ADV. COMP. NETWORK-22520….

- CHAPTER-1 -2 QUESTION BANK

Q. Sketch diagram of VPN configuration used in the software industry.

OR

Virtual private network (VPN): is an encrypted connection over the Internet from
a device to a network. The encrypted connection helps ensure that sensitive
data is safely transmitted. It prevents unauthorized people from
eavesdropping on the traffic and allows the user to conduct work remotely.
Use of a Wi-Fi network, one that is unsecured, means potential exposure of
personal information to third parties, some of which may have malicious
intentions
Mobile virtual private networks are used in settings where an endpoint of the
VPN is not fixed to a single IP address, but instead roams across various
networks such as data networks from cellular carriers or between multiple Wi-
Fi access points without dropping the secure VPN session or losing application
sessions.
 masks Internet protocol (IP) address,
 creates a private connection from a public wi-fi connection.
 one of the best tools for privacy and anonymity for a user connected to
any public internet service because it establishes secure and encrypted
connections.
Functioning of VPN:
 VPNs use virtual connections to create a private network,
 Keeps any device you connect to a public wi-fi safe from hackers and
malware,
  protecting sensitive information from unauthorized viewing or
interception. A VPN routes your device’s connection through a private
server rather than the ISP, so that when your data reaches the Internet,
it’s not viewable as coming from your device.
 A virtual network keeps your data private using encryption, which turns
your information into unreadable form only decipherable using a key,
which is known to only your device.
 Different VPNs use somewhat different encryption processes, but the
general process includes tunnelling and data is encoded as it travels
between client device and the server, which then decrypts the data and
sends it on to your destination,
 such as a website. The encryption process prevents anyone who may
intercept the data between you and the server, such as a government
agency or hacker, from being able to decipher its contents.
The following considerations should help guide selection of a VPN service /
Following features are needed in a well−designed VPN:
 Security
 Reliability
 Scalability
 Network Management
 Policy Management
Drawback: But in some cases, organizations may choose to installing a VPN
Blocker to prevent employees from accessing sites that may hinder their
productivity, such as social networking or shopping sites.
Use of Virtual Private Network (VPN):
Use of the Internet is now essential to global business, from shopping to
banking to medicine to entertainment. Using Internet services involves
transmitting very important information online, including credit card and
social security numbers, and personal information, such as medical histories
or home addresses.
VPNs keep your Internet use safe from different attacks, and, when used in a
corporate setting, help keep business information from getting into the wrong
hands.
 provide improved security overall, improved remote access,
 VPNs also provide safe and secure data sharing between employees
and with individuals and groups outside of the business when
necessary.
Q. List types of VPN and explain any one concept in short.
Most users encounter VPNs depending on their use as individual, personal, or
corporate.
1. Remote Access VPN
A remote access VPN enables the user to connect their device to a network
from outside their organization’s office. This device-to-network approach
typically involves a user connecting their laptop, smartphone, or tablet to a
network through their VPN.
Increasingly, advances in VPN technology enable security checks to be carried
out to ensure the device is secure before it is granted permission to connect.
Remote access VPNs include cloud VPNs, which enable users to securely
access applications and data via their web browser.
The limitations of remote access business VPN connections include increased
lag time depending on the user's distance from the central network. A user
may experience severe latency issues causing signal-quality degradation and
disruptions for intensive data transmissions, such as video conference calls.
Individual VPN
Individual VPNs refer to services meant for the personal use of individuals.
Basic remote access networks, for example, allow users to connect to a
secure remote server to access a private network. Reputable services include
encryption to ensure the individual’s security isn’t compromised.
2. Site-to-Site VPN / Business VPN
A site-to-site VPN enables connections between multiple networks. This
network-to- network approach is typically used to connect multiple offices or
branch locations to a central office. Site-to-site VPN encryption is useful for
organizations with several offices based in various geographical locations. It
enables them to share resources from a primary network, such as email
servers or data storage facilities, across multiple locations. It also allows
access to all users as if servers were located in the physical office.
Site-to-site enterprise VPN/ Business:
 improve transmission speeds and reduce latency with higher bandwidth
connection speeds and faster encryption.
 intended for use by businesses in protecting their users and devices.
 Remote access business VPN creates a temporary VPN connection that
encrypts data transmissions.
 After the data transmission stops, the business VPN disbands.
 provide multiple users in various locations with the ability to securely
access each other’s resources.
 Secure communication among business departments, including those in
different countries, is critical for corporate security, business continuity,
and employee productivity.
The greater use of cloud services and applications increases the cybersecurity
risk of relying solely on perimeter-based security protections. When using
cloud services, enterprises using a corporate VPN also rely on cloud network
security. Any unencrypted transmission or storage may cause a data breach.
Types of VPN protocols
· Two VPN types are based on different VPN security protocols.
· Each of these VPN protocols offer different features and levels of security,
1. Internet Protocol Security or IPSec:
· IPSec is used to secure Internet communication across an IP network.
· Secures Internet Protocol communication by authenticating the session and
· Encrypts each data packet during the connection.
· IPSec operates in two modes, Transport mode and Tunnelling mode, to
protect data transfer between two different networks.
· The transport mode encrypts the message in the data packet and
· the tunnelling mode encrypts the entire data packet.
· Also used with other security protocols to enhance the security system.
2. Layer 2 Tunnelling Protocol (L2TP):
· is a tunnelling protocol that is usually combined with another VPN security
protocol like IPSec to create a highly secure VPN connection.
· creates a tunnel between two L2TP connection points and
· IPSec protocol encrypts the data and handles secure communication between
the tunnel.
3. Point – to – Point Tunnelling Protocol (PPTP):
· Creates a tunnel and encapsulates the data packet.
· It uses a Point-to-Point Protocol (PPP) to encrypt the data between the
connection.
· is one of the most widely used VPN protocol and
· has been in use since the time of Windows 95. Apart from Windows, PPTP
is also supported on Mac and Linux.
4. Secure Sockets Layer (SSL) and Transport Layer Security (TLS):
SSL (Secure Sockets Layer) and TLS (Transport Layer
Security)
· Create a VPN connection where the web browser acts as the client and user
access is restricted to specific applications instead of entire network.
· is most commonly used by online shopping websites and service providers.
· Web browsers switch to SSL with ease and with almost no action required
from the user, since web browsers come integrated with SSL and TLS. SSL
connections have https in the beginning of the URL instead of http.
5. OpenVPN:
· is an open source VPN that is useful for creating Point-to-Point and Site-to-
Site connections.
· uses a custom security protocol based on SSL and TLS protocol.
6. Secure Shell (SSH):
· Secure Shell or SSH creates the VPN tunnel through which the data transfer
happens and also ensures that the tunnel is encrypted.
· SSH connections are created by a SSH client and data is transferred from a
local port on to the remote server through the encrypted tunnel.

