Cisco (300-410-ENARSI) Exam Questions And Answers page 21

The ip address dhcp command when issued from interface configuration mode will allow a router to obtain an IP address for that interface from a DHCP server.
In this scenario, the router is acting as a DHCP client, not a server, so the command would not be issued from dhcp-config mode. In addition, the IP address is being assigned to an interface on the router, not the router as a whole so the command would not be entered at global config mode.
The most common situation in which a router interface might be set as a DHCP client is to enable one DHCP router to obtain configuration options from another router providing this service.
Consider an example where RouterA is connected to RouterB. RouterA contains a complete DHCP configuration including the options (DNS server, domain name). RouterB is connected to RouterA through its FastEthernet0 interface. The following configuration would allow RouterB to issue a different set of addresses than RouterA while importing the options from Router A. The configuration of RouterB is below as shown in the partial output of the show run command:

Note that for this configuration to function properly, the FastEthernet0 interface on RouterB must be set as a DHCP client.
The command router(config)# ip address dhcp is incorrect because it is executed at the global configuration prompt. The command must be executed in interface configuration mode.
The command router(dhcp-config)# ip address dhcp is incorrect because it is executed at the DHCP configuration prompt. The command must be executed in interface configuration mode.
The command router(config)# address dhcp is incorrect because it is missing the ip part of the command.
The command router(dhcp-config)# address dhcp is incorrect because it is missing the ip part of the command and it is executed at the DHCP configuration prompt. It must be executed in interface configuration mode.
Objective:
Layer 3 Technologies
Sub-Objective:
Identify, configure, and verify IPv4 addressing and subnetting
Cisco > Cisco IOS IP Addressing Services Command Reference > ip address dhcp

The command snmp-server host 192.168.5.5 informs version 3 noauth CISCO will configure the host to authenticate a user by username and send clear text notifications. The receiver will then acknowledge receipt of the notification. The keyword informs indicates that an inform message type will be used. Unlike a trap, an inform message is acknowledged by the receiver.
The version 3 keyword indicates that version 3 is in use, which is the ONLY version that supports authentication and encryption. Finally, the noauth keyword specifies authentication by username only and no encryption.
The command snmp-server host 192.168.5.5 traps version 3 auth CISCO configures the host to send traps rather than informs.
The command snmp-server host 192.168.5.5 informs version 2c CISCO specifies version 2c, which only support community string-based authentication.
The command snmp-server host 192.168.5.5 informs version 3 authpriv CISCO specifies the keyword authpriv, which indicates encryption will be used and authentication based on HMAC-MD5 or HMAC-SHA algorithms.
Objective:
Infrastructure Services
Sub-Objective:
Configure and verify SNMP
Configuring SNMP Support > Understanding SNMP > SNMP Versions
Cisco IOS Network Management Command Reference > snmp-server engineID local through snmp trap link-status > snmp-server host

The show ipv6 interface command is used to verify the link-local, global unicast, and multicast addresses assigned to an IPv6-enabled router interface. The show ipv6 interface command displays information regarding that interface, such as the physical state, MTU, and IPv6 enable/disable state.
A partial output of the show ipv6 interface command on an IPv6-enabled router named rtrA is as follows:

In the given sample output, you can see that the Fa0/1 interface of rtrA has the link-local address FE80::6339:7BFF:FE5D:A031/64 and the global unicast address 2001:7067:90D1:1::1. The global unicast address is not in EUI-64 format because when the ipv6 address command was issued, the eui64 keyword was not used. If EUI-64 format had been specified with the eui64 keyword, the global unicast address would have been 2001:7067:90D1:1:6339:7BFF:FE5D:A031.
An IPv6-enabled interface has not only a link-local and global unicast address, but also one or more multicast addresses. A multicast address is an IPv6 address that has the prefix FF00::/8. These addresses are assigned to interfaces of different nodes such that they appear as a logical group. This implies that when a packet is destined for a multicast address, that packet is delivered to all the interfaces that have the same multicast address. The various multicast groups are as follows:
• FF02::1 Indicates the group of all the nodes on the local segment
• FF02::2 Indicates the group of all the routers on the local segment
• FF02::1:FF00:0/104 Indicates a solicited-node multicast group for every unicast or anycast address assigned to the interface
You can also notice in the sample output that the Fa0/1 interface belongs to three multicast groups: FF02::1, FF02::2, and FF02::1:FF5D:A031. The first two multicast groups refer to the all-host and all-router multicast groups, respectively. The third group, FF02::1:FF5D:A031, is the solicited-node multicast address. This address is created for every unicast or anycast address. A solicited-node multicast address is determined by assigning the least significant 24 bits of the unicast address to the least significant 24 bits of the FF02::1:FF00:0 address.
The show ipv6 neighbors command displays the link-local /global unicast addresses of the neighbors, including other information such as state and the next-hop interface.
The show ipv6 route command is used to view the IPv6 routing table on the router. This command displays the prefixes, administrative distance, metric, and next-hop addresses for various IPv6 networks.
The show ipv6 protocols command is used to view the active routing protocols for IPv6 on the router. This command shows the interfaces, redistribution status, and summarization status about each of the routing protocols enabled on the router.
Objective:
Layer 3 Technologies
Sub-Objective:
Identify IPv6 addressing and subnetting
Cisco IOS IPv6 Command Reference > show ipv6 eigrp topology through show ipv6 nat statistics > show ipv6 interface
Cisco IOS IPv6 Command Reference > show ipv6 nat translations through show ipv6 protocols > show ipv6 neighbors
Cisco IOS IPv6 Command Reference > show ipv6 nat translations through show ipv6 protocols > show ipv6 protocols
Cisco > Products & Services > Cisco IOS and NX-OS Software > Cisco IOS Technologies > IPv6 > Product Literature > White Papers > Cisco IOS IPv6 Multicast Introduction
Cisco > IPv6 Implementation Guide, Release 15.2M&T > Implementing IPv6 Multicast

The command ip cef must be present in the configuration to support Unicast Reverse Path Forwarding (RPF). If the router is set to its defaults, it will be present. Unicasts RPF uses the tables created by CEF to validate packet source addresses. Therefore, it must be enabled. Unicast RPF can be enabled in three modes:
• Strict mode - The source address must be must be reachable on the interface where the packet arrived.
• Loose mode - Traffic is allowed if the source address is reachable via any interface on the router as indicted in the routing table.
• VRF mode - Evaluates an incoming packet's source IP address against the VRF table configured for an eBGP neighbor.
The bandwidth command, while desirable to ensure proper cost calculation of the interface for routing purposes, is not a requirement for Unicast RPF.
The ip route 0.0.0.0 0.0.0 command creates a default route. A default route does not need to be present for Unicast RPF to function.
The log command is not required. This command should be used with caution with any access list, as it causes an increase in CPU usage in the router.
Objective:
Infrastructure Security
Sub-Objective:
Configure and verify router security features
Cisco IOS Security Configuration Guide, Release 12.2 > Part 5: Other Security Features > Configuring Unicast Reverse Path Forwarding
Cisco > Cisco IOS IP Switching Command Reference > ip cef

The show ip eigrp topology all-links command displays both feasible successors and non-feasible successors to a given destination network. This command displays the contents of the topology table and shows all the routes available for a given destination network.
An example of partial output of the command is below:

The 172.20.2.0/24 network has a feasible successor. This can be determined by looking at the values in the parenthesis next to each route. The second value after the / is the advertised distance from the successor. This value must be less than the value of the feasible distance for a route to be considered a feasible successor. There are two routes for 172.20.2.0/24. The first route listed, via 172.17.3.1, is the successor route. Its cost is 246983122, which matches the feasible distance (FD). The second route, via 172.17.1.1, has an advertised distance of 2443698 (the second value in the parentheses after the /). Because this value is less than the FD (2413698), it qualifies as a feasible successor.
The 172.25.1.0/24 network does not have a feasible successor. The second route listed via 172.17.1.1 has an advertised distance of 2501649, which is greater than the value of the FD, (2416381). Therefore, it is not a feasible successor.
You should not use the show ip route eigrp command. This command displays only the best metric routes (successors) to a given destination network. A route has the best metric if it has the least feasible distance, which refers to the sum of the metric from a given neighbor to a destination network and the metric to reach that neighbor.
You should not use the show ip eigrp topology command without the all-links parameter. This command displays only the feasible successors to a given destination network.
You should not use the show ip eigrp topology zero-successors command because this command lists those routes that do not have a valid successor.
Objective:
Layer 3 Technologies
Sub-Objective:
Configure and verify policy-based routing
Cisco IOS IP Routing: EIGRP Command Reference > show ip eigrp topology

