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QUESTION 231
On the basis of the definitions of different services in various RFCs, traffic with Expedited
Forwarding per-hop behavior should be marked as which of these?
A. IP ToS of 0xEF
B. IP experimental ECN
C. DSCP decimal 5
D. Binary value of 101110
Answer: D
Explanation:
The assured forwarding (AF) model is used to provide priority values to different data applications. The Expedited Forwarding (EF) model is used to provide resources to latency (delay) sensitive real- time, interactive traffic. The EF model uses one marking — DSCP 46. DSCP 46 is backward compatible with an IP Precedence value of 5 as seen in the following binary pattern:
101110 = DSCP 46
The EF marking of 46 does NOT follow the drop preference rules of the assured forwarding model.
Please do
NOT think that the 11 means high drop preference. The EF model is used for voice over IP media traffic (RTP) by default in most vendors phones. Cisco IP Phones mark signaling packets (SCCP or SIP) to CS3 (24), while media (RTP) is marked to EF (DSCP 46) by default. All EF traffic is normally mapped to the priority queue (PQ) on Cisco switches and routers. The priority queue guarantees three critical services:
Packet Loss
Delay
Jitter (delay variation)
The three most significant bits of 101 are only considered if IP Precedence was being used. The binary digits of 4 2 1 are used to factor the 101 binary pattern when only three digits are under consideration. The DSCP binary pattern of 101110 (46) uses six digits or binary values-32 16 8 4 2 1. It is good to know how to convert a DSCP decimal value to an entire ToS octet (byte) values as well. The ToS byte uses all eight bits, while the DSCP is only using the leading six digits. The EF pattern discussed above will become 10111000 when considering the entire octet. Notice the two least significant zeros that were added to the 101110 binary pattern. Many network management utilities will only allow administrators to configure or display the entire ToS byte. A ping V from a Microsoft operating system requires setting the entire ToS byte. An extended ping from a Cisco router will also allow administrators to see the entire ToS byte. Sniffer Pro LAN and Wire Shark sniffers show the entire ToS field as well. IP accounting shows the entire ToS byte, while Netflow shows the ToS byte in hexadecimal format. The ToS byte value for EF is as follows:
128 64 32 16 8 4 2 1
1 0 1 1 1 0 0 0
A DSCP value of 46 results in a ToS byte value of 184. Although you can mark a ping with a ToS value of 184, the ICMP (ping) traffic will probably not be mapped to the proper application class. In the next blog, we will learn QoS models for using markings for different application classes.
QUESTION 232
Prior to 802.1w, Cisco implemented a number of proprietary enhancements to 802.1D to improve
convergence in a Layer 2 network. Which statement is correct?
A. Only UplinkFast and BackboneFast are specified in 802.1w; PortFast must be manually
configured.
B. Only PortFast is specified in 802.1w; UplinkFast and BackboneFast must be manually configured.
C. None of the proprietary Cisco enhancements are specified in 802.1w.
D. PortFast, UplinkFast, and BackboneFast are specified in 802.1w.
Answer: D
Explanation:
Spanning-tree PortFast causes a spanning-tree port to enter the forwarding state immediately, bypassing the listening and learning states. You can use PortFast on switch ports connected to a single workstation or server to allow those devices to connect to the network immediately, rather than waiting for spanning tree to converge.
