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QUESTION 1
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.
Correct Answer: C Explanation
Explanation/Reference:
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).
QUESTION 2
Refer to the exhibit.
A network administrator checks this adjacency table on a router. What is a possible cause for the incomplete marking?
A. incomplete ARP information
B. incorrect ACL
C. dynamic routing protocol failure
D. serial link congestion Correct Answer: A
Explanation Explanation/Reference:
Explanation:
To display information about the Cisco Express Forwarding adjacency table or the hardware Layer 3-switching adjacency table, use the show adjacency
command.
Reasons for Incomplete Adjacencies
There are two known reasons for an incomplete adjacency:
The router cannot use ARP successfully for the next-hop interface.
After a clear ip arp or a clear adjacency command, the router marks the adjacency as incomplete. Then it fails to clear the entry.
In an MPLS environment, IP CEF should be enabeled for Label Switching. Interface level command ip route-cache cef No ARP Entry When CEF cannot locate a valid adjacency for a destination prefix, it punts the packets to the CPU for ARP resolution and, in turn, for completion of the adjacency.
Reference: http://www.cisco.com/c/en/us/support/docs/ip/express-forwarding-cef/17812-cef- incomp.html#t4
QUESTION 3
A network engineer notices that transmission rates of senders of TCP traffic sharply increase and decrease simultaneously during periods of congestion. Which condition causes this?
A. global synchronization
B. tail drop
C. random early detection
D. queue management algorithm
Correct Answer: A Explanation Explanation/Reference:
Explanation: TCP global synchronization in computer networks can happen to TCP/IP flows during periods of congestion because each sender will reduce their transmission rate at the same time when packet loss occurs. Routers on the Internet normally have packet queues, to allow them to hold packets when the network is busy, rather than discarding them. Because routers have limited resources, the size of these queues is also limited. The simplest technique to limit queue size is known as tail drop. The queue is allowed to fill to its maximum size, and then any new packets are simply discarded, until there is space in the queue again. This causes problems when used on TCP/IP routers handling multiple TCP streams, especially when bursty traffic is present. While the network is stable, the queue is constantly full, and there are no problems except that the full queue results in high latency. However, the introduction of a sudden burst of traffic may cause large numbers of established, steady streams to lose packets simultaneously. Reference: http://en.wikipedia.org/wiki/TCP_global_synchronization
QUESTION 4
Which three problems result from application mixing of UDP and TCP streams within a network with no QoS? (Choose three.)
A. starvation
B. jitter
C. latency
D. windowing
E. lower throughput
Correct Answer: ACE Explanation
Explanation/Reference:
Explanation: It is a general best practice not to mix TCP-based traffic with UDP-based traffic (especially streaming video) within a single service provider class due to the behaviors of these protocols during periods of congestion. Specifically, TCP transmitters will throttle-back flows when drops have been detected. Although some UDP applications have application-level windowing, flow control, and retransmission capabilities, most UDP transmitters are completely oblivious to drops and thus never lower transmission rates due to dropping. When TCP flows are combined with UDP flows in a single service provider class and the class experiences congestion, then TCP flows will continually lower their rates, potentially giving up their bandwidth to drop-oblivious UDP flows. This effect is called TCP-starvation/ UDP-dominance. This can increase latency and lower the overall throughput. TCP-starvation/UDP-dominance likely occurs if (TCP-based) mission-critical data is assigned to the same service provider class as (UDP-based) streaming video and the class experiences sustained congestion. Even if WRED is enabled on the service provider class, the same behavior would be observed, as WRED (for the most part) only affects TCP-based flows. Granted, it is not always possible to separate TCP-based flows from UDP-based flows, but it is beneficial to be aware of this behavior when making such application-mixing decisions. Reference: http://www.cisco.com/warp/public/cc/so/neso/vpn/vpnsp/spqsd_wp.htm
QUESTION 5
Which method allows IPv4 and IPv6 to work together without requiring both to be used for a single connection during the migration process?
