max: 255	No
tcp_ao_include_tcp_options	Boolean	true, false	No
tcp_ao_keychain	String		No

profiles (iosxr.devices.configuration.segment_routing.traffic_engineering.pcc)

Name	Type	Constraint	Mandatory	Default Value
id	Integer	min: 1, max: 65534	Yes
auto_route	Class	[auto_route]	No
steering_invalidation_drop	Boolean	true, false	No

entries (iosxr.devices.configuration.segment_routing.traffic_engineering.resource_lists)

Name	Type	Constraint	Mandatory	Default Value
index	Integer	min: 1, max: 65535	Yes
address	String		No
type	Choice	ipv4-address	No

mpls (iosxr.devices.configuration.segment_routing.traffic_engineering.segment_lists)

Name	Type	Constraint	Mandatory	Default Value
explicit_segments	List	[explicit_segments]	No

srv6 (iosxr.devices.configuration.segment_routing.traffic_engineering.segment_lists)

Name	Type	Constraint	Mandatory	Default Value
explicit_segments	List	[explicit_segments]	No
sid_format	Choice	usid-f3216	No
topology_check	Boolean	true, false	No

labeled_services (iosxr.devices.configuration.segment_routing.traffic_engineering.steering)

Name	Type	Constraint	Mandatory	Default Value
disable_all	Boolean	true, false	No
disable_bgp_sr_te	Boolean	true, false	No
disable_local	Boolean	true, false	No
disable_on_demand	Boolean	true, false	No
disable_pcep	Boolean	true, false	No

bfd (iosxr.devices.configuration.segment_routing.traffic_engineering.on_demand)

Name	Type	Constraint	Mandatory	Default Value
enable	Boolean	true, false	No
invalidation_action	Choice	down, none	No
logging_session_state_change	Boolean	true, false	No
minimum_interval	Integer	min: 50, max: 30000	No
multiplier	Integer	min: 1, max: 10	No
reverse_path_binding_label	Integer	min: 16, max: 1048575	No

constraints (iosxr.devices.configuration.segment_routing.traffic_engineering.on_demand)

Name	Type	Constraint	Mandatory	Default Value
segments	Class	[segments]	No

dynamic (iosxr.devices.configuration.segment_routing.traffic_engineering.on_demand)

Name	Type	Constraint	Mandatory	Default Value
affinities	List	[affinities]	No
anycast_sid_inclusion	Boolean	true, false	No
bounds	List	[bounds]	No
disjoint_path	Class	[disjoint_path]	No
metric_margin	Integer	min: 0, max: 2147483647	No
metric_margin_type	Choice	absolute, relative	No
metric_type	Choice	hopcount, igp, latency, te	No
pcep	Boolean	true, false	No

effective_metric (iosxr.devices.configuration.segment_routing.traffic_engineering.on_demand)

Name	Type	Constraint	Mandatory	Default Value
type	Choice	default, hopcount, igp, latency, te	No
value	Integer	min: 0, max: 4294967295	No

per_flow (iosxr.devices.configuration.segment_routing.traffic_engineering.on_demand)

Name	Type	Constraint	Mandatory	Default Value
default_class	Integer	min: 0, max: 7	No
enable	Boolean	true, false	No
forward_classes	List	[forward_classes]	No

performance_measurement (iosxr.devices.configuration.segment_routing.traffic_engineering.on_demand)

Name	Type	Constraint	Mandatory	Default Value
delay	Class	[delay]	No
liveness	Class	[liveness]	No
reverse_path_label	Integer	min: 16, max: 1048575	No
reverse_path_segment_list	String		No

srv6 (iosxr.devices.configuration.segment_routing.traffic_engineering.on_demand)

Name	Type	Constraint	Mandatory	Default Value
behavior	Choice	ub6-encaps-reduced, ub6-insert-reduced	No
locator	String		No

steering (iosxr.devices.configuration.segment_routing.traffic_engineering.on_demand)

