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CCNA Semester 2
Chapter 4 Distance Vector Routing Protocols
60
Computer Networking
Undergraduate 1
01/27/2013

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Term
What are some of the key characteristics of RIPv1 and 2?
Definition
Hop count is used as the metric for path selection if the Hop count is greater than 15 RIP cannot supply a route. Routing updates are broadcast or multicast every 30 seconds.
Term
What are the key characteristics of EIGRP?
Definition
-Unequal cost load balancing
-Uses DUAL to calcualte the shortest path
-Routing updates are sent only when there is a change in the topology.
Term
How are distance vector routes advertised?
Definition
As vectors of distance and direction.
Term
Does a router in a distance vector network have complete knowledge of the entire path to a destination network?
Definition
NO
Term
What are the 2 pieces of information that a distance vector router knows?
Definition
-the direction or interface in which packets should be forwarded.
-The distance or how far it is to the destination network.
Term
What are the two reasons why sending an entire routing table in an update is inefficient?
Definition
This method is inefficient because the updates not only consume bandwidth, but also consume router CPU resources to process the updates.
Term
What is the periodic update time for RIP?
Definition
30 seconds
Term
What is the periodic update time for IGRP?
Definition
90 seconds
Term
What is the IP and MAC address for broadcast updates?
Definition
-255.255.255.255
-FF:FF:FF:FF:FF:FF
Term
What is the algorithm used for?
Definition
To calculate the best paths and then send that info to the neighbors.
Term
What process does the routing protocol define?
Definition
-Sending & receiving routing info
-Calculating the best paths and installing routes in the routing table.
-detecting and reacting to topology changes.
Term
Define Time to Convergence?
Definition
How quickly the routers in the network topology share routing info.
Term
Define Scalability
Definition
Defines how large a network can become based on the routing protocol.
Term
Define Classless or Classful
Definition
-Classless routing protocols include the subne mask in the updates.
-Classful routing protocols do not include the subnet mask and cannot support VLSM.
Term
Define resource usage
Definition
Includes the requirements of a routing protocol such as memory space, CPU utilization,and bandwidth link utilization.
Term
Define implementation and Maintenance
Definition
Describes the level of knowledge that is required for a network admin to implement and maintain the network based on the routing protocol deployed.
Term
List some advantages for distance vector protocols.
Definition
-Simple implementation & maintenance
-Low resource requirements
Term
List some disadvantages for distance vector protocols.
Definition
-Slow convergence
-Limited scalability
-Routing loops
Term
Immediately after booting, what routes are initially discovered?
Definition
Directly connected networks
Term
After completing the initial route discovery, what does the routerstart to do?
Definition
Initially discovers their own directly connected networks and subnet masks. This information is added to their routing tables.
Term
What does the initial exchange of routing information contain?
Definition
Includes info about their directly connected networks.
Term
What does the router do with the information that is not contained in its routing table?
Definition
Any routes that are not currently in its routing are added.
Term
After the first exchange of routing updates, what has been added to each routing table?
Definition
Each router knows about the connected networks of their directly connected neighbors.
Term
What is convergence?
Definition
The state of a set of routers that have the same topological info about the internetwork in which they operate.
Term
What is split horizon?
Definition
Routing technique in which info about routes is prevented from exiting the router interface through which that information was received. Useful in preventing routing loops.
Term
The amount of time it takes for a network to converge is directly proportional to what?
Definition
The size of the network.
Term
The speed of achieving convergence consists of what two things?
Definition
-How quickly the routers propagate a change in the topology in a routing update to its neighbors.
-The speed of calculation best path routes using the new routing information collected.
Term
What are the two reasons routers exchange routing updates?
Definition
-Exchange routing info with their neighbors
-Maintain up-to-date routing info in the routing table.
Term
What are four reasons listed for topology changes?
Definition
-Failure of a link
-Intro of a new link
-Failure of a router
-Change of link parameters
Term
What are three additional timers?