A. dual-stack method
B. 6to4 tunneling
C. GRE tunneling
D. NAT-PT
Correct Answer: A Explanation
Explanation/Reference:
Explanation:
Dual stack means that devices are able to run IPv4 and IPv6 in parallel. It allows hosts to simultaneously reach IPv4 and IPv6 content, so it offers a very flexible
coexistence strategy. For sessions that support IPv6, IPv6 is used on a dual stack endpoint. If both endpoints support IPv4 only, then IPv4 is used.
Benefits:
Native dual stack does not require any tunneling mechanisms on internal networks
Both IPv4 and IPv6 run independent of each other
Dual stack supports gradual migration of endpoints, networks, and applications. Reference: http://www.cisco.com/web/strategy/docs/gov/IPV6at_a_glance_c45-625859.pdf
QUESTION 6
Which statement about the use of tunneling to migrate to IPv6 is true?
A. Tunneling is less secure than dual stack or translation.
B. Tunneling is more difficult to configure than dual stack or translation.
C. Tunneling does not enable users of the new protocol to communicate with users of the old protocol without dual-stack hosts.
D. Tunneling destinations are manually determined by the IPv4 address in the low-order 32 bits of IPv4-compatible IPv6 addresses.
Correct Answer: C Explanation
Explanation/Reference:
Explanation:
Using the tunneling option, organizations build an overlay network that tunnels one protocol over the other by encapsulating IPv6 packets within IPv4 packets and
IPv4 packets within IPv6 packets. The advantage of this approach is that the new protocol can work without disturbing the old protocol, thus providing connectivity
between users of the new protocol. Tunneling has two disadvantages, as discussed in RFC 6144:
Users of the new architecture cannot use the services of the underlying infrastructure.
Tunneling does not enable users of the new protocol to communicate with users of the old protocol without dual-stack hosts, which negates interoperability. Reference: http://www.cisco.com/c/en/us/products/collateral/ios-nx-os-software/enterprise-ipv6- solution/white_paper_c11-676278.html
QUESTION 7
A network administrator executes the command clear ip route. Which two tables does this command clear and rebuild? (Choose two.)
A. IP routing
B. FIB
C. ARP cache
D. MAC address table
E. Cisco Express Forwarding table
F. topology table
Correct Answer: AB Explanation
Explanation/Reference:
Explanation:
To clear one or more entries in the IP routing table, use the following commands in any mode:
Command Purpose
clear ip route {* |
Clears one or more routes from both the
{route |
unicast RIB and all the module FIBs. The
prefix/length}[next-hop route options are as follows:
interface]}
· *–All routes.
[vrf vrf-name]
Example:
· route–An individual IP route.
switch(config)# clear ip
· prefix/length–Any IP prefix.
route
· next-hop–The next-hop address
· interface–The interface to reach the
next-hop address.
The vrf-name can be any case-sensitive, al-phanumeric string up to 32 characters.
Reference:
http://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus5000/sw/unicast/5_0_3_N1_1/Ci sco_n5k_layer3_ucast_cfg_rel_503_N1_1/l3_manage-routes.html
QUESTION 8
Which switching method is used when entries are present in the output of the command show ip cache?
A. fast switching
B. process switching
C. Cisco Express Forwarding switching
D. cut-through packet switching
Correct Answer: A Explanation
Explanation/Reference:
Explanation:
Fast switching allows higher throughput by switching a packet using a cache created by the initial packet sent to a particular destination. Destination addresses
are stored in the high-speed cache to expedite forwarding. Routers offer better packet-transfer performance when fast switching is enabled. Fast switching is
enabled by default on all interfaces that support fast switching.
To display the routing table cache used to fast switch IP traffic, use the “show ip cache” EXEC command.
Reference:
http://www.cisco.com/c/en/us/td/docs/ios/12_2/switch/command/reference/fswtch_r/xrfscmd5.ht ml#wp1038133
QUESTION 9
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.
