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csc3002f > network layer > Flashcards

network layer Flashcards

1
Q

what is the network layer

A

transport seg from sender to receiver

  • send side: encapsulates seg into datagram
  • net layer protocols in every host, router
  • router examines header field
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2
Q

2 key net layer principles

A

addressing, link layer independence

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3
Q

what is link layer independence

A

services provided does not depend on internal organization of the underlying datalink layers

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4
Q

what is addressing

A

each net layer entity is identified by net layer address

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5
Q

What are the two net layer planes

A

control

data

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6
Q

what control plane used for

A

compute and install routing tables on routers - needs to understand entire network that host is part of - network wide logic

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7
Q

what is data plane used for

A

local -per router - used by hosts and routers to create and process packets that contain user data - transform to transport packet

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8
Q

two key net layer functions

A

routing, forwarding

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9
Q

what is routing

A

determine route taken by packets using routing algos

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10
Q

what is forwarding

A

move packets from router inp to router out

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11
Q

describe the interplay between routinng and forwarding

A

routing algo determines end-end path through network, forwarding table determines local forwarding for this router

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12
Q

describe IP fragmentation and reassembly

A

network links have Max Transfer Size which is the largest possible link-level frame
large IP datagram fragmented within the net
- one DGram becomes several
-reassembled at final dest
- IP header bits identify and order fragments

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13
Q

name and explain 2 network layer service models

A

Datagram network - connectionless service

Virtual circuit - connection service

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14
Q

difference between DG network/virtual circuit vs UDP/TCP

A

service - host to host

no choice in which service is used - implemented in network core

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15
Q

What are some properties of datagram networks

A
  • no call setup at net layer
  • pkt contains src and dest host addresss plus data
  • routers: no state about end-to-end connections (hop by hop forwarding)
  • pkts forwarded using dest host address
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16
Q

what is IP address

A

32 bit identifier for host, router interface

17
Q

what is an interface

A

connection between host/router and physical link - routers have multiple interface, hosts typically have one or two interfaces (e.g. ethernet, wifi 802.111)

18
Q

what is a subnet

A

device interfaces with same same subnet part of the ip address - can physically reach each other without intervening router

19
Q

how to change subnet sizes - explain what happens when you change the size of the host part of the IP address

A

increase host part - fewer subnets - more hosts in each subnet
decrease - smaller subnets - less hosts - more subnets

20
Q

where do ISPs get addresses?

A

ICANN - internet corporation for assigned names and numbers - allocate addresses and manage DNS

21
Q

motivation for IPv6

A

32 bit addresses run out
header format helps speed processing/forwarding
header changes to facilitate QoS

22
Q

IPv6 header format

A

fixed length - 40byte
no fragmentation
128 bit address space

23
Q

IPv6 header changes from IPv4

A
  • priority
  • flow label - identify DG in same flow
  • next header - identify upper layer protocol for data
  • no checksum
  • options are outside of header - indicated by next header field
  • ICMPv6
    • additional message types - pkt too big
    • multicast group management functions
24
Q

what is tunneling?

A

IPv6 datagram carried as payload in IPv4 DG among IPv4 routers

25
Q

What is created when aggregating routers into regions

A

Autonomous Systems

26
Q

Do routers in the same AS run different routing protocols?

A

No, routers in same AS run the same routing prots - intra AS routing prot

27
Q

what is a gateway router?

A

At edge of own AS - links to router in another AS

28
Q

interconnected AS - what is the forwarding table configured by?

A

Intra - sets entries for internal dests

inter - sets entries for internal and external dests

29
Q

Most common intra AS routing protocols

A

RIP - routing info prot
OSPF - Open shortest path first
IGRP - Interior gateway routing prot

30
Q

OSPF properties

A

Link state algo
-uses Djikstra
-net topology at each node
-ls packet dissemation
ospf advertisement carries one entry per neighbor
advertisements flooded to entire AS - carried in OSPF messages over IP rather than TCP/UDP

31
Q

Hierarchical OSPF - components

A

local area, backbone

  • link state adverts only in area
  • each nodes detailed area topology only know direction (shortest path) to nets in other areas
32
Q

what are area border routers

A

summarize distances to nets in own area, advertise to other Area border routers

33
Q

what are backbone routers

A

run ospf routing limited to backbone

34
Q

what are boundary routers

A

connect to other AS’s

35
Q

what is BGP

A

Border gateway prot - glue that holds internet together, allows subnet to advertise its existence to the rest of the internet

36
Q

eBGP

A

obtain subnet reachability from neighboring AS’s

37
Q

iBGP

A

propogates reachability to all AS internal routers

38
Q

what does BGP provide to each AS

A

means to: eBGP, iBGP, determine good routes based on reachability info

39
Q

why different Intra and inter AS routing?

A

Policy
-inter AS wants control over how its traffic is routed, who routes through its net
- intra AS: single admint so no policy decisions needed
Scale
-Hierarchical routing saves table size, reduced update traffic
performance
- intra - can only focus on performance
- inter - policy may dominate over performance

csc3002f (16 decks)

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