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Week 9: Routing Protocols, OSPF, RIP, BGP

#Routing Protocols

#Routing Protocols 1

Why is there only one inter-AS routing protocol while there are multiple intra-AS routing protocols?

#Routing Protocols 2

Which of the following is an administrative domain (AS) equivalent to?

  1. A single institution
  2. A block of IP addresses
  3. A DNS domain
  4. None of the above

Answer with a number, like 1.

#OSPF

#OSPF 1

Which of the following pieces of information can uniquely identify a link-state advertisement (LSA) when taken together?

  1. Link-state advertisement age
  2. Link-state advertisement length
  3. Source router ID
  4. Advertising router ID
  5. Sequence number
  6. Payload

Answer with a comma-separated list of numbers, like 1,2,3.

#OSPF 2

In a network using OSPF, how many LSA messages traverse each link per unique network change?

Answer with a number, like 1.

#OSPF 3

Which of the following scenarios would cause a router to broadcast or retransmit an LSA?

  1. A periodic (30-minute) timer expires
  2. A router sends a HELLO message to a neighbor and gets a response before a timeout
  3. A router sends a HELLO message to a neighbor and does not get a response before a timeout
  4. A router sends an LSA to a neighbor and gets an ACK from the neighbor before a timeout
  5. A router sends an LSA to a neighbor and does not get an ACK from the neighbor before a timeout
  6. A router sends an LSA to a neighbor and gets an ACK from a different node (not the neighbor) before a timeout

Answer with a comma-separated list of numbers, like 1,2,3.

#RIP

#RIP 1

Which of the following is used as the distance metric for RIP?

  1. Link bandwidth
  2. Hop count
  3. Path latency
  4. Maximum transmission unit (MTU)

Answer with a number, like 1.

#RIP 2

Consider the network topology given by the graph. The nodes represent routers, and the labels on the edges represent the prefixes for the networks connected by the routers. Once distance vectors have stabilized, what are the distances sent by R1 to R2 in an update message? Assume split horizon with poison reverse is used.

RIP network topology

Answer with a list of 5 numbers like 1,2,3,4,inf representing values corresponding to 10.1.1.0, 10.1.2.0, 10.1.3.0, 10.1.4.0, and 10.1.5.0, respectively. For the purposes of this problem, use inf for networks advertised as unreachable.

#RIP 3

Consider the network topology from RIP 2. Once distance vectors have stabilized, what are the distances sent by R2 to R1 in an update message? Assume split horizon with poison reverse is used.

Answer with a list of 5 numbers like 1,2,3,4,inf representing values corresponding to 10.1.1.0, 10.1.2.0, 10.1.3.0, 10.1.4.0, and 10.1.5.0, respectively. For the purposes of this problem, use inf for networks advertised as unreachable.

#BGP

#BGP 1

Which layer of the Internet protocol stack does BGP run in?

  1. Application layer
  2. Transport layer
  3. Network layer
  4. Link layer

Answer with a number, like 1.

#BGP 2

Consider the following network topology between ASes. This is a subset of a larger network topology. Vertical arrows are from the provider to the consumer. Horizontal arrows are between peers. Only ASes with arrows between them are directly connected. Which of the following routes are allowed?

BGP topology between ASes
  1. AS1 -> AS2 -> AS3 -> AS4 -> AS5
  2. AS1 -> AS2 -> AS4 -> AS5
  3. AS1 -> AS2 -> AS3 -> AS2 -> AS3 -> AS4 -> AS5
  4. AS5 -> AS4 -> AS3
  5. AS5 -> AS4 -> AS3 -> AS2 -> AS1
  6. AS5 -> AS4 -> AS3 -> AS6

Answer with a comma-separated list of numbers, like 1,2,3.

#BGP 3

Consider the following network topology. There are two ASes, each with two routers. According to BGP hot-potato routing, what are the distances from A1 to B2 and from B2 to A1?

BGP hot-potato routing topology
  1. 6,6
  2. 6,8
  3. 8,6
  4. 8,8

Answer with a number, like 1.

#BGP 4

Why do we need both iBGP and an IGP when advertising routes inside an AS? Explain how each protocol is different and how they work together.

#BGP 5

BGP is a very fragile protocol. If you wanted to take down a website by sending BGP advertisements, how could you do so?