Segment Routing v6 Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

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Segment Routing v6 Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

Techniques for effective SID management

Updated: September 8, 2026

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Compares full-length SIDs and uSIDs to help users select an efficient SID representation based on scalability, header overhead, hardware utilization, and operational requirements.

SIDs are a fundamental building block of SRv6, enabling flexible and programmable routing by encoding instructions directly into IPv6 headers. ​ As networks grow in complexity, efficient management of SIDs becomes critical to ensure scalability, reduce overhead, and optimize network operations.

SRv6 employs specific techniques to effectively uses the 128-bit SID for optimized network operations. The main techniques are:

  • Micro-SID (uSID): This technique divides a single 128-bit SID into smaller sub-SIDs, referred to as micro-segments. It allows multiple operations to be represented within a single SID, which results in reduced header overhead and improved scalability, particularly useful in environments with limited resources. For more information, see SRv6 Micro-segment (uSID) Overview.

  • Full-Length SID: This technique utilizes a full 128-bit IPv6 address to represent each segment, function, or instruction. This method ensures simplicity and aligns with standard IPv6 routing practices.

Difference between full-length SID and uSID

Table 1. Comparison of full-length SID and uSID

Feature

Full-Length SID

uSID

Definition

A full 128-bit IPv6 address used to represent a single segment, function, or instruction.

A single 128-bit SID divided into smaller sub-SIDs (micro-segments) to represent multiple operations.

Size

Each SID uses 128-bits in the SRH.

Multiple smaller sub-SIDs are packed into a single 128-bit SID.

Header size

Larger SRH due to 128-bits per SID.

Smaller SRH by encoding multiple operations into fewer SIDs.

Examples

Each SID is a full 128-bit IPv6 address.

SRH = [2001:db8:1::1, 
2001:db8:2::1, 
2001:db8:3::1]

Multiple sub-SIDs are encoded in one 128-bit SID.

SRH = [2001:db8:1::1]

Reference

SRv6 Micro-segment (uSID) Overview

SRv6 with Full-Length SIDs