CCNA CCNP INTERVIEW QUESTION
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| CCNA CCNP INTERVIEW QUESTION |
Q-1 Which layer of the OSI model is responsible for reliable connections?
Answer: The Transport layer of the OSI model is responsible for
reliable connections.
Q-2 What is the difference between acknowledgments and
handshaking?
Answer: Handshaking is used to negotiate the properties of a
connection that is being established. Acknowledgments are used to tell the
sender that data has been successfully received by the destination during the
use of a connection.
Q-3 How many VTP modes are there and what are they?
Answer: Three: Server, Client, and Transparent
Q-4 What are the two types of Trunk encapsulation protocols?
Answer: IEEE 802.1Q and Cisco’s ISL
Q-5 What are the four primary no routable protocols?
Answer: SNA, NetBIOS, DEC LAT, DEC MOP
Q-6 What is the difference between TCP and UDP?
Answer: The primary difference between TCP and UDP is that TCP
is a connection oriented protocol and UDP is a connectionless protocol.
Q-7 What is HSRP?
Answer: HSRP, or the Hot Standby Routing Protocol, is a Cisco
proprietary protocol that brings routing functionality to end devices that
would otherwise not be capable of taking advantage of redundant network connections.
HSRP enables a pair of Cisco routers to work together to present the appearance
of a single virtual default-gateway to end devices on a LAN segment.
Q-8 What is the difference between a Public IP address and a
Private IP address?
Answer: Public address space is a unique address that is
assigned to a company. Private address space is not recognized by the Internet
and can be used by anyone
within their private network.
Q-9 What does AAA stand for?
Answer: Authentication, authorization, and accounting
Q-10 The H.323 protocol is used for what?
Answer: H.323 is used for multiservice (multimedia)
applications, usually in a Voice Over IP environment.
Q-1 What type of routing protocol maintains neighbors?
Answer- Link State
Q-2 what is the range of values for administrative distance?
Answer: 0-255
Q-3 Describe the difference between unicast, multicast, and
broadcast traffic?
Answer: Unicast traffic flows from a single source to a single
destination MAC address. Multicast traffic flows from a single source MAC
address to many destinations and uses a functional MAC address. Broadcast
traffic is from a single source to all devices on the Ethernet segment. This is
specified by a destination MAC address of all ones.
Q-4 What are the four different Ethernet encapsulation types?
Answer: From the Cisco IPX encapsulation command they are ARPA,
NOVELL-ETHER, SAP and SNAP
Q-5 What are the three main tasks of a transparent bridge?
Answer: Learning, Forwarding, Filtering
Q-6 What type of routing protocol is EIGRP?
Answer: Hybrid
Q-7 While troubleshooting a connectivity problem on the network,
you issue the ping command from your PC command prompt, but the output shows
"request times out." At which OSI layer is this problem associated
with?
Answer: The Network Layer
Q-8 What algorithm does OSPF use to compute its route table?
Answer: OSPF uses the shortest path first (SPF) algorithm, which
is also known as the Dijkstra algorithm.
Q-9 What is a stub area?
Answer: A stub area is an area that does not accept routing
updates from outside its autonomous system.
Q-10 What does the TTL field of an IP packet header do?
Answer: The TTL field indicates the maximum time that a packet
can be on the network. Each router that processes this packet decrements the
TTL value by 1. If the value reaches zero, the packet is discarded from the
network. The purpose of this field is to eliminate the possibility of a packet
endlessly traversing the network.
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1 What is the primary purpose of a LAN?
A: The
primary purpose of a local-area network is to allow resource sharing. The
resources may be devices, applications, or information. Examples of shared
resources are files, databases, e-mail, modems, and printers.
2: What
is a protocol?
A: A
protocol is an agreed-upon set of rules. In data communications, the rules
usually govern a
procedure or a format.
3: What
is the purpose of a MAC protocol?
A: A
Media Access Control protocol defines how a given LAN medium is shared, how LAN
devices
connected to the medium are identified, and
how frames transmitted onto the medium are
formatted.
4: What
is a frame?
A: A
frame is a digital "envelope" that provides the information necessary
for the delivery of data across a data link. Typical components of a frame are
identifiers (addresses) of the source and destination devices on the data link,
an indicator of the type of data enclosed in the frame, anderror-checking
information.
5: What
feature is common to all frame types?
A: A
feature common to all frame types is a format for identifying devices on the
data link.
6: What
is a MAC address or MAC identifier?
A: A
Media Access Control address or identifier is a means by which individual
devices connected to a data link are uniquely identified for the purpose of
delivering data.
7: Why
is a MAC address not a true address?
A: An
address specifies a location. A MAC address is not a true address because it is
permanently associated with the interface of a specific device and moves
whenever the device moves. A MAC identifies the device, not the location of the
device.
8: What
are the three sources of signal degradation on a data link?
A: The
three sources of signal degradation on a data link are attenuation,
interference, and distortion. Attenuation is a function of the resistance of
the medium. Interference is a function of noise entering the medium. Distortion
is a function of the reactive characteristics of the medium, which react
differently to different frequency components of the signal.
9: What
is the purpose of a repeater?
A: A
repeater is a device that extends the useful range of a physical medium by
reading a degradedsignal and producing a "clean" copy of the signal.
