5. Naming and Addressing

Question 1

What addresses do switching and routing use?

Answer 1

Switching: hardware addresses, link layer
Routing: IP addresses, network layer

Question 2

What is a MAC address?

Answer 2

Each device has a hardware address for each interface. (WiFi interface, ethernet interface etc…)
48 bits long e.g. 00-16-c7-33-9b-c6 so 2^48 unique addresses
Batches of addresses are allocated by IEEE to manufacturers
Usually globally unique
Does not change (the IP address on a mobile device changes with it’s surrounding network)

Question 3

What is the role of a MAC address in datagram delivery?

Answer 3

Only used in the context of LAN. Used in the transfer of IP datagrams because they refer to physical interfaces, whereas the IP address refers to the actual network.

Question 4

What is the ARP protocol used for?

Answer 4

A node looking for the MAC address that corresponds to the destination IP broadcasts an ARP request. All nodes on the LAN see the request. The node with the correct IP responds with an ARP response. Sender saves the mapping. Other nodes may take note of this mapping too.

Question 5

Describe the IPv4 exhaustion problem.

Answer 5

A class A network has 2^24 nodes - too many. A class C network has 2^8 - often not enough. Class B has 2^16 which is too many but is the best fit. This means many are not used and wasted. Having a bunch of class C’s would result in cluttered routing tables. The solution is IPv6 which has 2^128 address, but it is not backwardly compatible with IPv4.

Question 6

What is the purpose of CIDR?

Answer 6

Allows for creation of flexible IP address ranges so just the right amount of addresses can be used, no waste. Notation is /n

Question 7

What are the private network ranges?

Answer 7

10. 0.0.0/8
11. 16.0.0/12
12. 168.0.0/16

Question 8

What is the purpose of the Domain Name System? (DNS)

Answer 8

Maps addresses to names. Application layer protocol. If the IP address is not found in memory the application will query DNS servers. Non-root servers forward queries they cannot answer to a root name server. Root name server refers to an authoritative server.

Question 9

What is DHCP?

Answer 9

Assigns IP addresses to hosts. Can also return the address of the first-hop router for the client, the name and IP of a DNS server, and network mask. Expire after time to prevent waste of IP addressing.