IPv6 Explained: Address Format, Header, Features & IPv4 vs IPv6

COMPUTER NETWORKS • CHAPTER 28

IPv6 Explained: Address Format, Header, Features & IPv4 vs IPv6

IPv4 gave us billions of addresses, but the Internet kept growing.

Phones, laptops, smart TVs, cloud servers, sensors, vehicles and thousands of other devices all need network addresses.

IPv6 was designed to provide a much larger address space and a cleaner Internet Protocol header while keeping the basic idea of packet delivery across networks.

128-bit Address 8 Hextets 40-byte Base Header No Broadcast Extension Headers Source Fragmentation

Direct Answer

IPv6 means Internet Protocol version 6. It uses 128-bit addresses, normally written as eight hexadecimal groups separated by colons.

IPv6 has a fixed 40-byte base header containing Version, Traffic Class, Flow Label, Payload Length, Next Header, Hop Limit, Source Address and Destination Address.

Compared with IPv4, IPv6 provides a much larger address space, a simpler fixed base header, extension headers, no broadcast addressing and different fragmentation behaviour.

Complete IPv6 Study Map

1. What Is IPv6?
2. Why IPv6 Was Needed
3. IPv6 Address Format
4. Hexadecimal in IPv6
5. What Is a Hextet?
6. IPv6 Address Shortening
7. Leading Zero Rule
8. Double Colon Rule
9. Expand an IPv6 Address
10. IPv6 Prefix Length
11. IPv6 Address Types
12. Global Unicast
13. Link-Local
14. Unique Local
15. Multicast
16. Anycast
17. Special IPv6 Addresses
18. IPv6 Header Format
19. Version
20. Traffic Class
21. Flow Label
22. Payload Length
23. Next Header
24. Hop Limit
25. Source & Destination Address
26. Extension Headers
27. Why No Header Checksum?
28. IPv6 Fragmentation
29. Neighbor Discovery
30. SLAAC
31. DHCPv6
32. Features of IPv6
33. IPv4 vs IPv6
34. IPv4–IPv6 Coexistence
35. Solved Examples
36. Remember Tricks
37. Common Mistakes
38. 40 Questions With Answers
39. 20 MCQs With Answers
40. FAQs

What Is IPv6?

IPv6 stands for:

Internet Protocol Version 6

It is a Network Layer protocol used for logical addressing and packet delivery across interconnected networks.

IPv6 performs the same basic Internet Layer job that IPv4 performs, but it uses a much larger address space and a redesigned header.

Simple Definition: IPv6 is the newer Internet Protocol that uses 128-bit addresses to identify network interfaces and deliver packets across networks.

Why Was IPv6 Needed?

IPv4 addresses are 32 bits long.

That gives:

IPv4 Address Space = 2^32

≈ 4.29 billion possible addresses

That sounds huge, but the Internet became far larger than early designers expected.

IPv6 uses:

IPv6 Address Space = 2^128

This is an enormously larger address space.

More Devices Phones, servers, sensors, cloud systems and embedded devices all need addresses.

Address Scalability 128-bit addressing gives IPv6 a huge address space.

Cleaner Header IPv6 redesigns the base header and moves optional information to extension headers.

Better Hierarchy Prefix-based addressing supports structured routing and allocation.

Modern Features IPv6 supports concepts such as Flow Label, Neighbor Discovery and SLAAC.

Long-Term Internet Growth IPv6 provides address space for continued network expansion.

IPv6 Address Format

An IPv6 address contains:

128 bits

The address is normally written as eight groups of hexadecimal digits.

Each group contains 16 bits.

Pictorial IPv6 Address

2001 16 bits

:

0db8 16 bits

:

0000 16 bits

:

0000 16 bits

:

0000 16 bits

:

ff00 16 bits

:

0042 16 bits

:

8329 16 bits

IPv6 Size Trick: 8 groups × 16 bits = 128 bits

Hexadecimal in IPv6

IPv6 uses hexadecimal because writing 128 binary bits would be very difficult to read.

