Q1. Refer to the exhibit. The network setup is running the RIP routing protocol. Which two events will occur following link failure between R2 and R3? (Choose two.)
A. R2 will advertise network 192.168.2.0/27 with a hop count of 16 to R1.
B. R2 will not send any advertisements and will remove route 192.168.2.0/27 from its routing table.
C. R1 will reply to R2 with the advertisement for network 192.168.2.0/27 with a hop count of 16.
D. After communication fails and after the hold-down timer expires, R1 will remove the 192.168.2.0/27 route from its routing table.
E. R3 will not accept any further updates from R2, due to the split-horizon loop prevention mechanism.
Answer: A,C
Explanation:
Q2. 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).
Q3. 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
Q4. After a recent DoS attack on a network, senior management asks you to implement better logging functionality on all IOS-based devices. Which two actions can you take to provide enhanced logging results? (Choose two.)
A. Use the msec option to enable service time stamps.
B. Increase the logging history .
C. Set the logging severity level to 1.
D. Specify a logging rate limit.
E. Disable event logging on all noncritical items.
Answer: A,B
Explanation:
The optional msec keyword specifies the date/time format should include milliseconds. This can aid in
pinpointing the exact time of events, or to correlate the order that the events happened. To limit syslog messages sent to the router's history table and to an SNMP network management station based on severity, use the logging history command in global configuration mode. By default, Cisco devices Log error messages of severity levels 0 through 4 (emergency, alert, critical, error, and warning levels); in other words, "saving level warnings or higher." By increasing the severity level, more granular monitoring can occur, and SNMP messages will be sent by the less sever (5-7) messages.
Q5. 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
Answer: B
Explanation:
Autoconfiguration is performed on multicast-enabled links only and begins when a multicastenabled
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
Q6. Scenario:
You have been asked to evaluate an OSPF network setup in a test lab and to answer questions a customer has about its operation. The customer has disabled your access to the show running-config command.
Which of the following statements is true about the serial links that terminate in R3
A. The R1-R3 link needs the neighbor command for the adjacency to stay up
B. The R2-R3 link OSPF timer values are 30, 120, 120
C. The R1-R3 link OSPF timer values should be 10,40,40
D. R3 is responsible for flooding LSUs to all the routers on the network.
Answer: B
Explanation: