Q41. CORRECT TEXT
ROUTE.com is a small IT corporation that has an existing enterprise network that is running IPv6 0SPFv3. Currently OSPF is configured on all routers. However, R4's loopback address (FEC0:4:4) cannot be seen in R1's IPv6 routing table. You are tasked with identifying the cause of this fault and implementing the needed corrective actions that uses OPSF features and does not change the current area assignments. You will know that you have corrected the fault when R4's loopback address (FEC0:4:4) can be seen in RTs IPv6 routing table.
Special Note: To gain the maximum number of points you must remove all incorrect or unneeded configuration statements related to this issue.
Answer: Here is the solution below:
Explanation:
To troubleshoot the problem, first issue the show running-config on all of 4 routers. Pay more attention to the outputs of routers R2 and R3 The output of the "show running-config" command of R2:
The output of the "show running-config" command of R3:
We knew that all areas in an Open Shortest Path First (OSPF) autonomous system must be physically connected to the backbone area (Area 0). In some cases, where this is not possible, we can use a virtual link to connect to the backbone through a non-backbone area. The area through which you configure the virtual link is known as a transit area. In this case, the area 11 will become the transit area. Therefore, routers R2 and R3 must be configured with the area <area id> virtual-link <neighbor router-id>command. + Configure virtual link on R2 (from the first output above, we learned that the OSPF process ID of R2 is 1):
R2>enable
R2#configure terminal
R2(config)#ipv6 router ospf 1
R2(config-rtr)#area 11 virtual-link 3.3.3.3
Save the configuration:
R2(config-rtr)#end
R2#copy running-config startup-config
(Notice that we have to use neighbor router-id 3.3.3.3, not R2's router-id 2.2.2.2) + Configure virtual link on R3 (from the second output above, we learned that the OSPF process ID of R3 is 1 and we have to disable the wrong configuration of "area 54 virtual-link 4.4.4.4"):
R3>enable
R3#configure terminal
R3(config)#ipv6 router ospf 1
R3(config-rtr)#no area 54 virtual-link 4.4.4.4
R3(config-rtr)#area 11 virtual-link 2.2.2.2
Save the configuration:
R3(config-rtr)#end
R3#copy running-config startup-config
You should check the configuration of R4, too. Make sure to remove the incorrect configuration statements to get the full points.
R4(config)#ipv6 router ospf 1
R4(config-router)#no area 54 virtual-link 3.3.3.3
R4(config-router)#end
After finishing the configuration doesn’t forget to ping between R1 and R4 to make sure they work.
Note. If you want to check the routing information, use the show ipv6 route command, not "show ip route".
Q42. Refer to the exhibit.
Based on this FIB table, which statement is correct?
A. There is no default gateway.
B. The IP address of the router on FastEthernet is 209.168.201.1.
C. The gateway of last resort is 192.168.201.1.
D. The router will listen for all multicast traffic.
Answer: C
Explanation:
The 0.0.0.0/0 route is the default route and is listed as the first CEF entry. Here we see the next hop for this default route lists 192.168.201.1 as the default router (gateway of last resort).
Q43. Refer to the exhibit. When summarizing these routes, which route is the summarized route?
A. OI 2001:DB8::/48 [110/100] via FE80::A8BB:CCFF:FE00:6F00, Ethernet0/0
B. OI 2001:DB8::/24 [110/100] via FE80::A8BB:CCFF:FE00:6F00, Ethernet0/0
C. OI 2001:DB8::/32 [110/100] via FE80::A8BB:CCFF:FE00:6F00, Ethernet0/0
D. OI 2001:DB8::/64 [110/100] via FE80::A8BB:CCFF:FE00:6F00, Ethernet0/0
Answer: A
Explanation:
Q44. A network engineer is notified that several employees are experiencing network performance related issues, and bandwidth-intensive applications are identified as the root cause. In order to identify which specific type of traffic is causing this slowness, information such as the source/destination IP and Layer 4 port numbers is required. Which feature should the engineer use to gather the required information?
A. SNMP
B. Cisco IOS EEM
C. NetFlow
D. Syslog
E. WCCP
Answer: C
Explanation:
NetFlow Flows Key Fields
A network flow is identified as a unidirectional stream of packets between a given source and destination--
both are defined by a network-layer IP address and
transport-layer source and destination port numbers. Specifically, a flow is identified as the combination of
the following key fields:
Source IP address
Destination IP address
Source Layer 4 port number
Destination Layer 4 port number
Layer 3 protocol type
Type of service (ToS)
Input logical interface Reference: http://www.cisco.com/en/US/docs/ios-xml/ios/netflow/configuration/12-4t/
cfg-nflow- data-expt.html
Q45. After you review the output of the command show ipv6 interface brief, you see that several IPv6 addresses have the 16-bit hexadecimal value of "FFFE" inserted into the address. Based on this information, what do you conclude about these IPv6 addresses?
A. IEEE EUI-64 was implemented when assigning IPv6 addresses on the device.
B. The addresses were misconfigured and will not function as intended.
C. IPv6 addresses containing "FFFE" indicate that the address is reserved for multicast.
D. The IPv6 universal/local flag (bit 7) was flipped.
E. IPv6 unicast forwarding was enabled, but IPv6 Cisco Express Forwarding was disabled.
Answer: A
Explanation:
Extended Unique Identifier (EUI), as per RFC2373, allows a host to assign iteslf a unique 64-
Bit IP Version 6 interface identifier (EUI-64). This feature is a key benefit over IPv4 as it eliminates the
need of manual configuration or DHCP as in the world of IPv4. The IPv6 EUI-64 format address is obtained
through the 48-bit MAC address. The Mac address is first separated into two 24-bits, with one being OUI
(Organizationally Unique Identifier) and the other being NIC specific. The 16-bit 0xFFFE is then inserted
between these two 24-bits to for the 64-bit EUI address. IEEE has chosen FFFE as a reserved value which
can only appear in EUI-64 generated from the an EUI-48 MAC address. Here is an example showing how
a the Mac Address is used to generate EUI.
Next, the seventh bit from the left, or the universal/local (U/L) bit, needs to be inverted. This bit identifies whether this interface identifier is universally or locally administered. If 0, the address is locally
administered and if 1, the address is globally unique. It is worth noticing that in the OUI portion, the globally
unique addresses assigned by the IEEE has always been set to 0 whereas the locally created addresses
has 1 configured. Therefore, when the bit is inverted, it maintains its original scope (global unique address
is still global unique and vice versa). The reason for inverting can be found in RFC4291 section 2.5.1.
Once the above is done, we have a fully functional EUI-64 format address.
Reference: https://
supportforums.cisco.com/document/100566/understanding-ipv6-eui-64-bit- address
Q46. A network administrator uses IP SLA to measure UDP performance and notices that packets on one router have a higher one-way delay compared to the opposite direction. Which UDP characteristic does this scenario describe?
A. latency
B. starvation
C. connectionless communication
D. nonsequencing unordered packets
E. jitter
Answer: A
Explanation:
Cisco IOS IP SLAs provides a proactive notification feature with an SNMP trap. Each measurement
operation can monitor against a pre-set performance threshold.
Cisco IOS IP SLAs generates an SNMP trap to alert management applications if this threshold is crossed.
Several SNMP traps are available: round trip time, average jitter, one-way latency, jitter, packet loss, MOS, and connectivity tests.
Here is a partial sample output from the IP SLA statistics that can be seen:
router#show ip sla statistics 1
Round Trip Time (RTT) for Index 55
Latest RTT: 1 ms
Latest operation start time: *23:43:31.845 UTC Thu Feb 3 2005 Latest operation return code: OK
RTT Values:
Number Of RTT: 10 RTT Min/Avg/Max: 1/1/1 milliseconds Latency one-way time:
Number of Latency one-way Samples: 0
Source to Destination Latency one way Min/Avg/Max: 0/0/0 milliseconds Destination to Source Latency
one way Min/Avg/Max: 0/0/0 milliseconds
Reference:
http://www.cisco.com/en/US/technologies/tk648/tk362/tk920/technologies_white_paper09186a0
0802d5efe.html
Q47. What is a function of NPTv6?
