Suppose there are three routers between a source host and a destination host. Ignoring fragmentation, an IP datagram sent from the source host to the destination host will travel over how many interfaces? How many forwarding tables will be indexed to move the datagram from the source to the destination?
Try an answer before revealing the guidance below.
Key Concepts
- Host interface
- Router input and output interfaces
- One forwarding lookup per router
- Hops
Answer Approach
- Count the source host’s outgoing interface.
- Count two interfaces (in and out) for each router.
- Count the destination host’s incoming interface.
- Count one forwarding-table lookup at each router.
Full Answer
Answer status: Draft answer (unofficial). Revision notes, not an official marking scheme.
8 interfaces: 1 at the source host + 2 at each of the 3 routers (input and output) + 1 at the destination host. 3 forwarding tables are indexed, one at each router. (This is the textbook answer for n routers: 2n + 2 interfaces and n forwarding tables.)
Interfaces = 2n + 2 for n routersRouter tables indexed = nShortcuts: K concepts · A approach · F answer · R reviewed · B bookmark · ← / → previous / next