3-Switching

Question 1

How does a host learn the MAC address of another host?

Answer 1

ARP - Address Resolution Protocol

Question 2

Host queries with an IP Address:
“Who has IP address 130.207.160.47?”
Response is the MAC address corresponding to 130.207.160.47. Once the host receives the reply, it starts to build the ARP table.

Answer 2

ARP - Address Resolution Protocol

Question 3

(When hosts wants to send a packet to a destination with a IP address… the hosts puts the IP packet and encapsulates it within an Ethernet frame with the corresponding destination MAC address.

Answer 3

ARP - Address Resolution Protocol

Question 4

What are the queries and responses in ARP?

Answer 4

Query: Broadcast asking about IP
Response: Unicast with MAC address

Question 5

Creates a broadcast medium and is now replaced by switches in todays networks

Answer 5

Hubs

Question 6

Issues with Hubs

Answer 6

flooding, collisions of frames ->latency, failures/misconfig

Question 7

Perform some amount of traffic isolation by partitioning the LAN into separate segments. This type of isolation maps destination MAC to output port.

Answer 7

Switches

Question 8

Maintains a table between destination addresses and output ports on a switch.

Answer 8

Learning Switched

Question 9

Initially, the forwarding table is empty.

1) If no entry in forwarding table, the host would simply flood
2) Otherwise, send to output port in table
3) Switches in turn forward broadcast frames (e.g. ARP queries)

Answer 9

Learning switch

Question 10

Cycles

Answer 10

1) forwarding loops

2) Broadcast storms

Question 11

Solution for cycles?

Answer 11

Spanning trees - a loop free topology

Question 12

Construct Spanning Tree part 1

Answer 12

1) Elect root(switch with smallest ID)
2) Each switch must decide which of its links to include in the spanning tree. Excludes link if not on shortest path to root.

Question 13

Construct Spanning Tree part 2 (determining the root)

Answer 13

Initially: every node thinks it is the root!

1) Each switch run an election process to determine smallest ID
2) Once smallest ID learned, it updates the view of root
3) Compute distance to new root

Question 14

Switches

Answer 14

Operate at layer 2 - common protocol at layer 2 is ethernet

• auto-configuring
• forwarding tends to be fast

Question 15

Routers

Answer 15

Typically operate at layer 3 where IP is the typical protocol
*Not restricted to spanning tree

Question 16

SDN

Answer 16

Blurring the lines between layer 2 and layer 3 (Software defined networking)

Question 17

Buffer Sizing

Answer 17

B = 2T*C

Question 18

The more variables that we have, the narrower the gaussian will be

Answer 18

Central Limit Theorem (CLT)

Question 19

If TCP flows are synchronized

Answer 19

B=2T*C/square root of N