Cisco CCNA ICND2 (Interconnecting Cisco Networking Devices Part 2)Exam Cram

4. Infrastructure Services

4.4 IPv6 addressing

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.

images/ipv6header.jpg

The following list describes the function of each header field.

a. version (4 bit): Indicates the protocol version, and will thus contain the number 6.

b. DS byte (8 bit): This field is used by the source and routers to identify the packets belonging to the same traffic class and thus distinguish between packets with different priorities.

c. flow label (20 bit): Label for a data flow

d. payload length (16 bit): Indicates the length of the packet data field.

e. next header (8 bit): ): Identifies the type of header immediately following the IPv6 header.

f. hop limit (8 bit): Decremented by one by each node that forwards the packet. When the hop limit field reaches zero, the packet is discarded.

g. source address (128 bit): The address of the originator of the packet.

h. destination address ( 128 bit) : The address of the intended recipient of the packet.

The extension header may include the following:

  • Hop-by-Hop options
  • Destination options
  • Routing (specifies intermediate routers that the route must include forcing an administratively defined path)
  • Fragment (Used to divide packets that are too large for the maximum unit (MTU) )
  • Authentication and Encapsulating Security Payload (ESP)

IPv6 hosts should support the following addresses:

  • Assigned global unicast and anycast addresses (2000::/3)
  • Loopback address (::1/128)
  • Link-local address (FE80::/10), autoconfigured
  • All-nodes multicast addresses (FF01::1 and FF02::1)

Solicited-nodes multicast addresses (FF02::1:FF00:/104 and appending the last 24 bits of the corresponding unicast or anycast address of the device)

Any other assigned multicast addresses (in the range FF00::/8)

Routers should additionally support at least the following:

  • Subnet-router anycast address
  • All-routers multicast addresses (FF01::2, FF02::2, and FF05::2)
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IP helper addresses : IP helper addresses forward a client broadcast address (such as a DHCP or BOOTP requests) to a unicast or directed broadcast address. Helper-address is required due to the fact that routers do not forward broadcasts. By defining a helper-address, a router will be able to forward a broadcast from a client to the desired server or network. There can be more than one helper-address on a network. The helper-address must be defined on the interface that receives the original client broadcast.

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Note that "ip unnumbered" command is used to enable IP processing on a serial interface without assigning a specific IP address to the interface.

To enable routing of IPv6 packets, we need to enable IPv6 on a router by using the command : Router(config)# ipv6 unicast-routing

To enable IPv6 on an interface, use the command :Router(config-if)#ipv6 enable

To add an IPv6 address to an interface : ipv6 address <address>/<prefix> [link-local] [eui-64]

Examples: ipv6 address 2001:100:1::1/64

To leave the interface unnumbered : ipv6 unnumbered eth 0/0

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