Agent Login Security

Replication implements login security by requiring a user to have a valid login account and password to connect to a Publisher, Distributor, or Subscriber. Replication agents run under SQL Server Agent and use the associated logins and passwords to connect to the various replication objects and to perform their roles in the synchronization process. On Microsoft® Windows® 95/98 platforms, SQL Server Agent and the replication agents run under the security account of the user logging on to Windows. On Microsoft® Windows NT® platforms, the replication agents run under the login or security context of the SQLServerAgent service.

Each agent connects to one or more servers and must have a valid login to complete the connection:

The Snapshot Agent connects to the publishing database on the Publisher and to the distribution database on the Distributor. The Snapshot Agent also writes to the snapshot folder on the Distributor when storing the snapshot files.
The Log Reader Agent connects to the publishing database at the Publisher and to the distribution database at the Distributor.
In a push subscription, the Distribution Agent is located on the Distributor and connects first to the distribution database on the Distributor. While connected to the Distributor, the Distribution Agent connects to the subscribing database at the Subscriber. The Distribution Agent also reads from the snapshot folder on the Distributor when applying the snapshot files.
In a pull subscription, the Distribution Agent is located on the Subscriber and connects first to the subscribing database on the Subscriber. While connected to the Subscriber, the Distribution Agent connects to the distribution database at the Distributor. The Distribution Agent also reads from the snapshot folder on the Distributor when applying the snapshot files.
In a push subscription, the Merge Agent is located on the Distributor and connects first to the distribution database on the Distributor. While connected to the Distributor, the Merge Agent connects to the subscribing database at the Subscriber and then to the publishing database at the Publisher. The Merge Agent also reads from the snapshot folder on the Distributor when applying the snapshot files.
In a pull subscription, the Merge Agent is located on the Subscriber and connects first to the subscribing database on the Subscriber. While connected to the Subscriber, the Merge Agent connects to the distribution database at the Distributor and then to the publishing database at the Publisher. The Merge Agent also reads from the snapshot folder on the Distributor when applying the snapshot files.

Note For an agent that holds simultaneous connections, Microsoft® SQL Server™ allows you to configure the login for each connection independently. For example, if the Snapshot Agent connects to the Publisher and to the Distributor, each connection can use a different login.