The show ip protocols command gives information about any dynamic routing protocol, including EIGRP. With respect to EIGRP, it will show the K values as a part of the output. A sample is shown below:
Routing Protocol is "eigrp 77"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates
Default networks accepted from incoming updates
EIGRP metric weight K1=1,K2=0,K3=1,K4=0,K5=0
EIGRP maximum, hopcount 100

The debug ip eigrp command displays real-time information about EIGRP packets that are received and sent. It does not contain K values. A single line of this command output is shown below:
Router# debug ip eigrp
IP-EIGRP: Processing incoming UPDATE packet
IP-EIGRP: Ext 192.168.5.0 255.255.255.0 M 386560 - 256000 130560 SM 360960 - 256000 104960

The debug eigrp packet command displays general debug information, but not K values. A sample of this command output is shown below:
Router# debug eigrp packet
EIGRP: Sending HELLO on Ethernet0/1
AS 109, Flags 0x0, Seq 0, Ack 0
EIGRP: Received UPDATE on Ethernet0/1 from 192.195.78.24,
AS 109, Flags 0x1, Seq 1, Ack 0

The show ip eigrp traffic command displays packets received, as well as statistics on hello packets, updates, queries, and acknowledgments, but not K values. Partial output of this command is shown below:
Router# show ip eigrp traffic
IP-EIGRP Traffic Statistics for process 151
Hellos sent/received: 220/205
Updates sent/received: 7/29
Queries sent/received: 2/0
Replies sent/received: 0/2
Acks sent/received: 29/14

Objective:
Layer 3 Technologies
Sub-Objective:
Describe and optimize EIGRP metrics
Cisco IOS Master Command List, Release 12.4T > sa ipsec through show ip route dhcp > show ip protocols

The show ip eigrp topology all-links command displays both the feasible successors and the non-feasible successors. Feasible successors refer to backup routes to a particular destination network.
Routers compute the metric/distance of every route they learn from their EIGRP neighbors. There can be multiple routes to the same destination network. The route with the least metric value to a specific destination network is selected as the best path, or successor, to that network. However, if the successor goes down, the router computes the next best loop-free path to the same destination network, which is called the feasible successor.
Feasible successors must have a reported (or advertised) distance that is less than the feasible distance, or current best metric. The routes that are neither successors nor feasible successors are called non-feasible successors. The feasible successors and the non-feasible successors can be viewed by running the show ip eigrp topology all-links command. Sample output is shown below:

The router at 172.17.3.1 is directly connected to three networks: 172.25.1.0/24, 172.20.2.0/24, and 172.18.2.0/24. The second network, 172.20.2.0/24, is listed as the source of the successor routes to those networks. The connection to the last network, 172.18.2.0/4, can deduced by the fact that the local router uses the Serial1 interface to connect to the two networks that the router at 172.17.3.1 is a successor for. Therefore, that router must be directly connected to the network on the Serial1 interface of the local router.
Objective:
Layer 3 Technologies
Sub-Objective:
Configure and verify policy-based routing
Cisco IOS IP Routing: EIGRP Command Reference > show ip eigrp topology

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
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

The Broadband Network Gateway does not send a PPPoE Active Discovery Offer to the client during the PPP Session Phase. That action occurs during the Active Discovery Phase.
During the PPP Session Phase, the following steps occur:
• PPP options are negotiated.
• Authentication is performed.
• Network Control Protocols (NCP) for any Layer 3 protocols that will traverse the link are started, and these Layer 3 packets will be transmitted within PPPoE headers.
Objective:
Layer 2 Technologies
Sub-Objective:
Configure and verify PPP
Cisco Support Community > ASR9000 BNG debugging PPPoE sessions
Cisco > Cisco Security Appliance Command Line Configuration Guide, Version 8.0 > Configuring the PPPoE Client > PPPoE Client Overview

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
Cisco IOS IPv6 Configuration Guide, Release 12.4 > Implementing Tunneling for IPv6 > Configuration Examples for Implementing Tunneling for IPv6 > Example: Configuring Manual IPv6 Tunnels