Name	Type	Constraint	Mandatory	Default Value
invalidation_drop	Boolean	true, false	No
labeled_services	Class	[labeled_services]	No

auto_route (iosxr.devices.configuration.segment_routing.traffic_engineering.policies)

Name	Type	Constraint	Mandatory	Default Value
force_sr_include	Boolean	true, false	No
forward_class	Integer	min: 0, max: 7	No
include_all_ipv4	Boolean	true, false	No
include_all_ipv6	Boolean	true, false	No
include_prefixes	List	[include_prefixes]	No
metric	Integer	min: -10, max: 2147483647	No
metric_type	Choice	constant, relative	No

bfd (iosxr.devices.configuration.segment_routing.traffic_engineering.policies)

Name	Type	Constraint	Mandatory	Default Value
disable	Boolean	true, false	No
enable	Boolean	true, false	No
invalidation_action	Choice	down, none	No
logging_session_state_change	Boolean	true, false	No
minimum_interval	Integer	min: 50, max: 30000	No
multiplier	Integer	min: 1, max: 10	No
reverse_path_binding_label	Integer	min: 16, max: 1048575	No

candidate_paths (iosxr.devices.configuration.segment_routing.traffic_engineering.policies)

Name	Type	Constraint	Mandatory	Default Value
backup_ineligible	Boolean	true, false	No
bidirectional_association_id	Integer	min: 1, max: 65534	No
bidirectional_corouted	Boolean	true, false	No
constraints	Class	[constraints]	No
effective_metric	Class	[effective_metric]	No
preference	Integer	min: 1, max: 65535	Yes
lock_duration	Integer	min: 0, max: 3000	No
paths	List	[paths]	No
pce_group	String		No
per_flow	Class	[per_flow]	No

effective_metric (iosxr.devices.configuration.segment_routing.traffic_engineering.policies)

Name	Type	Constraint	Mandatory	Default Value
type	Choice	hopcount, igp, latency, te	No
value	Integer	min: 0, max: 4294967295	No

performance_measurement (iosxr.devices.configuration.segment_routing.traffic_engineering.policies)

Name	Type	Constraint	Mandatory	Default Value
delay	Class	[delay]	No
liveness	Class	[liveness]	No
reverse_path_label	Integer	min: 16, max: 1048575	No
reverse_path_segment_list	String		No

srv6 (iosxr.devices.configuration.segment_routing.traffic_engineering.policies)

Name	Type	Constraint	Mandatory	Default Value
behavior	Choice	ub6-encaps-reduced, ub6-insert-reduced	No
locator	String		No

steering (iosxr.devices.configuration.segment_routing.traffic_engineering.policies)

Name	Type	Constraint	Mandatory	Default Value
invalidation_drop	Boolean	true, false	No
labeled_services	Class	[labeled_services]	No

areas (iosxr.devices.configuration.segment_routing.traffic_engineering.path_disable_algo_checks.strict_spf)

Name	Type	Constraint	Mandatory	Default Value
id	Integer	min: 0, max: 4294967295	Yes
protocol	Choice	ospf	Yes

auto_route (iosxr.devices.configuration.segment_routing.traffic_engineering.pcc.profiles)

Name	Type	Constraint	Mandatory	Default Value
force_sr_include	Boolean	true, false	No
forward_class	Integer	min: 0, max: 7	No
include_all_ipv4	Boolean	true, false	No
include_all_ipv6	Boolean	true, false	No
metric	Integer	min: -10, max: 2147483647	No
metric_type	Choice	constant, relative	No

explicit_segments (iosxr.devices.configuration.segment_routing.traffic_engineering.segment_lists.mpls)

Name	Type	Constraint	Mandatory	Default Value
name	String		Yes
entries	List	[entries]	No

explicit_segments (iosxr.devices.configuration.segment_routing.traffic_engineering.segment_lists.srv6)

Name	Type	Constraint	Mandatory	Default Value
name	String		Yes
entries	List	[entries]	No
topology_check	Boolean	true, false	No

segments (iosxr.devices.configuration.segment_routing.traffic_engineering.on_demand.constraints)