UplinkFast provides fast convergence after a spanning-tree topology change and achieves load balancing between redundant links using uplink groups. An uplink group is a set of ports (per VLAN), only one of which is forwarding at any given time. Specifically, an uplink group consists of the root port (which is forwarding) and a set of blocked ports, except for self-looping ports. The uplink group provides an alternate path in case the currently forwarding link fails. BackboneFast is initiated when a root port or blocked port on a switch receives inferior BPDUs from its designated bridge. An inferior BPDU identifies one switch as both the root bridge and the
designated bridge. When a switch receives an inferior BPDU, it indicates that a link to which the switch is not directly connected (an indirect link) has failed (that is, the designated bridge has lost its connection to the root bridge). Under normal spanning-tree rules, the switch ignores inferior BPDUs for the configured maximum aging time, as specified by the aging time variable of the “set spantree MaxAge” command. The switch tries to determine if it has an alternate path to the root bridge. If the inferior BPDU arrives on a blocked port, the root port and other blocked ports on the switch become alternate paths to the root bridge. (Self-looped ports are not considered alternate paths to the root bridge.) If the inferior BPDU arrives on the root port, all blocked ports become alternate paths to the root bridge. If the inferior BPDU arrives on the root port and there are no blocked ports, the switch assumes that it has lost connectivity to the root bridge, causes the maximum aging time on the root to expire, and becomes the root switch according to normal spanning-tree rules. If the switch has alternate paths to the root bridge, it uses these alternate paths to transmit a new kind of PDU called the Root Link Query PDU. The switch sends the Root Link Query PDU out all alternate paths to the root bridge. If the switch determines that it still has an alternate path to the root, it causes the maximum aging time on the ports on which it received the inferior BPDU to expire. If all the alternate paths to the root bridge indicate that the switch has lost connectivity to the root bridge, the switch causes the maximum aging times on the ports on which it received an inferior BPDU to expire. If one or more alternate paths can still connect to the root bridge, the switch makes all ports on which it received an inferior BPDU its designated ports and moves them out of the blocking state (if they were in blocking state), through the listening and learning states, and into the forwarding state.
QUESTION 233
In Frame Relay, FECN messages indicating congestion are sent or received by which of
following?
A. Sent by the destination
B. Received by the sender
C. Received by the destination
D. Sent by the sender
Answer: C
QUESTION 234
Which statement is correct in reference to IPv6 multicast?
A. IPv6 multicast uses Multicast Listener Discovery.
B. The first 8 bits of an IPv6 multicast address are always FF (1111 1111).
C. IPv6 multicast requires MSDP.
D. PIM dense mode is not part of IPv6 multicast.
Answer: A
QUESTION 235
As a network administrator, can you tell me what the root guard feature provides in a
bridgednetwork?
A. It ensures that BPDUs sent by the root bridge are forwarded in a timely manner
B. It enforces the root bridge placement in the network
C. It ensures that all ports receiving BPDUs from the root bridge are in the forwarding state.
D. It ensures that the bridge is elected as root bridge in the network.
Answer: B
Explanation:
Root Guard–Enabled per port; ignores any received superior BPDUs to prevent a switch connected to this port from becoming root. Upon receipt of superior BPDUs, this switch puts the port in a loop- inconsistent state, ceasing forwarding and receiving frames until the superior BPDUs cease. The STP topology can be changed based on one of these unexpected and undesired switches being added to the network. For instance, this newly added and unexpected switch might have the lowest bridge ID and become the root. To prevent such problems, BPDU Guard and Root Guard can be enabled on these access ports to monitor for incoming BPDUs.
QUESTION 236
If you have overlapping IP address between two different networks or routing domains, which two
commands are needed to globally configure NAT to get this to work?
A. ip nat outside source static udp x.x.x.x y.y.y.y and ip nat inside source udp x.x.x.x y.y.y.y
B. ip nat outside source static x.x.x.x y.y.y.y and ip nat inside source static x.x.x.x y.y.y.y
C. ip nat outside source static tcp x.x.x.x y.y.y.y and ip nat outside source tcp x.x.x.x y.y.y.y
D. ip nat outside source list 1 interface x and ip nat inside source list 1 interface x
Answer: B
Explanation:
IP nat outside source list
Translates the source of the IP packets that are traveling outside to inside. Translates the destination of the IP packets that are traveling inside to outside
IP nat inside source list Translates the source of IP packets that are traveling inside to outside. Translates the destination of the IP packets that are traveling outside to inside
QUESTION 237
Two directly connected routers, R1 and R2, are both configured for OSPF graceful restart. R2 is
able to switch packets in hardware, but R1 is not. If a network administrator logs on to R2 and
performs a system reload, which will be the result?
