Connect to db server from an app server: (0x80131904): Login failed for user 'NT AUTHORITY\ANONYMOUS LOGON'

I have two servers: AppServer with IP 192.168.1.2 and DBServer with IP 192.168.1.3

On DBServer I have the database EMSMVC in the DBSERVER\SQLEXPRESS instance. The database is working.

On the AppServer in web.config I have:

<add name="DefaultConnection" 
     connectionString="Data Source=;Initial Catalog=EMSMVC;Integrated Security=True;Server=192.168.1.3;user id=DBSERVER\admin;password=admin" 
     providerName="System.Data.SqlClient" />
<add name="EMSMVCEntities" 
     connectionString="metadata=res://*/Models.EMSModel.csdl|res://*/Models.EMSModel.ssdl|res://*/Models.EMSModel.msl;provider=System.Data.SqlClient;provider connection string=&quot;data source=DBSERVER\SQLEXPRESS;initial catalog=EMSMVC;integrated security=True;Server=192.168.1.3;user id=admin;password=DBSERVER\admin;multipleactiveresultsets=True;application name=EntityFramework&quot;" 
     providerName="System.Data.EntityClient" />

When I browse the app in the AppServer I get the following error:

[SqlException (0x80131904): Login failed for user 'NT AUTHORITY\ANONYMOUS LOGON'.]

However, I'm not trying to connect using Anonymous logon.

Your connection string is flawed with several problems:

<add name="DefaultConnection" 
     connectionString="Data Source=;Initial Catalog=EMSMVC;Integrated Security=True;Server=192.168.1.3;user id=DBSERVER\admin;password=admin" 
     providerName="System.Data.SqlClient" />

1. You have both a Data Source (with no value) and a Server - you should use one or the other - but not both. Both basically mean the same thing - you neither of them is specifying the \SQLEXPRESS instance name ....

2. You're specifying an User Id (and password) in the connection string - but also Integrated Security=True, which means use the built-in Windows authorization - again: if you want to use User Id; then you must NOT also specify Integrated Security at the same time - this setting will take precedence over the specified User Id.

So your connection string should really be:

<add name="DefaultConnection" 
     connectionString="Data Source=DBSERVER\SQLEXPRESS;Initial Catalog=EMSMVC;User id=DBSERVER\admin;password=admin" 
     providerName="System.Data.SqlClient" />

or using the IP address instead of the machine name:

<add name="DefaultConnection" 
     connectionString="Data Source=192.168.1.3\SQLEXPRESS;Initial Catalog=EMSMVC;User id=DBSERVER\admin;password=admin" 
     providerName="System.Data.SqlClient" />

or if you prefer the Server= instead of the Data Source= setting:

<add name="DefaultConnection" 
     connectionString="Server=192.168.1.3\SQLEXPRESS;Initial Catalog=EMSMVC;User id=DBSERVER\admin;password=admin" 
     providerName="System.Data.SqlClient" />