IPv6 Questions 2
Address Family Translation (AFT) using NAT64 technology can be achieved by either stateless or stateful means:
+ Stateless NAT64 is a translation mechanism for algorithmically mapping IPv6 addresses to IPv4 addresses, and IPv4 addresses to IPv6 addresses. Like NAT44, it does not maintain any bindings or session state while performing translation, and it supports both IPv6-initiated and IPv4-initiated communications.
+ Stateful NAT64 is a stateful translation mechanism for translating IPv6 addresses to IPv4 addresses, and IPv4 addresses to IPv6 addresses. Like NAT44, it is called stateful because it creates or modifies bindings or session state while performing translation. It supports both IPv6-initiated and IPv4-initiated communications using static or manual mappings.
When a change is made to one of the IP header fields in the IPv6 pseudo-header checksum (such as one of the IP addresses), the checksum field in the transport layer header may become invalid. Fortunately, an incremental change in the area covered by the Internet standard checksum [RFC1071] will result in a well-defined change to the checksum value [RFC1624]. So, a checksum change caused by modifying part of the area covered by the checksum can be corrected by making a complementary change to a different 16-bit field covered by the same checksum.
Link-local addresses are always configured with the FE80::/64 prefix. Most routing protocols use the link-local address for a next-hop.
A link-local address is an IPv6 unicast address that can be automatically configured on any interface using the link-local prefix FE80::/10 (1111 1110 10) and the interface identifier in the modified EUI-64 format. Link-local addresses are not necessarily bound to the MAC address (configured in a EUI-64 format). Link-local addresses can also be manually configured in the FE80::/10 format using the ipv6 address link-local command.
Stateless Address Auto Configuration (SLAAC) is a method in which the host or router interface is assigned a 64-bit prefix, and then the last 64 bits of its address are derived by the host or router with help of EUI-64 process.
The components of IPv6 header is shown below:
The Traffic Class field (8 bits) is where quality of service (QoS) marking for Layer 3 can be identified. In a nutshell, the higher the value of this field, the more important the packet. Your Cisco routers (and some switches) can be configured to read this value and send a high-priority packet sooner than other lower ones during times of congestion. This is very important for some applications, especially VoIP.
The Flow Label field (20 bits) is originally created for giving real-time applications special service. The flow label when set to a non-zero value now serves as a hint to routers and switches with multiple outbound paths that these packets should stay on the same path so that they will not be reordered. It has further been suggested that the flow label be used to help detect spoofed packets.
The Hop Limit field (8 bits) is similar to the Time to Live field in the IPv4 packet header. The value of the Hop Limit field specifies the maximum number of routers that an IPv6 packet can pass through before the packet is considered invalid. Each router decrements the value by one. Because no checksum is in the IPv6 header, the router can decrease the value without needing to recalculate the checksum, which saves processing resources.
We need to summarize three IPv6 prefixes with /64 subnet mask so the summarized route should have a smaller subnet mask. As we can see all four answers have the same summarized route of 2001:DB8:: so /48 is the best choice.
Note: IPv6 consists of 8 fields with each 16 bits (8×16 = 128).