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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 IPv4-compatible 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 IPv4Tunnels > Automatic IPv4-Compatible Tunnel

Translating IPv4 addresses to and from IPv6 addresses is the best method to allow communication between the IPv4 and IPv6 hosts. This translation of IPv4 and IPv6 addresses is known as Network Address Translation-Protocol Translation (NAT-PT). NAT-PT is a technique available for deploying IPv6 and IPv4 addresses in a unified network. With NAT-PT, the network requires fewer modifications and software for the IPv4 and IPv6 hosts. Additionally, it provides easy and quick interoperability between the IPv4 and IPv6 hosts. 
NAT-PT is configured on one of the routers on the border of the IPv4 and IPv6 networks. Whenever an IPv4 packet intended for a host in the IPv6 network is received by the NAT-PT router, the router applies NAT-PT on the packet and translates all the headers in the IPv4 headers. In addition, it translates the IPv4 source and destination addresses to IPv6 source and destination addresses. The IPv6 packet is then set by the NAT-PT router to the intended IPv6 host. The NAT-PT router performs the reverse translation when an IPv6 host sends a packet to an IPv4 host. 
Embedding IPv6 packets into IPv4 packets is not the best method to allow communication between the IPv4 and IPv6 hosts. When IPv6 packets are embedded inside IPv4 packets, the process is referred to as tunneling. 
Tunneling is appropriate when two IPv6 networks are separated by an IPv4 network. When an IPv6 host of one network sends an IPv6 packet destined for a host on the other IPv6 network, an IPv4 tunnel is created between the two IPv6 networks. The IPv6 packet is then embedded into an IPv4 packet that traverses through the IPv4 tunnel to reach the intended IPv6 host, where the embedded packet is extracted by the recipient. In this scenario, a single IPv6 network is available; hence, a tunnel cannot be formed. 
Configuring IPv6 on the hosts and routers in the IPv4 network, or configuring IPv4 on the hosts and routers in the IPv6 network, are not the best methods to allow communication between the IPv4 and IPv6 hosts. Each of these two methods is cumbersome and not the most efficient for providing interoperability between IPv4 and IPv6 in this case. Furthermore, the IPv4 hosts on the acquired company's network do not support IPv6 as stated. 
Objective:
Network Principles 
Sub-Objective:
Recognize proposed changes to the network 
References:
Cisco NAT Configuration Guide, Release 15M&T > NAT-PT for IPv6

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

The Forwarding Information Base (FIB) table is created when Cisco Express Forwarding (CEF) is enabled on the router. FIB is a mapping of destination networks and IP addresses to next-hop IP addresses and exit interfaces. 
In the scenario, multicast routing has NOT enabled in the router. If it were enabled, the next hop for the 224.0.0.0/4 network would not be listed as drop. A drop means any packets sent to multicast IP addresses will be dropped. If multicast routing were enabled, the entry for 224.0.0.0 would appear as follows:
Prefix             Next Hop                Interface 
224.0.0.0/4        0.0.0.0 
The next hop of 0.0.0.0 means that this traffic will be process switched, and CEF cannot forward the packets. 
The table displayed in the scenario contains the default entries in the FIB. These entries will change based on further configuration of the router interfaces and the addition of routes to the routing table through either static routing or through routing protocols. 
No IP addresses have been configured on the router. Had they been configured, the addresses of the networks to which they were connected would be in the table. For example, if the IP address of the FastEthernet 0/1 interface were set to 192.168.1.1/24, three entries would have been added to the table as follows:

    

While the first IP address represents the directly attached network of which the interface is a member, the second IP address represents the network ID of the network, the third IP address represents the specific IP address assigned to the interface, and the last IP address represents the broadcast address of the network. 
The gateway of last resort has not been set on the router. If it were set, it would be listed along with an IP address for the next hop and the exit interface. An entry for a gateway of last resort (or default route) would resemble the following:
Prefix        Next Hop       Interface 
0.0.0.0/0     192.168.5.5    FastEthernet 0/0 
Objective:
Network Principles 
Sub-Objective:
Identify Cisco Express Forwarding concepts 
References:
Cisco IOS Switching Services Configuration Guide, Release 12.2 > Cisco Express Forwarding Overview 
Cisco > Home > Support > Product Support > Routers > Cisco 12000 Series Routers > Troubleshoot and Alerts 
> Troubleshooting Technotes > Understanding Cisco Express Forwarding (CEF)https://www.ccexpert.us/traffic-share/fib-entries.html

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 > MixingTCP 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 IPv4-compatible 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

This behavior is caused by asymmetric routing. This is quite common in a routed network and usually is not a problem. It can, however, become an issue when firewalls reside in a routed path. Firewalls can cause problems when they maintain state information about connections. State information is used to determine if return connection is allowed. If the return path is routed through a different firewall, it will not have the correct state information for the connection, and the return will be disallowed. 
It is not caused by windowing. This is a technique used to adjust the number of packets that can be 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. 
The behavior is not caused by the maximum segment size (MSS). This value specifies the largest amount of data, in octets, that a computer or communications device can receive in a single TCP segment. This will not cause a packet to take a different path in the return than it did on its way to the destination. 
The behavior is not caused by global synchronization. This occurs when congestion on the network causes all devices to reduce their transmission rates at the same time. The result is the network cycling between sharp increases and sharp decreases in traffic. 
Objective:
Network Principles 
Sub-Objective:
Explain TCP operations 
References:
Home > Services > Technical services newsletter > Tech insights > Chalk talk > Asymmetric Routing and Firewalls