Section 12. Introducing IPv6

Question 1

Q1-How many bits are in an IPv6 address?

Answer 1

An IPv6 address is 128 bits long and is represented in eight 16-bit hexadecimal segments. An example of an IPv6 address is as follows:

2001:0D02:0000:0000:0000:C003:0001:F00D

Question 2

Q2-Besides a larger address space, what are some additional benefits of IPv6 when compared to IPv4?

Answer 2

Some additional benefits of IPv6 when compared to IPv4 are as follows:

Simplified header

Autoconfiguration

Enhanced multicast support

Extension headers

Flow labels

Security and mobility built in

Improved address allocation

Strict aggregation

Question 3

Q3-What are the three types of IPv6 addresses?

Answer 3

The three types of IPv6 addresses are as follows:

Unicast

Anycast

Multicast

Question 4

Q4-What is an IPv6 unicast address?

Answer 4

An IPv6 unicast address is an address that identifies a single device. It has a one-to-one mapping.

Unicast addresses include global, link local, loopback (::11), and unspecified (::).

Question 5

Q5-What is a global unicast address?

Answer 5

A global unicast address is a unicast address that is globally unique and can be routed globally. RFC 4291 specifies 2000::/3 to be reserved as global unicast address space to be allocated by the IANA.

Question 6

Q6-What is a link-local unicast address?

Answer 6

A link-local unicast address is an IPv6 address whose address is confined to a single physical link. Thus the address is not routable off the physical subnet. Link-local addresses typically begin with FE80. The next digits can be assigned manually. If the interface ID is not assigned manually, it can be based on the interface MAC address.

An interface can have multiple link-local and global addresses.

Question 7

Q7-What is an IPv6 anycast address?

Answer 7

An IPv6 anycast address is an address that represents a group of devices that support a similar service. Each device will be assigned the same anycast address. Routers will deliver data to the nearest node that is used in the common anycast address. Anycast addresses have a one-to-nearest mapping.

To assign an anycast address to a router interface, configure a global unicast address with the keyword anycast appended to the end of the command line.

Question 8

Q8-What is an IPv6 multicast address?

Answer 8

An IPv6 multicast address identifies a set of devices called a multicast group. It has a one-to-many mapping and also replaces IPv4 broadcast addresses. IPv6 multicast addresses use the reserved address space FF00::0/8.

Question 9

Q9-What is the address used for the IPv6 loopback address?

Answer 9

The address used for the IPv6 loopback address is 0:0:0:0:0:0:0:1, which is normally expressed as ::1.

Question 10

Q10-What are the IPv6 addresses that are reserved by the IETF?

Answer 10

The IETF reserved approximately 1/256 of all the total IPv6 address space. The reserved addresses are

The lowest address within each subnet prefix (the interface identifier set to all 0s) is reserved as the “subnet-router” anycast address.

Within each subnet, the highest 128 interface identifier values are reserved for the subnet anycast addresses.

Question 11

Q11-What are the two rules for reducing the size of written IPv6 addresses?

Answer 11

The two rules for reducing the size of written IPv6 addresses are as follows:

Rule 1: The leading 0s in any fields do not have to be written. If a field has fewer than four hexadecimal digits, it is assumed that the missing digits are leading 0s. For example, 2001:0D02:0000:0000:0000:C003:0001:F00D can be written as follows:

2001:D02:0:0:0:C003:1:F00D

Rule 2: Any single, consecutive fields of all 0s can be represented with a double colon. For example, 2001:D02:0:0:0:C003:1:F00D can be further reduced to the following:

2001:D02::C003:1:F00D

The double colon can be used only once.

Question 12

Q12-What is the EUI-64 standard?

Answer 12

The EUI-64 standard explains how to stretch 802.3 MAC addresses from 48 to 64 bits by inserting the 16-bit 0xFFFE at the 24th bit of the MAC address to create a 64-bit unique identifier. Secondly, the universal/local (U/L) flag (bit 7) in the OUI portion of the address is flipped from 0 to 1 so that 1 now means universal. The EUI-64 standard is used to allow a host to automatically assign itself a unique 64-bit IPv6 address without the need for manual configuration or DHCP.