Definition
-Invalid
-Flush
-Holddown
Term
If an update has not been received to refresh an existing route after 180 seconds, what happens to that route in the routing table?
Definition
The route is marked as invalid by setting the metric to 16.
Term
What happens to the route after 240 seconds have elapsed?
Definition
When the flush timer expires, the route is removed from the routing table.
Term
What does a holddown timer?
Definition
The timer stabilizes routing info and helps prevent routing loops during periods when the topology is converging on new information.
Term
What are the two commands that will show the timers?
Definition
R1#show ip route
R1#show ip protocols
Term
Define bounded update
Definition
Updates are sent only to those routers that need the updated info.
Term
What are characteristic of EIGRP updates?
Definition
-Non-periodic
-Partial updates
-Bounded
Term
What is a triggered update?
Definition
Is a routing table update that is sent immediately in response to a routing change.
Term
What are three reasons to send a triggered update?
Definition
-An interface change state
-A route has entered(or exited)the unreachable state
-A route installed in the routing table
Term
What are the two problems with triggered updates?
Definition
Packets containing the update message can be dropped or corrupted by some link in the network. The triggered updates do not happen instantaneously.
Term
What is it called when all the routers send updates at the same time on a network with a hub at the center?
Definition
Synchronization of updates
Term
What is a routing loop?
Definition
A condition in which a packet is continuously transmitted within a series of routers without ever reaching its intended destination.
Term
What are some causes for routing loops?
Definition
-Incorrectly configured static routes
-Incorrectly configure route redistribution
-Inconsistent routing tables
-Incorrectly configured or installed discarded routes.
Term
What mechanism is built into IP to overcome routing loops?
Definition
Time-to-Live (TTL)
Term
What conditions can be created because of routing loops?
Definition
-Link bandwidth will be used for traffic looping back and forth between routers in a loop.
-A routers CPU will be strained due to looping packets.
Term
What are some mechanisms use to avoid routing loops?
Definition
-Define maximum metric to prevent count to infinity
-Holddown timers
-Split Horizon
-Route poisoning or poison reverse
Term
What is count to infinity?
Definition
A condition that exists when inaccurate routing updates increase the metric value to infinity for a network that is no longer reachable.
Term
What is infinity defined by?
Definition
Setting a maximum metric value
Term
What is infinity for RIP?
Definition
16 Hops
Term
What is it called when a route goes up, then down, then up etc?
Definition
The route is flapping.
Term
What are holddown timers?
Definition
They are used to prevent regular update messages from inappropriately reinstating a route that may have gone bad.
Term
What is split horizon rule?
Definition
That a router should not advertise a network through the interface which the update came.
Term
What is route poisoning?
Definition
It is used to mark the route as unreachable in a routing update that is sent to other routers.
Term
What is split horizon with poison reverse?
Definition
States when sending updates out a specific interface, designate any networks that were learned on that interface as unreachable.
Term
What is time-to-live (TTL)?
Definition
An 8-bit field in the IP header that limits the number of hops a packet can traverse through the network before it is discarded.
Term
What happens when a packet's TTL reaches 0?
Definition
The packet is discarded and the routes send an ICMP error message back to the source of the IP packet.
Term
What are the factors that affect the distnace vector protocol?
Definition
-Size of the network
-Compatibility between models of routers
-Admin knowlege required
Term
What are features of RIP?
Definition
-Split Horizon
-Split Horizon with poison reverse
-Load balancing six equal paths
Term
What are the feature introduced with RIPv2?
Definition
-Subnet mask in routing updates
-Authentication mechanism
-Supports VLSM
-Manual route summary
-Uses multicast addresses
Term
What are the features of EIGRP?
Definition
-Triggered updates
-Use of the topology table
-Supports VLSM
-Establishment of adjancies with neighboring rotuers.
Term
What are advantages of EIGRP?
Definition
-Minimum bandwidth and cumulative delay of the path.
-Fast convergence
-Bounded updates
-Supports multiple layer protocols.
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