IP

Question 1

How to do scalable forwarding?

Answer 1

Need location aware forwarding - global hierarchical addresses

Question 2

What does the IP protocol do?

Answer 2

glues together different netowrk technologies

1) run the IP layer, 2) have interfaces that speak different protocols

Question 3

IP runs on what?

Answer 3

routers

Question 4

Problems with classful addressing?

Answer 4

1) inefficient use of address space

2) too many routing entries

Question 5

Host, subnet mask, and subnet number interaction

Answer 5

Host & mast = subnet number

Question 6

Forwarding table with subnet number/mask

Answer 6

subnet number, network mask, next hop

Question 7

Steps for finding next hop with subnetting

Answer 7

get packet -> apply mask to addr -> get subnet # -> see if subnet # you got matches the subset number listed

Question 8

Switch vs. Router layer

Answer 8

Switch - link/mac

Router - IP/network

Question 9

use for Switch vs. Router

Answer 9

switch - connect LAN to form switch networks

router - connecct switch networks to form internetworks

Question 10

hardware for switch vs. router

Answer 10

switch - ports belong to some link layer technology

router - ports running different technologies

Question 11

function for switch vs. router

Answer 11

switch - lookups on mac address

router - lookups on IP address

Question 12

types of routing protocols

Answer 12

intradomain and interdomain

Question 13

intradomain routing protocols

Answer 13

run inside an internetwork

ex - Open shortest path first (OSPF), routing information protocol (RIP)

Question 14

interdomain routing protocols

Answer 14

establish connectivity across internetworks (BGP)

Question 15

benefits of subnetting

Answer 15

prevent external enity from using a disproportionately large number of addresses

Question 16

subnetting

Answer 16

way of taking a classful network address and slicing it into multiple subnetwork addresses using subnet masks

Question 17

Benefits of classless routing (prefixes)

Answer 17

1) decrease # forwarding table entries, 1 entry per prefix

2) address space utilitization

Question 18

route aggregation

Answer 18

if multiple entries in router have contiguous prefix and next hops are the same, can collapse into 1 entry

Question 19

ARP

Answer 19

address resolution protocol

given an IP address, get mac address

Question 20

How does ARP work?

Answer 20

special broadcast mac frame - has sender who is requesting (their mac and IP) and the IP you are requesting Mac for

Question 21

Intradomain routing

Answer 21

w/in an internetwork
DV - RIP
LS -OSPF, IS-IS

Question 22

Distance Vector

Answer 22

each router only knows cost of its neighbors

Question 23

When are DV messages sent?

Answer 23

periodically or in a triggered fashion

Question 24

How does DV work?

Answer 24

host receives a message from neighbor and sees if current cost for each destination is less than currently stored

Question 25

Problem with DV?

Answer 25

Count to infinity

Question 26

solution

Answer 26

use small count to infinity, poisoned reverse

Question 27

Poisoned reverse

Answer 27

when a router uses another router to reach a destination, announce distance to that router as infinity

Question 28

Reliable flooding

Answer 28

gets link stement, update local state and send out to other links

Question 29

What happens if get multiple link state updates from same host?

Answer 29

Use sequence number to make sure only update when needed

Question 30

Link state update

Answer 30

each router has a view of network topology

Question 31

line cards

Answer 31

router interfaces

Question 32

routing processor

Answer 32

has/does routing protocols | computes routing tables but does not do forwarding decisions (want to avoid 1 central forwarding table)

Question 33

Problem with input buffering?

Answer 33

Head of line blocking

Question 34

Solution for head of line blocking?

Answer 34

virtualize input paths | virtual output queuing - organize input buffer based on output buffer

Question 35

Interdomain routing protocol

Answer 35

BGP (border gateway protocol)

Question 36

AS types

Answer 36

ISPs, stub networks

Question 37

3 special routers in BGP

Answer 37

1) backbone/core routers 2) edge routers 3) BGP speaking routers

Question 38

BGP routers

Answer 38

connect to other BGP speaking routers in other ISPs and participate in BGP protocol - connect an autonomous system to another autonomous system

Question 39

Relationships is BGP

Answer 39

provider, customer, peers

Question 40

If receive 3 advertisements for same prefix, which one to choose?

Answer 40

No provider because will have to pay - choose route though customer because they are paying you

Question 41

Who do I tell of route learned through customer?

Answer 41

Everyone

Question 42

Who do I tell of route learned through provider?

Answer 42

Customer

Question 43

Who do I tell of route learned through peer?

Answer 43

Customer

Question 44

BGP import policy

Answer 44

cust > peers > prov