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1. VLSM stands for:
Variable Length Subnet Masking
2. The purpose VLSM was designed was to:
Conserve IP addresses when using IPv4, maximizing the number of
useable IP addresses available in a network.
3. Dynamic routing protocols that support VLSM include:
•
•
•
•
OSPF
RIP v. 2
EIGRP
IS-IS
4. VLSM is sometimes referred to as __________________________.
Subnetting a subnet
5. What is an “autonomous system”?
it’s a network used in one enterprise
6. What is meant by “route aggregation”?
It’s the same thing as route summarization; it’s a way to summarize more
than 1 route with one route entry in a router’s routing table.
7. How can you take advantage of route aggregation using VLSM?
Make sure your VLSM routes are not distant from each other. This way
routes can be aggregated into one route in the routing table.
8. Is RIP v. 1 a classful or classless protocol? RIP v. 2? What does this mean?
RIP v. 1 is classful; RIP v. 2 is classless. It means that RIP v. 1 must stay
within the “normal” IP class system (A, B, C); classless means RIP v. 2 can
use VLSM.
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9. Because it’s a new protocol, can RIP v. 2 hop more than 16 times?
No. It still has many of the same characteristics of RIP v. 1, including hop
count max of 16.
10. What is the configuration command to start RIP v. 2 running?
Router(config)#router rip
Router(config-router)#version 2
Router (config-router)#network [attached network(s)]
or
Router(config)#router rip ver 2
11. What show commands can you use to ensure that RIP v. 2 has started running?
show ip route
show ip protocols
12. What is the command to flush (clear) the routing table to force an update?
clear ip route *
13. What will you see if you use the debug ip rip command?
You’ll see all the RIP updates as they are sent and received by the router.
14. How do you turn off the debugging function?
Add “no” to the same command you used to turn it on, or you can use the
“no debug all” to turn off all debugging.
15. What are the three (3) ways that routers learn about routes (networks)? Briefly
explain each one.
•
•
•
Static routing - additions to the routing table put in by the network
administrator
Dynamic routing – additions to the routing table are added automatically as
routers update themselves using protocols
Default routes - default routes added to the routing table by the network
administrator that indicates the path to take when there is no known route
to the destination
16. What are the two commands that can be used to enter a default route?
ip route [network no.] [subnet mask] [next hop IP address]
ip default-network [network to use as default]
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17. If you want to use the ip route command to specify a default network, how would
you enter it?
ip route 0.0.0.0 0.0.0.0 [next hop IP address]
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INTERNETWORKING III
MODULE 1
VLSM EXERCISE 1
Objective
Create an addressing scheme using variable-length subnet masking (VLSM).
Scenario
You are assigned the Class C address 192.168.10.0 and must support the network shown in the diagram.
Create an addressing scheme that meets the requirements shown in the diagram above.
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INTERNETWORKING III
MODULE 1
VLSM EXERCISE 2
Objective
Create an addressing scheme using VLSM.
Scenario
You are assigned the CIDR address 192.168.30.0 /23 and must support the network shown in the
diagram. Create an addressing scheme that meets the requirements shown in the diagram.
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CCNA 3.0 – RIPv2
Basic RIPv2 Commands
Enabling the RIPv2 process
Router(config)# router rip
Router(config-router)# version 1|2
Enabling the RIP on an interface
Router(config-router)# network network
Summarization Commands
RIPv2 Commands
Router(config-router)# no auto-summary
• Like RIPv1, RIPv2 automatically summarizes as major network boundaries.
• This command turns off automatic summarization, useful for discontiguous networks.
•
This command can only be used with RIPv2, and not with RIPv1.
Extra: Interface Commands
Router(config-if)# ip summary-address rip ip-address ip_network_mask
Propagating a Default Route
Method 1: Quad-Zero Static Route
Router(config)# ip route 0.0.0.0 0.0.0.0 exit-interface|ip-address
Router(config)# router rip
Router(config-router)# default-information originate
•
Required starting with IOS 12.1
Method 2: ip default-network command
Router(config)# router rip
Router(config-router)# ip default-network network-address
Router(config)# ip route 0.0.0.0 0.0.0.0 network-address
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What are the two main ways of classifying dynamic IGP routing protocols?
Distance-vector
Link-state
2.
Which ones are also known as “shortest path first” protocols? Why?
Link-state, because that’s exactly what they do: they look for the shortest
path to the destination (regardless of whether or not this is the BEST path).
3.
Fill in the following table:
Type
Distance-Vector
Protocol(s) Advantages
RIP v. 1
Easy to configure
RIP v. 2
Updates regularly
IGRP
Link-State
OSPF,
IS-IS
4.