Q. Draw detailed diagram of Mobile IP configuration showing different hosts

and agents.
 OR

Q. State phases of Mobile and explain any one in short.

The working of Mobile IP can be described in 3 phases:
Agent Discovery
In the Agent Discovery phase, the mobile nodes discover their Foreign and
Home Agents. The Home Agent and Foreign Agent advertise their services on
the network using the ICMP Router Discovery Protocol (IRDP).
Registration
The registration phase is responsible for informing the current location of the
home agent and foreign agent for the correct forwarding of packets.
Tunnelling
This phase is used to establish a virtual connection as a pipe for moving the
data packets between a tunnel entry and a tunnel endpoint.
Applications of Mobile IP
The mobile IP technology is used in many applications where the sudden
changes in network connectivity and IP address can cause problems. It was
designed to support seamless and continuous Internet connectivity.
It is used in many wired and wireless environments where users have to carry
their mobile devices across multiple LAN subnets.
Although Mobile IP is not required within cellular systems such as 3G, it is
often used in 3G systems to provide seamless IP mobility between different
packet data serving node (PDSN) domains.

OR
Process of Mobile IP:
The mobile IP process has following three main phases, which are:
1. Agent Discovery: During the agent discovery phase the HA and FA advertise
their services on the network by using the ICMP router discovery protocol
(IROP). Mobile IP defines two methods: agent advertisement and agent
solicitation which are in fact router discovery methods plus extensions. o
Agent advertisement: For the first method, FA and HA advertise their
presence periodically using special agent advertisement messages. These
messages advertisement can be seen as a beacon broadcast into the subnet.
For this advertisement internet control message protocol (ICMP) messages
according to RFC 1256, are used with some mobility extensions. o Agent
solicitation: If no agent advertisements are present or the inter arrival time is
too high, and an MN has not received a COA, the mobile node must send
agent solicitations. These solicitations are again bases on RFC 1256 for router
solicitations.
2. Registration The main purpose of the registration is to inform the home
agent of the current location for correct forwarding of packets. Registration
can be done in two ways depending on the location of the COA. o If the COA is
at the FA, the MN sends its registration request containing the COA to the FA
which is forwarding the request to the HA. The HA now set up a mobility
binding containing the mobile node's home IP address and the current COA.
Additionally, the mobility biding contains the lifetime of the
registration which is negotiated during the registration process. Registration
expires automatically after the lifetime and is deleted; so a mobile node
should register before expiration. After setting up the mobility binding, the HA
send a reply message back to the FA which forwards it to the MN. o If the COA
is co-located, registration can be very simpler. The mobile node may send the
request directly to the HA and vice versa. This by the way is also the
registration procedure for MNs returning to their home network.
3. Tunneling A tunnel is used to establish a virtual pipe for data packets
between a tunnel entry and a tunnel endpoint. Packets which are entering in
a tunnel are forwarded inside the tunnel and leave the tunnel unchanged.
Tunneling, i.e., sending a packet through a tunnel is achieved with the help of
encapsulation. Tunneling is also known as "port forwarding" is the
transmission and data intended for use only within a private, usually
corporate network through a public network.
State steps followed at Senders side for CHECK-SUM computation.
CHECKSUM
● The error detection method used by most TCP/IP protocols is called the
checksum.
● The checksum protects against the corruption that may occur during the
transmission of a packet. It is redundant information added to the packet.
● The checksum is calculated at the sender and the value obtained is sent
with the packet. The receiver repeats the same calculation on the whole
packet including the checksum. If the result is satisfactory (see below), the
packet is accepted; otherwise, it is rejected. Checksum Calculation at the
Sender
● At the sender, the packet header is divided into n-bit sections (n is usually
16).
● These sections are added together using one’s complement arithmetic
resulting in a
sum that is also n bits long. ● The sum is then complemented (all 0s changed
to 1s and all 1s to 0s) to produce the checksum.
To create the checksum the sender does the following:
 The packet is divided into k sections, each of n bits.
 All sections are added together using one’s complement arithmetic.
 The final result is complemented to make the checksum.
State steps followed at Receiver’s side for CHECK-SUM computation.
The packet is divided into k sections, each of n bits.
All sections are added together using one’s complement
arithmetic. The final result is complemented to make the
checksum.
Checksum Calculation at the Receiver
● The receiver divides the received packet into k sections and adds all
sections.
●It then complements the result. If the final result is 0, the packet is
accepted; otherwise, it is rejected.
Fig. shows what happens at the sender and the receiver.
●when the receiver adds all of the sections and complements the result, it
should get
zero if there is no error in the data during transmission or processing. ● This is
true because of the rules in one’s complement arithmetic. ● Assume that a
number called T when we add all the sections in the sender. When we
complement the number in one’s complement arithmetic, we get the
negative of the number. This means that if the sum of all sections is
T, the
checksum is −T.
The checksum
 How to compute a checksum?
 Put a 0 in the checksum field.
 Add each 16-bit value together.
 Add in any carry
 Inverse the bits and put that in the checksum field.
 To check the checksum:
 Add each 16-bit value together (including the checksum).
 Add in carry.
 Inverse the bits.
 The result must be 0.
 Remember, only the bits in the header are calculated in the IP checksum.

