Network Slicing with SRv6¶

Network slicing creates isolated logical networks over a shared physical infrastructure, each with its own topology, SIDs, QoS guarantees, and service-level objectives. SRv6 enables slicing natively through the combination of Flex-Algorithm, QoS policies, and SR Policy color steering — no additional overlay protocols required.

What Is Network Slicing?¶

A network slice is an end-to-end logical partition that provides:

• Topology isolation — each slice uses a different set of paths through the network
• Resource guarantees — dedicated bandwidth, latency, or jitter targets per slice
• Independent policies — each slice can have its own TE, protection, and routing constraints

Slicing vs VPN vs Traffic Engineering¶

SRv6 Slicing Building Blocks¶

SRv6 network slicing combines three mechanisms:

graph TB
    subgraph Slice Architecture
        FA[Flex-Algorithm<br/>Topology Slicing] --> SLICE[Network Slice]
        QOS[QoS Policy<br/>Resource Slicing] --> SLICE
        COLOR[SR Policy + Color<br/>Service Steering] --> SLICE
    end
    SLICE --> S1[Slice 1: Low Latency]
    SLICE --> S2[Slice 2: High Bandwidth]
    SLICE --> S3[Slice 3: Best Effort]

1. Flex-Algorithm (Topology Slicing)¶

Each slice maps to a Flex-Algorithm (128-255), which computes an independent topology based on constraints like latency, affinity, or TE metric. Every node in the slice advertises a per-algorithm locator and SID.

For full details, see Flex-Algorithm.

2. QoS (Resource Slicing)¶

Flex-Algorithm provides topology isolation, but bandwidth guarantees require QoS policies:

• DSCP marking per slice — each slice gets a distinct DSCP value
• Per-slice scheduling — strict priority, weighted fair queuing, or bandwidth reservation
• Policers — rate limiting per slice to enforce SLA boundaries

For full details, see QoS.

3. SR Policy + Color (Service Steering)¶

BGP color extended communities map services into the correct slice:

1. Service route is advertised with a color community (e.g., color 128 = low-latency slice)
2. Headend PE matches the color to an SR Policy or Flex-Algo SID
3. Traffic is steered into the slice automatically

For full details, see SR Policy.

Use Case 1: 5G Network Slicing¶

3GPP defines standardized slice types that map directly to SRv6 Flex-Algorithm slices:

End-to-End 5G Slice¶

graph LR
    RAN[RAN / gNB] -->|URLLC: Algo 128| TR1[Transport PE]
    RAN -->|eMBB: Algo 129| TR1
    TR1 -->|Slice-specific path| CORE((SRv6 Core))
    CORE --> UPF[UPF / Core PE]

The SRv6 MUP (Mobile User Plane) behaviors from RFC 9433 integrate with Flex-Algo slicing to provide end-to-end slice awareness from RAN to core.

For the full 5G transport architecture, see 5G Transport.

Use Case 2: Enterprise Network Slicing¶

Enterprise operators use slicing to offer tiered services with guaranteed SLAs:

Configuration Example¶

!! Flex-Algorithm definitions
router isis CORE
 flex-algo 128
  metric-type delay
  advertise-definition
 !
 flex-algo 129
  affinity exclude-any CONGESTED
  advertise-definition
 !
!

!! Per-slice locators
segment-routing
 srv6
  locators
   locator GOLD
    micro-segment behavior unode psp-usd
    prefix fc00:128:1::/48
    algorithm 128
   !
   locator SILVER
    micro-segment behavior unode psp-usd
    prefix fc00:129:1::/48
    algorithm 129
   !
   locator BEST-EFFORT
    micro-segment behavior unode psp-usd
    prefix fc00:0:1::/48
   !
  !
 !
!

!! Color steering for VPN → slice mapping
route-policy SET-GOLD-COLOR
 set extcommunity color 128
end-policy

router bgp 65000
 vrf GOLD-CUSTOMER
  address-family ipv4 unicast
   route-policy SET-GOLD-COLOR out
  !
 !
!

# Flex-Algo definition
set protocols isis flex-algorithm 128 metric-type min-delay
set protocols isis flex-algorithm 129 affinity exclude CONGESTED

# Per-slice locators
set routing-options segment-routing-v6 locator GOLD fc00:128:1::/48 algorithm 128
set routing-options segment-routing-v6 locator SILVER fc00:129:1::/48 algorithm 129
set routing-options segment-routing-v6 locator BEST-EFFORT fc00:0:1::/48

# Color steering
set policy-options community GOLD-COLOR color 128
set policy-options policy-statement GOLD-EXPORT term 1 then community add GOLD-COLOR

Use Case 3: Data Center Slicing¶

In CLOS fabrics, Flex-Algorithm slicing isolates different traffic types:

Each slice gets its own Flex-Algo and locator, ensuring that GPU traffic never contends with storage replication on the same path.

For CLOS fabric design, see CLOS & Load Balancing. For AI/ML-specific networking, see AI/ML Networks.

Slice Design Considerations¶

SID Allocation per Slice¶

Each slice requires a dedicated locator block. Plan allocations carefully:

Monitoring and SLA Assurance¶

Per-slice monitoring is essential for SLA compliance:

• SRPM (SR Performance Measurement) — per-slice delay/loss probes using slice-specific SIDs. See SRPM.
• Telemetry — per-slice counters on interfaces and forwarding entries. See Telemetry.
• IPFIX — per-slice flow records using RFC 9487 SRv6 Information Elements.

Scalability¶

Comparison: SRv6 Slicing vs Alternatives¶

Further Reading¶

• Flex-Algorithm — Constraint-based topology computation
• QoS — Per-slice quality of service policies
• SR Policy — Color steering and ODN for slice assignment
• 5G Transport — 3GPP slicing with SRv6 transport
• AI/ML Networks — GPU fabric slicing
• SD-WAN — SD-WAN overlay with network slicing

References¶

1. RFC 9350 - IGP Flexible Algorithm - Defines Flex-Algo for constraint-based path computation, the foundation of SRv6 network slicing
2. RFC 9256 - SR Policy Architecture - SR Policy framework including color steering for mapping services to slices
3. 3GPP TS 23.501 - System architecture for the 5G System - 5G system architecture defining network slice types (eMBB, URLLC, mMTC)
4. RFC 9433 - SRv6 for the Mobile User Plane - MUP behaviors integrating with network slicing for 5G
5. draft-ietf-teas-ietf-network-slices - IETF framework for network slicing