Only sends out
updates as needed
Doesn’t use much
bandwidth to maintain
tables
Fast to converge
Not subject to routing
loops
Knows complete
topology of network so
knows all routes
Uses cost metrics
instead of distance
metrics
Can use VLSM and
CIDR
Disadvantages
Takes up significant
bandwidth
Slow to converge
Subject to routing loops
RIP only has 1 metric
Only RIP v. 2 can use
VLSM
Difficult to configure
correctly
Requires more memory
and more powerful
CPUs in routers
Takes a lot of bandwidth
when first started
What are “hello” packets used for?
Link state protocols use them to make sure a link is still active. They’re
very small packets.
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What are the five things that link state protocols use to maintain their tables:
•
•
•
•
•
6.
Link-state advertisements (LSAs)
A topological database
The shortest path first (SPF) algorithm
The resulting SPF tree
A routing table of paths and ports to each network to determine the best
paths for packets
What is meant by a “link” when talking about link state protocols?
A link is an interface on a router.
7.
How does a link state protocol build its topological database? What kind of
information is in it?
It’s a database of the entire topology of the network and includes each link and
how to reach it. It’s built by using the LSAs that have been received by the router.
8.
What are the three types of networks recognized by OSPF?
•
•
•
9.
Broadcast multi-access, such as Ethernet
Nonbroadcast multi-access (NBMA), such as frame relay
Point-to-point networks
What is the DR and the BDR in an OSPF network? What do they do?
DR – Designated Router acts as the “brains” of the network. This router
makes sure that all the LSAs are sent to all the other routers in the
Area.
BDR – Backup Designated Router acts as the “second in command” of the
network. If the DR goes down, the BDR takes over as DR. However,
until the DR goes down, the BDR does not send out LSAs to any other
routers in the Area.
10.
What is the multicast address used by the DR to send out LSAs to all other
OSPF routers? For LSAs just to other designated (and backup) routers?
224.0.0.5
224.0.0.6
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What is a hello packet used for and what is the multicast address used for it?
Why this address?
A hello packet is the way OSPF routers make sure that a link is still active.
224.0.0.5 is the address used so that all links are checked, not just DRs and
BDRs.
12.
What is the default hello interval?
10 seconds
13.
What is the main area of an OSPF network designated?
Area 0 (zero)
14.
What is the command used to start OSPF routing on a router?
Router(config)#router ospf [process ID]
15.
What is the processor ID?
It’s an identifier for the OSPF routing process on the router
16.
What is the command used to identify networks on an OSPF router?
Router(config-router)#network [network no.] [wildcard-mask] area [area-id]
17.
What does an OSPF router use for its router ID? How can you force a different
ID?
It uses the highest active IP address on any of the interfaces (where OSPF
is running). If you want to change the ID, set a Loopback interface with a
higher IP address so it will be forced to be the ID.
18.
What is a Loopback?
It is a logical (virtual) interface; not a physical (real) one
19.
What is the command used to set a Loopback?
Router(config)int Loopback[No.]
Router(config-if) ip addr [IP number] [subnet mask]
20.
What is the recommended subnet mask to use on a Loopback interface?
255.255.255.255
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What is a “priority” number used for? How can you change it?
If there is more than 1 router in the Area (broadcast multi-access), then
there must be a DR and maybe a BDR for the Area. The priority number is
used to determine which routers will be the DR and the BDR.
You can change it with the following command:
Router(config-if)#ip ospf [priority number]
22.
Why must you set the bandwidth on an interface running OSPF? What is the
default bandwidth? How can you change it?
Cost (the default metric of OSPF) uses bandwidth to determine the best
route. The default is 1.544 Mbps. You can change it with the command:
Router(config)#interface [type] [number]
Router(config-if)#bandwidth [Kbps]
23.
How can OSPF routers authenticate each other?
They exchange passwords that only other OSPF routers will know. Use the
commands below to set authentication:
Router(config-if)#ip ospf authentication-key [password]
Router(config-router)#area [area-number] authentication
24.
What is the difference between default authentication and a message-digest
authentication procedure? What is the command to do the latter?
The default authentication sends the password in plain text; messagedigest encrypts the password that’s sent.
Router(config-if)#ip ospf authentication message-digest-key [key-id] md5
[encryption-type key]
Router(config-router)#area [area-id] authentication message-digest
25.
What is the relationship between the “hello” packet interval and the “dead”
interval? What is meant by the “dead” interval?
The dead interval is 4 times the hello interval (e.g., hello is 10 seconds, so
dead is 40 seconds).
The dead interval is the time used to determine that a link is down, or dead.
In other words, if a hello isn’t received from a link for the space of 4 times
the normal hello interval, it’s considered dead.
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What would happen if routers in the OSPF network have different hello intervals
configured?
They wouldn’t be able to “talk” to each other, so would be considered
inactive. Hello intervals must be the same on all the routers in the network.