Correct Answer: AB Explanation
Explanation/Reference:
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
QUESTION 10
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
Correct Answer: BCD Explanation
Explanation/Reference:
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 2018 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
QUESTION 11
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
Correct Answer: A Explanation
Explanation/Reference:
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
QUESTION 12
Under which condition does UDP dominance occur?
A. when TCP traffic is in the same class as UDP
B. when UDP flows are assigned a lower priority queue
C. when WRED is enabled
D. when ACLs are in place to block TCP traffic
Correct Answer: A Explanation
Explanation/Reference:
Explanation: Mixing TCP with UDP It is a general best practice to not mix TCP-based traffic with UDP-based traffic (especially Streaming-Video) within a single service-provider class because of the behaviors of these protocols during periods of congestion. Specifically, TCP transmitters throttle back flows when drops are detected. Although some UDP applications have application-level windowing, flow control, and retransmission capabilities, most UDP transmitters are completely oblivious to drops and, thus, never lower transmission rates because of dropping. When TCP flows are combined with UDP flows within a single service-provider class and the class experiences congestion, TCP flows continually lower their transmission rates, potentially giving up their bandwidth to UDP flows that are oblivious to drops. This effect is called TCP starvation/UDP dominance. TCP starvation/UDP dominance likely occurs if (TCP-based) Mission-Critical Data is assigned to the same service-provider class as (UDP-based) Streaming-Video and the class experiences sustained congestion. Even if WRED is enabled on the service-provider class, the same behavior would be observed because WRED (for the most part) manages congestion only on TCP-based flows. Reference: http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoS- SRND-Book/VPNQoS.html
Question Set 2
QUESTION 1
Prior to enabling PPPoE in a virtual private dialup network group, which task must be completed?
A. Disable CDP on the interface.
B. Execute the vpdn enable command.
C. Execute the no switchport command.
D. Enable QoS FIFO for PPPoE support.
Correct Answer: B Explanation
Explanation/Reference:
Explanation:
Enabling PPPoE in a VPDN Group
Perform this task to enable PPPoE in a virtual private dial-up network (VPDN) group.
Restrictions
This task applies only to releases prior to Cisco IOS Release 12.2(13)T.
SUMMARY STEPS
1.
enable
2.
configure terminal
3.
vpdn enable
4.
vpdn-group name
5.
request-dialin
6.
protocol pppoe DETAILED STEPS Command or Action Purpose Step 1 enable Enables privileged EXEC mode. Example: · Enter your password if Router> enable prompted. Step 2 configure terminal Enters global configuration mode. Example: Router# configure terminal Step 3 vpdn enable Enables virtual private dialup Example: networking. Router(config)# vpdn enable Step 4 vpdn-group name Associates a VPDN group with a Example: customer or VPDN profile. Router(config)# vpdn-group group1 Step 5 request-dialin Creates a request-dialin VPDN Example: subgroup. Router(config-vpdn)# request-dialin Step 6 protocol pppoe Enables the VPDN subgroup to Example: establish PPPoE Router(config-vpdn-req-in)# pro tocol pppoe
Reference:
http://www.cisco.com/en/US/docs/ios/12_2t/12_2t2/feature/guide/ftpppoec_support_TSD_Island _of_Content_Chapter.html
QUESTION 2
A network engineer has been asked to ensure that the PPPoE connection is established and authenticated using an encrypted password. Which technology, in combination with PPPoE, can be used for authentication in this manner?
