Scaling Networks Version 6 – ScaN Chapter 7 Exam

Scaling Networks (Version 6.00) – ScaN Chapter 7 Exam


Which routing protocol has the smallest default administrative distance?


Correct Answer: D
Section: (none)

Explanation: distance.html
Default Distance Value TableThis table lists the administrative distance default values of the protocols that
Cisco supports:
Route Source
Default Distance Values
Connected interface
Static route
Enhanced Interior Gateway Routing Protocol (EIGRP) summary route External Border Gateway Protocol
Internal EIGRP
Intermediate System-to-Intermediate System (IS-IS) Routing Information Protocol (RIP) Exterior Gateway
Protocol (EGP)
On Demand Routing (ODR)
External EIGRP
Internal BGP


Which statement about static routes is true?

A.The source interface can be configured to make routing decisions.
B.A subnet mask is entered for the next-hop address.
C.The subnet mask is 255.255 255.0 by default
D.The exit interface can be specified to indicate where the packets will be routed.

Correct Answer: D
Section: (none)

Static routing can be used to define an exit point from a router when no other routes are available or
necessary. This is called a default route.


Under which circumstance should a network administrator implement one-way NAT?

A.when the network must route UDP traffic
B.when traffic that originates outside the network must be routed to internal hosts
C.when traffic that originates inside the network must be routed to internal hosts
D.when the network has few public IP addresses and many private IP addresses require outside access

Correct Answer: B
Section: (none)

NAT operation is typically transparent to both the internal and external hosts. Typically the internal host is
aware of the true IP address and TCP or UDP port of the external host. Typically the NAT device may
function as the default gateway for the internal host. However the external host is only aware of the public IP
address for the NAT device and the particular port being used to communicate on behalf of a specific
internal host.
“Pure NAT”, operating on IP alone, may or may not correctly parse protocols that are totally concerned with IP information, such as ICMP, depending on whether the
payload is interpreted by a host on the “inside” or “outside” of translation. As soon as the protocol stack is
traversed, even with such basic protocols as TCP and UDP, the protocols will break unless NAT takes
action beyond the network layer. IP packets have a checksum in each packet header, which provides error
detection only for the header. IP datagrams may become fragmented and it is necessary for a NAT to
reassemble these fragments to allow correct recalculation of higher-level checksums and correct tracking of
which packets belong to which connection. The major transport layer protocols, TCP and UDP, have a
checksum that covers all the data they carry, as well as the TCP/UDP header, plus a “pseudo-header” that
contains the source and destination IP addresses of the packet carrying the TCP/UDP header.
For an originating NAT to pass TCP or UDP successfully, it must recompute the TCP/UDP header
checksum based on the translated IP addresses, not the original ones, and put that checksum into the
TCP/UDP header of the first packet of the fragmented set of packets. The receiving NAT must recompute
the IP checksum on every packet it passes to the destination host, and also recognize and recompute the
TCP/UDP header using the retranslated addresses and pseudo-header. This is not a completely solved
problem. One solution is for the receiving NAT to reassemble the entire segment and then recompute a
checksum calculated across all packets.
The originating host may perform Maximum transmission unit (MTU) path discovery to determine the
packet size that can be transmitted without fragmentation, and then set the don’t fragment (DF) bit in the
appropriate packet header field. Of course, this is only a one-way solution, because the responding host
can send packets of any size, which may be fragmented before reaching the NAT.


Which component of a routing table entry represents the subnet mask?

A.routing protocol code
C.metric mask

Correct Answer: D
Section: (none)

IP Routing Table Entry TypesAn entry in the IP routing table contains the following information in the order
Network ID. The network ID or destination corresponding to the route. The network ID can be class-based,
subnet, or supernet network ID, or an IP address for a host route. Network Mask. The mask that is used to
match a destination IP address to the network ID.
Next Hop. The IP address of the next hop.
Interface. An indication of which network interface is used to forward the IP packet. Metric. A number used
to indicate the cost of the route so the best route among possible multiple routes to the same destination
can be selected. A common use of the metric is to indicate the number of hops (routers crossed) to the
network ID. Routing table entries can be used to store the following types of routes:
Directly Attached Network IDs. Routes for network IDs that are directly attached. For directly attached
networks, the Next Hop field can be blank or contain the IP address of the interface on that network.
Remote Network IDs. Routes for network IDs that are not directly attached but are available across other
routers. For remote networks, the Next Hop field is the IP address of a local router in between the
forwarding node and the remote network. Host Routes. A route to a specific IP address. Host routes allow
routing to occur on a per- IP address basis. For host routes, the network ID is the IP address of the
specified host and the network mask is Default Route. The default route is designed to be
used when a more specific network ID or host route is not found. The default route network ID is with the network
mask of


When a router makes a routing decision for a packet that is received from one network and destined to
another, which portion of the packet does if replace?