Name	Type	Constraint	Mandatory	Default Value
protection_type	Choice	protected-only, protected-preferred, unprotected-only, unprotected-preferred	No
sid_algorithm	Integer	min: 0, max: 255	No

affinities (iosxr.devices.configuration.segment_routing.traffic_engineering.on_demand.dynamic)

Name	Type	Constraint	Mandatory	Default Value
entries	List	[entries]	No
type	Choice	include-any, include-all, exclude-any	Yes

bounds (iosxr.devices.configuration.segment_routing.traffic_engineering.on_demand.dynamic)

Name	Type	Constraint	Mandatory	Default Value
scope	Choice	cumulative, link	Yes
type	Choice	hopcount, igp, latency, te	Yes
metric	Integer	min: 1, max: 4294967295	Yes

disjoint_path (iosxr.devices.configuration.segment_routing.traffic_engineering.on_demand.dynamic)

Name	Type	Constraint	Mandatory	Default Value
fallback_disable	Boolean	true, false	No
group_id	Integer	min: 1, max: 65535	No
shortest_path	Boolean	true, false	No
sub_id	Integer	min: 0, max: 65535	No
type	Choice	link, node, srlg, srlg-node	No

forward_classes (iosxr.devices.configuration.segment_routing.traffic_engineering.on_demand.per_flow)

Name	Type	Constraint	Mandatory	Default Value
color	Integer	min: 1, max: 4294967295	Yes
id	Integer	min: 0, max: 7	Yes

delay (iosxr.devices.configuration.segment_routing.traffic_engineering.on_demand.performance_measurement)

Name	Type	Constraint	Mandatory	Default Value
logging_delay_exceeded	Boolean	true, false	No
profile	String		No

liveness (iosxr.devices.configuration.segment_routing.traffic_engineering.on_demand.performance_measurement)

Name	Type	Constraint	Mandatory	Default Value
backup_profile	String		No
invalidation_action	Choice	down, none	No
logging_session_state_change	Boolean	true, false	No
profile	String		No

labeled_services (iosxr.devices.configuration.segment_routing.traffic_engineering.on_demand.steering)

Name	Type	Constraint	Mandatory	Default Value
disable	Boolean	true, false	No

include_prefixes (iosxr.devices.configuration.segment_routing.traffic_engineering.policies.auto_route)

Name	Type	Constraint	Mandatory	Default Value
address	IP		Yes
length	Integer	min: 0, max: 32	Yes
type	Choice	ipv4	Yes

constraints (iosxr.devices.configuration.segment_routing.traffic_engineering.policies.candidate_paths)

Name	Type	Constraint	Mandatory	Default Value
affinities	List	[affinities]	No
bounds	List	[bounds]	No
disjoint_path	Class	[disjoint_path]	No
segments	Class	[segments]	No

effective_metric (iosxr.devices.configuration.segment_routing.traffic_engineering.policies.candidate_paths)

Name	Type	Constraint	Mandatory	Default Value
type	Choice	hopcount, igp, latency, te	No
value	Integer	min: 0, max: 4294967295	No

paths (iosxr.devices.configuration.segment_routing.traffic_engineering.policies.candidate_paths)

Name	Type	Constraint	Mandatory	Default Value
anycast_sid_inclusion	Boolean	true, false	No
hop_type	Choice	mpls, srv6	No
metric_margin	Integer	min: 0, max: 2147483647	No
metric_margin_type	Choice	absolute, relative	No
metric_sid_limit	Integer	min: 1, max: 255	No
metric_type	Choice	hopcount, igp, latency, te	No
pcep	Boolean	true, false	No
reverse_path_segment_list	String		No
segment_list	String		No
type	Choice	dynamic, explicit	Yes
weight	Integer	min: 1, max: 4294967295	No

per_flow (iosxr.devices.configuration.segment_routing.traffic_engineering.policies.candidate_paths)