10: What is the purpose of a bridge?
A: A
bridge is a device that increases the capacity of a LAN. A bridge divides the
data link into
segments, forwarding only traffic that is
generated on one segment and is destined for another
segment. By controlling and limiting the
traffic on a data link, more devices may be attached to the LAN.
11: What makes a transparent bridge transparent?
A: A
transparent bridge "listens promiscuously" on each of its ports. That
is, it examines all frames on all media to which it is attached. It records the
source MAC identifiers of the frames, and the ports on which it learns the
identifiers, in a bridging table. It can then refer to the table when deciding
whether to filter or forward a frame. The bridge is transparent because it
performs this learning function independently of the devices that originate the
frames. The end devices themselves have no knowledge of the bridge.
12: Name three fundamental differences between LANs and WANs.
A: Three
fundamental differences between local-area and wide-area networks are:
LANs are limited to a small geographic area,
such as a single building or small campus.
WANs cover a large geographic area, from
citywide to worldwide.
LANs usually consist entirely of privately owned
components. Some components of a
WAN, such as a packet switching network or
point-to-point serial links, are usually leased
from a service provider.
A LAN provides high bandwidth at a relatively
cheap price. The bandwidth across a WAN
is significantly more expensive.
13: What is the purpose of a broadcast MAC identifier? What is the
broadcast MAC identifier, in hex and in binary?
A: A
broadcast MAC identifier, when used as the destination address of a frame,
signifies that the data is for all devices attached to the data link. In
binary, the broadcast MAC identifier is all ones. In hex, it is ffff.ffff.ffff.
14: What is the primary similarity between a bridge and a router? What
is the primary difference
between a bridge and a router?
A: The
primary similarity between a bridge and a router is that both devices increase
the number of hosts that may be interconnected into a common communications
network. The difference is that a bridge works by interconnecting separate
segments of a single network, whereas a router
interconnects separate networks.
15: What is a packet? What is the primary similarity between a frame
and a packet? What is the
primary difference between a frame and a packet?
A: A
packet is the means by which data is transported from one network to another.
The similarity between a frame and a packet is that they both encapsulate data
and provide an addressing scheme for delivering the data. The difference
between a frame and a packet is that the frame delivers data between two
devices sharing a common data link, whereas a packet delivers data across a
logical pathway, or route, spanning multiple data links.
16: As a packet progresses across an internetwork, does the source
address change?
A: Neither
the source nor the destination address of a packet changes as it progresses
from the source of the packet to the destination.
17: What is a network address? What is the purpose of each part of a
network address?
A: Network
addresses are the addresses used in packets. Each network address has a network
part, which identifies a particular data link, and a host or node part, which
identifies a specific device on the data link identified by the network part.
18: What is the primary difference between a network address and a
data link identifier?
A: A
packet identifies a device from the perspective of the entire internetwork. A
frame identifies a device from the perspective of a single data link. Because
the connection between two devices across an internetwork is a logical path, a
network address is a logical address. Because the connection between two
devices across a data link is a physical path, a data link identifier is a
physical address.
1: What are the five layers
of the TCP/IP protocol suite? What is the purpose of each layer?
A: The five layers of the TCP/IP protocol suite are the following:
Physical layer
Data link layer
Internet (or IP) layer
Host-to-host layer
Application layer
CC
2: What
is the most common IP version presently in use?
A: The
most common IP version now in use is version 4.
3: What
is fragmentation? What fields of the IP header are used for fragmentation?
A: Routers
perform fragmentation when a packet is longer than the maximum packet length
(Maximum Transmission Unit, or MTU) supported
by a data link onto which the packet must be
transmitted. The data within the packet will
be broken into fragments, and each fragment will be
encapsulated in its own packet. The receiver
uses the Identifier and Fragment Offset fields and the
MF bit of the Flags field to reassemble the
fragments.
4: What
is the purpose of the TTL field in the IP header? How does the TTL process
work?
A:
The Time to Live (TTL) field prevents "lost" packets
from being passed endlessly through the IP internetwork. The field contains an
8-bit integer that is set by the originator of the packet. Each router through
which the packet passes will decrement the integer by one. If a router
decrements the TTL to zero, it will discard the packet and send an ICMP
"time exceeded" error message to the packet's source address.
5: What
is the first octet rule?
A: The
first octet rule determines the class of an IP address as follows:
Class A: The first bit of the first octet is
always 0.
Class B: The first two bits of the first octet
are always 10.
Class C: The first three bits of the first octet
are always 110.
Class D: The first four bits of the first octet
are always 1110.
Class E: The first four bits of the first octet
are always 1111.
6: How
are class A, B, and C IP addresses recognized in dotted decimal? How are they
recognized inbinary?
A: The
A, B, C IP addresses are recognized in dotted decimal and binary as follows:
Class
Binary Range of First Octet Decimal Range of First Octet
A 0000000 - 01111110 1 - 126
B 10000000 - 10111111 128 - 191
C 11000000 - 11011111 192- 223
7: What
is an address mask, and how does it work?
A: An
IP address mask identifies the network part of an IP address. Each one in the
32-bit mask marks the corresponding bit in the IP address as a network bit. A
zero in the mask marks the
Corresponding bit in the IP address as a host
bit. A Boolean AND is performed in all 32 bits of the address and the mask; in
the result, all network bits of the mask will be repeated, and all host bits
will be changed to zero.
