ibps-so 2016 · Question 34 of 394

Chandrabhaga Urban Bank has joined its regional o ce at Solapur to its data centre over the public internet rather than over a leased line. A gateway stands at each end. Whenever a workstation at Solapur raises tra c for the data centre, the gateway takes the entire original IP datagram, ciphers it whole, pre xes a fresh IP header addressed to the far gateway, and sends the result across the public network; the far gateway strips the outer header, deciphers the payload and releases the original datagram upon the data-centre network. No application at either end has been altered, and the workstations and servers are unaware that anything unusual is being done to their tra c. A virtual private network built in that manner — the IPsec tunnel being the standard instance — operates at:

1. AThe physical layer, layer 1, since the private network takes the place of the leased circuit that was previously hired
2. BThe network layer, layer 3, since it encapsulates and ciphers whole IP datagrams and presents a fresh IP header to the intervening networkCorrect
3. CThe data link layer, layer 2, since the original datagram is carried as the payload of a frame across the public network
4. DThe transport layer, layer 4, since the tunnel is set up between two endpoints and is torn down when they have nished
5. EThe application layer, layer 7, since the encipherment is performed by software running upon the gateway rather than by the hardware