Name	Type	Constraint	Mandatory	Default Value
default_class	Integer	min: 0, max: 7	No
enable	Boolean	true, false	No
forward_classes	List	[forward_classes]	No

delay (iosxr.devices.configuration.segment_routing.traffic_engineering.policies.performance_measurement)

Name	Type	Constraint	Mandatory	Default Value
logging_delay_exceeded	Boolean	true, false	No
profile	String		No

liveness (iosxr.devices.configuration.segment_routing.traffic_engineering.policies.performance_measurement)

Name	Type	Constraint	Mandatory	Default Value
backup_profile	String		No
invalidation_action	Choice	down, none	No
logging_session_state_change	Boolean	true, false	No
profile	String		No

labeled_services (iosxr.devices.configuration.segment_routing.traffic_engineering.policies.steering)

Name	Type	Constraint	Mandatory	Default Value
disable	Boolean	true, false	No

entries (iosxr.devices.configuration.segment_routing.traffic_engineering.segment_lists.mpls.explicit_segments)

Name	Type	Constraint	Mandatory	Default Value
index	Integer	min: 1, max: 65535	Yes
address	String		No
interface_identifier	Integer	min: 1, max: 65535	No
label	Integer	min: 0, max: 1048575	No
type	Choice	adjacency, label	No

entries (iosxr.devices.configuration.segment_routing.traffic_engineering.segment_lists.srv6.explicit_segments)

Name	Type	Constraint	Mandatory	Default Value
index	Integer	min: 1, max: 65535	Yes
address	String		No
type	Choice	srv6sid	No

entries (iosxr.devices.configuration.segment_routing.traffic_engineering.on_demand.dynamic.affinities)

Name	Type	Constraint	Mandatory	Default Value
name	String		Yes

affinities (iosxr.devices.configuration.segment_routing.traffic_engineering.policies.candidate_paths.constraints)

Name	Type	Constraint	Mandatory	Default Value
entries	List	[entries]	No
type	Choice	exclude-any, include-all, include-any	Yes

bounds (iosxr.devices.configuration.segment_routing.traffic_engineering.policies.candidate_paths.constraints)

Name	Type	Constraint	Mandatory	Default Value
scope	Choice	cumulative, link	Yes
type	Choice	hopcount, igp, latency, te	Yes
metric	Integer	min: 1, max: 4294967295	Yes

disjoint_path (iosxr.devices.configuration.segment_routing.traffic_engineering.policies.candidate_paths.constraints)

Name	Type	Constraint	Mandatory	Default Value
fallback_disable	Boolean	true, false	No
group_id	Integer	min: 1, max: 65535	No
shortest_path	Boolean	true, false	No
sub_id	Integer	min: 0, max: 65535	No
type	Choice	link, node, srlg, srlg-node	No

segments (iosxr.devices.configuration.segment_routing.traffic_engineering.policies.candidate_paths.constraints)

Name	Type	Constraint	Mandatory	Default Value
adjacency_sid_only	Boolean	true, false	No
protection_type	Choice	protected-only, protected-preferred, unprotected-only, unprotected-preferred	No
sid_algorithm	Integer	min: 0, max: 255	No

forward_classes (iosxr.devices.configuration.segment_routing.traffic_engineering.policies.candidate_paths.per_flow)

Name	Type	Constraint	Mandatory	Default Value
color	Integer	min: 1, max: 4294967295	Yes
id	Integer	min: 0, max: 7	Yes

entries (iosxr.devices.configuration.segment_routing.traffic_engineering.policies.candidate_paths.constraints.affinities)

Name	Type	Constraint	Mandatory	Default Value
name	String		Yes

Data Normalization

uSID Block Range Values

The uSID local ID block range fields accept both hexadecimal and integer values. YAML natively parses hex literals (e.g., 0xe000) to their integer equivalents.

• usid_local_id_block_explicit_from: 0xe000 or 57344
• usid_local_id_block_explicit_to: 0xe064 or 57444
• usid_wide_local_id_block_start: 0xfff0 or 65520

Both formats can be used interchangeably in YAML.