A. PAP
B. dot1x
C. IPsec
D. CHAP
E. ESP
Correct Answer: D Explanation
Explanation/Reference:
Explanation: With PPPoE, the two authentication options are PAP and CHAP. When CHAP is enabled on an interface and a remote device attempts to connect to it, the access server sends a CHAP packet to the remote device. The CHAP packet requests or “challenges” the remote device to respond. The challenge packet consists of an ID, a random number, and the host name of the local router. When the remote device receives the challenge packet, it concatenates the ID, the remote device’s password, and the random number, and then encrypts all of it using the remote device’s password. The remote device sends the results back to the access server, along with the name associated with the password used in the encryption process. When the access server receives the response, it uses the name it received to retrieve a password stored in its user database. The retrieved password should be the same password the remote device used in its encryption process. The access server then encrypts the concatenated information with the newly retrieved password–if the result matches the result sent in the response packet, authentication succeeds. The benefit of using CHAP authentication is that the remote device’s password is never transmitted in clear text (encrypted). This prevents other devices from stealing it and gaining illegal access to the ISP’s network. Reference: http://www.cisco.com/c/en/us/td/docs/ios/12_2/security/configuration/guide/fsecur_c/scfathen.ht ml
QUESTION 3
A corporate policy requires PPPoE to be enabled and to maintain a connection with the ISP, even if no interesting traffic exists. Which feature can be used to accomplish this task?
A. TCP Adjust
B. Dialer Persistent
C. PPPoE Groups
D. half-bridging
E. Peer Neighbor Route
Correct Answer: B Explanation Explanation/Reference:
Explanation:
A new interface configuration command, dialer persistent, allows a dial-on-demand routing (DDR) dialer profile connection to be brought up without being triggered
by interesting traffic. When configured, the dialer persistent command starts a timer when the dialer interface starts up and starts the connection when the timer
expires. If interesting traffic arrives before the timer expires, the connection is still brought up and set as persistent. The command provides a default timer interval,
or you can set a custom timer interval. To configure a dialer interface as persistent, use the following commands beginning in global configuration mode:
Command Purpose
Step 1 Router(config)# interface dialer Creates a dialer interface and number enters interface configuration
mode.
Step 2 Router(config-if)# ip address Specifies the IP address and mask address mask of the dialer interface as a node in
the destination network to be
called.
Step 3 Router(config-if)# encapsulation Specifies the encapsulation type.
type
Step 4 Router(config-if)# dialer string Specifies the remote destination to dial-string class class-name call and the map class that defines characteristics for calls to
this
destination.
Step 5 Router(config-if)# dialer pool Specifies the dialing pool to use number for calls to this destination.
Step 6 Router(config-if)# dialer-group Assigns the dialer interface to a group-number dialer group.
Step 7 Router(config-if)# dialer-list Specifies an access list by list dialer-group protocol protocol- number or by protocol and list name {permit | deny | list number to
define the interesting access-list-number} packets that can trigger a call. Step 8 Router(config-if)# dialer (Optional) Specifies the remote-name user-name
authentication name of the remote router on the destination
subnetwork for a dialer interface.
Step 9 Router(config-if)# dialer Forces a dialer interface to be persistent [delay [initial] connected at all times, even in seconds | max-attempts the absence of
interesting traffic.
number]
Reference:
http://www.cisco.com/c/en/us/td/docs/ios/dial/configuration/guide/12_4t/dia_12_4t_book/dia_dia ler_persist.html
QUESTION 4
Which PPP authentication method sends authentication information in cleartext?
A. MS CHAP
B. CDPCP
C. CHAP
D. PAP
Correct Answer: D Explanation
Explanation/Reference:
Explanation: PAP authentication involves a two-way handshake where the username and password are sent across the link in clear text; hence, PAP authentication does not provide any protection against playback and line sniffing. CHAP authentication, on the other hand, periodically verifies the identity of the remote node using a three-way handshake. After the PPP link is established, the host sends a “challenge” message to the remote node. The remote node responds with a value calculated using a one-way hash function. The host checks the response against its own calculation of the expected hash value. If the values match, the authentication is acknowledged; otherwise, the connection is terminated. Reference: http://www.cisco.com/c/en/us/support/docs/wan/point-to-point-protocol-ppp/10241- ppp-callin-hostname.html
QUESTION 5
Which protocol uses dynamic address mapping to request the next-hop protocol address for a specific connection?