8: What
is a subnet? Why are subnets used in IP environments?
A: A
subnet is a sub grouping of a class A, B, or C IP address. Without subletting,
the network part of a major class A, B, or C IP address can only identify a
single data link. Subnetting uses some of the host bits of a major IP address
as network bits, allowing the single major address to be “Subdivided" into
multiple network addresses.
9: Why
can't a subnet of all zeros or all ones be used in a classful routing
environment?
A: A
classful routing protocol has no way to differentiate between the all-zeroes
subnet and the major IP address, and between the all-ones subnet and the
all-hosts, all-subnets broadcast address of the major IP address.
10: What is ARP?
A: ARP,
or Address Resolution Protocol, is a function that maps the IP addresses of
interfaces on a data link to their corresponding MAC identifiers.
11: What is proxy ARP?
A: Proxy
ARP is a function of an IP router. If the router hears an ARP request, and
The destination network or subnet is in the
router's routing table, and
The table indicates that the destination is
reachable via a different router interface than the
one on which the ARP request was received, The
router will respond to the ARP request with its own MAC address.
12: What is a redirect?
A: A
redirect is an IP router function. If a device has sent a packet to the router
and the router must forward the packet to a next-hop router on the same data
link, the router will send a redirect to the originating device. The redirect
will inform the device that it can reach the next-hop router directly.
13: What is the essential difference between TCP and UDP?
A: TCP,
or Transmission Control Protocol, provides a connection-oriented service over
the
Connectionless internet layer. UDP, or User
Datagram Service, provides a connectionless service.
14: What mechanisms does TCP use to provide connection-oriented service?
A: Correct
sequencing is accomplished with sequence numbers. Reliability is accomplished
by using checksums, acknowledgments, timers, and retransmissions. Flow control
is accomplished by windowing.
15: Instead of ARP, Novell NetWare uses a network address that
includes a device's MAC address as the host portion. Why can't IP do this?
A: A
MAC identifier is a fixed-length binary integer. If IP used MAC identifiers as
the host part of the IP address, subnetting would not be possible because there
would be no flexibility in using some of the host bits as network bits.
16: NetWare has a transport layer service similar to TCP called
Sequenced Packet Exchange (SPX), but no service similar to UDP. Applications
requiring connectionless service directly access the connectionless IPX at the
network layer. What purpose does UDP serve by providing aconnectionless service
on top of what is already a connectionless service?
A: The
only purpose of the UDP header is to add fields for the source and destination
port numbers.
1: What
information must be stored in the route table?
A: At
a minimum, each entry of the routing table must include a destination address
and the address of a next-hop router or an indication that the destination
address is directly connected.
2: What
does it mean when a route table says that an address is variably subnetted?
A: Variably
subnetted means that the router
knows of more than one subnet mask for subnets of the same major IP address.
3: What
are discontiguous subnets?
A: Discontiguous
subnets are two or more subnets of a major IP network address that are
separated by a different major IP address.
4: What
command is used to examine the route table in a Cisco router?
A: show ip route is used to examine the routing table of a Cisco router.
5: What
are the two bracketed numbers associated with the non-directly connected routes
in the route table?
A: The
first bracketed number is the administrative distance of the routing protocol
by which the route was learned. The second number is the metric of the route.
6: When
static routes are configured to reference an exit interface instead of a
next-hop address, in what way will the route table be different?
A: When
a static route is configured to reference an exit interface instead of a
next-hop address, the destination address will be entered into the routing
table as directly connected.
7: What
is a summary route? In the context of static routing, how are summary routes
useful?
A: A
summary route is a single route entry that points to multiple subnets or major
IP addresses. In the context of static routes, summary routes can reduce the
number of static routes that must be configured.
8: What
is an administrative distance?
A: An
administrative distance is a rating of preference for a routing protocol or a
static route. Every routing protocol and every static route has an
administrative distance associated with it. When a router learns of a
destination via more than one routing protocol or static route, it will use the
route with the lowest administrative distance.
9: What
is a floating static route?
A: A
floating static route is an alternative route to a destination. The
administrative distance is set high enough that the floating static route is
used only if a more-preferred route becomes unavailable.
10: What is the difference between equal-cost and unequal-cost load
sharing?
A: Equal-cost
load sharing distributes traffic equally among multiple paths with equal
metrics.
Unequal-cost load sharing distributes packets
among multiple paths with different metrics. The
traffic will be distributed inversely
proportional to the cost of the routes.
11: How does the switching mode at an interface affect load sharing?
A: If
an interface is fast switched, per destination load sharing is performed. If an
interface is process switched, per packet load sharing is performed.
12: What is a recursive table lookup?
A: A
recursive routing table lookup occurs when a router cannot acquire all the
information it needs to forward a packet with a single routing table lookup.
For example, the router may perform one lookup to find the route to a destination
and then perform another lookup to find a route to the next hop router of the
first route.
1: What
is a routing protocol?
A: A
routing protocol is a "language" that routers speak to each other to
share information about
network destinations.
2: What
basic procedures should a routing algorithm perform?