Example:
Consider the following IP header, with source IP address of 146.149.186.20
and destination address of 169.124.21.149. All values are given in hex:
45 00 00 6c
92 cc 00 00
38 06 00 00
92 95 ba 14
a9 7c 15 95

45 00 00 6c
92 cc 00 00
38 06 e4 04
92 95 ba 14
a9 7c 15 95
So, first add all 16-bit values So, we get: 5ce8 + 1 =
together, adding in the carry 5ce9.
each time: 5ce9
4500 +
+ a97c
006c ----
---- 10665 <---Again, we have a carry here!
456 So, remove the leftmost bit
c and add it back in. So, we get: 0665 +
+ 92cc 1 = 0666.
---- 0666
d83 +
8 1595
+ 0000
1bfb
d838 Now we have to inverse the
+ bits. 1bfb = 0001 1011
3806 1111 1011
---- inverse bits: 1110 0100 0000 0100 =
1103e <---But, we have a e404 So, the checksum is e404. So, the
carry here! So, remove IP header we send looks like:
the leftmost bit 45 00 00 6c
and add it back in. So, we get: 92 cc 00 00
103e + 1 = 103f. 38 06 e4 04
103f 92 95 ba 14
+ 0000 a9 7c 15 95
---- As an exercise, please act as the
103 receiver, compute the checksum on that
f packet, and make sure the result is 0!
+ 9295
----
a2d4
+ ba14

15ce8 <---Again, we have a

carry here! So, remove the
leftmost bit and add it back in.
Q. Describe the concept of fragmentation with proper data and assume MTU.
 OR

IP Fragmentation
●Note: the total_length field in the IP header is 16 bits. that means the max
size of of an IP datagram is 65535 bytes.
●BUT, the physical layer may not allow a packet size of that many bytes (for
example, a max ethernet packet is 1500 bytes)
●SO, IP must sometimes fragment packets.
●When an IP datagram is fragmented, each fragment is treated as a
separate datagram. o it is reassembled at the final destination, not at a
router!
o it does that because the router may have to fragment it again!
●Each fragment has its own header.
● The identification number is copied into each fragment.
● One bit in the "flags" field says "more fragments are coming. If that bit is
0, then it signifies this is the last fragment.
● The "fragment offset" field contains the offset of the data. o Fragment
flag of 0 and offset of 0 means the datagram is not fragmented.
o Fragment offset is measured in units of 8 bytes (64 bits). That is because the
fragment offset field is 3 bits shorter than the total length field (and 2^3 is 8).
● The entire flags field looks like this:

Example:
● Suppose we have a physical layer that can transmit a maximum of 660
bytes. And, suppose IP wants to send 1460 bytes of data. So, the IP datagram
is a total of 1480 bytes, including the 20 byte IP header:

●In that packet, "fragment flag" is 0, offset is 160. The offset is 160 because
(160 * 8) is 1280, so the offset of that data is 1280 byes into the packet.
● Note: all other fields of the IP header are identical to the first packet except
the checksum.
● IMPORTANT: The routers see 3 separate packets. The final destination
reassembles the packet before passing the packet to the upper layers.