Hexadecimal uses:

0
0

1
1

2
2

3
3

4
4

5
5

6
6

7
7

8
8

9
9

A
10

B
11

C
12

D
13

E
14

F
15

Why One Hex Digit Represents 4 Bits

Binary: 1111

Hex: F

Remember: 1 hexadecimal digit = 4 bits
4 hexadecimal digits = 16 bits = 1 hextet

What Is a Hextet?

One group of four hexadecimal digits in an IPv6 address is commonly called a hextet.

Example:

2001 : db8 : 0 : 1 : 0 : 0 : 42 : 1

Each group can represent 16 bits.

IPv6 Address Shortening Rules

IPv6 addresses can look very long.

Two major rules make them easier to write:

1. Remove leading zeros inside a hextet.
2. Replace one consecutive run of all-zero hextets with ::.

Rule 1: Remove Leading Zeros

Consider:

FULL

2001:0db8:0000:0001:0000:0000:0042:8329

REMOVE LEADING ZEROS

2001:db8:0:1:0:0:42:8329

Leading zeros may be removed. Zeros at the end of a hextet cannot simply be removed. For example, 1200 cannot become 12.

Rule 2: Double Colon Compression

A consecutive sequence of zero hextets can be replaced by:

::

ORIGINAL

2001:db8:0:0:0:0:42:8329

COMPRESSED

2001:db8::42:8329

Very Important: The double-colon abbreviation can normally appear only once in a valid textual IPv6 address because otherwise it would be ambiguous how many zero groups each :: represents.

How to Expand a Short IPv6 Address

Example:

2001:db8::5

Count the visible hextets:

Visible groups = 2001, db8, 5

Visible groups = 3

Total groups required = 8

Missing zero groups = 8 - 3 = 5

Expanded address:

2001:0db8:0000:0000:0000:0000:0000:0005

IPv6 Prefix Length

IPv6 uses CIDR-style prefix notation just like modern IPv4 routing.

Example:

2001:db8:1234:5678::/64

The /64 means the first 64 bits form the network prefix.

Typical /64 IPv6 Split

First 64 Bits Network Prefix

Last 64 Bits Interface Identifier Portion

/64 Trick: 128 total bits − 64 prefix bits = 64 remaining bits

Main IPv6 Address Types

IPv6 does not use broadcast addressing in the same way IPv4 does.

Important IPv6 address types include:

Unicast Identifies one interface. A packet is delivered to that interface.

Multicast Identifies a group of interfaces. A packet can be delivered to group members.

Anycast The same address is assigned to multiple interfaces, and routing normally delivers the packet to one suitable or nearest instance according to routing.

Remember: IPv6 = Unicast + Multicast + Anycast

No traditional broadcast address.

Global Unicast Address

Global unicast addresses are used for globally routable IPv6 communication.

A commonly discussed global unicast allocation range begins within:

2000::/3

Example documentation prefix:

2001:db8::/32

2001:db8::/32 is reserved for documentation and examples. It should not be treated as an ordinary globally assigned production prefix.

Link-Local IPv6 Address

Link-local addresses are used for communication on the local network link.

They use:

fe80::/10

IPv6 interfaces normally have link-local addressing that can be used for operations such as Neighbor Discovery.

Link-Local Trick: FE80 → Think “local link”.

Unique Local IPv6 Addresses

Unique Local Addresses are intended for local/private-style IPv6 communication rather than global Internet routing.

Their address block is:

fc00::/7

IPv6 Multicast Address

IPv6 multicast addresses begin with:

ff00::/8

Multicast replaces several functions for which IPv4 networks might previously have used broadcast.

IPv6 Anycast

An anycast address may be assigned to more than one interface.

Routing delivers the packet to one member of the anycast set, normally based on routing topology.

Anycast Trick: Same address at many places → packet reaches one suitable location.

Important Special IPv6 Addresses

:: Unspecified Address
Represents the absence of a specified IPv6 address in certain contexts.

::1 Loopback Address
IPv6 equivalent concept of local loopback testing.

fe80::/10 Link-Local
Local-link communication.

fc00::/7 Unique Local
Local/private-style addressing.

ff00::/8 Multicast
Multicast address space.