A: At
a minimum, a routing protocol should define procedures for:
Passing reachability information about networks
to other routers
Receiving reachability information from other
routers
Determining optimal routes based on the
reachability information it has and for recording
this information in a route table
Reacting to, compensating for, and advertising
topology changes in an internetwork
3: Why
do routing protocols use metrics?
A: A
route metric, also called a route cost or a route distance, is used to
determine the best path to a destination. Best is defined by
the type of metric used.
4: What
is convergence time?
A: Convergence
time is the time a group of routers take to complete the exchange of routing
information.
5: What
is load balancing? Name four different types of load balancing.
A: Load
balancing is the process of sending packets over multiple paths to the same
destination. Four types of load balancing are:
Equal cost, per packet
Equal cost, per destination
Unequal cost, per packet
Unequal cost, per destination
6: What
is a distance vector routing protocol?
A: A
distance vector protocol is a routing protocol in which each router calculates
routes based on the routes of its neighbors and then passes its routes to other
neighbors.
7: Name
several problems associated with distance vector protocols.
A: Several
problems associated with distance vector protocols are:
A susceptibility to incorrect routing
information because of its dependence on neighbors for
correct information
Slow convergence
Route loops
Counting to infinity
8: What
are neighbors?
A: Neighbors
are routers connected to the same data link.
9: What
is the purpose of route invalidation timers?
A: Route
invalidation timers delete routes from a route table if they exceed a certain
age.
10: Explain the difference between simple split horizon and split
horizon with poisoned reverse.
A: Simple
split horizon does not send route information back to the source of the route
information. Split horizon with poisoned reverse sends the information back to
the source but sets the metric to unreachable.
11: What is the counting-to-infinity problem, and how can it be
controlled?
A: Counting
to infinity occurs when routes update a route over a loop; each router
increases the metric of the route until the metric reaches infinity. The
effects of counting to infinity are controlled by defining infinity as
a fairly low metric so that infinity is reached fairly quickly and the route is
declared unreachable.
12: What are holddown timers, and how do they work?
A: Holddown
timers help prevent routing loops. If a route is declared unreachable or if the
metric increases beyond a certain threshold, a router will not accept any other
information about that route until the hold down timer expires. This approach
prevents the router from accepting possibly bad
routing information while the internetwork is
reconverging
.
13: What are the differences between distance vector and link state
routing protocols?
A: A
distance vector router sends its entire route table, but it only sends the
table to directly connected neighbors. A link state router sends only
information about its directly connected links, but it floods the information
throughout the internetworking area. Distance vector protocols usually use a
variant of the Bellman-Ford algorithm to calculate routes, and link state
protocols usually use a variant of the Dijkstra algorithm to calculate routes.
14: What is the purpose of a topological database?
A: A
topological database holds the link state information originated by all routers
in the link state routing domain.
15: Explain the basic steps involved in converging a link state
internetwork.
A: Each
router floods a link state information advertisement describing its links, the
states of its links,
and any neighboring routers connected to those
links, throughout the internetworking area. All
routers store all received copies of the link
state advertisement in a link state database. Each router calculates a shortest
path tree from the information in the topological database and enters routes in
its routing tables based on the shortest path tree.
16: Why are sequence numbers important in link state protocols?
A: Sequence
numbers help a router differentiate between multiple copies of the same link
state
advertisement and also prevent flooded link
state advertisements from circulating endlessly
throughout the internetwork.
17: What purpose does aging serve in a link state protocol?
A: Aging
prevents old, possibly obsolete, link state information from residing in a
topological
database or from being accepted by a router.
18: Explain how an SPF algorithm works.
A: A
router builds a shortest path tree by first adding itself as the root. Using
the information in the topological database, the router creates a list of all
of its directly connected neighbors. The lowest cost link to a neighbor becomes
a branch of the tree, and that router's neighbors are added to the list. The
list is checked for duplicate paths, and if they exist, the higher-cost paths
are removed from the list. The lowest-cost router on the list is added to the
tree, that router's neighbors are added to the list, and the list is again
checked for duplicate paths. This process continues until no routers remain on
the list.
19: How do areas benefit a link state internetwork?
A: Within
a routing domain, areas are subdomains. They make link state routing more
efficient by limiting the size of the link state database of each router in the
area.
20: What is an autonomous system?
A: Depending
on the usage, an autonomous system can be defined as an internetwork under a
common administrative domain or a single routing domain.
21: What is the difference between an IGP and an EGP?
A: An
Interior Gateway Protocol is a routing protocol that routes within an
autonomous system. An Exterior Gateway Protocol is a routing protocol that
routes between autonomous systems.
1: What
port does RIP use?
A: RIP
uses UDP port 520.
2: What
metric does RIP use? How is the metric used to indicate an unreachable network?
A: RIP
uses a hop count metric. An unreachable network is indicated by setting the hop
count to 16, which RIP interprets as an infinite distance.
3: What
is the update period for RIP?
A: RIP
sends periodic updates every 30 seconds minus a small random variable to
prevent the updates of neighboring routers from becoming synchronized.
4: How
many updates must be missed before a route entry will be marked as unreachable?
A: A
route entry is marked as unreachable if six updates are missed.
5: What
is the purpose of the garbage collection timer?