Q. Describe Subnetting and supernetting concept in networking with proper

diagram and Net-id and Host-id
Subnetting
 is done by borrowing bits from the host part and add them the network
part
 IP addresses are designed with two levels of hierarchy.
 A network with two levels of hierarchy (not subnetted)
 A network with three levels of hierarchy (subnetted)

Fig. 1.14: Network Address without and with Subnet Mask

Fig. 1.15: Default Subnet without and with Subnet Mask

What is Supernetting?
 Supernetting is the opposite of subnetting
 In subnetting you borrow bits from the host part
 Supernetting is done by borrowing bits from the network side.
 And combine a group of networks into one large super-network.

Rules:
 The number of blocks must be a power of 2 (1, 2, 4, 8, 16, . . .).
 The blocks must be contiguous in the address space (no gaps between
the blocks).
  The third byte of the first address in the superblock must be evenly
divisible by the number of blocks.
 In other words, if the number of blocks is N, the third byte must be
divisible by N.

Q. Explain following types of OPTIONs for routing with proper diagram (any
OPTIONS:
TWO)
The header of the IP datagram is made of two parts:
 a fixed part- The fixed part is 20 bytes long and was discussed in the
previous section.
 a variable part-The variable part comprises the options, which can be a
maximum of 40 bytes.
Options,
 as the name implies, are not required for a datagram.
 They can be used for network testing and debugging.
 Although options are not a required part of the IP header, option
processing is required of the IP software.
 This means that all implementations must be able to handle options
if they are present in the header.
Format
The format of an option is composed of:
 A 1-byte type field,
 A 1-byte length field, and
 A variable-sized value field.
The three fields are often referred to as Type-Length-Value or TLV.

Fig.: Option format

Type
The type field is 8 bits long and contains three subfields: copy, class, and
number.
  Copy. This 1-bit subfield controls the presence of the option in
fragmentation When its value is 0, it means that the option must be
copied only to the first fragment. If its value is 1, it means the option
must be copied to all fragments.
 Class. This 2-bit subfield defines the general purpose of the option.
When its value is 00, it means that the option is used for datagram
control. When its value is 10, it means that the option is used for
debugging and management. The other two possible values (01 and 11)
have not yet been defined.
 Number. This 5-bit subfield defines the type of option. Although 5 bits
can define up to 32 different types, currently only 6 types are in use.
These will be discussed in a later section.
Length
The length field defines the total length of the option including the type field
and the length field itself. This field is not present in all of the option types.
Value
The value field contains the data that specific options require. Like the length
field, this field is also not present in all option types.
 Option Types
There are only six options are currently being used. Two of these are1-byte
options, and they do not require the length or the data fields. Four of them
are multiple-byte options; they require the length and the data fields.

Fig.: Categories of Options

Ano-operation optionis a 1-byte option used as a filler between options.
For example, it can be used to align the next option on a 16-bit or 32-bit
boundary.
 Fig. No-Operation Option

End-of-Option Option is also

 a 1-byte option used for padding at the end of the option field.
 It, however, can only be used as the last option.
 Only one end-of-option option can be used.
 After this option, the receiver looks for the payload data.
 This means that if more than 1 byte is needed to align the option field,
 some no-operation options must be used, followed by an end-of-option
option.

Fig. End of Option- option

Record-Route Option
 is used to record the Internet routers that handle the datagram.
 It can list up to nine router IP addresses since the maximum size of the
header is 60 bytes,
 which must include 20 bytes for the base header.
 This implies that only 40 bytes are leftover for the option part.
 The source creates placeholder fields in the option to be filled by the

visited routers.

Fig.: The format of the record route option: Both the code and length fields have
been described
  The pointer field is an offset integer field containing the byte number of
the first empty entry/ it points to the first available entry.
 The source creates empty fields for the IP addresses in the data field of
the option.
When the datagram leaves the source, all of the fields are empty.
 The pointer field has a value of 4, pointing to the first empty field.
 When the datagram is traveling, each router that processes the
datagram compares the value of the pointer with the value of the length.
 If the value of the pointer is greater than the value of the length, the option
is full and no changes are made.
 However, if the value of the pointer is not greater than the value of the
length, the router inserts its outgoing IP address in the next empty field
 (Remember that a router has more than one IPaddress).
In this the router adds the IP address of its interface from which the datagram is
leaving.
The router then increments the value of the pointer by 4.

Fig.: Record Route Concept:An entry as the datagram travels left to right from
router to router.
A strict-source-route option is
 Used by the source to predetermine a route for the datagram as it
travels through the Internet. Dictation of a route by the source can be
useful for several purposes.
 The sender can choose a route with a specific type of service, such as
minimum delay or maximum throughput. Alternatively, it may choose a
route that is safer or more reliable for the sender’s purpose. For example, a
sender can choose a route so that its datagram does not travel through
a competitor’s network.
 If a datagram specifies a strict source route, all of the routers defined in
the option must be visited by the datagram. A router must not be
visited if its IP address is not listed in the datagram.
 If the datagram visits a router that is not on the list, the datagram is
discarded and an error message is issued.
 If the datagram arrives at the destination and some of the entries were
not visited, it will also be discarded and an error message issued.
 Regular users of the Internet, however, are not usually aware of the
physical topology of the Internet. Consequently, strict source routing is
not the choice of most users.

Fig. Format of the strict source route option.

