$4\mathrm{.}04-5.$ IPv$4/$IPv$6$ co$-$existence: tunneling $($b$).$ Consider the mixed IPv$4/$IPv$6$ network shown below, where an IPv$4$ tunnel exists between IPv$6$ routers B and F$.$ Suppose that IPv$6$ Host $2$ sends a datagram to IPv$6$ Host $4$; the sequence of routers traversed are B$,$c$,$b$,$F$.$ IPv$6$ datagrams are shown in blue; the IPv$4$ datagram is in red $($containing the encapsulated IPv$6$ datagram in blue$).$