Chapter 2

1: For each of the fields in the following table, give the field's length and indicate whether it is used in the IPv4 header or IPv6 header.
FieldLength in BitsIPv4 HeaderIPv6 Header
Type of Service   
Identification   
Version   
Time to live   
Header checksum   
Header length   
Traffic Class   
Total Length   
Flow Label   
Flags   
Padding   
Extension header   
Payload Length   
Protocol Number   
Hop Limit   
Source Address   
Destination Address   
Options   
Next Header   
Fragment Offset   

A1: Answer:
FieldLength in BitsIPv4 HeaderIPv6 Header
Type of Service8X 
Identification16X 
Version4XX
Time to live8X 
Header checksum16X 
Header length4X 
Traffic Class8 X
Total Length16X 
Flow Label20 X
Flags3X 
PaddingVariableX 
Extension headerVariable X
Payload Length16 X
Protocol Number8X 
Hop Limit8 X
Source Address32, 128XX
Destination Address32, 128XX
OptionsVariableX 
Next Header8 X
Fragment Offset13X 

2: List the fields removed from the IPv4 header.
A2: Answer: Header length, Identification, Flags, Fragment Offset, Header checksum, Options, Padding
3: What new field is added in the IPv6 header?
A3: Answer: Flow Label
4: Describe the use of the Next Header field in the IPv6 header.
A4: Answer: The Next Header field defines the type of information following the basic IPv6 header. The type of information can be a transport-layer protocol such as TCP or UDP, or it can be an extension header.
5: List the extension headers that may be placed after the basic IPv6 header, and place them in the order they must appear.
A5: Answer:

IPv6 header

Hop-by-Hop Options header

Destination Options header (if the Routing header is used)

Routing header

Fragment header

Authentication header

Encapsulating Security Payload header

Destination Options header

Upper-layer header (TCP, UDP, ICMPv6, ...)

6: What is mandatory with UDP when used over IPv6?
A6: Answer: The UDP Checksum field within the UDP packet is mandatory with IPv6. This field was optional in IPv4.
7: What is recommended as a mechanism for nodes in IPv6 to avoid fragmentation?
A7: Answer: The path MTU discovery (PMTUD) mechanism
8: What are IPv6's minimum MTU and recommended minimum MTU?
A8: Answer: The minimum MTU in IPv6 is 1280 octets, and the recommended minimum MTU is 1500 octets.
9: What are the three representations of IPv6 addresses?
A9: Answer:

Preferred representation (always a series of eight 16-bit hexadecimal fields)

Compressed representation (successive 16-bit fields made up of 0s are replaced by a double colon; leading 0s in 16-bit fields are removed)

IPv6 address with an embedded IPv4 address (used by transition mechanisms)

10: Compress the following IPv6 addresses into the shortest form possible.
Preferred RepresentationCompressed Representation
A0B0:10F0:A110:1001:5000:0000:0000:0001 
0000:0000:0000:0000:0000:0000:0000:0001 
2001:0000:0000:1234:0000:0000:0000:45FF 
3ffe:0000:0010:0000:1010:2a2a:0000:1001 
3FFE:0B00:0C18:0001:0000:1234:AB34:0002 
FEC0:0000:0000:1000:1000:0000:0000:0009 
FF80:0000:0000:0000:0250:FFFF:FFFF:FFFF 

A10: Answer:
Preferred RepresentationCompressed Representation
A0B0:10F0:A110:1001:5000:0000:0000:0001A0B0:10F0:A110:1001:5000::1
0000:0000:0000:0000:0000:0000:0000:0001::1
2001:0000:0000:1234:0000:0000:0000:45FF2001::1234:0:0:0:45FF
3ffe:0000:0010:0000:1010:2a2a:0000:10013ffe:0:10:0:1010:2a2a:0:1001
3FFE:0B00:0C18:0001:0000:1234:AB34:00023ffe:b00:c18:1:0:1234:ab34:2
FEC0:0000:0000:1000:1000:0000:0000:0009FEC0::1000:1000:0:0:9
FF80:0000:0000:0000:0250:FFFF:FFFF:FFFFFE80::250:FFFF:FFFF:FFFF

11: Describe the IPv6 address representation for URL.
A11: Answer: Because the colon specifies an optional port number in a URL, the IPv6 address must be enclosed in brackets.
12: List the three kinds of addresses in the IPv6 addressing architecture.
A12: Answer: Multicast, unicast, anycast
13: For each of the following address types, find the IPv6 prefix and write the address in the compressed representation.

