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The IPv4 address of the IPv6 router is 208.48.107.192. In an automatic 6-to-4 tunnel, IPv6 addresses have the 2002::/16 prefix. The 32-bit IPv4 address of the IPv6 router is then embedded into the IPv6 address. The 32 bits of the IPv4 address is embedded in the second and third quartet of the IPv6 address. The second and third quarters in the IPv6 address correspond to D030:6BC0. The conversion of these hexadecimal digits into decimal is given as follows: 

        

The IPv6 router does not have 10.176.15.131 as its IPv4 address. The 10.176.15.131 address is the IPv4 equivalent of the second and third quarter (05B0:0F81) 
in the source IPv6 address.  
The other two IPv4 addresses are incorrect as they pertain to neither of the two IPv6 hosts.  
Objective: 
Network   
Principles Sub- 
Objective: 
Recognize proposed changes to the network  
References: 
Cisco IOS IPv6 Implementation Guide > Implementing Tunneling for IPv6

The correct answer is to use the tunnel mode ipv6ip 6to4 command to complete the configuration of an automatic 6-to-4 tunnel. This command requires the use of IPv6 unicast addresses that have the 2002::/16 prefix. 
The types of tunneling mechanisms supported by IPv6 are: 
Automatic 6-to-4 tunnel  
ISATAP tunnel  
Manually configured tunnel  
GRE tunnel   
Apart from using a tunneling mechanism, interoperability between IPv4 and IPv6 can be provided by using a dual-stack infrastructure or Network Address Translation-Protocol Translation (NAT-PT). A dual-stack infrastructure allows you to use both IPv4 and IPv6 addresses on the same router/host. NAT-PT is used to translate IPv4 addresses to IPv6 and vice versa.  
The tunnel mode ipv6ip command should not be used to complete the configuration because this command specifies IPv6 as the passenger protocol and creates a manually configured tunnel.  
The tunnel mode ipv6ip auto-tunnel command is not required to enable automatic 6-to-4 tunneling on the border routers. This command creates an automatic IPv4compatible IPv6 tunnel between the routers.  
The tunnel mode ipv6ip isatap command should not be used because this command creates an ISATAP tunnel.  
Objective: 
Network  
Principles Sub- 
Objective: 
Recognize proposed changes to the network  
References: 
Cisco IOS IPv6 Configuration Guide; Implementing Tunneling for IPv6 > Configuring Manual IPv6 Tunnels Cisco > Cisco IOS IPv6 Command Reference > tunnel mode ipv6ip   

The 2002:c0a8:4b01::1/64 and the 2002:c0a8:7d01::1/64 IPv6 addresses should be assigned to the Fa0/1 interfaces of rtrB and rtrC, respectively. Automatic 6-to-4 tunnels embed the IPv4 address of the tunnel interfaces into the second and third quartets of the IPv6 address that has the 2002::/16 prefix. 
To assign IPv6 addresses to the tunnel interfaces, perform the following steps: 
Convert the IPv4 address of the tunnel interface into binary.  
Convert the binary equivalent of the IPv4 address into hexadecimal (IPv6).  
Append the hexadecimal equivalent to the 2002::/16 prefix to form the IPv6 prefix of the tunnel interface.  
For the Fa0/1 interface of rtrB, its IPv4 address of 192.68.75.1 is equivalent to the IPv6 address c0a8:4b01. This address is then appended to the 2002::/16 prefix, resulting in 2002:c0a8:4b01::/48. The remaining host bits can be filled with zeros. Similarly, the IPv4 address of the Fa0/1 interface of rtrC is converted to the IPv6 address 2002:c0a8:7d01::/48. 
The 2002::c0a8:2d01/64 IPv6 address should not be assigned to the Fa0/1 interface of rtrA. The Fa0/1 interface of rtrA has the IPv4 address 192.168.45.1. The IPv6 equivalent of the IPv4 address, which is c0a8:2d01, should be embedded in the second and third quartets of the IPv6 address instead of the seventh and eighth quartets. IPv4 addresses are embedded into the last 32 bits for ISATAP tunnels.  
The 2002:c0a8:4b01::1/64 IPv6 addresses should not be assigned to the Fa0/1 interface of rtrA. This IPv6 address is the equivalent of the IPv4 address 192.168.75.1, which is the address of the Fa0/2 interface of rtrB and not rtrA. Therefore, this IPv6 address should be assigned to the Fa0/1 interface of rtrB.  
Objective: 
Network  
Principles Sub- 
Objective: 
Recognize proposed changes to the network  
References: 
Cisco Press > Articles > Cisco Certification > CCNP > CCNP Self-Study: Advanced IP Addressing 
Cisco Press > Articles > Network Technology > General Networking > Cisco Self-Study: Implementing Cisco IPv6 Networks (IPV6) 
Cisco > Support > Technology Support > IP > IP Version 6 (IPV6) > Configure > Configuration Examples and Technotes > IPv6 Tunnel Through an IPv4 Network  
Cisco IOS IPv6 Implementation Guide, Release 15.2M&T > Implementing Tunneling for IPv6

