This exercise examines deterministic packet selection. Assume that the packet header contains spaces for routers to enter their IP addresses.

a. Suppose the header contains space for 30 router addresses. Initially, these spaces contain all zero bits. As the packet passes through a router, the router inserts its IP address into the first available location in this space. If there is no room left (because the packet has passed through 30 routers), the router does not insert its address. Describe how an attacker could conceal the route that the packet takes as it travels to its destination.

b. Now suppose the header uses variable-sized space for a list of router addresses. Initially, no router addresses are attached. As the packet passes through a router, the router adds its IP address to this list. Would this prevent the attack in your answer to part (a)? Why or why not? What other problems would this variable-length router address field cause?