A. Frame Relay inverse ARP
B. static DLCI mapping
C. Frame Relay broadcast queue
D. dynamic DLCI mapping
Correct Answer: A Explanation
Explanation/Reference:
Explanation:
Dynamic address mapping uses Frame Relay Inverse ARP to request the next-hop protocol address for a specific connection, given its known DLCI. Responses
to Inverse ARP requests are entered in an address-to-DLCI mapping table on the router or access server; the table is then used to supply the next-hop protocol
address or the DLCI for outgoing traffic.
Reference:
http://www.cisco.com/c/en/us/td/docs/ios/12_2/wan/configuration/guide/fwan_c/wcffrely.html
QUESTION 6
What is the default OSPF hello interval on a Frame Relay point-to-point network?
A. 10
B. 20
C. 30
D. 40
Correct Answer: A Explanation
Explanation/Reference:
Explanation: Before you troubleshoot any OSPF neighbor-related issues on an NBMA network, it is important to remember that an NBMA network can be configured in these modes of operation with the ip ospf network command: Point-to-Point Point-to-Multipoint Broadcast NBMA The Hello and Dead Intervals of each mode are described in this table: Hello Interval Dead Interval Network Type (secs) (secs) Point-to-Point 10 40 Point-to-Multipoint 30 120 Broadcast 10 40 Non-Broadcast 30 120
Reference: http://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13693- 22.html
QUESTION 7
PPPoE is composed of which two phases?
A. Active Authentication Phase and PPP Session Phase
B. Passive Discovery Phase and PPP Session Phase
C. Active Authorization Phase and PPP Session Phase
D. Active Discovery Phase and PPP Session Phase
Correct Answer: D Explanation
Explanation/Reference:
Explanation:
PPPoE is composed of two main phases:
Active Discovery Phase–In this phase, the PPPoE client locates a PPPoE server, called an access concentrator. During this phase, a Session ID is assigned and
the PPPoE layer is established.
PPP Session Phase–In this phase, PPP options are negotiated and authentication is performed. Once the link setup is completed, PPPoE functions as a Layer 2
encapsulation method, allowing data to be transferred over the PPP link within PPPoE headers. Reference: http://www.cisco.com/c/en/us/td/docs/security/asa/
asa92/configuration/vpn/asa-vpn- cli/vpn-pppoe.html
QUESTION 8
Which statement is true about the PPP Session Phase of PPPoE?
A. PPP options are negotiated and authentication is not performed. Once the link setup is completed, PPPoE functions as a Layer 3 encapsulation method that allows data to be transferred over the PPP link within PPPoE headers.
B. PPP options are not negotiated and authentication is performed. Once the link setup is completed, PPPoE functions as a Layer 4 encapsulation method that allows data to be transferred over the PPP link within PPPoE headers.
C. PPP options are automatically enabled and authorization is performed. Once the link setup is completed, PPPoE functions as a Layer 2 encapsulation method that allows data to be encrypted over the PPP link within PPPoE headers.
D. PPP options are negotiated and authentication is performed. Once the link setup is completed, PPPoE functions as a Layer 2 encapsulation method that allows data to be transferred over the PPP link within PPPoE headers.
Correct Answer: D Explanation
Explanation/Reference:
Explanation:
PPPoE is composed of two main phases:
Active Discovery Phase–In this phase, the PPPoE client locates a PPPoE server, called an access concentrator. During this phase, a Session ID is assigned and the PPPoE layer is established.
PPP Session Phase–In this phase, PPP options are negotiated and authentication is performed. Once the link setup is completed, PPPoE functions as a Layer
2 encapsulation method, allowing data to be transferred over the PPP link within PPPoE headers. Reference: http://www.cisco.com/c/en/us/td/docs/security/asa/asa92/configuration/vpn/asa-vpn- cli/vpn-pppoe.html
Question Set 3 QUESTION 1
Refer to the exhibit.
Which one statement is true?
A. Traffic from the 172.16.0.0/16 network will be blocked by the ACL.
B. The 10.0.0.0/8 network will not be advertised by Router B because the network statement for the 10.0.0.0/8 network is missing from Router B.