2001:db8::/32 Documentation
Used in examples and documentation.

IPv6 Header Format

The IPv6 base header has a fixed size:

40 bytes

Unlike IPv4, optional features are usually moved into separate extension headers rather than making the base header variable in size.

Pictorial IPv6 Base Header — 40 Bytes

Version 4 bits

Traffic Class 8 bits

Flow Label 20 bits

Payload Length 16 bits

Next Header 8 bits

Hop Limit 8 bits

Source IPv6 Address 128 bits

Destination IPv6 Address 128 bits

IPv6 Header Memory: Version → Traffic → Flow → Payload → Next → Hop → Source → Destination

Version

Identifies Internet Protocol version 6.

Traffic Class

Used for traffic treatment and congestion-related marking.

Flow Label

Can identify packets belonging to a particular flow.

Payload Length

Gives the length of data following the 40-byte base header.

Next Header

Identifies the next extension header or upper-layer protocol.

Hop Limit

Limits how many router hops a packet can cross.

1. Version Field

The Version field is 4 bits long.

For IPv6:

Version = 6

2. Traffic Class

Traffic Class is an 8-bit field.

It supports packet classification and congestion-related treatment.

Its role is conceptually similar to modern DSCP and ECN use in IPv4.

3. Flow Label

The Flow Label field contains:

20 bits

It can identify packets belonging to the same flow so network devices can recognise related traffic.

Flow Label Trick: Same communication flow → same flow identity can be indicated.

4. Payload Length

Payload Length is 16 bits.

It normally gives the number of bytes after the fixed 40-byte IPv6 base header.

Do not treat IPv6 Payload Length exactly like IPv4 Total Length. IPv4 Total Length includes the IPv4 header, while the normal IPv6 Payload Length describes data following the 40-byte base header.

5. Next Header

The Next Header field is 8 bits long.

It tells what comes immediately after the IPv6 base header.

That may be:

• An IPv6 extension header
• TCP
• UDP
• ICMPv6

Next Header = “What comes next?”

6. Hop Limit

Hop Limit performs the job similar to IPv4 TTL.

Each router decreases it.

Source
Hop Limit = 64

Router 1
Hop Limit = 63

Router 2
Hop Limit = 62

When Hop Limit reaches zero, the packet is discarded.

IPv4: TTL
IPv6: Hop Limit

7. Source and Destination IPv6 Addresses

Both fields contain:

128 bits each

The source field identifies the packet's source address, while the destination field identifies where the packet should be delivered.

IPv6 Extension Headers

One of the major design changes in IPv6 is that optional information does not have to make the base header variable in the same way as IPv4 options.

IPv6 can place extra information into separate extension headers.

IPv6 Base Header
40 Bytes

Extension Header
Optional

TCP / UDP / ICMPv6
Payload

Examples of IPv6 Extension Headers

• Hop-by-Hop Options
• Routing Header
• Fragment Header
• Destination Options
• Authentication Header

Remember: IPv6 Base Header = Fixed
Extra Information = Extension Headers

Why Does IPv6 Have No Header Checksum?

IPv4 contains a Header Checksum.

IPv6 removes this field from the base header.

Removing it reduces per-hop header-processing work because routers do not need to recalculate an IPv6 header checksum every time a hop-related field changes.

Important Difference: IPv4 base header → Header Checksum exists.

IPv6 base header → No header checksum field.

IPv6 Fragmentation

IPv6 handles fragmentation differently from IPv4.

IPv6 routers do not fragment transit packets.

If fragmentation is required, the source can use the IPv6 Fragment extension header.

IPv6 Source
Packet must fit the path

Fragment 1 Source-created fragment

Fragment 2 Source-created fragment

Destination Reassembles fragments

Fragmentation Trick: IPv4 router may fragment.
IPv6 router does not fragment.
IPv6 source handles fragmentation when needed.

IPv6 Neighbor Discovery

IPv6 uses Neighbor Discovery Protocol functions through ICMPv6.

