Final answer:
An IP datagram sent from a source host to a destination host passing through three routers will travel over a total of 8 interfaces. This includes both the outgoing and incoming interfaces at each of the three routers, as well as the single interface connecting the source and the destination hosts.
Step-by-step explanation:
If we consider a network with a source host, three routers, and a destination host (s-r1-r2-r3-d), to calculate the number of interfaces an IP datagram travels over without fragmentation, we need to consider each segment between the devices. Starting from the source host to the first router (r1) is one interface, r1 to r2 is a second interface, r2 to r3 is the third, and finally r3 to the destination host (d) is the fourth. However, each router also has an incoming interface. Therefore, r1 will have two (one incoming from s, one outgoing to r2), r2 will have two (one incoming from r1, one outgoing to r3), and r3 will also have two (one incoming from r2, one outgoing to d). Adding these up:
- Source to r1: 1 outgoing interface
- r1: 1 incoming + 1 outgoing = 2 interfaces
- r2: 1 incoming + 1 outgoing = 2 interfaces
- r3: 1 incoming + 1 outgoing = 2 interfaces
- Destination host has 1 incoming interface
Altogether, this adds up to 8 interfaces that the IP datagram will travel over. Hence, the correct answer to the question is 8 interfaces.