Unlocking SRv6: Key Considerations for Migrating from MPLS

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Before delving into MPLS to SRv6 migration, it is essential to first understand the challenges of MPLS that necessitate the transition to SRv6.

Limited Label Space – MPLS has a constrained label space, which can be a challenge in large-scale deployments.

Summarization Breaks LSPs – IP route summarization can disrupt Label Switched Paths (LSPs), leading to suboptimal routing.

Limited TE (Traffic Engineering) Capabilities – Traditional MPLS TE mechanisms have limitations in dynamically optimizing traffic flow.

Limited FRR (Fast Reroute) Capabilities – MPLS Fast Reroute has constraints, particularly in complex network topologies.

Limited Interdomain Capabilities – MPLS struggles with seamless operation across multiple domains.

Lot of Operational Overhead – MPLS requires significant management and configuration effort.

Limited Integration with Modern Applications – MPLS was designed before cloud-native applications, making integration with modern needs challenging.

Lack of End-to-End Encryption – MPLS does not inherently provide encryption, making security a concern in certain scenarios.

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In this modern era of networking, SRv6 offers numerous benefits over MPLS, compelling the migration from MPLS to SRv6.

Native IPv6 Integration - SRv6 is built on IPv6, eliminating the need for MPLS-specific protocols. It simplifies network operations and enables direct IPv6 transport.

Prefix Summarization - Unlike MPLS, SRv6 supports route summarization, improving scalability and efficiency.

TI-LFA (Topology Independent Loop-Free Alternates) - Provides fast reroute (FRR) capabilities for improved resiliency and fast recovery.

Network Slicing (Flex Algorithms) - Enables network slicing for differentiated service levels and optimized routing based on specific needs.

Greater Scalability - Uses IPv6-based Segment Identifiers (SIDs) instead of MPLS labels, allowing for virtually unlimited scalability.

End-to-End Encryption - Unlike MPLS, SRv6 natively supports security features such as IPSec for encryption, enhancing data protection.

Simplified Protocol Stack - Reduces the dependency on multiple MPLS control plane protocols (LDP, RSVP-TE), simplifying network management.

Flexibility for Service Chaining - Enables dynamic service function chaining (SFC) for efficient traffic engineering and NFV integration.

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MPLS to SRv6 Migration considerations

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Before migrating from MPLS to SRv6, careful planning is essential.

• Addressing Plan - Loopback IPv6 Address

Interface IPv6 Address Can be auto-assigned using a link-local address or manually defined (auto-assignment is recommended).

SRv6 Locator ID Requires careful planning, considering factors like Flex Algorithm, summarization, and node ID for each domain or area. The Locator ID can Different from the loopback address Using the same IPv6 range as the loopback address offers several benefits:

-????? Smaller LSP

-????? No separate loopback addressing planning

-????? Easy summarization

-????? And many more.

• QoS Considerations

Mapping from IPv4 DSCP to IPv6 DSCP

Mapping from MPLS EXP to IPv6 DSCP

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Migration Scenarios

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1.??????? Single domain

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1.??????? Configure SRv6 Underlay (Parallel to LDP or SR-MPLS Underlay) - Includes Interface IPv6 Address and ISISv6.

2.??????? Verify SRv6 Reachability.

3.??????? Add RRv6 (Route Reflector for IPv6) - It is recommended to use a separate RRv6 router instead of sharing the same router for both RRv4 and RRv6.

- Configure BGPv6.

4.??????? Verify BGPv6.

5.??????? Enable SRv6 Features on VRF - Set BGPv6/SRv6 Local Preference (LP) = 90.

6.??????? Increase Local Preference for BGPv6 Routes (BGPv6/SRv6 route should be preferred) - Set BGPv6/SRv6 LP = 110.

7.??????? Verify End-to-End Reachability.

8.??????? Repeat Steps 1 to 7 for Additional Nodes - By following this step-wise approach, the entire migration can be completed gradually.

9.??????? Remove MPLS and IPv4 from the Network.

L2VPN Migration Considerations - If migrating L2VPNs, transition from L2VPN to EVPN must also be planned accordingly.

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2.??????? Multidomain

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Migrating from MPLS to SRv6 in a multi-domain environment presents unique challenges, such as interoperability, route propagation, and service continuity across domains. There are three primary multi-domain scenarios to consider:

1. L3/L2 VPN SRv6 MPLS Gateway (Using an Internetworking Gateway (IGW)) In this scenario, an Internetworking Gateway (IGW) is used to facilitate communication between MPLS and SRv6 domains. The IGW acts as a bridge, ensuring seamless L3/L2 VPN service continuity between legacy MPLS networks and the new SRv6-enabled domains. This approach is useful when a phased migration strategy is required while maintaining service availability across both domains.

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2. MPLS Over SRv6 (BGP-LU + SID ) – No IGW Required This method allows MPLS-labeled traffic to traverse an SRv6 core using BGP-Labeled Unicast (BGP-LU). Since BGP-LU is used to exchange labeled routes between domains, there is no need for an IGW. The ingress PE encapsulates the payload in an MPLS service label. Payload is delivered to egress PE with IPv6 header with destination address as SRv6 service SID that it advertised with service prefixes.

3. SRv6 Over MPLS (6PE/6VPE) – No IGW Required In this scenario, SRv6 traffic is transported over an MPLS core using the 6PE (IPv6 Provider Edge) or 6VPE (IPv6 VPN Provider Edge) approach. This method enables IPv6 services (via SRv6) to be delivered over an existing MPLS infrastructure without requiring a dedicated IGW. The ingress PE encapsulates the payload in an outer IPv6 header where the destination address is the SRv6 Service SID[RFC9252]. Payload is delivered to egress PE with MPLS service label[RFC4364] that it advertised with service prefixes.