The IPv6 address of the tunnel source is ::172.168.111.65 and the IPv6 address of the tunnel destination is ::172.168.222.80. 
These two addresses are IPv4compatible IPv6 addresses, which are addresses that contain the IPv4 addresses of the tunnel source and destination.   
In automatic IPv4-compatible IPv6 tunnel, the IPv4 addresses of the tunnel source and the tunnel destination are used to determine their IPv6 addresses. The IPv4 addresses of the tunnel source/destination are embedded into the least significant 32 bits of an all-zero unicast IPv6 address. The resultant IPv6 address has zeros in the most significant 96 bits and the IPv4 address of the tunnel source/destination in the remaining 32 bits.  
In this case, the source of an automatic IPv4-compatible IPv6 tunnel has the IPv6 address 0:0:0:0:0:0:172.168.111.65, abbreviated as ::2.168.111.65. You can also convert this address into pure hexadecimal format, which would be ACA8:6F41. 
Any of the following three addresses could be used to identify the BGP neighbor at 172.168.11.65: 
0:0:0:0:0:0:172.168.111.65 
::172.168.111.65 
::ACA8:6F41 
Similarly, the tunnel destination has the IPv6 address 0:0:0:0:0:0:172.168.222.80 (abbreviated as ::172.168.222.80). The hexadecimal form of the IPv6 address of the tunnel destination is ::ACA8:DE50. 
Any of the following three addresses could be used to identify the BGP neighbor at 172.168.222.80: 
0:0:0:0:0:0:172.168.222.80 
::172.168.222.80 
::ACA8:DE50  
The other two options state incorrect IPv6 addresses of the tunnel source and the tunnel destination. Both options specify an IPv6 address that has the IPv4 address of the tunnel source/destination in the most significant 32 bits and zeros in the least significant 96 bits.  
Objective: 
Network  
Principles Sub- 
Objective: 
Recognize proposed changes to the network  
References: 
Home > Support > Technology Support > IP > IP Version 6 (IPv6) > Configure > Configuration Examples and Technotes > IPv6 Tunnel Through an IPv4 Network >  
Configure > Configurations (Automatic IPv4-Compatible Mode)  
Cisco IOS IPv6 Implementation Guide > Implementing Tunneling for IPv6  
Cisco > Support > Technology Support > IP > IP Version 6 (IPv6) > Technology Information > Technology White Paper > IPv6 Deployment Strategies > Selecting a  
Deployment Strategy > Deploying IPv6 Over IPv4 Tunnels > Automatic IPv4-Compatible Tunnel