A: The
garbage collection timer, or flush timer, is set when a route is declared
unreachable. When the
timer expires, the route is flushed from the
route table. This process allows an unreachable route to
remain in the routing table long enough for
neighbors to be notified of its status.
6: Why
is a random timer associated with triggered updates? What is the range of this
timer?
A: The
random timer, whose range is 1 to 5 seconds, prevents a "storm" of
triggered updates during a topology change.
7: What
is the difference between a RIP Request message and a RIP Response message?
A: A
Request message asks a router for an update. A Response message is an update.
8: Which
two types of Request messages does RIP use?
A: A
Request message may either ask for a full update or in some special cases it
may ask for specific routes.
9: Under
what circumstances will a RIP response be sent?
A: A
Response is sent when the update timer expires, or upon reception of a Request
message.
10: Why does RIP hide subnets at major network
boundaries?
A: RIP
updates do not include the subnet mask of the destination address, so a RIP
router depends on the subnet masks of its own interfaces to determine how an
attached major network address is subnetted. If a router does not have an
attachment to a particular major network address, it has no way to know how
that major network is subnetted. Therefore, no subnets of a major network
address can be advertised into another major network.
1: Which
UDP port number is used to access IGRP?
A: IGRP
does not use a UDP port. It is accessed directly from the network layer, as
protocol number 9.
2: What
is the maximum IGRP internetwork diameter, in hops?
A: The
maximum IGRP network diameter is 255 hops.
3: What
is the default update period for IGRP?
A: The
default IGRP update period is 90 seconds.
4: Why
does IGRP specify an autonomous system number?
A: IGRP
specifies an autonomous system number so that multiple IGRP processes can be
enabled within the same routing domain and even on the same router.
5: Referring
to
A: McCloy
will advertise 192.168.1.0 to Acheson as a system route because the address is
being
advertised into another major network. Acheson
will advertise 172.16.0.0 as a system route to
McCloy, and as an interior route to Kennan.
6: What
is the default IGRP holddown time?
A: The
default IGRP holddown time is 280 seconds.
7: Which
variables can IGRP use to calculate its composite metric?
A: IGRP
can use bandwidth, delay, load, and reliability to calculate its metric. By
default, it uses only bandwidth and delay.
8: How
many entries can be carried within a single IGRP update packet?
A: An
IGRP update packet can carry up to 104 route entries.
1: Which
three fields are new to the RIPv2 message format?
A: The
Route Tag field, the Subnet Mask field, and the Next Hop field are RIPv2
extensions that do not exist in RIPv1 messages. The basic format of the RIP
message remains unchanged between the two versions; version 2 merely uses
fields that are unused in version 1.
2: Besides
the extensions defined by the three fields of question 1, what are the other
two major
changes from RIPv1?
A: In
addition to the functions that use the new fields, RIPv2 supports
authentication and multicast updates.
3: What
is the multicast address used by RIPv2? What is the advantage of multicasting
messages overbroadcasting them?
A: RIPv2
uses the multicast address 224.0.0.9. Multicasting of routing messages is
better than
broadcasting because hosts and non-RIPv2
routers will ignore the multicast messages.
4: What
is the purpose of the Route Tag field in the RIPv2 message?
A: When
another routing protocol uses the RIPv2 domain as a transit domain, the
protocol external to RIPv2 can use the Route Tag field to communicate information
to its peers on the other side of the RIPv2 domain.
5: What
is the purpose of the Next Hop field?
A: The
Next Hop field is used to inform other routers of a next-hop address on the
same multi-access network that is metrically closer to the destination than the
originating router.
6: What
is the UDP port number used by RIPv2?
A: RIPv2
uses the same UDP port number as RIPv1, port number 520.
7: Which
one feature must a routing protocol have to be a classless routing protocol?
A: A
classless routing protocol does not consider the major network address in its
route lookups, but just looks for the longest match.
8: Which
one feature must a routing protocol have to use VLSM?
A: To
support VLSM, a routing protocol must be able to include the subnet mask of
each destination address in its updates.
9: Which
two types of authentication are available with Cisco's RIPv2? Are they both
defined in RFC 1723?
A: Cisco's
implementation of RIPv2 supports clear-text authentication and MD5 authentication.
Only clear-text authentication is defined in RFC 1723.
1: Is
EIGRP a distance vector or a link state routing protocol?
A: EIGRP
is a distance vector protocol.
2: What
is the maximum configured bandwidth EIGRP will use on a link? Can this
percentage be changed?
A: By
default, EIGRP uses no more than 50% of the link's bandwidth, based on the
bandwidth
configured on the router's interface. This
percentage to be changed with the command ip
bandwidth-percent
eigrp.
3: How
do EIGRP and IGRP differ in the way they calculate the composite metric?
A: EIGRP
and IGRP use the same formula to calculate their composite metrics, but EIGRP
scales the metric by a factor of 256.
4: What
are the four basic components of EIGRP?
A: The
four basic components of EIGRP are:
The Protocol Dependent Modules
The Reliable Transport Protocol
The Neighbor Discovery and Recovery Module
The Diffusing Update Algorithm
5: In
the context of EIGRP, what does the term reliable delivery mean? Which two
methods ensure reliable delivery of EIGRP packets?
