链接服务器在同一服务器上的双跃点，Diff服务器上的客户端？

I'm trying to solve a mystery. We have two SQL Server instances residing on the same server. SQL instance A is linked to SQL instance B. Connections are made using pass through authentication. The calling service is on a different server. No settings were put in place for Kerberos delegation, no SPN, no trust for delegation, etc. However, we weren't getting authentication failures when running distributed queries through the linked server connection. This makes no sense to me unless having the two instances on a single server results in a single hop scenario (from calling client service to server on which both instances reside). The underlying Kerberos config is now in place, so Kerberos is being used successfully, I'm just trying to understand how the connection would have worked before I made the necessary changes. Does anyone have any insight into this? Thanks.I'm trying to solve a mystery. We have two SQL