Network layer (osi 3)

Question 1

Basic function of layer 3

Answer 1

• routing (path selection for packets across network)

- internetworking

Question 2

InternetProtocol

Answer 2

IP and ICMP

Best effort, connectionless packet delivery

IP header:
Version, Header length, ToS, tot. Length, identification, flags, fragment offset, time to live, upper layer protocol, checksum, addresses, options

Question 3

IP fragmentation

Answer 3

Each packet data set has same ID,

Fragment offset gives location in the original frame payload in units of octets

Question 4

IP address

Answer 4

32 bit (ipv4)
two parts: netID and hostID

Many classes: format for types of IP address used for networks

Reserved IP addresses:

broadcast: hostID all 1 (netID all 1 in local network)
intranetwork: netID all 0

0. 0.0.0 this host on bootup
1. 0.0.1 this host (loopback)

Question 5

Subnetting

Answer 5

To split one network into multiple smaller network Subnetting is used:

In a subnet: all IP addresses have a part that is same, starting from the leftmost bit

To determine the subnet: subnetmask: 1111…1|00…0 with /n zeros

Find subnet IP by AND operation with subnetmask

Question 6

DHCP

Answer 6

Dynamic Host Configuration Protocol

Builds on BOOTP to allow server to deliver IP configuration to host
-serves to utilize the IP range more effectively by making IP address dynamic(temporary)

Question 7

CIDR

Answer 7

Classless Inter Domain Routing

Subnet portion of arbitrary length, not like in class-based addresses

a.b.c.d/length

Used to reduce size explosion of routing tables

Question 8

NAT

Answer 8

Network Address Translation

Local network uses one IP address to communicate with outside networks

Edge Routers uses TCP or UDP ports to map outgoing traffic from the intranet to outernet;
ISP can provide a LAN with only 1 address and therefore slowlier exhaust the max amount of administerable addresses;

Question 9

IP transition ipv4 to ipv6

Answer 9

Tunneling: ipv6 carried as payload in ipv4 payload among routers
Dual stack: some routers can do both and function as translators

Question 10

Routing

Answer 10

• connectivity by finding path for packets to travel along from host to host
• performance metric: efficient routes with low prop. delay, losses etc.
• traffic engineering: balance traffic by choosing links based on combined efficiency

Types:
Centralized global state: one entity calculates routes
Distributed global state: multiple entities know entire network, calculate routes
Distributed global computation: every router knows neighbors, participates in global computation effort

Question 11

Forwarding and routing

Answer 11

Forwarding: packet directed to outgoing node based on made calculations
Routing: routers communicating to find optimal forwarding process