C. The 10.0.0.0/8 network will not be in the routing table on Router B.
D. Users on the 10.0.0.0/8 network can successfully ping users on the 192.168.5.0/24 network, but users on the 192.168.5.0/24 cannot successfully ping users on the 10.0.0.0/8 network.
E. Router B will not advertise the 10.0.0.0/8 network because it is blocked by the ACL.
Correct Answer: E Explanation
Explanation/Reference:
Explanation:
You can filter what individual routes are sent (out) or received (in) to any interface within your EIGRP configuration.
One example is noted above. If you filter outbound, the next neighbor(s) will not know about anything except the 172.16.0.0/16 route and therefore won’t send it to
anyone else downstream. If you filter inbound, YOU won’t know about the route and therefore won’t send it to anyone else downstream.
QUESTION 2
A router with an interface that is configured with ipv6 address autoconfig also has a link-local address assigned. Which message is required to obtain a global unicast address when a router is present?
A. DHCPv6 request
B. router-advertisement
C. neighbor-solicitation
D. redirect
Correct Answer: B Explanation
Explanation/Reference:
Explanation: Autoconfiguration is performed on multicast-enabled links only and begins when a multicast- enabled interface is enabled (during system startup or manually). Nodes (both, hosts and routers) begin the process by generating a link-local address for the interface. It is formed by appending the interface identifier to well-known link-local prefix FE80 :: 0. The interface identifier replaces the right-most zeroes of the link-local prefix. Before the link-local address can be assigned to the interface, the node performs the Duplicate Address Detection mechanism to see if any other node is using the same link-local address on the link. It does this by sending a Neighbor Solicitation message with target address as the “tentative” address and destination address as the solicited-node multicast address corresponding to this tentative address. If a node responds with a Neighbor Advertisement message with tentative address as the target address, the address is a duplicate address and must not be used. Hence, manual configuration is required. Once the node verifies that its tentative address is unique on the link, it assigns that link-local address to the interface. At this stage, it has IP-connectivity to other neighbors on this link. The autoconfiguration on the routers stop at this stage, further tasks are performed only by the hosts. The routers will need manual configuration (or stateful configuration) to receive site-local or global addresses. The next phase involves obtaining Router Advertisements from routers if any routers are present on the link. If no routers are present, a stateful configuration is required. If routers are present, the Router Advertisements notify what sort of configurations the hosts need to do and the hosts receive a global unicast IPv6 address. Reference: https://sites.google.com/site/amitsciscozone/home/important-tips/ipv6/ipv6-stateless- autoconfiguration
QUESTION 3
An engineer has configured a router to use EUI-64, and was asked to document the IPv6 address of the router. The router has the following interface parameters:
mac address C601.420F.0007 subnet 2001:DB8:0:1::/64
Which IPv6 addresses should the engineer add to the documentation?
A. 2001:DB8:0:1:C601:42FF:FE0F:7
B. 2001:DB8:0:1:FFFF:C601:420F:7
C. 2001:DB8:0:1:FE80:C601:420F:7
D. 2001:DB8:0:1:C601:42FE:800F:7
Correct Answer: A Explanation
Explanation/Reference:
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 EUI-48 MAC address. Here is an example showing how 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. Reference: https://supportforums.cisco.com/document/100566/understanding-ipv6-eui-64-bit- address
QUESTION 4
For security purposes, an IPv6 traffic filter was configured under various interfaces on the local router. However, shortly after implementing the traffic filter, OSPFv3 neighbor adjacencies were lost. What caused this issue?
A. The traffic filter is blocking all ICMPv6 traffic.
B. The global anycast address must be added to the traffic filter to allow OSPFv3 to work properly.
C. The link-local addresses that were used by OSPFv3 were explicitly denied, which caused the neighbor relationships to fail.
D. IPv6 traffic filtering can be implemented only on SVIs.
Correct Answer: C Explanation
Explanation/Reference:
Explanation:
OSPFv3 uses link-local IPv6 addresses for neighbor discovery and other features, so if any IPv6 traffic filters are implemented be sure to include the link local
address so that it is permitted in the filter list.