 It is similar to the record route option with the exception that all of the
IP addresses are entered by the sender.
 When the datagram is traveling, each router that processes the
datagram compares the value of the pointer with the value of the
length.
 If the value of the pointer is greater than the value of the length, the
datagram has visited all of the predefined routers.
 The datagram cannot travel anymore; it is discarded and an error
message is created.
 If the value of the pointer is not greater than the value of the length, the
router compares the destination IP address with its incoming IP address:
 If they are equal, it processes the datagram, swaps the IP address
pointed by the pointer with the destination address, increments the
pointer value by 4, and forwards the datagram.
 If they are not equal, it discards the datagram and issues an error
message. Figure 7.17 shows the actions taken by each router as a
datagram travels from source to destination.
Fig. Strict source route Concept

Q. Explain following Option

Loose-Source-Route types of OPTIONs for routing: i) Record route ii) Strict Route
iii)Loose source Route iv) Timestamp
A loose-source-route option is similar to the strict source route, but it
is more relaxed.
 Each router in the list must be visited, but the datagram can visit other
routers as well.

Fig. Format of the loose source route option.

Timestamp
 A timestamp option is used to record the time of datagram processing by
a route.
 The time is expressed in milliseconds from midnight, Universal Time.
Knowing the time a datagram is processed can help users and
managers track the behavior of the routers in the Internet.
 Estimate the time it takes for a datagram to go from one router to
another.
 Estimate because, although all routers may use Universal Time, their
local clocks may not be synchronized.
 Non-privileged users of the Internet are not usually aware of the
physical topology of the Internet. Consequently, a timestamp option is
not a choice for most users.
Fig. The format of the time-stamp option.
 Definitions of the code and length fields are the same as before.
 The overflow field records the number of routers that could not add their
timestamp because no more fields were available.
 The flags field specifies the visited router responsibilities.
 If the flag value is 0, each router adds only the timestamp in the provided
field.
 If the flag value is 1, each router must add its outgoing IP address
and the timestamp.
 If the value is 3, the IP addresses are given, and each router must check
the given IP address with its ownincoming IP address.
 If there is a match, the router overwrites the IP address with its outgoing
IP address and adds the timestamp (seeFigure7.20).

Fig. Use of Flag in time stamp

 .
Fig. Time-stamp concept- shows the actions taken by each router when a
datagram travels from source to destination. The figure assumes a flag value
of 1.

Q. Draw
IPv6 IPv6 address
Address representation
Representation of EUI-64 Auto-configuration
EUI 64-Autoconfiguration IPv6 useswith
thedetails of
extended
bit configurations
universal of (EUI)-64
identifier U and G. format to do stateless auto-configuration. This
format expands the 48- bit MAC address to 64 bits by inserting ―FFFE‖ into
the middle 16 bits. To make sure that the chosen address is from a unique
Ethernet MAC address, the universal/local (U/L bit) is set to 1 for global scope
(0 for local scope)

Stateless Auto-configuration:
 Stateless Address Configuration (IP Address, Default Router Address)
 Routers sends periodic Router Advertisement
 Node gets prefix information from the Router advertisement and
generates the complete address using its MAC address
 Global Address=Link Prefix + EUI 64 Address
 Router Address is the Default Gateway Stateless Autoconfiguration
Example
  MAC address: 00:0E:0C:31:C8:1F
 EUI 64 Address: 20E:0CFF:FE31:C81F
 Router Solicitation is sent on FF01::2 (All Router Multicast Address) and
 Advertisement sent on FF01::1 (All Node Multicast Address)

Q. Explain Auto-configuration and Re-numbering concepts used in IPv6 useful

AUTOCONFIGURATION:
in industry.
One of the interesting features of IPv6 addressing is the auto-
configuration of hosts.
 In IPv4, the host and routers are originally configured manually by the
network manager. Dynamic Host Configuration Protocol, DHCP, can be
used to allocate an IPv4 address to a host that joins the network.
 In IPv6, DHCP protocol can still be used to allocate an IPv6 address to a
host, but a host can also configure itself.
When a host in IPv6 joins a network, it can configure itself using the following
process:
1. The host first creates a link local address for itself. This is by taking the 10-
bit link Local prefix (1111 1110 10), adding 54 zeros, and adding the 64-bit
interface identifier, which any host knows how to generate it from its
interface card. The result is a 128-bit link local address.
2. The host then tests to see if this link local address is unique and not used by
other hosts. Since the 64-bit interface identifier is supposed to be unique,
the link local address generated is unique with a high probability. However,
to be sure, the host sends a neighbor solicitation message (see Chapter 28)
and waits for neighbor advertisement message. If any host in the subnet is
using this link local address, the process fails and the host cannot auto-
configure itself; it needs to use other means such as DHCP protocol for this
purpose.
3. If the uniqueness of the link local address is passed, the host stores this
address as its link-local address (for private communication), but it still
needs a global unicast address. The host then sends a router solicitation
message (see Chapter 28) to a local router. If there is a router running on
the network, the host receives a router advertisement message that
includes the global unicast prefix and the subnet prefix that the host needs
to add to its interface identifier to generate its global unicast address. If the
router cannot help the host with the configuration, it informs the host in the
router advertisement message (by setting a flag). The host then needs to
use other means for configuration.
Example: Assume a host with Ethernet address ( F5-A9-23-11-9B-E2) has
joined the network. What would be its global unicast address if the global
unicast prefix of the organization is 3A21:1216:2165 and the subnet identifier
is A245:1232.
Solution The host first creates its interface identifier as
F7A9:23FF:FE11:9BE2
using the Ethernet address read from its card. The host then creates its link-
local address as
FE80::F7A9:23FF:FE11:9BE2
Assuming that this address is unique, the host sends a router solicitation
message and receives the router advertisement message that announces the
combination of global unicast prefix and the subnet identifier as
3A21:1216:2165:A245:1232.
The host then appends its interface identifier to this prefix to find and store its
global unicast address as:
3A21:1216:2165:A245:1232:F7A9:23FF:FE11:9BE2
RENUMBERING:
 To allow sites to change the service provider, renumbering of the
address prefix ( ) was built into IPv6 addressing.
 Each site is given a prefix by the service provider to which it is
connected.
 If the site changes the provider, the address prefix needs to be changed.
 A router to which the site is connected can advertise a new prefix and
 let the site use the old prefix for a short time before disabling it.
 In other words, during the transition period, a site has two prefixes.
 The main problem in using the renumbering mechanism is the support
of the DNS, which needs to propagate the new addressing associated
with a domain name.
 A new protocol for DNS, called Next Generation DNS, is under study
to provide support for this mechanism.