Neighbor Discovery helps with tasks such as:

• Discovering neighboring nodes
• Resolving local-link addresses
• Finding routers
• Learning network prefixes
• Detecting certain reachability information

IPv6 Host
Needs Neighbor Information

ICMPv6 Neighbor Discovery

Neighbor / Router Information Learned

IPv6 does not use IPv4 ARP for address resolution. Neighbor Discovery provides the corresponding IPv6 functions.

SLAAC — Stateless Address Autoconfiguration

SLAAC allows an IPv6 host to configure addressing information using information advertised by IPv6 routers.

Step 1 Host has local IPv6 capability and link-local communication.

Step 2 Router advertisements provide prefix and configuration information.

Step 3 Host can form an IPv6 address according to the advertised configuration.

SLAAC Trick: Router advertises → Host configures itself.

DHCPv6

DHCPv6 is the IPv6 version of Dynamic Host Configuration Protocol.

It can provide IPv6 hosts with configuration information and, depending on the network design, addresses or other parameters.

IPv6 networks can use SLAAC, DHCPv6 or combinations of configuration mechanisms depending on requirements.

Main Features of IPv6

128-Bit Addressing Provides an extremely large address space.

Fixed 40-Byte Base Header Base header size does not vary like the normal IPv4 header.

Extension Headers Optional functions can be carried separately.

No Traditional Broadcast IPv6 uses multicast and other mechanisms instead.

Flow Label Supports identification of packet flows.

Neighbor Discovery Uses ICMPv6 rather than IPv4 ARP.

SLAAC Supports stateless address autoconfiguration.

Source Fragmentation Transit routers do not fragment IPv6 packets.

Hierarchical Prefixing Supports structured address allocation and routing.

IPv4 vs IPv6 Difference

Point	IPv4	IPv6
Address Size	32 bits	128 bits
Address Writing	Dotted decimal	Colon-separated hexadecimal
Example	192.168.1.10	2001:db8::10
Base Header Size	Minimum 20 bytes, variable with options	Fixed 40 bytes
Header Checksum	Present	Not present in base header
TTL Equivalent	TTL	Hop Limit
Protocol Field Equivalent	Protocol	Next Header
Router Fragmentation	Can occur when required and allowed	Transit routers do not fragment
Address Resolution	ARP in IPv4 local networks	Neighbor Discovery using ICMPv6
Broadcast	Supported	No traditional broadcast addressing
Multicast	Supported	Supported and used extensively
Anycast	Can be implemented through routing practices	Defined as part of IPv6 addressing architecture
Autoconfiguration	Commonly uses DHCP or manual configuration	Supports SLAAC and DHCPv6
Options	Can exist inside IPv4 header	Mostly handled through extension headers
Address Exhaustion Pressure	Severe due to 32-bit space	Massively expanded 128-bit space

Fast Comparison: IPv4 = 32 bit + dotted decimal + TTL + checksum

IPv6 = 128 bit + hexadecimal + Hop Limit + no base-header checksum

IPv4 and IPv6 Coexistence

The Internet cannot replace every IPv4 system at one moment.

Therefore IPv4 and IPv6 can coexist using transition approaches.

Dual Stack A host or router supports both IPv4 and IPv6.

Tunneling One protocol can be carried across a network using another protocol in certain transition designs.

Translation Translation mechanisms can help communication between IPv4-only and IPv6-only environments.

Solved IPv6 Examples

Example 1: Number of Bits

How many bits are present in:

2001:db8:1:2:3:4:5:6

IPv6 always contains:

8 hextets × 16 bits

= 128 bits

Answer = 128 bits

Example 2: Expand 2001:db8::25

Visible hextets = 2001, db8, 25

Visible groups = 3

Required groups = 8

Missing groups = 5

Expanded:

2001:0db8:0000:0000:0000:0000:0000:0025

Example 3: Compress an IPv6 Address

Given:

2001:0db8:0000:0000:0000:0000:0000:0042

Remove leading zeros:

2001:db8:0:0:0:0:0:42

Compress the zero run:

2001:db8::42

Example 4: /64 Address Count

A /64 prefix leaves:

128 - 64 = 64 bits

Number of possible values in those remaining 64 bits:

2^64

Answer = 2^64 possible interface-identifier values within the /64 prefix space.