A: Reliable
delivery means EIGRP packets are guaranteed to be delivered, and they are
delivered in order. RTP uses a reliable multicast, in which received packets
are acknowledged, to guarantee delivery; sequence numbers are used to ensure
that they are delivered in order.
6: Which
mechanism ensures that a router is accepting the most recent route entry?
A: Sequence
numbers ensure that a router is receiving the most recent route entry.
7: What
is the multicast IP address used by EIGRP?
A: EIGRP
uses the multicast address 224.0.0.10.
8: What
are the packet types used by EIGRP?
A: The
packet types used by EIGRP are:
Hellos
Acknowledgments
Updates
Queries
Replies
9: At
what interval, by default, are EIGRP Hello packets sent?
A: The
default EIGRP Hello interval is 5 seconds, except on some slow-speed (T1 and
below)
interfaces, where the default is 60 seconds.
10: What is the default hold time?
A: The
EIGRP default hold time is three times the Hello interval.
11: What is the difference between the neighbor table and the topology
table?
A: The
neighbor table stores information about EIGRP-speaking neighbors; the topology
table lists all known routes that have feasible successors.
12: What is a feasible distance?
A: The
feasible distance to a destination is a router's lowest calculated distance to
the destination.
13: What is the feasibility condition?
A: The
feasibility condition is the rule by which feasible successors are chosen for a
destination. The feasibility condition is satisfied if a neighbor's advertised
distance to a destination is lower than the receiving router's feasible
distance to the destination. In other words, a router's neighbor meets the
feasibility condition if the neighbor is metrically closer to the destination
than the router. Another way to describe this is that the neighbor is
"downstream" relative to the destination.
14: What is a feasible successor?
A: A
feasible successor to a destination is a neighbor that satisfies the
feasibility condition for that destination.
15: What is a successor?
A: A
successor to a destination is a feasible successor that is currently being used
as the next hop to the destination.
16: What is the difference between an active route and a passive
route?
A: A
route is active on a particular router if the router has queried its neighbors
for a feasible
successor and has not yet received a reply
from every queried neighbor. The route is passive when there are no outstanding
queries.
17: What causes a passive route to become active?
A: A
route becomes active when no feasible successor exists in its topology table.
18: What causes an active route to become passive?
A: An
active route becomes passive when a reply has been received from every queried
neighbor.
19: What does stuck-in-active mean?
A: If
a router does not receive a reply from a queried neighbor within the active
time (3 minutes, by default), the route is declared stuck-in-active. A response
with an infinite metric is entered on the neighbor's behalf to satisfy DUAL,
and the neighbor is deleted from the neighbor table.
20: What is the difference between subnetting and address aggregation?
A: Subnetting
is the practice of creating a group of subnet addresses from a single IP
network address.Address aggregation is the practice of summarizing a group of
network or subnet addresses with a single IP network address.
1: What is an OSPF neighbor?
A: From the perspective of an OSPF router, a
neighbor is another OSPF router that is attached to oneof the first router's
directly connected links.
2: What is an OSPF adjacency?
A: An OSPF adjacency is a conceptual link to a
neighbor over which LSAs can be sent.
3: What are the five OSPF packet types? What is
the purpose of each type?
A: The five OSPF packet types, and their
purposes, are:
Hellos - which
are used to discover neighbors, and to establish and maintain adjacencies
Updates - which are used to send
LSAs between neighbors
Database Description packets -
which a router uses to describe its link state database to a
neighbor during database synchronization
Link State Requests - which a
router uses to request one or more LSAs from a neighbor's
link state database
Link State Acknowledgments -
used to ensure reliable delivery of LSAs
4: What is an LSA? How does an LSA differ from
an OSPF Update packet?
A: A router originates a link state
advertisement to describe one or more destinations. An OSPF
Update packet transports LSAs from one
neighbor to another. Although LSAs are flooded
throughout an area or OSPF domain, Update
packets never leave a data link.
5: What are LSA types 1 to 5 and LSA type 7?
What is the purpose of each type?
A: The most common LSA types and their
purposes are:
Type 1 (Router LSAs) are originated by every
router and describe the originating router, the
router's directly connected links and their
states, and the router\xd5 s neighbors.
o Type 2 (Network LSAs) are originated by
Designated Routers on multiaccess links
and describe the link and all attached
neighbors.
o Type 3 (Network Summary LSAs) are originated
by Area Border Routers and
describe inter-area destinations.
o Type 4 LSAs (ASBR Summary LSAs) are
originated by Area Border Routers to
describe Autonomous System Boundary Routers
outside the area.
o Type 5 (AS External LSAs) are originated by
Autonomous System Boundary
Routers to describe destinations external to
the OSPF domain.
o Type 7 (NSSA External LSAs) are originated
by Autonomous System Boundary
Routers within not-so-stubby areas.
6: What is a link state database? What is link
state database synchronization?
A: The link state database is where a router
stores all the OSPF LSAs it knows of, including its own. Database
synchronization is the process of ensuring that all routers within an area have
identical link state databases.
7: What is the default HelloInterval?
A: The default OSPF HelloInterval is 10
seconds.
8: What is the default RouterDeadInterval?
A: The default RouterDeadInterval is four
times the HelloInterval.