For example, MAC address 00-AA-11-17-FC-0F on the network 2001:0DB8:0:1::/64 becomes 02-AA-11-17-FC-0F. The resulting EUI-64 address on the network is 2001:0DB8:0:1:02AA:11FF:17FE:FC0F.

Question 13

Q13-What are the three ways that an IPv6 host can be assigned an address?

Answer 13

An IPv6 host can be assigned an address statically, with stateless autoconfiguration, or by Dynamic Host Configuration Protocol version 6 (DHCPv6).

Question 14

Q14-Before you can forward IPv6 addresses on router interfaces, what must you enable?

Answer 14

You must enable IPv6 unicast routing.

By default, IPv6 is not enabled on a Cisco router. As such, before you can forward IPv6 addresses on router interfaces, you must enable IPv6 routing by issuing the ipv6 unicast-routing global command.

Question 15

Q15-After enabling IPv6 on the router, how would you configure an IPv6 address to an interface?

Answer 15

The ipv6 address ipv6-address/ipv6-length [eui-64] interface command configures an IPv6 address to a router interface.

Question 16

Q16-What IPv4 headers were removed in IPv6 headers and why?

Answer 16

The following IPv4 headers were removed in IPv6:

Image Internet Header Length: Removed because all IPv6 headers are a fixed 40-byte length, unlike IPv4.

Flags: Used in fragmentation, and IPv6 routers no longer process fragmentation.

Fragmentation Offset: IPv6 routers no longer process fragmentation.

Header Checksum: Removed because most data link layer technologies already perform checksum and error control.

Identification: No longer needed based on IPv6 implementations.

Padding: Because the Options field was changed, the Padding field is no longer needed.

Question 17

Q17-What are the eight fields contained in IPv6?

Answer 17

The eight fields in IPv6 are as follows:

Version: 4-bit field; contains the number 6.

Traffic Class: 8-bit field that is similar to the IPv4 ToS field.

Flow Label: New 20-bit field used to mark individual traffic flows with unique values.

Payload Length: Describes the length of the payload only.

Next Header: Used to determine the type of information that follows the IPv6 header.

Hop Limit: Specifies the maximum number of hops that an IP packet can traverse.

Source Address: 128-bit (16 octets) identifying the source of the packet.

Destination Address: 128-bit field identifying the destination of the packet.

Question 18

Q18-What are the functions of ICMPv6?

Answer 18

The functions of ICMPv6 are

Diagnostic tests: Like ICMPv4, ICMPv6 provides diagnostic tests using echo and echo reply.

Router discovery: Router solicitation and router advertisements.

Neighbor discovery: Neighbor solicitation and neighbor advertisements.

Question 19

Q19-What two message types does ICMPv6 use?

Answer 19

The two message types that ICMPv6 implements are

Error messages: Examples include Destination Unreachable, Packet Too Big, or Time Exceeded

Informational messages: Echo Request and Echo Reply

Question 20

Q20-How are ICMPv6 packets identified in the Next Header field?

Answer 20

ICMPv6 packets are identified as 58 in the Next Header field.

Question 21

Q21-In IPv6, what is neighbor discovery?

Answer 21

Neighbor discovery in IPv6 is used for router and neighbor solicitation and advertisements, and for redirection of nodes to the best gateway. It performs the same functions as ARP in IPv4. These functions include

Determining the link layer address of a neighbor

Finding neighbor routers on a link

Querying for duplicate addresses

Neighbor discovery is performed using ICMPv6 with a multicast address.

Question 22

Q22-In IPv6, what is stateless autoconfiguration?

Answer 22

Stateless autoconfiguration is a feature in IPv6 that uses neighbor discovery to find routers, and it will also dynamically create an IPv6 address based on a prefix found in the router advertisement and EUI-64 standard. When stateless autoconfiguration is enabled on the interface, additional addresses will also be assigned to the interface, one of these being a link-local unicast address.

Question 23

Q23-What is contained in the router solicitation message?

Answer 23

The router solicitation messages contains the following:

ICMP type of 133

The source address is unspecified or ::

Destination address is the all-routers multicast address FF02::2

Question 24

Q24-What Cisco IOS command configures a router interface for stateless autoconfiguration?