Unspecified

Loopback

IPv4-compatible IPv6

Link-local

Site-local

Multicast

Solicited-node multicast

Aggregatable global unicast

A13: Answer:

Unspecified—::

Loopback—::1

IPv4-compatible IPv6—::/96

Link-local—FE80::/10

Site-local—FEC0::/10

Multicast—FF00::/8

Solicited-node multicast—FF02::1:FF00:0000/104

Aggregatable global unicast—2000::/3

14: What is a link-local address?
A14: Answer: Link-local addresses are used by nodes on a local link scope only. These addresses cannot be routed between segments. Each IPv6 node by default owns one link-local address per network interface.
15: What is similar to the site-local address in IPv4?
A15: Answer: Site-local addresses are similar to the private addressing space in IPv4, such as 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. Site-local addresses must not be routed to the IPv6 Internet.
16: In the following table, list the solicited-node multicast address that corresponds to each unicast address.
Unicast AddressSolicited-Node Multicast Address
A0B0:10F0:A110:1001:5000:0000:0000:0001 
2001:0000:0000:1234:0000:0000:0000:45FF 
3ffe:0000:0010:0000:1010:2a2a:0000:1001 
3FFE:0B00:0C18:0001:0000:1234:AB34:0002 
FEC0:0000:0000:1000:1000:0000:0000:0009 

A16: Answer:
Unicast AddressSolicited-Node Multicast Address
A0B0:10F0:A110:1001:5000:0000:0000:0001FF02::1:FF00:0001
2001:0000:0000:1234:0000:0000:0000:45FFFF02::1:FF00:45FF
3ffe:0000:0010:0000:1010:2a2a:0000:1001FF02::1:FF00:1001
3FFE:0B00:0C18:0001:0000:1234:AB34:0002FF02::1:FF34:0002
FEC0:0000:0000:1000:1000:0000:0000:0009FF02::1:FF00:0009

17: Give the length in bits of the host and site parts of an aggregatable global unicast IPv6 address.
A17: Answer:

Host—64-bit

Site—16-bit

18: What three prefixes are assigned by IANA and are available as public addresses in IPv6?
A18: Answer:

2001::/16—IPv6 Internet

2002::/16—6to4 transition mechanism

3ffe::/16—6bone

19: What is the Cisco IOS Software command to enable IPv6 on a Cisco router?
A19: Answer: ipv6 unicast-routing
20: What protocol ID is used for IPv6 in Ethernet frames?
A20: Answer: 0x86DD
21: Explain how IPv6 multicast addresses are mapped over Ethernet.
A21: Answer: Multicast mapping over Ethernet uses the multicast Ethernet prefix to which the low-order 32-bit of the IPv6 addresses is appended.
22: Generate IPv6 interface IDs (in EUI-64 format) from the following Ethernet link-layer addresses.
Ethernet Link-Layer AddressIPv6 Interface ID
00:90:27:3a:9e:9a 
00:90:27:3a:8d:c3 
00:00:86:4b:fe:ce 

A22: Answer:
Ethernet Link-Layer AddressEUI-64 Format
00:90:27:3a:9e:9a02:90:27:FF:FE:3a:9e:9a
00:90:27:3a:8d:c302:90:27:FF:FE:3a:8d:c3
00:00:86:4b:fe:ce02:00:86:FF:FE:4b:fe:ce

23: What command assigns one IPv6 address to an interface using EUI-64 format?
A23: Answer: ipv6 address ipv6-address/prefix-length eui-64
24: What is the goal of the path MTU discovery mechanism?
A24: Answer: The main goal of the path MTU discovery mechanism is to find out the maximum MTU value along a path when a packet is sent.
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