Chap 6 - IP Routing Essentials

Question 1

What is a network of interconnected routers and systems under a common administration called?

Answer 1

Autonomous System or Routing Domain

Question 2

What are the 5 most common routing protocols found on most routing platforms?

Answer 2

• RIPv2
• EIGRP
• OSPF
• IS-IS
• BGP

Question 3

What is the difference between an IGP and an EGP?

Answer 3

• IGPs are optimized for routing within an AS
• EGPs are optimized for routing between Ass

Question 4

What is BGP called when it is used within an autonomous system?

Answer 4

Interior BGP

Question 5

What is BGP called when it is used to route between autonomous systems?

Answer 5

Exterior BGP

Question 6

What does a Distance Vector routing protocol base its route computation on?

Answer 6

• Distance (number of hops)
• Vector (the local interface it uses to send the packet on its way)

Question 7

What are 2 advantages of a Distance Vector routing protocol?

Answer 7

• Requires less CPU and memory
• Can run on low-end routers

Question 8

What is the name of an enhanced Distance Vector algorithm used to calculate the shortest path to a destination?

Answer 8

Diffusing Update Algorithm (DUAL)

Question 9

Which routing protocol uses DUAL?

Answer 9

EIGRP

Question 10

Which routing protocol uses Bellman-Ford?

Answer 10

RIP or other Distance Vector protocols

Question 11

What are 5 enhancements introduced by DUAL?

Answer 11

• Rapid Convergence
• Sends updates only when there’s a change
• Uses Hellos and forms Neighborships
• Uses bandwidth, delay, reliability, load and MTU
• can Load Balance across equal or un-equal cost links

Question 12

Why is EIGRP called a Hybrid Routing Protocol?

Answer 12

Because it has characteristics of both Distance Vector and Link State routing protocols

Question 13

By default what does EIGRP advertise?

Answer 13

• Total path delay
• Minimum bandwidth

Question 14

What are 2 Link State routing protocols?

Answer 14

• OSPF
• IS-IS

Question 15

What are OSPF advertisements called?

Answer 15

Link State Advertisements (LSAs)

Question 16

What are IS-IS advertisements called?

Answer 16

Link State Packets (LSPs)

Question 17

Where does an OSPF router store its LSAs?

Answer 17

Link State Database (LSDB)

Question 18

What calculation method does OSPF use?

Answer 18

Djikstra Shortest Path First algorithm

Question 19

What does OSPF use to enable features for Service Providers?

Answer 19

Opaque LSAs

Question 20

What does IS-IS use to enable features for Service Providers?

Answer 20

TLVs (type, length, value)

Question 21

What disadvantage is there to using a link state routing protocol?

Answer 21

They use more CPU and memory.

Question 22

What 2 advantages are there to using a link state routing protocol rather than a distance vector routing protocol?

Answer 22

• Link State protocols make better routing decisions
• Link State protocols are less prone to routing loops

Question 23

What type of routing protocol is BGP?

Answer 23

Path Vector Algorithm

Question 24

What does BGP use to compute routes?

Answer 24

BGP Path Attributes

Question 25

What are the 13 BGP Path Attributes?

Answer 25

* Weight * Local Pref * Locally originated * AIGP * Shortest AS\_PATH * Origin Type * Lowest MED * EBGP over IBGP * Lowest IGP Next Hop * If eBGP then oldest route * Peer with lowest router-id * Minimum cluster length * Peer with the Lowest Neighbor IP address

Question 26

How does a Path Vector Algorithm prevent loops?

Answer 26

If it receives an advertisement that already includes its AS in it drops the advertisement

Question 27

What 3 steps does a router take to identify the path a packet should take?

Answer 27

* Routing table populated with routes presented from routing protocol processes * FIB is programed through the routing table * Forwarding decision is a function of the FIB and results from calculations performed in the RIB

Question 28

What 3 components determine Path Selection?

Answer 28

* Prefix Length * Administrative Distance * Metrics

Question 29

What is the forwarding decision a function of?

Answer 29

* The FIB * Calculations done in the routing table

Question 30

How is the RIB calculated?

Answer 30

* Administrative Distance * Metric

Question 31

What is ECMP?

Answer 31

Equal Cost Multipathing

Question 32

What are 2 cases when static routes are needed?

Answer 32

* Dynamic routing protocols can't be used due to limited CPU and/or memory * Routes learned from Dynamic Routing Protocol needs to be superseded.

Question 33

What are 3 types of static routes?

Answer 33

* Directly attached static routes * Recursive static routes * Fully specified static routes

Question 34

If a directly attached static route has been configured and the interface goes down what happens to the route?

Answer 34

It is removed from the RIB.

Question 35

What 3 advantages does using VRFs with IP routing have over Layer 2 technology?

Answer 35

* improved convergence times * dynamic traffic load sharing * the ability to use ping and traceroute troubleshooting tools

Question 36

Display the routes in a VRF.

Answer 36

show ip route vrf (vrf\_name)

Question 37

What 4 pieces of information does every routing protocol present to the RIB for insertion?

Answer 37

* Destination network * Next-hop IP address * AD * Metric values

Question 38

What are the 3 factors are used by the RIB when deciding to accept or reject a route?

Answer 38

* If the route does not exist in the RIB then accept the route * If the route exists and its AD is lower than that of the new route then the new route is rejected. * If the route exists and its AD is higher than that of the new route then the new route is accepted and the old route is removed

Question 39

When configuring a static route in IPV6 when would you need to use a fully specified static route?

Answer 39

If the next hop address is a link local address

Question 40

What is the name of a distance vector algorithm that is not enhanced?

Answer 40

Bellman-Ford