Modules 11-13 IP Addressing

Question 1

How is the IPv4 address built up?

Answer 1

32 bits
A netowrk portion and a host portion

Question 2

What is a subnet mask used for? And what is prefix length?

Answer 2

To seperate net and host with an AND operator

Prefix length is the number of bits set to 1.

Question 3

Difference between public and private Ipv4 addresses?

Answer 3

Public IPv4 addresses are addresses which are globally routed between internet service provider (ISP) routers. These are special.

Private address blocks used by orgs for internal
hosts; can be re-used by different orgs and not
unique; not globally routable!

Question 4

What is network address translation (NAT)

Answer 4

Translating private IPv4 addresses to public IPv4 addresses

Typically, at the edge router with internet connectivity.

Question 5

What is a link local address? How do we write it?

Answer 5

Link-local addresses are known as Automatic Private IP addressing (APIPA) or self assigned addresses. They are used by a windows DHCP client to self-configure in the event that there are no DHCP servers available.

Ipv6 fe80::/10
Ipv4 169.254.0.0/16

Link Local FE80::/10
Communicate with other Ipv6 enabled devices on the same subnet.
Not routable

Question 6

Classful vs Classless IPv4 addressing

Answer 6

Classful addressing: Customers were allocated a network address based on one of three classes, A(BIG),B(MEDIUM), or C(SMALL). networks.

Classless addressing ignores the rules of A,B,C. Public Ipv4 netowork addresses (network addresses and subnet masks) are allocated based on the number of addresses that can be justified.

Question 7

How do we assign internet addresses around the world?Who?

Answer 7

The internet Assigned Numbers Authority (IANA) (PART OF ICANN) manages the allocation of IPv4 and IPv6 address blocks using five regional Internet Registries (RIRs)

RIRs allocate IPv4 addresses to Internet Service Providers(ISPs) which in turn assign them to smaller ISPs and orgs

Question 8

Why do we subnet? (Segmentation of networks)

Answer 8

a) Reduce overall net traffic
b)Implement security policies between nets
c) reduce number of devices affected by abnormal broadcast traffic (broadcast in smaller areas)

Question 9

What is Intranet and DMZ

Answer 9

Intranet - This is the internal part of a company’s network, accessible only within the organization. Devices in the intranet use private IPv4 addresses.

DMZ - This is part of the company’s network containing resources available to the internet such as a web server. Devices in the DMZ use public IPv4 addresses.

Question 10

How is Ipv6 built up? And what rules come with writing the addres?

Answer 10

128-bits address written in HEX with 8 hextetes
example:
x:x:x:x:x:x:x:x

Omit leading zeroes

Preferred 2001 : 0db8 : 0000 : 1111 : 0000 : 0000 : 0000 : 0200
No leading zeros 2001 : db8 : 0 : 1111 : 0 : 0 : 0 : 200

: double colon (::) can replace any single, contiguous string of one or more 16-bit
hextets consisting of all zeros; can only be used once within an address else ambigious!

Preferred 2001 : 0db8 : 0000 : 1111 : 0000 : 0000 : 0000 : 0200
Compressed 2001:db8:0:1111::200

Question 11

Which two unicast IPv6 addresses do we have?

Answer 11

Global Unicast Address (GUA): like a public IPv4 address; globally unique,
internet-routable addresses.

Link-local Address (LLA): required for every IPv6-enabled device and used to
communicate with other devices on the same local link.
LLAs are not
routable and are confined to a single link – e.g., for automatic address config
or net discovery

Question 12

Explain how Dynamic Addressing for Ipv6 GUAs work

Answer 12

First a host sends out a Router Solicidiation message (RS) to discover Ipv6 routers.
Then Router Advertisement(RA) messages are sent by the router to inform hosts on how to obtain an IPv6 Global Unicast Address (GUA) and provide:

Network prefix length
DGW address
DNS addresses and domain name

Question 13

Which three methods does the RA provide for configuring an Ipv6 GUA:How

Answer 13

SLAAC: Stateless, no central server allocating GUAs and keeping a list of devices and their addresses. With SLAAC the client device uses the information in the RA message to create its own GUA.

SLAAC with stateless DHCPv6 server:
SLAAC still creates its own IPv6 GUA, then uses the RA source IPv6 address (router link-local address) as default gateway and then uses a stateless DHCPv6 server to obtain DNS server address and a domain name.

Stateful DHCPv6 only (NO SLAAC) : Stateful DHCPv6 is similar to DHCP for IPv4. A device can automatically receive its addressing information including a GUA, prefix length, and the addresses of DNS servers from a stateful DHCPv6 server.

Question 14

Explain the process of SLAAC

Answer 14

First the router sends an RA message with the prefix for the local link, then the PC uses SLAAC to obtain a prefix from the RA message and creates its own interface ID.

Question 15

Explain the process of SLAAC and Stateless DHCpv6

Answer 15

First the PC sends an RS to all IPv6 routers “I need addressing information”

Secondly the router sends an RA message to all Ipv6 nodes (SLAAC and DHCPv6) specified, this will only give: prefix, prefix-length and default gateway information.

And at last the PC sends a DHCPv6 message to all DHCPv6 servers that says: it used SLAAC to create IPv6 address and default gateway, but it still needs to get the DNS information.

Question 16

Explain the method of Stateful DHCPv6

Answer 16

1. Send RS to all Ipv6 routers (I need addressing information)
2. The router then responds with an RA message to all Ipv6 nodes with (Stateful DHCPv6) specified that says: This is the default gateway, but ask a stateful DHCPv6 server for Ipv6 address and other addressing info.
3. The PC gets the message from the router and proceeds to send a DHPv6 Solicit message to all DHCPv6 servers where it says that is has received default gateway from the RA message, but it needs an Ipv6 address and all other addressing information from a stateful DHCPv6 server.