Example 5: /48 to /64 Subnets

Suppose an organisation has:

2001:db8:abcd::/48

If /64 subnets are created:

Subnet Bits = 64 - 48

= 16 bits

Number of /64 Subnets = 2^16

= 65,536

Answer = 65,536 /64 subnets

Example 6: Hop Limit

An IPv6 packet begins with:

Hop Limit = 20

Routers Crossed = 6

Remaining Hop Limit = 20 - 6

= 14

Answer = 14

Example 7: IPv6 Packet Size

Suppose:

IPv6 Base Header = 40 bytes

Payload Length = 1200 bytes

Ignoring special jumbogram cases:

Total Packet Size = 40 + 1200

= 1240 bytes

Answer = 1240 bytes

IPv6 Remember Tricks

Address: IPv6 = 128 bits = 8 hextets

Writing: IPv4 uses dots.
IPv6 uses colons.

Shortening: Remove leading zeros.
Use :: for one zero sequence.

Header: Fixed 40-byte base header.

Hop: IPv4 = TTL
IPv6 = Hop Limit

Resolution: IPv4 = ARP
IPv6 = Neighbor Discovery

Fragmentation: IPv4 router may fragment.
IPv6 router does not.

Address Types: Unicast + Multicast + Anycast
No traditional broadcast.

Common IPv6 Exam Mistakes

1. IPv6 is 64 bits.

Wrong. IPv6 addresses are 128 bits.

2. IPv6 is written using four decimal octets.

Wrong. That is IPv4 notation. IPv6 normally uses hexadecimal groups separated by colons.

3. One IPv6 hextet contains 8 bits.

Wrong. One hextet contains 16 bits.

4. :: can be used many times inside one IPv6 address.

Wrong. Double-colon compression normally appears only once in one textual address.

5. IPv6 has a variable base header from 20 to 60 bytes.

Wrong. That describes IPv4 header length. The IPv6 base header is fixed at 40 bytes.

6. IPv6 has an IPv4-style header checksum.

Wrong. The IPv6 base header does not contain a header checksum field.

7. IPv6 routers fragment large transit packets.

Wrong. IPv6 transit routers do not perform fragmentation.

8. IPv6 uses ARP exactly like IPv4.

Wrong. IPv6 uses Neighbor Discovery functions through ICMPv6.

9. IPv6 uses broadcast addresses.

IPv6 does not use traditional broadcast addressing.

10. Hop Limit increases at each router.

Wrong. Routers decrease Hop Limit.

11. 2001:db8::/32 is an ordinary production prefix.

Wrong. It is reserved for documentation and examples.

12. IPv6 completely removed NAT by protocol requirement.

IPv6's huge address space reduces the address-conservation pressure that drove widespread IPv4 NAT, but that does not mean translation mechanisms or policy-based address translation can never exist.

40 Important IPv6 Questions With Answers

1. What is IPv6?

IPv6 is Internet Protocol version 6, a Network Layer protocol using 128-bit logical addresses for communication across IP networks.

2. What is the size of an IPv6 address?

128 bits.

3. How many groups are normally written in a full IPv6 address?

Eight hexadecimal groups.

4. How many bits are in one IPv6 hextet?

16 bits.

5. How many hexadecimal digits are normally in one full hextet?

Four hexadecimal digits.

6. Why is hexadecimal used in IPv6?

Hexadecimal makes 128-bit addresses much shorter and easier to read than writing all 128 binary bits.

7. What is the first IPv6 shortening rule?

Leading zeros inside each hextet may be removed.

8. What does :: mean in an IPv6 address?

It represents one or more consecutive all-zero hextets that have been compressed.

9. Can :: normally appear twice in the same IPv6 textual address?

No, because using it more than once would make expansion ambiguous.

10. Expand 2001:db8::1.

2001:0db8:0000:0000:0000:0000:0000:0001.

