cisco 300-101 online test

Question 1 Topic 1

Topic 1
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.

Answer:

C

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 2 Topic 1

Topic 1
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

Answer:

A

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 3 Topic 1

Topic 1
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

Answer:

A

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 enameled 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 4 Topic 1

Topic 1
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

Answer:

A C E

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 Topic 1

Topic 1
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 32bit 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.

Question 6 Topic 1

Topic 1
Which difference in the packet fragmentation feature between IPv4 and IPv6 devices is true?

• A. Only IPv6 headers support the DF bit.
• B. Only IPv6 packets can be fragmented at the destination.
• C. Only IPv4 headers support the more fragments bit.
• D. Unlike IPv4 routers, IPv6 routers cannot fragment packets by default.

Answer:

D

Question 7 Topic 1

Topic 1
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

Answer:

A

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 (UDPbased) 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 8 Topic 1

Topic 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.

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).

Question 9 Topic 1

Topic 1
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

Answer:

A

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.

Question 10 Topic 1

Topic 1
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

Answer:

A B

Explanation:
To clear one or more entries in the IP routing table, use the following commands in any mode:

Reference:
http://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus5000/sw/unicast/5_0_3_N1_1/Cisco_n5k_layer3_ucast_cfg
_rel_503_N1_1/ l3_manage-routes.html