Question 17

What is Internet Control Message Protocol’s job? ICMP

Answer 17

To provide feedback about isses related to the processing of IP packets under certain conditions.

Question 18

What is ICMpv6 and ICMPv4, what is common between them? Which one is required and why?

Answer 18

ICMPv6 and ICMPv4 are the Interner Control Message Protocol for Ipv6 and Ipv4

Host reachability: ICMP Echo Request and ICMP Echo reply.

Destination or Service Unreachable: Used to notify the source that a destination/service is unreachable; includes a code indiciating why packet couldn’t be delivered

Time exceeded/ Hop field limit: When TTL field is decremented to 0, an ICMPv4 Time exceeded message is sent to the source. ICMpv6 uses Hop Limit Field

Ipv6 is required, Ipv4 is not required and often blocked for security reasons?

Question 19

What 4 protocols are new in ICMPv6

Answer 19

RS (Router Solicidation) and RA (Router advertisement) messages

NS (Neighour solicidation) and NA( Neighbour advertisement) messages

DAD Duplicate address detection

ND (Neighbour discovery)

Question 20

What does the RS and RA messages do?

Answer 20

They make it so we can send messages between Ipv6 router and Ipv6 device, including dynamic address allocation.

Question 21

What does the NS and NA messages do?

Answer 21

Messaging between Ipv6 devices, including duplicate address detection and address resolution with NS and NA messages.

Question 22

What is DAD? How does it work?

Answer 22

DAD: A device assigned a global IPv6 unicast or link-local unicast address, may perform duplicate address detection(DAD) to ensure that the IPv6 is unique

Send a Neighbour Solicidation (NS) message with its own Ipv6 address as the targeted IPv6 address

If another device on the network has this address, it will respons with a Neighbour Advertisement message (NA) notifying it to the sending device that the address is in use.

Question 23

What is ND (Neighbour Discovery)? How does it work?

Answer 23

ND: To determine the MAC address for the destination

The device sends an NS message to the solicited node address
This message will includ the known(targeted) IPv6 address. The device with target IPv6 address will respons with an NA message containing its Ethernet MAC address.

Question 24

What is ping? Which commands and outputs does it have?

Answer 24

Ping is an utility that uses ICMP Echo Request and Echo Reply messages to test connectivity and report min/av/max RTT.

Ping time-out indicates lack of connectivity, but first ping might sometimes timeout due to potentially time-consuming address.

Pinging loopback interface (127.0.0.1 or 1) to test internal config.

Ping DGW for checking network access

Ping remote host for internet connectivity or routing check (ICMP can be blocked)

Question 25

What is Traceroute? What can you use it for? How does it work?

Answer 25

Traceroute is a command that tests the path between two hosts and prived a list of reachable hops with RTT for each hop along the path and indicates if a hop fails to respons.
* indicates a lost or unreplied packet, info can be used to locate a problematic router along the path, or a router configured not to reply.

Traceroute uses Time To LIve, the first message will have field value of 1. This causes TTL to time out the IPv4 packet at the first router. This router responds with an ICMPv4 Time Exceeded message. Traceroute now has the address at the first hop.

Traceroute then increments the TTL field by 1 for each sequence of messages. This provides a trace with address of each hop. The TTL field will bu increased until destination is reached, or it is incremented to a predefined maximum, and the host will respond with either ICMP Port Unreachable message or an ICMP Echo Reply message.

TLDR

Traceroute starts at one router with TTL=1, it times out, router responds with time exceeded message, traceroute gets address of first hop, then TTL+=1 for each hop, gets address of each hop. TTL will be increased until destination or max increment is reached.

Question 26

What is broadcast?

Answer 26

Broadcast
transmission refers to a device sending a message to all the devices on a network in one-to-all communications.

Question 27

What is unicast?

Answer 27

Unicast
transmission refers to one device sending a message to one other device in one-to-one communications.

Question 28

What is a loopback address?

Answer 28

Any traffic that a computer program sends on the loopback network is addressed to the same computer. The most commonly used IP address on the loopback network is 127.0. 0.1 for IPv4 and ::1 for IPv6.

Question 29

What is a Global Unicast Address? How do we write it?

Answer 29

Global Unicast address (Globally unique and routable on Ipv6 internet) 2000::/3

Question 30

What is a unique local address? How do we write it?

Answer 30

Unique Local FC00::/7 - Fdff::/7
Not globally routed, used on devices that don’t need another network,

Question 31

What is multicast? How do we write it?

Answer 31

MULTICAST FF00::/8
Single IPv6 packet to multiple
destinations.

Question 32

What is anycast? How do we write it?

Answer 32

ANYCAST 2000::/3
any IPv6 unicast address that can be
assigned to multiple devices.

A packet sent to an anycast address is routed to the nearest device having that address.

Question 33

Which two types of Ipv6 Multicast addresses do we have?

Answer 33

Well known multicast addresses; Assigned and reserved for predefined groups of devices:

-ff02::1 All nodes multicast group: All Ipv6 enabled devices join.
-ff02::2 All routers multicast group: all Ipv6 routers join

Question 34

What are solicited node multicast addresses?

Answer 34

Almost the same as All nodes, except but it can filter the frame by examining the destination MAC address without sending it to the Ipv6 process to see if the device is the indended target of the Ipv6 packet.