11. What does /64 mean in IPv6?

It means the first 64 bits form the network prefix.

12. Name the three important IPv6 address delivery types.

Unicast, multicast and anycast.

13. Does IPv6 use traditional broadcast addresses?

No. IPv6 does not use traditional broadcast addressing.

14. What is a global unicast address?

It is an IPv6 unicast address intended for globally routed communication.

15. What is the common IPv6 link-local prefix?

fe80::/10.

16. What is the IPv6 loopback address?

::1.

17. What is the IPv6 unspecified address?

::.

18. Which prefix represents IPv6 multicast addresses?

ff00::/8.

19. Which block is used for IPv6 Unique Local Addresses?

fc00::/7.

20. What is the size of the IPv6 base header?

40 bytes.

21. What value is present in the Version field?

6.

22. What is the size of the Traffic Class field?

8 bits.

23. What is the size of the Flow Label field?

20 bits.

24. What does Payload Length represent?

It normally specifies the number of bytes following the fixed 40-byte IPv6 base header.

25. What is the purpose of Next Header?

It identifies the next extension header or upper-layer protocol after the current IPv6 header.

26. What is Hop Limit?

Hop Limit restricts how many router hops an IPv6 packet may cross before being discarded.

27. Which IPv4 field is similar to IPv6 Hop Limit?

IPv4 TTL.

28. Does IPv6 contain a base-header checksum?

No. The IPv6 base header does not contain a header checksum field.

29. What are IPv6 extension headers?

They are optional headers placed after the IPv6 base header to carry additional control information.

30. Can IPv6 routers fragment transit packets?

No. IPv6 routers do not fragment transit packets.

31. Who performs IPv6 fragmentation when required?

The source node performs fragmentation using the Fragment extension header.

32. What replaces IPv4 ARP functions in IPv6?

IPv6 Neighbor Discovery functions using ICMPv6.

33. What is SLAAC?

SLAAC means Stateless Address Autoconfiguration and allows an IPv6 host to configure addressing information using router advertisements.

34. What is DHCPv6?

DHCPv6 is the IPv6 form of DHCP used to provide hosts with addressing or other configuration information depending on network design.

35. What is dual stack?

Dual stack means a device or network supports both IPv4 and IPv6.

36. What is IPv6 anycast?

Anycast allows the same address to be assigned to multiple interfaces so routing delivers traffic to one suitable member.

37. How many /64 subnets can be made from a /48 prefix?

2^(64-48) = 2^16 = 65,536 /64 subnets.

38. An IPv6 packet has 1200 bytes after its base header. What is its basic total size?

40 + 1200 = 1240 bytes, ignoring special jumbogram cases.

39. If Hop Limit is 15 and a packet crosses 4 routers, what value remains?

15 - 4 = 11.

40. Give the easiest IPv6 memory line.

IPv6 means 128-bit hexadecimal addressing, fixed 40-byte base header, no traditional broadcast, Neighbor Discovery instead of ARP and source-controlled fragmentation.

20 IPv6 MCQs With Answers

1. IPv6 address size is:

A. 32 bits
B. 64 bits
C. 128 bits
D. 256 bits

Answer: C — 128 bits

2. A full IPv6 address normally contains:

A. 4 hextets
B. 6 hextets
C. 8 hextets
D. 16 hextets

Answer: C — 8 hextets

3. One IPv6 hextet contains:

A. 8 bits
B. 16 bits
C. 32 bits
D. 64 bits

Answer: B

4. IPv6 addresses are normally written using:

A. Decimal only
B. Hexadecimal
C. Octal
D. ASCII names

Answer: B — Hexadecimal

5. IPv6 loopback address is:

A. 127.0.0.1
B. ::1
C. ::
D. ff00::1

Answer: B — ::1

6. IPv6 unspecified address is:

A. ::
B. ::1
C. fe80::1
D. ff00::

Answer: A — ::

