China Unicom China Unicom China Unicom Huawei This document specifies the IGP protocol extensions required to support SRv6 path egress protection using the Mirror SID (End.M) mechanism. It reuses the existing SRv6 End SID sub-TLV defined in [RFC9352] (IS-IS, Section 7.2) and [RFC9513] (OSPFv3, Section 8) with the End.M endpoint behavior (74) to advertise the Mirror SID and the set of protected locators, and defines a new Protected Locators sub-(sub-)TLV, enabling a backup egress node (protector) to signal its capability to protect a primary egress node within a single link- state IGP area. This document is a companion to [I-D.ietf-rtgwg-srv6-egress-protection], which specifies the overall SRv6 path egress protection mechanism and the End.M behavior. The IGP encoding defined herein provides the signaling substrate for that mechanism.