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The main downside to distance vector route discovery is the overhead required in broadcasting the entire routing table every 30 seconds. Link state route discovery is more efficient. Routers using link state route discovery routers send out their routing table via a multicast, not a broadcast packet, every five minutes or so. If there is an update, only the update is sent. NetWare Link Services Protocol (NLSP) for IPX and Open Shortest Path First (OSPF) for TCP/IP are two link state route discovery protocols.


Several protocols can be routed, but a few protocols can’t be routed.


It is important to know which protocols are routable and which aren’t so that you can choose the appropriate protocol when it comes time to design an internetwork. Table 2.3 shows a few of the most common routable and nonroutable protocols and the routing protocols they use, if any.


TABLE 2.3 Routable and Nonroutable Protocols


Protocol


Route Discovery Protocol


Routable?


IPX


RIP


Yes


IPX


NLSP


Yes


NetBEUI


None


No


TCP/IP


RIP


Yes


TCP/IP


OSPF


Yes


XNS


RIP


Yes

When setting up routing on your network, you may have to configure a default gateway. A default gateway, when configured on a workstation, is the router that all packets are sent to when the workstation doesn’t know where the station is or can’t find it on the local segment. TCP/IP networks sometimes have multiple routers as well and must use this parameter to specify which router is the default. Other protocols don’t have very good routing functions at the workstation, so they must use this feature to «find» the router.

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