7. IPv6 link-local addresses use:

A. fe80::/10
B. 192.168.0.0/16
C. 10.0.0.0/8
D. 127.0.0.0/8

Answer: A

8. IPv6 multicast addresses begin from:

A. ff00::/8
B. fc00::/7
C. fe80::/10
D. 2001:db8::/32

Answer: A

9. Size of IPv6 base header is:

A. 20 bytes
B. 32 bytes
C. 40 bytes
D. 60 bytes

Answer: C — 40 bytes

10. IPv6 Version field contains:

A. 4
B. 5
C. 6
D. 8

Answer: C — 6

11. IPv6 Flow Label is:

A. 4 bits
B. 8 bits
C. 16 bits
D. 20 bits

Answer: D — 20 bits

12. IPv6 equivalent concept of IPv4 TTL is:

A. Flow Label
B. Hop Limit
C. Traffic Class
D. Next Header

Answer: B

13. Which field identifies what follows the IPv6 header?

A. Next Header
B. Flow Label
C. Source Address
D. Version

Answer: A

14. IPv6 base header contains:

A. Header checksum
B. No header checksum field
C. IPv4 IHL
D. IPv4 Fragment Offset

Answer: B

15. IPv6 routers:

A. Fragment every large packet
B. Do not fragment transit packets
C. Use ARP to fragment packets
D. Always remove extension headers

Answer: B

16. IPv6 Neighbor Discovery uses:

A. ICMPv6
B. FTP
C. SMTP
D. HTTP

Answer: A

17. SLAAC stands for:

A. Stateless Address Autoconfiguration
B. Secure Link Address Allocation Control
C. Static Local Address Access Control
D. System Layer Automatic Address Code

Answer: A

18. IPv6 uses traditional broadcast addressing:

A. Yes
B. No

Answer: B — No

19. 2001:db8::/32 is reserved for:

A. Documentation and examples
B. Loopback only
C. Link-local only
D. Multicast

Answer: A

20. A /64 IPv6 prefix leaves:

A. 32 bits
B. 48 bits
C. 64 bits
D. 128 bits

Answer: C — 64 bits

Frequently Asked Questions

What is IPv6?

IPv6 is Internet Protocol version 6, a Network Layer protocol using 128-bit addresses for communication across IP networks.

How many bits are in an IPv6 address?

An IPv6 address contains 128 bits.

How many hextets are in a full IPv6 address?

A full IPv6 address contains eight 16-bit hexadecimal groups called hextets.

What does :: mean in IPv6?

It compresses one consecutive sequence of all-zero hextets in an IPv6 address.

What is the size of the IPv6 header?

The fixed IPv6 base header is 40 bytes.

Does IPv6 use broadcast?

IPv6 does not use traditional broadcast addressing. It uses multicast and other addressing mechanisms instead.

What is the IPv6 loopback address?

The IPv6 loopback address is ::1.

What is a link-local IPv6 address?

A link-local IPv6 address is used for communication on the local network link and uses the fe80::/10 block.

Can IPv6 routers fragment packets?

IPv6 transit routers do not fragment packets. Fragmentation, when required, is performed by the source.

What replaces ARP in IPv6?

Neighbor Discovery functions using ICMPv6 provide address-resolution and neighbor-discovery functions in IPv6.

What is SLAAC?

SLAAC is Stateless Address Autoconfiguration, which allows IPv6 hosts to configure address information using router advertisements.

What is the main difference between IPv4 and IPv6?

IPv4 uses 32-bit addresses, while IPv6 uses 128-bit addresses and introduces a redesigned fixed-size base header and other architectural changes.

Quick IPv6 Revision

IPv6 Size: 128 bits

Address Groups: 8 hextets

One Hextet: 16 bits

Writing: Hexadecimal separated by colons

Base Header: 40 bytes

Loopback: ::1

Unspecified: ::

Link Local: fe80::/10

Unique Local: fc00::/7

Multicast: ff00::/8

IPv4 TTL: IPv6 Hop Limit

Protocol Field: IPv6 uses Next Header

Header Checksum: Not present in IPv6 base header

ARP Replacement: Neighbor Discovery / ICMPv6

Broadcast: No traditional IPv6 broadcast

Fragmentation: Source, not transit router