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What are the 2 things a router must know from the packet in order to route it?
- Destination address
- egress interface
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What is the official name of the interface which traffic is sent out on a router?
egress interface
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What is the official name of the interface that traffic comes in on?
ingress interface
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What are the steps that the router take when taking a packet in to decide what to do with it?
- looks up the destination address on the routing table
- The routing table tells the router which interface the packet should be sent out on
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Where is the routing table stored?
RAM
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What arethree ways to control routing decisions on your router?
- Static Routes
- Default Routes
- Dynamic Routes
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When do you use static routes?
- When you want to manually define the path that the packet will take through your network
- in small networks with rarely changing routes
- when you have little bandwidth and do not want the overhead of a dynamic routing protocol
- when you want to manually define all of your routes for security reasons
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Which CLI do you create static Routes?
global configuration mode
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What is the command syntax for configuring static routes?
ip route [destination network address] [subnet mask] [next hop address or interface] [distance]
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What is a default route?
Where you configure the router to know where to send traffic for any network not found in its routing table.
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What is a default route also known as?
a gateway of last resort
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What are the 2 command syntax for configuring a default route?
- ip route 0.0.0.0 0.0.0.0 [next hop address or interface] [distance]
- ip default-network [network address to the next router]
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Are static and default routes scalable?
no
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What are the characteristics of routing protocols?
- administrative distances
- metrics
- distance vector
- link state operations
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What is Administrative distance?
the measure of trustworthiness that a router assigns to how a route to a network was learned.
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What are the different ways that a route can be learned?
- networks that are directly connected
- static routes
- dynamic routing protocols
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What are the default administrative distance values?
- connected 0
- static 1
- EIGRP (internal) 90
- OSPF 110
- RIP 120
- EIGRP (external) 170
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When a router has learned mutliple paths to a router, how is it decided which path to take?
The route with the lowest administrative distance value
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Explain the definition of what a Routing protocol's metrics
the variable used in the algorithm when making routing decisions
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What metric does RIP use?
Hop Count
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What metric does EIGRP use?
Bandwidth and delay
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What metric does OSPF use?
Cost
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What is a hop count?
The number of routers that a packet must pass through to reach a destination. The route with the fewest number of hops is preferred.
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How is cost determined for the OSPF metrics?
10^8/bandwidth
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Which Wouting protocol uses Hop Count Metrics?
RIP
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Which Wouting protocol uses Bandwidth delay Metrics?
EIGRP
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Which Wouting protocol uses Cost Metrics?
OSPF
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What are the 2 categories that routing protocols can be further divided?
- Distance Vector routing protocols
- Link State routing protocols
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Which Routing protocols are Distance Vector Protocols?
- RIP
- unsupported legacy protocols
- IGRP
- EIGRP
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What are the characteristics of distance vector routing protocols?
they periodically broadcasts entire routing table out of all interfaces and trust what the other router tells it
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What is distance vector also known as?
Routing by Rumor
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What is the risk of using distance vector routing protocols?
creating loops
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What are the built in mechanisms that distance vector protocols use to avoid creating loops?
- Maximum hop count
- Split-horizon
- Route poisoning
- Poison reverse
- Hold down timers
- Triggered updates
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What is the split-horizon rule?
information about a route should not be sent back in the direction in which it was learned.
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What is the default max hop count used by RIP?
15
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What is the default max hop count used by EIGRP?
224
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What is Route Poisoning?
In an attempt to preventing loops, as soon as a network is thought to be down, it is advertised out with a hop count that is one greater than what is allowed. This would declare the route as being inaccessible.
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How does Poison Reverse prevent loops?
The router that hears about a down network, violates split-horizon, and sends back an update with the network being unreachable.
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How does holddown timers prevent loops?
When a router receives information that a network is possibly down from a neighbor router, it will not accept any new information from that router for a specified period of time. This is to prevent regular update messages from reinstating a down route.
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What is the default hold down timer for RIP?
180 seconds
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How does triggered updates prevent loops?
by exchanging routing information whenever there is a change. In other words, a change in the routing topology will trigger routers to update each other.
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What does RIP stand for?
Routing information protocol
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What algorithm does RIP use?
Bellman-Ford
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How often will RIP routers exchange information?
every 30 seconds
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How does RIP exchange routing information?
by broadcasting the entire routing table every 30 seconds out all interfaces with RIP enabled.
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What does RIP version 2 also sends out every 30 seconds?
only updates of the routing table
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What multicast address does RIP v2 send updates to every 30 seconds?
224.0.0.9
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What other pieces of information does RIP v2 send out every 30 seconds other that routing table updates?
- Routing Authentication
- Classless routing
- Summarization
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What are the 4 steps to configuring a routing protocol?
- enable the routing protocol
- activate it on the interfaces
- advertise directly on the networks
- configure optional parameters
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Which CLI do you enable a routing protocol?
global configuration mode
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What is the command to enable RIP routing?
router rip
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Which command activates RIP on interfaces and advertises the network?
network [network address]
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How does a router handle RIP advertisments?
It replaces its existing routing table with the one it received, adds its own networks, then sends the new table to the next networks in line so that they can do the same.
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What does the optional "version 2" RIP command do?
enables RIP version 2 on your router
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What does the optional "no auto-summary" RIP command do?
disables automatic summarization
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What are the 2 commands used to verify RIP configuration?
- Show IP Route
- Show IP Protocols
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What does the "show ip route" command do?
displays your routing table
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Which command displays your routing table?
show IP route
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What does the "show ip protocols" command do?
the timers and the networks you are routing
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Which command do you use to debug the routing?
debug ip rip
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