Q. Compare IPv4 with IPv6 using any 8 points.

The following shows a quick comparison between the options used in IPv4 and
the options used in IPv6 (as extension headers).
 The no-operation and end-of-option options in IPv4 are replaced by Pad1
and PadN options in IPv6.
 The record route option is not implemented in IPv6 because it was not
used.
 The timestamp option is not implemented because it was not used.
 The source route option is called the source route extension header in
IPv6.
 The fragmentation fields in the base header section of IPv4 have
moved to the fragmentation extension header in IPv6.
 The authentication extension header is new in IPv6.
 The encrypted security payload extension header is new in IPv6.
 Q. List IPv6 Extension headers. Draw diagram of IPv6 packet structure and
explain
IPv6 any twoHeaders:
Extension in detail.Building Blocks of IPv6 Packets:

While the core IPv6 header is vital for packet routing and forwarding, it lacks
the flexibility to address a multitude of specific use cases and advanced
features. Extension headers step in to fill this gap by introducing additional
layers of information that can be included
within an IPv6 packet. Unlike the fixed structure of the main header,
extension headers are optional and can be added as needed, creating a
dynamic and adaptable packet structure.
Types of IPv6 Extension Headers:
IPv6 supports several types of extension headers, each serving a distinct
purpose and adding specific functionalities to the packet. Let’s explore the
common extension headers and their roles:
1. Hop-by-Hop Options Header:
The Hop-by-Hop Options Header (HbH) is examined by every router along the
packet’s path, ensuring that specific options are applied to the packet as it
traverses each hop. HbH options can include parameters related to network
management, quality of service (QoS), and packet handling. This header is
particularly useful for delivering specialized treatments to packets as they
move through the network.
2. Routing Header:
The Routing Header (RH) defines a list of intermediate destinations that the
packet must visit before reaching its final destination. This is useful for
scenarios where source routing is desirable or when packets need to be
routed through specific segments of the network. RH can facilitate efficient
traffic engineering and load balancing.
3. Fragment Header:
In situations where packets are larger than the maximum transmission unit
(MTU) of a network link, the Fragment Header ensures proper fragmentation
and reassembly. This header allows a packet to be split into smaller
fragments that can be transmitted across the network and then reassembled
at the destination.
4 and 5 Encapsulating Security Payload (ESP) and Authentication Header (AH)
AH and ESP extension headers cater to security needs. The Authentication
Header provides data integrity, authenticity, and replay protection, while the
Encapsulating Security Payload ensures confidentiality, data integrity, and
anti-replay protection through encryption
6. No Next Header: in the Next Header field indicates that there is no next
header whatsoever following this one, not even a header of an upper-layer
protocol. It means that, from the header's point of view, the IPv6 packet ends
right after it: the payload should be empty.
7. Destination Options Header:
The Destination Options Header (DOH) provides additional options that are
examined only by the final destination node. Similar to HbH options, DOH
options offer a way to convey specific requirements or treatments for the
packet’s destination.
8. Mobility extension header This has a new routing header type and a new
destination option, and it is used during the BU process. This header is used
by mobile nodes, correspondent nodes, and home agents in all messaging
related to the creation and management of bindings.
Q. Explain Dual stack implementation diagram in short
Three strategies have been devised by the IETF to help the transition shown in
fig:

Dual Stack It is recommended that all hosts, before migrating completely to

version 6, have a dual stack of protocols. In other words, a station must run
IPv4 and IPv6 simultaneously until all the Internet uses IPv6. The layout of a
dual-stack configuration is
:

 To determine which version to use when sending a packet to a

destination, the source host queries the DNS.
 If the DNS returns an IPv4 address, the source host sends an IPv4 packet.
 If the DNS returns an IPv6 address, the source host sends an IPv6 packet.