9: What is a Router ID? How is a Router ID
determined?
A: A Router ID is an address by which an OSPF
router identifies itself. It is either the numerically highest IP address of
all the router's loopback interfaces, or if no loopback interfaces are
configured, it is the numerically highest IP address of all the router's LAN
interfaces.
10: What is an area?
A: An area is an OSPF sub-domain, within which
all routers have an identical link state database.
11: What is the significance of area 0?
A: Area 0 is the backbone area. All other
areas must send their inter-area traffic through the backbone.
12: What is MaxAge?
A: MaxAge, 1 hour, is the age at which an LSA
is considered to be obsolete.
13: What are the four OSPF router types?
A: The four OSPF router types are:
Internal Routers, whose OSPF interfaces all
belong to the same area
Backbone Routers, which are Internal Routers
in Area 0
Area Border Routers, which have OSPF
interfaces in more than one area
Autonomous System Boundary Routers, which
advertise external routes into the OSPF
Domain
14: What are the four OSPF path types?
A: The four OSPF path types are:
Intra-area paths
Inter-area paths
Type 1 external paths
Type 2 external paths
15: What are the five OSPF network types?
A: The five OSPF network types are:
Point-to-point networks
Broadcast networks
Non-broadcast multi-access (NBMA) networks
Point-to-multipoint networks
Virtual links
16: What is a Designated Router?
A: A Designated Router is a router that
represents a multiaccess network, and the routers connected to the network, to
the rest of the OSFP domain.
17: How does a Cisco router calculate the
outgoing cost of an interface?
A: Cisco IOS calculates the outgoing cost of
an interface as 108/BW, where BW is the configured bandwidth of the interface.
18: What is a partitioned area?
A: An area is partitioned if one or more of
its routers cannot send a packet to the area's other routers without sending
the packet out of the area.
19: What is a virtual link?
A: A virtual link is a tunnel that extends an
OSPF backbone connection through a non-backbone area.
20: What is the difference between a stub area,
a totally stubby area, and a not-so-stubby area?
A: A stub area is an area into which no type 5
LSAs are flooded. A totally stubby area is an area into which no type 3, 4, or
5 LSAs are flooded, with the exception of type 3 LSAs to advertise a default
route. Not-so-stubby areas are areas through which external destinations are
advertised into the OSPF domain, but into which no type 5 LSAs are sent by the
ABR.
21: What is the difference between OSPF network
entries and OSPF router entries?
A: OSPF network entries are entries in the
route table, describing IP destinations. OSPF router entries are entries in a
separate route table that record only routes to ABRs and ASBRs.
22: Why is type 2 authentication preferable over
type 1 authentication?
A: Type 2 authentication uses MD5 encryption,
whereas type 1 authentication uses clear-text
passwords.
23: Which three fields in the LSA header
distinguish different LSAs? Which three fields in the LSA header distinguish
different instances of the same LSA?
A: The three fields in the LSA header that
distinguish different LSAs are the Type, Advertising
Router, and the Link State ID fields. The
three fields in the LSA header that distinguish different
instances of the same LSA are the Sequence
Number, Age, and Checksum fields.
1: What
is an intermediate system?
A: An
Intermediate System is the ISO term for a router.
2: What
is a network protocol data unit?
A: A
Network Protocol Data Unit is the ISO term for a packet.
3: What
is the difference between an L1, an L2, and an L1/L2 router?
A: An
L1 router has no direct connections to another area. An L2 router only routes
inter-area traffic.
An L1/L2 router routes both inter-area and
intra-area traffic and acts as an inter-area gateway for
L1 routers.
4: Explain
the basic difference between an IS-IS area and an OSPF area.
A: The
borders of IS-IS areas are between routers, on links. The borders of OSPF areas
are defined by the routers themselves.
5: What
is a network entity title (NET)?
A: The
Network Entity Title is an address by which a router identifies both itself and
the area in which it resides.
6: To
what value must the NSAP Selector be set in a NET?
A: The
NSAP Selector should be set to 0x00 in a NET.
7: What
is the purpose of a System ID?
A: The
System ID uniquely identifies a router within an IS-IS domain.
8: How
does a router determine what area it is in?
A: The
portion of the NET preceding the last seven octets is the area address.
9: Does
IS-IS elect a Backup Designated Router on a broadcast subnetwork?
A: IS-IS
does not elect a BDR.
10: What is the purpose of the Pseudonode ID?
A: The
Pseudonode ID is the last octet of a LAN ID. Its purpose is to distinguish LAN
IDs which are originated by a single router which is the DR on multiple LANs.
11: What is the maximum age (MaxAge) of an IS-IS LSP?
A: The
MaxAge of an IS-IS LSP is 1200 seconds (20 minutes).
12: What is the basic difference between the way OSPF ages its LSAs
and the way IS-IS ages its
LSPs?
A: OSPF
increments the age up to MaxAge; IS-IS decrements the age down to 0. A new OSPF
LSA has an age of 0, whereas a new IS-IS LSP has an age of MaxAge.
13: How often does an IS-IS router refresh its LSPs?
A: The
refresh rate of an IS-IS router is 900 seconds (15 minutes).
14: What is a Complete Sequence Number Packet (CSNP)? How is it used?
