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37 Cards in this Set
- Front
- Back
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Internet
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large collection of networks and hostsinterconnected by routers. |
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Direct Routing |
Acomputer on any physical network can transmit a datagram to any other computeron the same network. |
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Indirect Routing |
- occurswhen the destination is not on a directly attached network. -requires that the source host send thedatagram to a router for delivery. |
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Types of Indirect Routing |
-Static routing -Default Routing - Dynamic Routing |
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Routing Tables |
Arouter examines its routing table to determine how to forward a packet. |
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Static Routing |
-network administrator keeps a table ofnetworks, and manually updates these tables whenever there is a change withinthe routing domain. |
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Stub networks |
networkswith only one entry and exit point. |
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Default Routes |
- special address 0.0.0.0/0 - onlysuitable for use on stub networks. - usedto reduce the size of a routing table. |
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Dynamic Routing |
-share routing information with associatedrouters -allows routers to choose the best of anumber of possible routes between networks based on metrics -updates use router resources, in the formof increased central processing unit (CPU) and memory usage |
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Routing Information |
-provide reliable and consistent routesfor all possible destinations - operatedas the backbone that held the Internet together and made universalcommunication possible. |
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Autonomous Systems |
single site having multiple networksunder its control. |
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Gateway Protocols |
–IGPs –EGPs |
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IGPs |
-Routers within a single AS communicateusing one of several dynamic routing protocols - Performanceis the key requirement of an IGP. |
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EGPs |
allows communication between exteriorneighbors (peers) in two different autonomous systems |
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Types of Dynamic Routing Protocols |
–DVAs (distance vector algorithm) –LSAs (link-state algorithm) |
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OSPF |
Open Shortest Path First |
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BGP |
Border Gateway Protocol |
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DVA |
-onemethod of determining routes that a packet can take to its destination. -requireonly a small number of CPU cycles to determine the shortest route to a distantnetwork. |
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LSA |
eachrouter must know the entire network topology before computing the shortest pathto each destination network. - caneliminate problems that occur in very large networks because of their abilityto partition an AS into areas. |
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Multipath Routing
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–If the primary route fails, therouter can still forward a packet using an alternative route. –If there is more than one best-costroute, the network administrator may elect to have the router split the loadbetween the equal-cost routes on a round-robin basis. |
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Two types of Router-based network |
- Flat - Hierarchical |
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Flat Router Networks |
DVAs,used in routing protocols such as RIP and Inter-Domain Routing Protocol (IDRP),create flat networks. -performsthe same job in the same way. |
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Hierarchical Networks |
twolevels: –Routers on Level 1 are generallyused for communication within defined areas of the network. –Higher performance routers form aspecial area called the backbone area. |
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RIP |
DVArouting protocol used by TCP/IP and Novell Internetwork PacketExchange/Sequenced Packet Exchange (IPX/SPX) networks. |
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Hop-count limit |
permitsa maximum hop count of 15 and considers any destination network greater than 15hops away unreachable. |
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Holddowns |
prevent regular update messages frominappropriately reinstating a route that has gone bad. |
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Split Horizons |
used between adjacent routers. source should never be updated by the destination |
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Poison Reverse Updates |
are intended to defeat larger routingloops |
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RIP Timers |
–Routing update timer –Route invalid (expiration) timer –Route flush timer |
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Novell RIP |
–Novell RIP sends updates by defaultevery 60 seconds. –Novell RIP adds a new metric calledticks. –Novell RIP can load share betweentied routes. |
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RIPv2 |
Whensubnettingbecame common, RIPv2 was created to handle this additional routing information. |
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Four elements added to RIPv1 to create RIPv2 |
–Route tag –Subnet mask –Next hop –Authentication |
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Route Tag |
providesa way to distinguish “internal” RIP routes from “external” RIP routes, whichmay have been imported from an EGP or another IGP. |
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Subnet Mask |
fieldcontains the subnet mask that is applied to the IP address to yield the nonhostportion of the address. |
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Next Hop |
indicates the IP address to which packetson the route should be forwarded |
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Metric |
representsthe hop count to a given network. |
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Authentication |
preventunauthorized people from inserting bogus routing information into routingtables. |