Reference: http://www.cisco.com/c/en/us/td/docs/switches/datacenter/sw/5_x/nx- os/unicast/configuration/guide/l3_cli_nxos/l3_ospfv3.html
QUESTION 5
What is the purpose of the autonomous-system {autonomous-system-number} command?
A. It sets the EIGRP autonomous system number in a VRF.
B. It sets the BGP autonomous system number in a VRF.
C. It sets the global EIGRP autonomous system number.
D. It sets the global BGP autonomous system number.
Correct Answer: A Explanation
Explanation/Reference:
Explanation: To configure the autonomous-system number for an Enhanced Interior Gateway Routing Protocol (EIGRP) routing process to run within a VPN routing and forwarding (VRF) instance, use the autonomous-system command in address-family configuration mode. To remove the autonomous-system for an EIGRP routing process from within a VPN VRF instance, use the no form of this command. autonomous-system autonomous-system-number no autonomous-system autonomous-system-number Reference: http://www.cisco.com/c/en/us/td/docs/ios/iproute_eigrp/command/reference/ire_book/ire_a1.htm l#wp1062796
QUESTION 6
Which type of traffic does DHCP snooping drop?
A. discover messages
B. DHCP messages where the source MAC and client MAC do not match
C. traffic from a trusted DHCP server to client
D. DHCP messages where the destination MAC and client MAC do not match
Correct Answer: B Explanation
Explanation/Reference:
Explanation:
The switch validates DHCP packets received on the untrusted interfaces of VLANs with DHCP snooping enabled. The switch forwards the DHCP packet unless
any of the following conditions occur (in which case the packet is dropped):
The switch receives a packet (such as a DHCPOFFER, DHCPACK, DHCPNAK, or DHCPLEASEQUERY packet) from a DHCP server outside the network or firewall.
The switch receives a packet on an untrusted interface, and the source MAC address and the DHCP client hardware address do not match. This check is performed only if the DHCP snooping MAC address verification option is turned on. · The switch receives a DHCPRELEASE or DHCPDECLINE message from an untrusted host with an entry in the DHCP snooping binding table, and the interface information in the binding table does not match the interface on which the message was received.
The switch receives a DHCP packet that includes a relay agent IP address that is not 0.0.0.0. To support trusted edge switches that are connected to untrusted aggregation-switch ports, you can enable the DHCP option-82 on untrusted port feature, which enables untrusted aggregation- switch ports to accept DHCP packets that include option-82 information. Configure the port on the edge switch that connects to the aggregation switch as a trusted port. Reference: http:// www.cisco.com/c/en/us/td/docs/switches/lan/catalyst6500/ios/12- 2SX/configuration/guide/book/snoodhcp.html
QUESTION 7
Refer to the exhibit.
Which command only announces the 1.2.3.0/24 network out of FastEthernet 0/0?
A. distribute list 1 out
B. distribute list 1 out FastEthernet0/0
C. distribute list 2 out
D. distribute list 2 out FastEthernet0/0
Correct Answer: D Explanation
Explanation/Reference:
Explanation:
Access list 2 is more specific, allowing only 1.2.3.0/24, whereas access list 1 permits all 1.0.0.0/8 networks. This question also asks us to apply this distribute list
only to the outbound direction of the fast Ethernet 0/0 interface, so the correct command is “distribute list 2 out FastEthernet0/0.”
QUESTION 8
Which prefix is matched by the command ip prefix-list name permit 10.8.0.0/16 ge 24 le 24?
A. 10.9.1.0/24
B. 10.8.0.0/24
C. 10.8.0.0/16
D. 10.8.0.0/23
Correct Answer: B Explanation
Explanation/Reference:
Explanation:
With prefix lists, the ge 24 term means greater than or equal to a /24 and the le 24 means less than or equal to /24, so only a /24 is both greater than or equal to
24 and less than or equal to 24. This translate to any prefix in the 10.8.x.0/24 network, where X is any value in the 0-255 range.
