Which CLI mode must be used to configure the BGP keychain in Cisco IOS XR...

 In Cisco IOS XR software, the keychain management for BGP is done in the routing configuration mode. This mode allows you to configure keychain parameters such as the key identifier, cryptographic algorithm, and other related settings. The keychain is essential for authentication and secure communication between BGP peers. By configuring the keychain in the routing context, you ensure that BGP sessions use the specified keys for authentication and integrity protection1.

References:

Implementing Keychain Management - Cisco IOS XR Routing Configuration Guide

BGP Configuration Guide for Cisco NCS 540 Series Routers, IOS XR Release 7.8.x - Master Key Tuple Configuration