Which option is the first task that a device that is configured with NAT64 performs when it receives an incoming IPv6 packet that matches the stateful NAT64 prefix?
A. It translates the IPv6 header into an IPv4 header.
B. It checks the IPv6 packet against the NAT64 stateful prefix.
C. It translates the IPv6 source address to an IPv4 header.
D. It translates the^ IPv4 destination address into a new NAT64 state.
E. It performs an IPv6 route lookup.
E -good answer too.
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipaddr_nat/configuration/xe-3s/nat-xe-3s-book/iadnat-stateful-nat64.html
Stateful IPv6-to-IPv4 Packet Flow
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The stateful IPv6-initiated packet flow is as follows:
– The first IPv6 packet is routed to the NAT Virtual Interface (NVI) based on the automatic routing setup that is configured for the stateful prefix. Stateful NAT64 performs a series of lookups to determine whether the IPv6 packet matches any of the configured mappings based on an access control list (ACL) lookup. Based on the mapping, an IPv4 address (and port) is associated with the IPv6 destination address. The IPv6 packet is translated and the IPv4 packet is formed by using the following methods:
Extracting the destination IPv4 address by stripping the prefix from the IPv6 address. The source address is replaced by the allocated IPv4 address (and port).
The rest of the fields are translated from IPv6-to-IPv4 to form a valid IPv4 packet.
Note
This protocol translation is the same for stateless NAT64.
– A new NAT64 translation is created in the session database and in the bind database. The pool and port databases are updated depending on the configuration. The return traffic and the subsequent traffic of the IPv6 packet flow will use this session database entry for translation.
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Stateful IPv4-to-IPv6 Packet Flow
The packet flow of IPv4-initiated packets for Stateful NAT64 is as follows:
– The destination address is routed to a NAT Virtual Interface (NVI).
A virtual interface is created when Stateful NAT64 is configured. For Stateful NAT64 translation to work, all packets must get routed to the NVI. When you configure an address pool, a route is automatically added to all IPv4 addresses in the pool. This route automatically points to the NVI.
– The IPv4-initiated packet hits static or dynamic binding.
Dynamic address bindings are created by the Stateful NAT64 translator when you configure dynamic Stateful NAT64. A binding is dynamically created between an IPv6 and an IPv4 address pool. Dynamic binding is triggered by the IPv6-to-IPv4 traffic and the address is dynamically allocated. Based on your configuration, you can have static or dynamic binding.
– The IPv4-initiated packet is protocol-translated and the destination IP address of the packet is set to IPv6 based on static or dynamic binding. The Stateful NAT64 translator translates the source IP address to IPv6 by using the Stateful NAT64 prefix (if a stateful prefix is configured) or the Well Known Prefix (WKP) (if a stateful prefix is not configured).
– A session is created based on the translation information.
The answer A is correct.
Good explanation as below.
– testking360.com
Follow the steps:
If the destination address matches the stateful NAT64 prefix, the IPv6 packet undergoes NAT64 translation (Figure 9):
i. The IPv6 header is translated into an IPv4 header.
ii. The IPv6 destination address is translated into an IPv4 address by removing the IPv6 stateful NAT64 prefix.
iii. The IPv6 source address is translated into an IPv4 address by using the configured IPv4 address pool. Depending on the NAT64 configuration, either 1:1 address translation or IPv4 address overloading is performed.
iv. Stateful NAT64 IP address translation states are created for both the source and destination IP addresses. States are created when the translation is performed for the first time; thereafter, a state is maintained until the traffic stops and the state maintenance timer expires. Subsequent IPv6 packets are translated using the NAT64 translation state created at this step
https://www.cisco.com/c/en/us/products/collateral/ios-nx-os-software/enterprise-ipv6-solution/white_paper_c11-676278.html