A.Layer 2 frame header and trailer
B.Layer 3 IP address
C.Layer 5 session
D.Layer 4 protocol

Correct Answer: A
Section: (none)

Router Switching Function ( primary function of a router is to forward packets toward their
destination. This is accomplished by using a switching function, which is the process used by a router to
accept a packet on one interface and forward it out of another interface. A key responsibility of the switching
function is to encapsulate packets in the appropriate data link frame type for the outgoing data link.
In this context, the term “switching” literally means moving packets from source to destination and should
not be confused with the function of a Layer 2 switch. After the router has determined the exit interface
using the path determination function, the router must encapsulate the packet into the data link frame of the
outgoing interface. What does a router do with a packet received from one network and destined for
another network? The router performs the following three major steps:
Step 1. De-encapsulates the Layer 3 packet by removing the Layer 2 frame header and trailer. Step 2.
Examines the destination IP address of the IP packet to find the best path in the routing table.
Step 3. If the router finds a path to the destination, it encapsulates the Layer 3 packet into a new Layer 2
frame and forwards the frame out the exit interface.


On which type of device is every port in the same collision domain?

A.a router
B.a Layer 2 switch
C.a hub

Correct Answer: C
Section: (none)

Collision domainA collision domain is, as the name implies, a part of a network where packet collisions can
occur. A collision occurs when two devices send a packet at the same time on the shared network segment.
The packets collide and both devices must send the packets again, which reduces network efficiency.
Collisions are often in a hub environment, because each port on a hub is in the same collision domain. By
contrast, each port on a bridge, a switch or a router is in a separate collision domain.


Which statement about routing protocols is true?

A.Link-state routing protocols choose a path by the number of hops to the destination.
B.OSPF is a link-state routing protocol.
C.Distance-vector routing protocols use the Shortest Path First algorithm.
D.IS-IS is a distance-vector routing protocol.

Correct Answer: A
Section: (none)

Link State Routing Protocols
Link state protocols are also called shortest-path-first protocols. Link state routing protocols have a
complete picture of the network topology. Hence they know more about the whole network than any
distance vector protocol.
Three separate tables are created on each link state routing enabled router. One table is used to hold
details about directly connected neighbors, one is used to hold the topology of the entire internetwork and
the last one is used to hold the actual routing table. Link state protocols send information about directly
connected links to all the routers in the network. Examples of Link state routing protocols include OSPF -Open Shortest Path First and IS-IS – Intermediate System to Intermediate System. There are also routing
protocols that are considered to be hybrid in the sense that they use aspects of both distance vector and
link state protocols. EIGRP – Enhanced Interior Gateway Routing Protocol is one of those hybrid routing


Which technology supports the stateless assignment of IPv6 addresses?


Correct Answer: B
Section: (none)

