Cisco (300-410-ENARSI) Exam Questions And Answers page 20

EIGRP update packets are sent as a multicast when a new route is discovered, and sent as a unicast to synchronize topology tables when a neighboring router initializes.
Whenever EIGRP only needs to communicate with a single neighbor, it sends a unicast to that neighbor instead of the standard multicast. In this case, it unicasts a packet to update a new EIGRP router on the network with the information that all other routers on that network already know.
Hellos for neighbor discovery and maintenance are always multicasts.
ACKs are hellos without data, and are always unicast.
Queries are always multicast.
Replies to queries are always unicast.
Objective:
Layer 3 Technologies
Sub-Objective:
Describe EIGRP packet types
Internetworking Technology Handbook > Enhanced Interior Gateway Routing Protocol (EIGRP) > EIGRP Packet Types

Tunnels and dual-stack are valid IPv4 to IPv6 migration strategies.
Tunneling mechanisms can transport IPv6 across an IPv4 infrastructure. Cisco supports the following types of tunneling for this purpose:
• Manual tunnels
• Generic Routing Encapsulation (GRE) tunnels
• IPv4 compatible tunnels
• 6-to-4 tunnels
• Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) tunnels
For all tunneling types, IPv6 packets are encapsulated in IPv4 packets for delivery across the IPv4 infrastructure. These tunnels require two endpoints, either two routers, or a router and a host. Both endpoints must support IPV4 and IPv6.
When implementing an automatic 6-to-4 tunnel each IPv6 site receives a /48-bit prefix. The hexadecimal equivalent of the IPv4 address of the edge router is appended to 0x2002 and followed with the prefix to identify each end of the tunnel. Each end of the tunnel must be a dual stack router, that is, one that can route both IPv4 and IPv6. For example if the edge router's IPv4 address were 192.168.99.1, the hexadecimal equivalent of the address (c0a8:6301) would be inserted between 0X2002 and the /48 prefix, resulting in 2002:c0a8:6301:: /48 to arrive at the tunnel endpoint address.
The following example shows a partial output of the show run command executed on a router hosting one end of a 6-to-4 tunnel:

The least significant 32 bits in the address referenced by the ipv6 route 2002::/16 Tunnel0 command correspond to the IPv4 address (64.101.64.1) assigned to the tunnel source. The hex equivalent is 4065:4001, yielding 2002:4065:4001::/48.
Another example of how IPv4 addresses can be used in the creation of the tunnel endpoint IPv6 identifier is shown in the partial output of the show run command executed on a router that is hosting one end of an automatic IPv4 compatible tunnel:

In the neighbor statement under the BGP configuration section, the neighbor address is derived from the IPv4 address of the other router (192.168.4.1). This could be implemented in one of three ways:
• ::192.168.4.1
• 0:0:0:0:0:0:192.168.4.1
• ::c0a8:0401
The IPv6 addresses ::192.168.4.1 and 0:0:0:0:0:0:192.168.4.1 are implemented by inserting the IP address at either the end of :: or 0:0:0:0:0:0. (:: is a IPv6 shortcut for 0:0:0:0:0:0). The IPv6 address::c0a8:0401 is implemented by inserting the hex equivalent of 192.168.4.1 (c0a8:0401) in the same location.
Another potential migration strategy is to run dual stacks. The TCP/IP stack, or stack, is the TCP/IP software that is included in most operating systems. It is possible to run dual TCP/IP stacks on a computer. For example, servers and other infrastructure equipment often run both an IPv4 and IPv6 IP stack for application compatibility. This dual-stack configuration allows applications that require IPv6 to use the IPv6 stack and applications that require IPv4 to use the IPv4 stack. The following partial output of the show run command shows the configuration of a dual stack router:

ipv6 unicast routing
interface fastethernet0/0
ip address 192.168.5.1 255.255.255.0
ipv6 address 3ffe:b00:c19:2::3/127

This configuration allows applications on the same segment to communicate via IPv4 or IPv6.
Dynamic Host Configuration Protocol (DHCP) provides no benefits in migrating from IPv4 to IPv6.
IPv4 is not encapsulated in IPv6 in any of the migration strategies. IPv6 is encapsulated into IPv4.
Objective:
Network Principles
Sub-Objective:
Recognize proposed changes to the network
Cisco > Cisco IOS IPv6 Implementation Guide, Release 12.4 > Implementing Tunneling for IPv6