Example YAML Code:

Example-1: SRGB and SRLB label ranges for a PE router in a dual-plane SR-MPLS backbone.

iosxr:
  devices:
    - name: router-1
      host: 10.10.10.1:57400
      configuration:
        segment_routing:
          global_block_from: 16000
          global_block_to: 23999
          local_block_from: 15000
          local_block_to: 15999

Example-2: Mapping server advertising prefix-SIDs for LDP-only routers in a brownfield migration.

iosxr:
  devices:
    - name: router-1
      host: 10.10.10.1:57400
      configuration:
        segment_routing:
          global_block_from: 16000
          global_block_to: 23999
          mapping_server:
            - address_family: ipv4
              prefix_sid_maps:
                - prefix: 198.51.100.0
                  length: 24
                  sid_index: 400
                  range: 50
                  attached: true
                - prefix: 203.0.113.0
                  length: 24
                  sid_index: 600
                  range: 10
            - address_family: ipv6
              prefix_sid_maps:
                - prefix: "2001:db8:cafe::"
                  length: 48
                  sid_index: 700
                  range: 20
                  attached: true

Example-3: SRv6 with dual locators for primary and Flex-Algo 128 traffic steering.

iosxr:
  devices:
    - name: router-1
      host: 10.10.10.1:57400
      configuration:
        segment_routing:
          srv6:
            enable: true
            encapsulation:
              source_address: "fccc:0:214::1"
            locators:
              - name: "MAIN"
                micro_segment_behavior_unode: "psp-usd"
                prefix: "fccc:0:214::"
                length: 48
              - name: "ALGO_128"
                micro_segment_behavior_unode: "psp-usd"
                prefix: "fccc:0:215::"
                length: 48
                algorithm: 128

Example-4: SRv6 encapsulation preserving original traffic class and TTL across the SR domain.

iosxr:
  devices:
    - name: router-1
      host: 10.10.10.1:57400
      configuration:
        segment_routing:
          srv6:
            enable: true
            encapsulation:
              source_address: "fccc:0:500::1"
              traffic_class: propagate
              hop_limit: propagate

---

Traffic Engineering (SR-TE)

Segment Routing Traffic Engineering (SR-TE) steers traffic along computed paths by encoding segment identifier stacks at the head-end router, eliminating per-hop signaling state. Each SR-TE policy is identified by a (head-end, color, end-point) tuple and carries one or more candidate paths composed of weighted segment lists. The head-end can compute paths locally using CSPF or delegate computation to a Path Computation Element (PCE) via PCEP, with support for affinity constraints, disjoint-path groups, and cumulative metric bounds. Automated steering maps BGP prefixes to SR-TE policies through color extended communities, while interface TE metrics and named affinity maps provide fine-grained control over link selection.

Example-1: PCC with redundant PCE peers for delegated path computation in a dual-stack backbone.

iosxr:
  devices:
    - name: router-1
      host: 10.10.10.1:57400
      configuration:
        segment_routing:
          traffic_engineering:
            logging:
              pcep_peer_status: true
              policy_status: true
            pcc:
              report_all: true
              source_address_ipv4: "192.168.255.1"
              delegation_timeout: 10
              dead_timer: 60
              initiated_state: 15
              initiated_orphan: 10
              redundancy: pcc_centric
              pces:
                - address: "198.51.100.10"
                  precedence: 100
                  pce_group: PCE-GROUP1
                - address: "2001:db8:ffff::10"
                  precedence: 200

Example-2: Affinity maps, TE-metric interfaces, and MPLS/SRv6 segment lists for explicit path steering.

