IPv4

Question 1

What is a subnet?

Answer 1

Device interfaces with same subnet part of IP address

Can physically reach each other without intervening router

Question 2

What is CIDR?

Answer 2

It is “Classless InterDomain Routing) - arbitrary subnet lengths
A.b.c.d/X where x is the number of bits for the subnet part

Question 3

Why is classful routing inefficient?

Answer 3

Class C: 256 addresses: to small for small enterprises
Class B: 65536 addresses: too small for large enterprises and universities
Class A: 16 mio addresses: too large

Question 4

Where is ICMP located (OSI)?

Answer 4

It resides in IP datagrams but is considered part of the IP layer

Question 5

What 2 classes of icmp messages exist?

Answer 5

Query messages: generate another icmp message
Error messages: contain IP and first 8 bytes of erroneous ip datagram; allows receiving icmp module to map message to protocol&port

Question 6

When should a host send ARP requests?

Answer 6

When an IP address does not appear in the host-local ARP table.

Question 7

How does ARP deal with hosts that change their address?

Answer 7

• Expiration timer

- some implementations send ARP request to revalidate to-be-removed table entries

Question 8

What are gratuitous ARP requests?

Answer 8

A host sends ARP request for its own IP address; this can check if the ip is already in use in the LAN

Question 9

Vulnerabilities of ARP?

Answer 9

• No authentication - packets can be forged
• Stateless: replies can be send without request
• Receiving ARP packet must update local cache

3. Option: Force overwrite (ARP Poisoning) - can redirect traffic
   ARP manipulation can also happen in WPA2 Wifi!

Question 10

What is the difference between routers and switches?

Answer 10

Router: forwarding tables, routing protocols
Forwards IP packets based on FWD table & dst IP

Switch: switching tables, filtering & learning algorithms, spanning tree protocols
Switch L2 frames based on sw table & dst MAC

Question 11

What are forwarding and routing?

Answer 11

Forwarding: data plane
- direct data packet to link
uses fwd table

Routing: control plane
- compute the paths the packet will follow
Creates fwd table

Question 12

Name 3 routing protocols

Answer 12

RIP
OSPF
BGP

Routers talk amongst themselves

Question 13

How does routing in SDN (software defined networking) work?

Answer 13

A router receives forwarding and routing information via SDN control plane

Control plane can be external