A. It interferes with encryption of the full IP payload.
B. It maintains a per-node state.
C. It is checksum-neutral.
D. It rewrites transport layer headers.
Answer: C
Explanation:
RFC 6296 describes a stateless IPv6-to-IPv6 Network Prefix Translation (NPTv6) function,
designed to provide address independence to the edge network. It is transport-agnostic with respect to
transports that do not checksum the IP header, such as SCTP, and to transports that use the TCP/UDP/
DCCP (Datagram Congestion Control Protocol) pseudo-header and checksum NPTv6 provides a simple
and compelling solution to meet the address-independence requirement in IPv6. The addressindependence
benefit stems directly from the translation function of the network prefix translator. To avoid
as many of the issues associated with NAPT44 as possible, NPTv6 is defined to include a two-way,
checksum-neutral, algorithmic translation function, and nothing else. Reference: http://tools.ietf.org/html/
rfc6296
Q48. A network engineer is configuring a routed interface to forward broadcasts of UDP 69, 53, and 49 to 172.20.14.225. Which command should be applied to the configuration to allow this?
A. router(config-if)#ip helper-address 172.20.14.225
B. router(config-if)#udp helper-address 172.20.14.225
C. router(config-if)#ip udp helper-address 172.20.14.225
D. router(config-if)#ip helper-address 172.20.14.225 69 53 49
Answer: A
Explanation:
To let a router forward broadcast packet the command ip helper-address can be used. The broadcasts will
be forwarded to the unicast address which is specified with the ip helper command.
ip helper-address {ip address}
When configuring the ip helper-address command, the following broadcast packets will be forwarded by
the router by default:
TFTP - UDP port 69
Domain Name System (DNS) UDP port 53
Time service - port 37
NetBIOS Name Server - port 137
NetBIOS Datagram Server - port 138
Bootstrap Protocol (BOOTP) - port 67
TACACS UDP port 49 Reference: http://www.cisco-faq.com/163/forward_udp_broadcas.html
Topic 6, Infrastructure Services
61. A network engineer is configuring SNMP on network devices to utilize one-way SNMP notifications. However, the engineer is not concerned with authentication or encryption. Which command satisfies the requirements of this scenario?
A. router(config)#snmp-server host 172.16.201.28 traps version 2c CISCORO
B. router(config)#snmp-server host 172.16.201.28 informs version 2c CISCORO
C. router(config)#snmp-server host 172.16.201.28 traps version 3 auth CISCORO
D. router(config)#snmp-server host 172.16.201.28 informs version 3 auth CISCORO
Answer: A
Explanation:
Most network admins and engineers are familiar with SNMPv2c which has become the
dominant SNMP version of the past decade. It's simple to configure on both the router/switch-side and just
as easy on the network monitoring server. The problem of course is that the SNMP statistical payload is
not encrypted and authentication is passed in cleartext. Most companies have decided that the information
being transmitted isn't valuable enough to be worth the extra effort in upgrading to SNMPv3, but I would
suggest otherwise. Like IPv4 to IPv6, there are some major changes under the hood. SNMP version 2
uses community strings (think cleartext passwords, no encryption) to authenticate polling and trap delivery.
SNMP version 3 moves away from the community string approach in favor of user- based authentication
and view-based access control. The users are not actual local user accounts, rather they are simply a
means to determine who can authenticate to the device. The view is used to define what the user account
may access on the IOS device. Finally, each user is added to a group, which determines the access policy
for its users. Users, groups, views. Reference: http://www.ccnpguide.com/snmp-version-3/
Q49. Which three TCP enhancements can be used with TCP selective acknowledgments? (Choose three.)
A. header compression
B. explicit congestion notification
C. keepalive
D. time stamps
E. TCP path discovery
F. MTU window
Answer: B,C,D
Explanation:
TCP Selective Acknowledgment
The TCP Selective Acknowledgment feature improves performance if multiple packets are lost from one
TCP window of data.