iosxr:
  devices:
    - name: router-1
      host: 10.10.10.1:57400
      configuration:
        segment_routing:
          traffic_engineering:
            te_latency: true
            affinity_maps:
              - name: CORE
                bit_position: 0
              - name: LOW_LATENCY
                bit_position: 1
            interfaces:
              - name: HundredGigE0/0/0/0
                metric: 10
                affinities:
                  - name: CORE
                  - name: LOW_LATENCY
            segment_lists:
              srv6:
                sid_format: usid-f3216
                topology_check: true
                explicit_segments:
                  - name: SRV6
                    topology_check: true
                    entries:
                      - index: 1
                        type: srv6sid
                        address: "fccc:0:214::"
              mpls:
                explicit_segments:
                  - name: CORE
                    entries:
                      - index: 1
                        type: adjacency
                        address: 198.51.100.1
                      - index: 2
                        type: mpls-label
                        label: 16001

On Demand Colors

SR-TE On-Demand Next-Hop (ODN) dynamically instantiates SR policies when a BGP next-hop is resolved with a color extended community that has no matching pre-provisioned policy. The router sends a path computation request to the PCE or computes locally using the optimization template defined for that color, which specifies metric type, affinity rules, disjoint-path constraints, and cumulative metric bounds. ODN eliminates the need to pre-provision per-destination policies across the network, scaling naturally as new BGP prefixes with color communities are advertised. Both MPLS and SRv6 data planes are supported, with optional BFD liveness detection, per-flow forwarding classes, and performance measurement profiles for SLA assurance.

Example-1: ODN color 100 — TE-metric optimized with PCE computation

iosxr:
  devices:
    - name: router-1
      host: 10.10.10.1:57400
      configuration:
        segment_routing:
          traffic_engineering:
            on_demand:
              - color: 100
                bandwidth: 500000
                maximum_sid_depth: 6
                source_address: 192.168.255.1
                dynamic:
                  metric_type: te
                  pcep: true

Example-2: ODN color 200 — full-featured low-latency template with PCE, BFD, and performance measurement

iosxr:
  devices:
    - name: router-1
      host: 10.10.10.1:57400
      configuration:
        segment_routing:
          traffic_engineering:
            on_demand:
              - color: 200
                maximum_sid_depth: 6
                source_address: 192.168.255.1
                dynamic:
                  metric_type: te
                  anycast_sid_inclusion: true
                  pcep: true
                  metric_margin_type: absolute
                  metric_margin: 10
                  affinities:
                    - type: include-any
                      entries:
                        - name: CORE
                        - name: LOW_LATENCY
                    - type: exclude-any
                      entries:
                        - name: MAINTENANCE
                  bounds:
                    - scope: cumulative
                      type: igp
                      metric: 100
                constraints:
                  segments:
                    protection_type: protected-preferred
                effective_metric:
                  type: igp
                  value: 100
                bfd:
                  enable: true
                  multiplier: 3
                  minimum_interval: 300
                  invalidation_action: down
                  reverse_path_binding_label: 16100
                  logging_session_state_change: true
                performance_measurement:
                  delay:
                    profile: PM-DELAY-PROFILE1
                    logging_delay_exceeded: true

Example-3: ODN color 300 — SRv6 uSID with IGP-metric optimization

iosxr:
  devices:
    - name: router-1
      host: 10.10.10.1:57400
      configuration:
        segment_routing:
          traffic_engineering:
            on_demand:
              - color: 300
                source_address: "2001:db8:ffff::1"
                dynamic:
                  metric_type: igp
                srv6:
                  locator: uSID_Primary
                  behavior: ub6-insert-reduced

Policies

SR-TE policies are statically provisioned traffic-engineered paths identified by a policy name, color, and endpoint address. Each policy carries one or more candidate paths ordered by preference, where the highest-preference valid path is installed in the forwarding table. Candidate paths can use dynamic computation with metric optimization objectives or explicit segment lists for deterministic forwarding. Policies support binding SIDs for hierarchical stitching, auto-route for IGP shortcut injection, BFD-based path liveness, performance measurement with delay and liveness profiles, and bidirectional co-routed associations for symmetric path requirements.

Example-1: Policy with a single dynamic candidate path using IGP-metric optimization

        policies:
          - name: POLICY1
            color: 100
            endpoint_address: 198.51.100.1
            candidate_paths:
              - preference: 100
                paths:
                  - type: dynamic
                    metric_type: igp