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EEE3093S - Communication and Network Engineering > Chapter 5 - Network Layer (Control Plane) > Flashcards

Chapter 5 - Network Layer (Control Plane) Flashcards

1
Q

What is fowarding?

A

move packets from router input port to appropriate output port

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2
Q

what is routing?

A

determine route taken by packets from source to destination

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3
Q

two approaches for network control plane

A
  • per router (traditional)
  • logically centralized control
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4
Q

logically centralized control plane?

A

Remote controller interacts with local control agents (CAs) in routers to compute fowarding tables

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5
Q

Per-router system?

A
  • routing algorithm components in EVERY ROUTER to compute fowarding tables
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6
Q

What is the cost of an edge?

A
  • physical length
  • link speed
  • monetary cost
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7
Q

centralized routing algortihm?

A
  • has complete topology (link cost info)
  • “link state” algorithms
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8
Q

Decentralized routing algorithm

A
  • router knows physically-connected neighbours and link cost for these
  • iterative process to exchange info with neighbours
  • “distance vector” algorithms
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9
Q

Static routing algorithms

A
  • routes change slowly over time
  • usually requires human intervention
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10
Q

dynamic routing algorithm

A
  • routes change more quickly
  • periodic update
  • in response to link cost changes
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11
Q

What does distributed mean for the distance vector algorithm

A
  • each node receives some info from one or more of its DIRECTLY ATTACHED neighbours
  • performs a calculation
  • distributes the results of its calculation back to its neighbours
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12
Q

what does “iterative” mean with the distance vector algorithm

A

continues until no more info is exchanged between neighbours

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13
Q

what does asynchronous mean with distance vector algorithm

A
  • it does not require all nodes to operate in lockstep with each other
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14
Q

Comparing LS and DV algorithms

A

Message complexity:
LS - with n nodes, E links, O(nE) messages sent
DV - exchange between neighbours only

Speed of convergence:
LS - O(n^2) algorithm requires O(nE) messages (could have oscillations)
DV - convergence time varies (routing loops or count to infinity)

Robustness (router malfunctions?):
LS - advertise incorrect link cost
each node only computes only its own table
DV - can advertise incorrect path cost

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15
Q

intra-AS routing

A
  • routing between routers in same network
  • routers must run SAME intra-domain protocol
  • routers in different AS (autonomous systems) can run different AS protocols
  • gateway router: edge of AS. has links to routers in other AS
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16
Q

inter-AS routing

A
  • routing amoung different AS
  • gateways performs inter-domain routing (and intra-domain routing)
17
Q

Hierarchy of OSPF

A
  • each area runs its own OSPF link-state rotuing algorithm
  • each router broadcasts link state to all other routers in area
  • area border routers:
    summarize distances to nets in own area and advertise to other area border routers
  • backbone routers:
    run OSPF routing
  • boundary routers:
    connect to other AS
17
Q

Open shortest path first (OSPF)

A
  • publically available
  • uses link state
  • router will flood OSPF link-state to all routers in AS
  • messages carried directly over IP rahter than TCP or UDP
18
Q

Border gateway protocol (BGP)

A

-inter domain protocol
- determines good routes based on reachability and policy

19
Q

eBGP

A

obtain subnet reachability info from neighbouring AS

19
Q

iBGP

A

propagate reachability info to all AS-internal routers

20
Q

Hot potato routing

A

choose local gateway that has least intra domain cost. Dont worry about inter-domain cost

21
Q

BGP route selection

A

1.) local preference (policy)
2.) shortest AS-path
3.) closest next-hop router (hot potato)
4.) additional criteria

21
Q

Why different intra-, inter-AS routing?

A

Policy:
inter - admin wants to control how traffic routed and who routes through its net
intra - single admin, so no policy decisions

scale:
- heriarchical routing saves table size, reduced update traffic

performance:
intra - can focus on performance
inter - policy can dominate over performance

22
Q

What is broadcast routing?

A
  • deliver packets from source to all other nodes
  • send separate copy to each destination using unicast routing
  • inefficient because packet traverses same link multiple times
23
Q

What is uncontrolled flooding?

A

-source sends copy of packet to all neighbours
- when node received packet, will duplicate and foward to all neighbours except one that sent it
- issues are cycles and broadcast storm

23
Q

What is controlled flooding?

A
  • chooses when to flood a packet and when to not. (ie do not flood id packet was already received and flooded)
  • using sequence numbers: unique identifier plus broadcast sequence number, each node maintains list, does not forward packets it has already received.
24
Q

What is Reverse Path Fowarding (RPF)?

A
  • only foward packet if it arrived on shortest path between node and source
  • router knows it has or will receive packet from shortest path link to sender
  • does not use unicast routing to deliver packet
25
Q
A
26
Q

What is multicast routing?

A
  • packets delivered to each and every node in network
  • multicast packet is delivered to only a subset of network nodes
27
Q

Problems with multicast routing

A
  • how to identify receivers of multicast packet
  • how to address a packet sent to these receivers
28
Q

What is address indirection?

A
  • single identifier is used for the group of receivers
  • a copy of packet is delivered to all of the multicast receivers associated with that group
29
Q

what is a multicast group?

A
  • a group of receivers associated with a class D address
30
Q

What is the Internet Group Management Protocol (IGMP)

A
  • Operates between a host and its directly attached router
  • allows host to inform its attached router that it wants to join a specific multicast group
31
Q

What does the IGMP message “membership_query” mean?

A
  • sent by router to all hosts on attached interface
  • determines the set of all multicast groups that have been joined by the hosts on that interface
32
Q

What does the IGMP message “membership_report” mean?

A
  • host indicates group membership to router
33
Q

What does the IGMP message “leave_group” mean?

A
  • optional message
  • soft-state internet protocol
34
Q
A

EEE3093S - Communication and Network Engineering (11 decks)

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