Prior to this feature, because of limited information available from cumulative acknowledgments, a TCP
sender could learn about only one lost packet per-round-trip
time. An aggressive sender could choose to resend packets early, but such re-sent segments might have
already been successfully received.
The TCP selective acknowledgment mechanism helps improve performance. The receiving TCP host
returns selective acknowledgment packets to the sender,
informing the sender of data that has been received. In other words, the receiver can acknowledge packets
received out of order. The sender can then resend only
missing data segments (instead of everything since the first missing packet).
Prior to selective acknowledgment, if TCP lost packets 4 and 7 out of an 8-packet window, TCP would
receive acknowledgment of only packets 1, 2, and 3. Packets
4 through 8 would need to be re-sent. With selective acknowledgment, TCP receives acknowledgment of
packets 1, 2, 3, 5, 6, and 8. Only packets 4 and 7 must be
re-sent.
TCP selective acknowledgment is used only when multiple packets are dropped within one TCP window.
There is no performance impact when the feature is
enabled but not used. Use the ip tcp selective-ack command in global configuration mode to enable TCP
selective acknowledgment.
Refer to RFC 2021 for more details about TCP selective acknowledgment.
TCP Time Stamp
The TCP time-stamp option provides improved TCP round-trip time measurements. Because the time
stamps are always sent and echoed in both directions and the time-stamp value in the header is always
changing, TCP header compression will not compress the outgoing packet. To allow TCP header
compression over a serial link, the TCP time-stamp option is disabled. Use the ip tcp timestamp command
to enable the TCP time-stamp option.
TCP Explicit Congestion Notification
The TCP Explicit Congestion Notification (ECN) feature allows an intermediate router to notify end hosts of
impending network congestion. It also provides enhanced support for TCP sessions associated with
applications, such as Telnet, web browsing, and transfer of audio and video data that are sensitive to delay
or packet loss. The benefit of this feature is the reduction of delay and packet loss in data transmissions.
Use the ip tcp ecn command in global configuration mode to enable TCP ECN.
TCP Keepalive Timer
The TCP Keepalive Timer feature provides a mechanism to identify dead connections. When a TCP
connection on a routing device is idle for too long, the device sends a TCP keepalive packet to the peer
with only the Acknowledgment (ACK) flag turned on. If a response packet (a TCP ACK packet) is not
received after the device sends a specific number of probes, the connection is considered dead and the
device initiating the probes frees resources used by the TCP connection. Reference: http://www.cisco.com/
c/en/us/td/docs/ios-xml/ios/ipapp/configuration/xe-3s/asr1000/iap-xe-3s-asr1000-book/iap-tcp.html#GUID-22A82C5F-631F-4390-9838-F2E48FFEEA01
Q50. Which two actions must you perform to enable and use window scaling on a router? (Choose two.)
A. Execute the command ip tcp window-size 65536.
B. Set window scaling to be used on the remote host.
C. Execute the command ip tcp queuemax.
D. Set TCP options to "enabled" on the remote host.
E. Execute the command ip tcp adjust-mss.
Answer: A,B
Explanation:
The TCP Window Scaling feature adds support for the Window Scaling option in RFC 1323,
TCP Extensions for High Performance . A larger window size is recommended to improve TCP performance in network paths with large bandwidth-delay product characteristics that are called Long Fat
Networks (LFNs).
The TCP Window Scaling enhancement provides that support. The window scaling extension in Cisco IOS software expands the definition of the TCP window to 32 bits and then uses a scale factor to carry this 32-bit value in the 16-bit window field of the TCP header.
The window size can increase to a scale factor of 14. Typical applications use a scale factor of 3 when deployed in LFNs.
The TCP Window Scaling feature complies with RFC 1323. The larger scalable window size will allow TCP to perform better over LFNs.
Use the ip tcp window-size command in global configuration mode to configure the TCP window size. In order for this to work, the remote host must also support this feature and its window size must be increased.
Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp/
configuration/12-4t/iap-12- 4t-book/iap-tcp.html#GUID-BD998AC6-F128-47DD-B5F7-B226546D4B08