Q. State three transition strategies of IPv6

Three strategies have been devised by the IETF to help the transition shown in
fig:

Dual Stack It is recommended that all hosts, before migrating completely to

version 6, have a dual stack of protocols. In other words, a station must run
IPv4 and IPv6 simultaneously until all the Internet uses IPv6. The layout of a
dual-stack configuration is
:
  To determine which version to use when sending a packet to a
destination, the source host queries the DNS.
 If the DNS returns an IPv4 address, the source host sends an IPv4 packet.
 If the DNS returns an IPv6 address, the source host sends an IPv6 packet.
Tunnelling: Is a strategy used when two computers using IPv6 want to
communicate with each other and the packet must pass through a region that
uses IPv4. To pass through this region, the packet must have an IPv4 address.
So the IPv6 packet is encapsulated in an IPv4 packet when it enters the
region, and it leaves its capsule when it exits the region. It seems as if the
IPv6 packet passes goes through a tunnel at one end and emerges at the
other end. To make it clear that the IPv4 packet is carrying an IPv6 packet as
data, the protocol value is set to 41.

Header Translation is necessary when the majority of the Internet has moved
to IPv6 but some systems still use IPv4. The sender wants to use IPv6, but the
receiver does not understand IPv6. Tunnelling does not work in this situation
because the packet must be in the IPv4 format to be understood by the
receiver. In this case, the header format must be totally changed through
header translation. The header of the IPv6 packet is converted to an IPv4
header
Header translation uses the mapped address to translate an IPv6 address to
an IPv4 address. The following lists some rules used in transforming an IPv6
packet header to an IPv4 packet header.
 The IPv6 mapped address is changed to an IPv4 address by extracting
the rightmost 32 bits.
 The value of the IPv6 priority field is discarded.
 The type of service field in IPv4 is set to zero.
 The checksum for IPv4 is calculated and inserted in the corresponding
field.
 The IPv6 flow label is ignored.
 Compatible extension headers are converted to options and inserted
in the IPv4 header. Some may have to be dropped.
 The length of IPv4 header is calculated and inserted into the
corresponding field.
 The total length of the IPv4 packet is calculated and inserted in the
corresponding field.
Q. Explain Any two IPv6 address representations.
IPv6 Address Representation
Examples:
2031:0000:130F:0000:0000:09C0:876A:130B
2031:0:130f::9c0:876a:130B
FF01:0:0:0:0:0:0:1 >>> FF01::1 0:0:0:0:0:0:0:1 >>> ::1
0:0:0:0:0:0:0:0 >>> ::
Notations in 128 bit
 Dotted decimal 123.145.20.34
 hexadecimal notation. 23BA:1234:00B1:0000:BF30:3456:000A:FFFF
 Mixed representation 23BA:1234:123:56:BF30:3456:000A:FFFF
 CIDR notation. FDC1:AB23:0:FFFF/27

Q. Draw diagram of IPv6 header format and explain version and payload length.
IPv6 Packet Header Format
The IPv6 protocol defines a set of headers, including the basic IPv6 header
and the IPv6 extension headers. The following figure shows the fields that
appear in the IPv6 header and the order in which the fields appear. Figure 11-
3 IPv6 Basic Header Format
fig. IPv6 Packet Header Format
The following list describes the function of each header field.
 Version – 4-bit version number of Internet Protocol = 6.
 Traffic class – 8-bit traffic class field.
 Flow label – 20-bit field. designed to provide special handling for a
particular flow of data.
 Payload length – 16-bit unsigned integer, which is the rest of the packet
that follows the IPv6 header, in octets.
 Next header – 8-bit selector. Identifies the type of header that
immediately follows the IPv6 header. Uses the same values as the IPv4
protocol field.
 Hop limit – 8-bit unsigned integer. Decremented by one by each node
that forwards the packet. The packet is discarded if the hop limit is
decremented to zero.
 Source address – 128 bits. The address of the initial sender of the packet.
 Destination address – 128 bits. The address of the intended recipient of
the packet. The intended recipient is not necessarily the recipient if an
optional routing header is present.

Q. Explain
There any two
are three of of
types theaddresses
following in
terms:
IPV6:i) Unicast ii) Multicast iii) Anycast
iv) Broadcast
1. Unicast Addresses: Single computer as a destination, means packet
delivered to specific address. In IPV6 it is possible to assign unicast
addresses to the interfaces.
2. Anycast Addresses: Used to define group computers with addresses which
have the same prefix. It delivers the packets only one of the member of
the group which is closest or the most easily accessible. No special or
separate address block is assigned for any casting in IPV6. These are
assigned for blocks of unicast addresses.
3. Multicast addressing: Defines group of computers which may or may not
share the same prefix and may not connected to the same physical
network. Packet sent by this is meant to be delivered to each of the group.
There is a broadcast address as multicast performs the same function.
Type of address is determined by leading bits.
OR
1. Unicast Address is for a single interface. o IPv6 has several types (for
2. Anycast Addresses: example, global and IPv4 mapped).
OR
2. Anycast o One-to-nearest (allocated from unicast address space).
 Multiple devices share the same address.
 All anycast nodes should provide uniform service.
 Source devices send packets to anycast address.
 Routers decide on the closest device to reach that destination.
 Suitable for load balancing and content delivery services.
3. Multicast
 One-to-many o Enables more efficient use of the network
 Uses a larger address range
Q. Explain in short Router solicitation and Router advertisement using diagram.