DHCPv6 Technology Overview
IPv6 Internet Address Assignment Overview
IPv6 has been developed with Internet Address assignment dynamics in mind. Being aware that IPv6
Internet addresses are 128 bits in length and written in hexadecimals makes automation of addressassignment an important aspect within network design. These attributes make it inconvenient for a user to
manually assign IPv6 addresses, as the format is not naturally intuitive to the human eye. To facilitate
address assignment with little or no human intervention, several methods and technologies have been
developed to automate the process of address and configuration parameter assignment to IPv6 hosts. The
various IPv6 address assignment methods are as follows:
1. Manual Assignment
An IPv6 address can be statically configured by a human operator. However, manual assignment is quite
open to errors and operational overhead due to the 128 bit length and hexadecimal attributes of the
addresses, although for router interfaces and static network elements and resources this can be an
appropriate solution.
2. Stateless Address Autoconfiguration (RFC2462)
Stateless Address Autoconfiguration (SLAAC) is one of the most convenient methods to assign Internet
addresses to IPv6 nodes. This method does not require any human intervention at all from an IPv6 user. If
one wants to use IPv6 SLAAC on an IPv6 node, it is important that this IPv6 node is connected to a network
with at least one IPv6 router connected. This router is configured by the network administrator and sends
out Router Advertisement announcements onto the link. These announcements can allow the on-link
connected IPv6 nodes to configure themselves with IPv6 address and routing parameters, as specified in
RFC2462, without further human intervention.
3. Stateful DHCPv6
The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) has been
standardized by the IETF through RFC3315. DHCPv6 enables DHCP servers to pass configuration
parameters, such as IPv6 network addresses, to IPv6 nodes. It offers the capability of automatic allocation
of reusable network addresses and additional configuration flexibility. This protocol is a stateful counterpart
to “IPv6 Stateless Address Autoconfiguration” (RFC 2462), and can be used separately, or in addition to the
stateless autoconfiguration to obtain configuration parameters.
4. DHCPv6-PD
DHCPv6 Prefix Delegation (DHCPv6-PD) is an extension to DHCPv6, and is specified in RFC3633.
Classical DHCPv6 is typically focused upon parameter assignment from a DHCPv6 server to an IPv6 host
running a DHCPv6 protocol stack. A practical example would be the stateful address assignment of
“2001:db8::1” from a DHCPv6 server to a DHCPv6 client. DHCPv6-PD however is aimed at assigning
complete subnets and other network and interface parameters from a DHCPv6-PD server to a DHCPv6-PD
client. This means that instead of a single address assignment, DHCPv6-PD will assign a set of IPv6
“subnets”. An example could be the assignment of “2001:db8::/60” from a DHCPv6-PD server to a
DHCPv6-PD client. This will allow the DHCPv6-PD client (often a CPE device) to segment the received
address IPv6 address space, and assign it dynamically to its IPv6 enabled interfaces.
5. Stateless DHCPv6
Stateless DHCPv6 is a combination of “stateless Address Autoconfiguration” and “Dynamic Host
Configuration Protocol for IPv6” and is specified by RFC3736. When using stateless- DHCPv6, a device will
use Stateless Address Auto-Configuration (SLAAC) to assign one or more IPv6 addresses to an interface,
while it utilizes DHCPv6 to receive “additional parameters” which may not be available through SLAAC. For
example, additional parameters could include information such as DNS or NTP server addresses, and are
provided in a stateless manner by DHCPv6. Using stateless DHCPv6 means that the DHCPv6 server does
not need to keep track of any state of assigned IPv6 addresses, and there is no need for state refreshment
as result. On network media supporting a large number of hosts associated to a single DHCPv6 server, this
could mean
a significant reduction in DHCPv6 messages due to the reduced need for address state refreshments. From
Cisco IOS 12.4(15)T onwards the client can also receive timing information, in addition to the “additional
parameters” through DHCPv6. This timing information provides an indication to a host when it should
refresh its DHCPv6 configuration data. This behavior (RFC4242) is particularly useful in unstable
environments where changes are likely to occur.


Which feature allows a device to use a switch port that is configured for half-duplex to access the network?

C.port security
D.split horizon

Correct Answer: A
Section: (none)

Ethernet began as a local area network technology that provided a half-duplex shared channel for stations
connected to coaxial cable segments linked with signal repeaters. In this appendix, we take a detailed look
at the half-duplex shared-channel mode of operation, and at the CSMA/CD mechanism that makes it work.
In the original half-duplex mode, the CSMA/CD protocol allows a set of stations to compete for access to a
shared Ethernet channel in a fair and equitable manner. The protocol’s rules determine the behavior of
Ethernet stations, including when they are allowed to transmit a frame onto a shared Ethernet channel, and
what to do when a collision occurs. Today, virtually all devices are connected to Ethernet switch ports over
full-duplex media, such as twisted-pair cables. On this type of connection, assuming that both devices can
support the full-duplex mode of operation and that Auto-Negotiation (AN) is enabled, the AN protocol will
automatically select the highest-performance mode of operation supported by the devices at each end of
the link. That will result in full-duplex mode for the vast majority of Ethernet connections with modern
interfaces that support full duplex and AN.


Which function enables an administrator to route multiple VLANs on a router?

A.IEEE 802 1X
C.port channel
D.router on a stick

Correct Answer: D
Section: (none)


Which dynamic routing protocol uses only the hop count to determine the best path to a destination?


Correct Answer: C
Section: (none)


What is one requirement for interfaces to run IPv6?

A.An IPv6 address must be configured on the interface.
B.An IPv4 address must be configured.
C.Stateless autoconfiguration must be enabled after enabling IPv6 on the interface.
D.IPv6 must be enabled with the ipv6 enable command in global configuration mode.

Correct Answer: A
Section: (none)

To use IPv6 on your router, you must, at a minimum, enable the protocol and assign IPv6 addresses to your interfaces.


Which destination IP address can a host use to send one message to multiple devices across different subnets?


Correct Answer: D
Section: (none)

Multicast is a networking protocol where one host can send a message to a special multicast IP address
and one or more network devices can listen for and receive those messages. Multicast works by taking
advantage of the existing IPv4 networking infrastructure, and it does so in something of a weird fashion. As
you read, keep in mind that things are a little confusing because multicast was “shoe-horned” in to an
existing technology. For the rest of this article, let’s use the multicast IP address of We’ll not
worry about port numbers yet, but make a mental note that they are used in multicast. We’ll discuss that later.


Which MTU size can cause a baby giant error?


Correct Answer: C
Section: (none)
Explanation: 175.html


Which entity assigns IPv6 addresses to end users?


Correct Answer: C
Section: (none)

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