Answer 24

The ipv6 address autoconfig interface command configures a router’s interface for stateless autoconfiguration.

Question 25

Q25-Because IPv6 uses a 128-bit address, routing protocols need to be modified to support IPv6. What routing protocols support IPv6?

Answer 25

The following routing protocols support IPv6:

RIPng

OSPFv3

EIGRP for IPv6

Intermediate System–to–Intermediate System (IS-IS) for IPv6

Multiprotocol Border Gateway Protocol (MP-BGP)

Question 26

Q26-What is RIPng?

Answer 26

RIPng is the IPv6 version of Routing Information Protocol (RIP), a distance vector protocol. RIPng is defined in RFC 2080 and is based on RIPv2. Thus RIPng uses hop count as its metric and has a maximum hop count of 15. However, some changes to RIPng are as follows:

Uses IPv6 for transport.

Uses multicast group FF02::09 to advertise routes every 30 seconds.

Updates are sent on User Datagram Protocol (UDP) port 521.

Question 27

Q27-How do you configure IPv6 static routes?

Answer 27

Static routing with IPv6 is configured the same way as with IPv4. The ipv6 route ipv6_network/ipv6_mask outgoing_interface/ipv6_next_hop global command adds static routes to a router.

The following example configures a static route for network 2001:DB8:123::/48 to route traffic to interface serial 0/0:
Router(config)# ipv6 route 2001:DB8:123::/48 serial 0/0

Question 28

Q28-How do you configure an IPv6 default route on a Cisco router?

Answer 28

To configure a default IPv6 route on a Cisco router, use the ipv6 route global configuration command with ::/0 specified as the ipv6_network/mask. The following example configures a default route to send all traffic to interface serial 2/0:
Router(config)# ipv6 route ::/0 serial 2/0

Question 29

Q29-What IOS command displays all IPv6 routes entered in the routing table?

Answer 29

The show ipv6 route command displays all IPv6 routes entered in the routing table.

Question 30

Q30-What features does OSFPv3 add?

Answer 30

Open Shortest Path First version 3 (OSPFv3) is based on the current version of OSPF for IPv4, which is version 2. Like version 2, OSPFv3 sends Hellos to neighbors, exchanges link-state advertisements (LSA), and exchanges database descriptor (DBD) packets. However, OSPFv3 runs directly over IPv6 and advertises using multicast groups FF02::5 and FF02::06, but uses its link-local address as the source address of its advertisements.

FF02::5 is the address listened to by “all OSPF routers,” and FF02::06 is the address listened to by the OSPF DRs and BDR.

Question 31

Q31-Does OSPFv3 require an IPv4 address for the router ID?

Answer 31

No. OSPFv3 does not require an IPv4 address for the router ID; however, a 32-bit number must be set for the router ID.

When a router has not been configured with an IPv4 address to be used by OSPFv3 for purposes of the router ID, the OSPFv3 process will not immediately start. The required step to then start the OSPF process will be to manually configure the router ID using the router-id router-id command. The value entered into the router-id command will use the format of a normal IPv4 address. However, it is not actually an IPv4 address nor does it need to be configured on an interface of the device.

Question 32

Q32-How do you configure OSPFv3 on a Cisco router?

Answer 32

The commands to configure OSPFv3 on a Cisco router are as follows from global configuration mode:

Image ipv6 ospf process-id area area_id interface command enables OSPFv3 routing on the interface.

Image ipv6 router ospf process_id enables the OSPFv3 routing process and enters the routing process configuration mode.

Image router-id router-id sets the OSPFv3 router ID with a 32-bit number.

The following example configures OSPF with process ID 10 and 0.0.0.2 as the router ID, and enables OSPF on gigabit interfaces g0/0 and g0/1, assigning them to area 0:
Router(config)# ipv6 router ospf 10
Router(config-rtr)# router-id 0.0.0.1
Router(config-rtr)# interface g0/0
Router(config-if)# ipv6 ospf 10 area 0
Router(config-if)# interface g0/0
Router(config-if)# ipv6 ospf 10 area 0