There are two main types of ICMPv6 Messages related with Router Discovery
(RD) in IPv6.
One is Router Solicitation (RS) Message and the other is Router Advertisement
(RA) Message. Router Solicitation (RS) Messages are sent by the hosts on the
network to find routers on an IPv6 network.
Router Advertisement (RA) Messages are sent by routers to hosts to inform
about the Default Gateway IPv6 address and other router related parameters.
IPv6 network hosts can learn about the presence of routers in the network,
upon receiving Router Advertisement (RA) Messages from the routers.
Following table explains about Router Solicitation (RS) Message in detail.

Type of Send Send Type of Destination Description

ICMPv6 by to communication IPv6
Message address

Router IPv6 All Multicast FF02::2 Router

Solicitatio capabl IPv6 (all- Solicitation (RS)
n e routing routers Messages are
device capabl Multica sent by IPv6
s e st capable devices
(excep device address to identify
t s in ) IPv6
router capable routers
s) the on the network.
networ The purpose is
k to get the

Default
Gateway
address and
other network
related
parameters
from the IPv6
routers in the
network.
The format for Router Solicitation (RS) Message is defined in RFC 4861. The
format for a Router Solicitation (RS) Message is based on a normal ICMPv6
message format.
Following image shows the format for Router Solicitation (RS) Message.

Router Solicitation (RS) Message fields are explained in below table.

Field Size Description Value

Type 8 bits Type field value denots the type of 133

the ICMPv6 message. Type field
value for a Router Solicitation (RS)
is 133.
Code 8 bits Code field provides further 0
classification of this ICMPv6
message. Code field value is 0 for
a Router Solicitation (RS)
Message.
Checksu 16 bits Checksum value
m

Reserved 32 bits Reserved field Currently 0

Options Variabl Contains optional values. Contains

e optional
values.

For example;
Source link-
layer address.
Exploring Router Advertisement (RA) Message
Following table explains about Router Advertisement (RA) Message in detail.
Two types of Router Advertisement (RA) Messages are Solicited Router
Advertisement Message and Unsolicited Router Advertisement Message.
Exploring Router Advertisement (RA) Message
Following table explains about Router Advertisement (RA) Message in detail.
Two types of Router Advertisement (RA) Messages are Solicited Router
Advertisement Message and Unsolicited Router Advertisement Message.

Type of Send Send to Type of Destinatio Description

ICMPv6 by communicatio n IPv6
Message n address

Solicited Route As reply Multicast FF02::1 Solicited

Router rs for a (all- Router
Advertisem Router nodes Advertisem
en t Solicitatio Multica en t
Messages n (RS) st
Message address (RA)
) Messages
are sent
by
a
router as
a
response,
when an
IPv6 device
sends a

Router
Solicitation
(RS)
Message to
routers,
to
obtain
Default
Gateway
IPv6
address
and
other

router
related
parameters.
Unsolicited Route To all Multicast FF02::1 Unsolicited
Router rs IPv6 (all- Router
Advertisem hosts nodes Advertisem
en t periodical Multica en t
Messages ly st
address (RA)
) Messages
and
send
 periodically
to all

network
devices
to
advertise
the
presence
of
routers.

The format for Router Advertisement (RA) Message is defined in RFC 4861.
The format for a Router Advertisement (RA) Message is different than a
normal ICMPv6 message format.
Router Advertisement (RA) Message fields are explained in below table.

Field Size Description Value

Type 8 bits Type field value denotes the type of the 133
ICMPv6 message. Type field value for a
Router Advertisement (RA) Message is
134.
Code 8 bits Code field provides further classification 0
of this ICMPv6 message. Code field value
is 0 for a Router Advertisement (RA)
Message.
Checksum 16 bits Checksum value 0

Cur Hop 8 bits The default value that the router

Limit recommending to devices, that should be
placed in the Hop Count field of the IPv6
header for outgoing IPv6 packets. If 0, the
router is not recommending a Hop Limit
value in this Router Advertisement.
M 1 bit "Managed address configuration" flag 0 or 1

O 1 bit "Other configuration" flag 0 or 1

Field Size Description Value

Reserved 6 bits Reserved and currently unused 0

Router 16 bit A Lifetime value of 0 is used to indicate

Lifetim that the router is not a default router and
e should not appear on the default router
list.
Reachabl 32 bits The time in milliseconds that a node
e Time assumes a neighbour is reachable after
having received a reachability
confirmation. If this field has a value of 0,
the reachable time is unspecified by the
router.
Re- 32 bits The time in milliseconds, between
transmissi retransmitted Neighbour Solicitation
on Timer Messages. if this field has a value of 0,
The Re-transmission time is unspecified
by the router.
Options variabl Message body contains options like
e Source link- layer address, MTU, Prefix
Information.