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.