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CHAPTER 22
Network Layer:
Delivery, Forwarding, and Routing
Solutions to Odd-Numbered Review Questions and Exercises
Review Questions
1. We discussed two different methods of delivery: direct and indirect. In a direct
delivery, the final destination of the packet is a host connected to the same physical
network as the deliverer. In an indirect delivery the packet goes from router to
router until it reaches the one connected to the same physical network as its final
destination.
3. A routing table can be either static or dynamic. A static routing table contains
information entered manually. A dynamic routing table is updated periodically by
using one of the dynamic routing protocols such as RIP, OSPF, or BGP.
5. A RIP message is used by a router to request and receive routing information
about an autonomous system or to periodically share its knowledge with its neigh-
bors.
7. The hop count limit helps RIP instability by limiting the number of times a mes-
sage can be sent through the routers, thereby limiting the back and forth updating
that may occur if part of a network goes down.
9. In OSPF, four types of links have been defined: point-to-point, transient, stub, and
virtual. A point-to-point link connects two routers without any other host or router
in between. A transient link is a network with several routers attached to it. The
packets can enter and leave through any of the routers. A stub link is a network
that is connected to only one router. The data packets enter the network through
this single router and leave the network through this same router. This is a special
case of the transient network. When the link between two routers is broken, the
administrator may create a virtual link between them, using a longer path that
probably goes through several routers.
11. BGP is an interdomain routing protocol using path vector routing.
Exercises
13. A host that is totally isolated needs no routing information. The routing table has
no entries.
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