5. IPSec (5-10 points): Imagine two branches of a corporate network are connected through the Internet. Specifically, each of the two branches has a router facing the Internet, commu- nicating with the router of the other branch over IPsec. Branch 1 10.1.1.0/8 Router 10.1.1.1 4.3.2.1 IPsec Router 8.7.6.5 IPsec 10.2.1.1 Branch 2 10.2.1.0/8 (a) If ESP is used to secure the communication between the two routers, which mode will be used, transport mode or tunnel mode? Why? (b) The network is setup such that two nodes from the two branches can communicate transparently. Imagine node 10.1.1.5 from branch 1 is sending a packet to node 10.2.1.6 from branch 2. Describe in detail the steps of how the packet travels between the two nodes and how it is encapsulated and decapsulated on the way.