Only the choice of 10.8.0.0.24 matches this.
QUESTION 9
Router A and Router B are configured with IPv6 addressing and basic routing capabilities using OSPFv3. The networks that are advertised from Router A do not show up in Router B’s routing table. After debugging IPv6 packets, the message “not a router” is found in the output. Why is the routing information not being learned by Router B?
A. OSPFv3 timers were adjusted for fast convergence.
B. The networks were not advertised properly under the OSPFv3 process.
C. An IPv6 traffic filter is blocking the networks from being learned via the Router B interface that is connected to Router A.
D. IPv6 unicast routing is not enabled on Router A or Router B.
Correct Answer: D Explanation
Explanation/Reference:
Explanation:
show ipv6 traffic Field Descriptions
Field Description
source- Number of source-routed packets.
routed
truncated Number of truncated packets.
format Errors that can result from checks performed on header fields, errors the version number, and packet length.
not a Message sent when IPv6 unicast routing is not enabled.
router
Reference:
http://www.cisco.com/c/en/us/td/docs/ios/ipv6/command/reference/ipv6_book/ipv6_16.html
QUESTION 10
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.
Correct Answer: A Explanation
Explanation/Reference:
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
QUESTION 11
A packet capture log indicates that several router solicitation messages were sent from a local host on the IPv6 segment. What is the expected acknowledgment and its usage?
A. Router acknowledgment messages will be forwarded upstream, where the DHCP server will allocate addresses to the local host.
B. Routers on the IPv6 segment will respond with an advertisement that provides an external path from the local subnet, as well as certain data, such as prefix discovery.
C. Duplicate Address Detection will determine if any other local host is using the same IPv6 address for communication with the IPv6 routers on the segment.
D. All local host traffic will be redirected to the router with the lowest ICMPv6 signature, which is statically defined by the network administrator.
Correct Answer: B Explanation
Explanation/Reference:
Explanation: Router Advertisements (RA) are sent in response to router solicitation messages. Router solicitation messages, which have a value of 133 in the Type field of the ICMP packet header, are sent by hosts at system startup so that the host can immediately autoconfigure without needing to wait for the next scheduled RA message. Given that router solicitation messages are usually sent by hosts at system startup (the host does not have a configured unicast address), the source address in router solicitation messages is usually the unspecified IPv6 address (0:0:0:0:0:0:0:0). If the host has a configured unicast address, the unicast address of the interface sending the router solicitation message is used as the source address in the message. The destination address in router solicitation messages is the all-routers multicast address with a scope of the link. When an RA is sent in response to a router solicitation, the destination address in the RA message is the unicast address of the source of the router solicitation message. RA messages typically include the following information:
One or more onlink IPv6 prefixes that nodes on the local link can use to automatically configure their IPv6 addresses
Lifetime information for each prefix included in the advertisement
Sets of flags that indicate the type of autoconfiguration (stateless or stateful) that can be completed
Default router information (whether the router sending the advertisement should be used as a default router and, if so, the amount of time (in seconds) the router should be used as a default router)
Additional information for hosts, such as the hop limit and MTU a host should use in packets that it originates Reference: http://www.cisco.com/c/en/us/td/docs/ios/ipv6/configuration/guide/12_4t/ipv6_12_4t_book/ip6- addrg_bsc_con.html
QUESTION 12
You have been asked to evaluate how EIGRP is functioning in a customer network.
Traffic from R1 to R61 s Loopback address is load shared between R1-R2-R4-R6 and R1-R3- R5-R6 paths. What is the ratio of traffic over each path?
A. 1:1
B. 1:5
C. 6:8
D. 19:80 Correct Answer: D
Explanation Explanation/Reference:
Explanation:
First, find the IP address of the loopback0 interface on R6:
We see that it is 150.1.6.6, so we issue the “show ip route 150.1.6.6” command from R1 and see this:
Notice the “traffic share count” shows 19 for the first path, and 80 for the second path.
QUESTION 13
You have been asked to evaluate how EIGRP is functioning in a customer network.
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