Let us say you have SQLServer1 and you want to setup a linked server to SQLServer2 using “pass-through authentication”, a double-hop happens as explain in the article below. Basically, the first hop is when the user authenticates to SQLServer1 and the second hop when that gets passed on from SQLServer1 to SQLServer2.
The below article is a must-read before you proceed:
The three nodes involved in the double-hop as illustrated in the example are
Client – The client PC from which the user is initiating connection to SQLServer1
Middle server – SQLServer1
Second server – SQLServer2
Dealing with the double-hop problem is far trickier than it should be; if you’ve had to deal with this, I recommend Jana’s guide.