A: A
Complete Sequence Number Packet contains a full listing of all LSPs in a
database. A CSNP is periodically sent by the Designated Router on a broadcast
network to maintain database
synchronization.
15: What is a Partial Sequence Number Packet (PSNP)? How is it used?
A: A
Partial Sequence Number Packet contains a listing of one or more LSPs. It has
two uses: On point-to-point networks, it is used to acknowledge the receipt of
LSPs. On broadcast networks, it is used to request LSPs.
16: What is the purpose of the Overload (OL) bit?
A: An
IS-IS router uses the Overload bit to inform its neighbors that it is
experiencing a memory
overload and cannot store the entire link
state database.
17: What is the purpose of the Attached (ATT) bit?
A: The
Attached bit is used by L1/L2 routers to inform L1 routers that it is attached
to the L2
backbone.
18: What metrics are specified by the ISO for IS-IS? How many of these
metrics does the Cisco IOS support?
A: The
ISO specifies four metrics: Default, Expense, Delay, and Error. Cisco supports
only the
Default metric.
19: What is the maximum value of the IS-IS default metric?
A: The
maximum value of any of the IS-IS metrics is 63.
20: What is the maximum metric value of an IS-IS route?
A: The
maximum metric value of an IS-IS route is 1023.
21: What is the difference between a level 1 IS-IS metric and a level
2 IS-IS metric?
A: L1
IS-IS metrics apply to intra-area routes, and L2 IS-IS metrics apply to
inter-area routes.
22: What is the difference between an internal IS-IS metric and an
external IS-IS metric?
A: Internal
metrics apply to routes to destinations within the IS-IS domain. External
metrics apply to routes to destinations external to the IS-IS domain.
1: From
what sources can a route be redistributed?
A: Routes
that are learned from another routing protocol, static routes, or a direct
connection to the destination network can be redistributed into a routing
domain.
2: What
is the purpose of an administrative distance?
A: In
contrast to metrics, which are used to determine the best path among multiple
routes to the same destination discovered by the same routing protocol,
administrative distances are used to determine the best path among multiple
routes to the same destination discovered by different routing protocols.
3: How
can administrative distances cause problems when redistributing?
A: A
route to a destination within a routing domain with a higher administrative
distance can be
redistributed into a routing domain with a
lower administrative distance. If that route is redistributed back into the
higher-distance domain, packets might be misrouted into the lower-distance
domain.
4: How
can redistribution from a classless to a classful routing protocol cause
problems?
A: Redistributing
variably subnetted destination addresses from a classless domain into a
classful domain can cause problems.
5: Which
IP IGPs can use the default redistribution metric, and which IGPs must have a
metric
configured in order for redistribution to work?
A: OSPF
and IS-IS understand the default metric. RIP, IGRP, and EIGRP do not.
6: What
is the difference between using the metric keyword with the redistributecommand
and using the default-metric command?
A: The metric command assigns a metric
to specific redistribution statements. The default-metric command assigns a metric to all redistribution
commands that do not include the metric command.
7: What
is the purpose of the subnets keyword when redistributing OSPF?
A: Without
the subnets keyword,
only major network addresses that are not directly connected to the router will
be redistributed.
8: How
is the null interface useful when summarizing routes?
A: A
router that originates a summary route should use the null interface as the
next hop of the
summary route. Any packets that match the
summary route, but for which there is no more-specific route to the packet's
destination address, will be dropped. This prevents the router from forwarding
"lost" packets.
1: What
is the destination address of default routes used by the open protocols?
A: The
default route address is 0.0.0.0.
2: How
are default routes identified and advertised by IGRP and EIGRP?
A: IGRP
and EIGRP advertise a default address as an external address type.
3: Can
a static route to 0.0.0.0 be used as the default route on a router running
IGRP?
A: Yes.
4: What
is a stub router? What is a stub network?
A: A
stub router is a router with only a single link to another router. A stub
network is a network with only one attached router.
5: What
is an advantage of using default routes instead of a full routing table?
A: Using
a default route rather than a full routing table can conserve router memory by
keeping the table small and can save router processing cycles by limiting the
routing information that must be processed.
6: What
is an advantage of using a full routing table instead of a default route?
A: Using
a full routing table rather than a default route can make routing more
accurate.
7: What
data link protocol does On-Demand Routing use to discover routes?
A: ODR
uses Cisco Discovery Protocol (CDP) to discover routes.
8: What
IOS restrictions are placed on ODR?
A: ODR
is available in IOS 11.2 and later.
9: What
media restrictions are placed on ODR?
A: The
medium over which ODR is to run must support SNAP.
1: How
are route maps similar to access lists? How are they different?
A: Route
maps are similar to access lists in that they define match criteria and an
action to take in theevent of a match. Route maps are different from access
lists in that they not only specify matchcriteria but also specify set
criteria. The set action can modify a route or route a packet according tothe
parameters of the packet.
2: What
are policy routes?
A: Policy
routes are static routes that use route maps to determine which packets should
be routed andwhere the packets should be routed.
3: What
are route tags?
A: Route
tags are fields within routing information packets that allow external
information to be carried through the routing domain.
4: In
what way do route tags affect routing protocols?
A: Route
tags have no effect on the routing protocols that carry them.
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