A. Traffic forwarded from R2 to or through R1 will continue to be forwarded based on the forwarding
table state at the time of the reload. OSPF will
B. R2 will continue to forward traffic to R1, but R1 will drop the traffic because its neighbor adjacency
with R2 has failed.
C. R2 will continue forwarding traffic to and through R1, but R1 will drop this traffic because it is not
capable of maintaining its forwarding state
D. All the traffic R2 is forwarding to or through R1 will be dropped while OSPF rebuilds its neighbor
adjacency and forwarding tables.
Answer: A
QUESTION 238
In which way can the IPv6 address of 2031:0000:130F:0000:0000:09C0:876A:130B be expressed
most efficiently?
A. 2031:0:130F:0:0:09C0:876A:130B
B. 2031::130F::9C0:876A:130B
C. 2031:0:130F::9C0:876A:130B
D. 2031:0:130F:0:0:9C0:876A:130B
Answer: C
Explanation:
IPv6 Addressing Notation
IP addresses change significantly with IPv6. IPv6 addresses are 16 bytes (128 bits) long rather than four bytes (32 bits). This larger size means that IPv6 supports more than 300,000,000,000,000,000,000,000,000,000,000,000,000 possible addresses! As an increasing number of cell phones and other consumer electronics expand their networking capability and require their own addresses, the smaller IPv4 address space will eventually run out and IPv6 become mandatory.
IPv6 addresses are generally written in the following form:
hhhh:hhhh:hhhh:hhhh:hhhh:hhhh:hhhh:hhhh
In this full notation, pairs of IPv6 bytes are separated by a colon and each byte in turns is represented as a pair of hexadecimal numbers, like in the following example:
E3D7:0000:0000:0000:51F4:9BC8:C0A8:6420
As shown above, IPv6 addresses commonly contain many bytes with a zero value. Shorthand notation in IPv6 removes these values from the text representation (though the bytes are still present in the actual network address) as follows:
E3D7::51F4:9BC8:C0A8:6420
Finally, many IPv6 addresses are extensions of IPv4 addresses. In these cases, the rightmost four bytes of an IPv6 address (the rightmost two byte pairs) may be rewritten in the IPv4 notation. Converting the above example to mixed notation yields E3D7::51F4:9BC8:192.168.100.32 IPv6 addresses may be written in any of the full, shorthand or mixed notation illustrated above.
http://compnetworking.about.com/od/tcpiptutorials/a/ipaddrnotation.htm
QUESTION 239
Internet Protocol version 6 (IPv6) is the next-generation Internet Layer protocol for
packet-switched internetworks and the Internet. IPv6 router solicitation is:
A. A request made by a node for the IP address of the local router
B. A request made by a node to join a specified multicast group
C. A request made by a node for a DHCP provided IP address
D. A request made by a node for the IP address of the DHCP server
Answer: A
Explanation:
In cases when the host (computer or server) needs to prompt an immediate router advertisement, it sends what is called as a Router Solicitation. Examples of this include commands for re-booting or re- starting a running computer. The system is alerted through router solicitation. Router solicitation messages belong to the ICMPv6 set of messages, specific to the IPv6 protocol. They are identified by a Next Header value “x’3A and decimal 58. An IPv6 router solicitation is closely associated to the Neighbor Discovery (ND) function of the IPv6. Under this, the hosts or routers obtain or discover the link-layer addresses for elements that reside on attached links (neighbor) and to cleansed or purge spaces with cached values that are no longer functioning.
QUESTION 240
Which two types of QoS functionality will be provided by Network-Based Application Recognition?
(Choose two.)
A. NBAR provides the ability to configure MCQ; it is a mandatory MCQ component.
B. NBAR provides deep packet inspection and is used for advanced packet classification.
C. NBAR provides per-protocol packet and byte accounting functionality; it is used to track bandwidth
utilization for all protocols described in the loaded PDLMs.
D. NBAR provides scheduling in an MQC policy map using an advanced algorithm.
Answer: BC
Explanation:
NBAR classes packets that are normally difficult to classify. For instance, some applications use dynamic port numbers. NBAR can look past the UDP and TCP header, and refer to the host name, URL, or MIME type in HTTP requests.
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