The following statements are TRUE about manually configured tunnels and GRE tunnels: 
Manually configured tunnels use the tunnel mode ipv6ip command, while GRE tunnels use the tunnel mode gre ip command.   
Manually configured tunnels do not support multiple passenger protocols, while GRE tunnels support them.   
Manually configured tunnels and Generic Routing Encapsulation (GRE) tunnels are static point-to-point tunneling methods. Both of these tunneling methods provide a permanent link between two IPv6 networks that are separated by an IPv4 backbone. For each link between two IPv6 networks, a separate tunnel needs to be created.   
Manually configured tunnels use a particular passenger protocol and do not support multiple passenger protocols at the same time. However, GRE tunnels can simultaneously use various passenger protocols.  
It is incorrect to state that manually configured tunnels support IPv6 IGPs, while GRE tunnels do not. GRE tunnels also support IPv6 IGPs, such as OSPF, RIP, and IS-IS.  
It is incorrect to state that manually configured tunnels block IPv6 multicasts, while GRE forwards them. Manually configured tunnels also forward IPv6 multicasts.  
Objective: 
Network Principles  
Sub-Objective: 
Recognize proposed changes to the network  
References: 
Cisco IOS IPv6 Configuration Guide, Release 12.4 > Implementing Tunneling for IPv6 > Configuration Examples for Implementing Tunneling for IPv6 > Example: 
Configuring Manual IPv6 Tunnels

When the routers in the network are capable of routing both IPv6 and IPv4 traffic, it is referred to as dual stack. The dual stack routers simply recognize the version a frame is using and react accordingly to each frame.  
Network Address Translation- Port Translation (NAT-PT) is a service that runs on a router or server that converts IPv4 traffic to IPv6, and vice versa. This eliminates the need for the routers or clients to be dual stack-capable. When only one router exists between the IPv4 and the IPv6 networks, this will be the only option, since all other methods listed require a dual stack capable device on each end of the tunnel. The IPv6 to IPv4 mapping can be obtained by the host from a DNS server, or the mapping can be statically defined on the NAT device.   
6to4 tunnels can be created between dual stack routers or between a dual stack router and a dual stack client. In either case, each tunnel endpoint will have both an IPv6 and an IPv4 address. When traffic needs to cross an area where IPv6 is not supported, the tunnel can be used to transport the IPv6 packet within an IPv4 frame. When the frame reaches the end of the tunnel, the IPv4 header is removed and the IPv6 frame is further routed based on its IPv6 address.  
Teredo is an alternate tunneling mechanism that encapsulates the IPv6 frame in an IPv4 UDP packet. It has the added benefit of traversing a NAT device that is converting private IP addresses to public IP addresses. 6to4 tunnels cannot traverse NAT devices by converting private IP addresses to public IP addresses.  
Objective: 
Network  
Principles Sub- 
Objective: 
Recognize proposed changes to the network  
References: 
Cisco > Home > Products and Services > Cisco IOS and NX-OS Software > Cisco IOS Technologies > IPV6 > Product Literature > White Papers > Federal  
Agencies and the Transition to IPv6  
Cisco > Cisco IOS IPv6 Configuration Guide, Release 15.2MT

When implementing an automatic 6to4 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, which is one that can route both IPv4 and IPv6 traffic. 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 a packet with the IPv6 address 2002:c0a8:6301::/48 to arrive at the tunnel endpoint address. 
A Network Address Translation - Port Translation (NAT-PT) router performs translation from IPv4 to IPv6. It is not used in a 6to4 tunnel.  
Each site does not have a /16 prefix with a 6to4 tunnel. Rather, each site has a /48 prefix.  
The IPv6 address of each IPv6 host is not part of the site prefix. These addresses are retained within the IPv6 portion of the header, and will be read after the frame reaches the end of the tunnel for eventual IPv6 routing on the far end.  
Objective: 
Network  
Principles Sub- 
Objective: 
Recognize proposed changes to the network  
References:  
Cisco > Products > Collateral > Whitepaper > Enterprise IPv6 Transition Strategy > IPv6 Deployment Solution Options

If either the clear ip arp or the clear adjacency commands were issued, the entry would temporarily be listed as incomplete in the adjacency table. The adjacency table is used by Cisco Express Forwarding (CEF) to maintain Layer 2 information about the next hop to remote networks. In CEF, an adjacency refers to a control structure that holds Layer 2 information for an IP address on a particular interface. When that information is not available the entry will be listed as incomplete, as shown in the example.  
Layer 2 information normally comes from the ARP process. Therefore, if the ARP table is cleared with the clear ip arp command, the Layer 2 information will be temporarily unavailable until the ARP process re-learns it the next time a frame must be sent to that hop. Moreover, if the adjacency table is emptied with the clear adjacency command, the entry must be created again. This will also result in the entry being marked incomplete for a short period of time until the ARP table can be consulted and the Layer 2 information re-added.  
The interface in the scenario is not a multipoint interface. A multipoint interface would include entries for multiple next hops, since a multipoint interface connects to multiple Layer 3 destinations. An example of this is shown below in sample output from a Frame Relay interface: 

       
  
The layer 3 information of the next hop is present in the entry in the scenario example. It is 10.10.10.2.  
Objective: 
Network  
Principles Sub- 
Objective: 
Identify Cisco Express Forwarding concepts  
References: 
Home > Support > Technology support > IP > IP switching > Troubleshoot and alerts > Troubleshooting Technotes > Troubleshooting Incomplete Adjacencies with CEF   

This behavior is called starvation and is caused by improper configuration of QoS queues. When TCP and UDP flows are assigned to the same QoS queue, they compete with one another. This is not a fair competition because the TCP packets will react to packet drops by throttling back TCP traffic, while UDP packets are oblivious to drops and will take up the slack created by the diminishing TCP traffic. The results from mixing UDP and TCP traffic in the same queue are:  
Starvation  
Latency  
Lower throughput  
While it is true that jitter can be caused by a lack of QoS, jitter is not what is being described in the scenario. Jitter is the variation in latency as measured in the variability over time of the packet latency across a network. This phenomenon seriously impacts time-sensitive traffic, such as VoIP, and can be prevented by placing this traffic in a high-priority QoS queue.  
While latency can be caused by the maximum transmission unit (MTU) in the network, this is not a case of latency, although latency may be one of the perceived effects of starvation. Latency is the delay in reception of packets. The MTU is the largest packet size allowed to be transmitted, and an MTU that is set too large can result in latency.  
While windowing can be caused by network congestion, this is not a case of windowing. This is a technique used to adjust the number of packets that can acknowledged at once by a receiving computer in a transmission. In times of congestion the window, or number of packets that can be acknowledged at a time, will be small. Later, when congestion goes down, the window size can be increased.  
Objective: 
Network   
Principles Sub- 
Objective: 
Describe UDP operations  
References: 
Design Guide > Service Provider Quality of Service > CE Guidelines for Collapsing Enterprise Classes > Mixing TCP with UDP

The correct answer is that IPv4 and IPv6 are running simultaneously on rtrA. The set of commands enables IPv6 on the rtrA router and assigns an IPv4 address and an IPv6 address to the Fa0/0 interface. This indicates that the router is a dual-stack router on which both IPv4 and IPv6 are running simultaneously.  
The IPv4 address is not translated to the IPv6 address by the given set of commands because NAT-PT is not enabled on the router. To enable NAT-PT on a router, you need to use the ipv6 nat command. In addition, the ipv6 nat prefix command should be used to specify an IPv6 prefix.  
The IPv6 address is not an IPv4-compatible address. IPv4-compatible IPv6 addresses are used in automatic IPv4-compatible IPv6 tunnels. These addresses refer to those IPv6 unicast addresses that have zeros in the first 96 bits and an IPv4 address in the last 32 bits. For example, 0:0:0:0:0:0:192.156.10.67 is an IPv4compatible IPv6 address where 192.156.10.67 is an IPv4 address. The IPv6 address (2001:0:1:1:D52::F3C/64), in this case, is not an IPv4-compatible IPv6 address.   
A tunnel is not created for the interoperability of the IPv4 and IPv6 addresses because the given set of commands configures the router as a dual-stack router.  
There are no commands for configuring a tunnel on the router.  
Objective: 
Network  
Principles Sub- 
Objective: 
Recognize proposed changes to the network  
References: 
Cisco IOS IPv6 Configuration Guide, Release 12.4 > Implementing IPv6 Addressing and Basic Connectivity > Configuration Examples for Implementing IPv6  
Addressing and Basic Connectivity > Example: Dual Protocol Stacks Configuration