27.
What is the best way to define a default route on an OSPF router?
Use the “quad zero” command:
Router(config)#ip route 0.0.0.0 0.0.0.0 [interface or IP address of next hop]
28.
How can you make sure that this information is propagated to other routers in the
area?
Router(config-router)#default-information originate
29.
List some of the show commands you can use to make sure that OSPF is
functioning correctly.
Show ip route
Show ip protocol
Show ip ospf interface
Show ip ospf
Show ip ospf neighbor [detail] (shows neighbor database)
Show ip ospf database (shows topological database)
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CCNA 3.0 – Single Area OSPF
Basic OSFP Commands
Enabling the OSPF process
Router(config)# router ospf process-id
process-id:
• 1 – 65,535
• Does not need to be the same as other routers.
Enabling OSPF on the interfaces
Router(config-router)# network address wildcard-mask area area-id
address wildcard-mask:
• The network address used to define the interfaces on which OSPF runs and to define the area ID for
those interfaces.
• The use of the wildcard-mask is the same as with ACLs.
area-id:
• Specifies the area to associate with the network address.
• For Single Area OSPF, use an area-id of 0.
Loopback and Router Priority Commands
Configuring a Loopback interface for use as an OSPF Router ID
Router(config)# interface loopback number
number:
• 1 – 65,535
• Extra: If the router-id command is used, this is the RouterID. (New command starting with IOS
12.01).
router ospf 1
router-id ip-address
• Highest Loopback interface is Router ID.
• If a Loopback interface is not configured, then the highest local active interface IP address is Router
ID.
• For broadcast multi-access networks such as Ethernet and non-broadcast multicaccess networks
such as Frame Relay, ATM, X.25, the router with the highest router ID is the DR, second highest is
BDR.
Configuring the OSPF priority of an interface to help determine DR/BDR
Router(config-if)# ip ospf priority number
number:
• 0 – 255
• Highest priority become DR, second highest BDR
• Preempts Router-ID
• 0 = Cannot become DR/BDR
• Default = 1
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Modifying the OSPF Cost Metric
Explicitly specifying the cost of sending a packet on an interface
Router(config-if)# ip ospf cost number
number:
• 1 – 65,535
• A lower number represents a faster link.
8
• Default: The bandwidth metric is used in the formula, 10 /bandwidth
8
Modifying the interface bandwidth metric used in the formula 10 /bandwidth
Router(config-if)# bandwidth kilobits
kilobits:
• Speed of the link in kilobits.
• Should be the same on both sides of a the link.
Configuring OSPF Authentication
Simple Authentication (plain text)
Router(config-if)# ip ospf authentication-key password
password
• Clear text unless message-digest is used.
• All neighboring routers on the same network must have the same password to be able to exchange
OSPF information.
• Must be the same between neighbors.
Router(config-router)# area area-id authentication
area-id:
• Specifies the area to associate with the authentication.
• For Single Area OSPF, use an area-id of 0.
Encrypted Authentication
Router(config-if)# ip ospf authentication message-digest-key key-id md5 encryptiontype password
password
• Clear text unless message-digest is used.
• All neighboring routers on the same network must have the same password to be able to exchange
OSPF information.
• Must be the same between neighbors.
key-id
• 1 to 255
• must match on each router to authenticate.
encryption-type
• 0 to 7
• 0 is default
• 7 is Cisco proprietary encryption
Router(config-router)# area area-id authentication message-digest
area-id:
• Specifies the area to associate with the authentication.
• For Single Area OSPF, use an area-id of 0.
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Configuring OSPF Timers
Configuring the Hello timer
Router( config-if)# ip ospf hello-interval seconds
seconds
• Must be same on neighboring routers.
• Default:
o 10 seconds on broadcast networks
o 30 seconds on non-broadcast networks
Configuring the Dead timer
Router (config-if)# ip ospf dead-interval seconds
seconds
• Must be same on neighboring routers.
• Default:
o 40 seconds on broadcast networks
o 120 seconds on non-broadcast networks
• Should be 4 times the Hello timer
Propagating a Default Route
Configure a Static Default Route
Router(config)# ip route 0.0.0.0 0.0.0.0 interface|address
Propagate default route to other OSPF Routers (Configured only on the ASBR)
Router(config-router)# default-information originate [always]
[always] (Optional)
Will propagate a default route to other OSPF routers even if a static route is not configured on the ASBR.
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Show Commands
Displaying the routing table
Router# show ip route
• “0” OSPF routes
• “IA” Inter-Area routes
• E1|E2 External routes
Displaying general information on the OSPF routing protocol
Router# show ip ospf
Displays:
• Router-ID
• Process-ID
• SPF schedule delay time
• Successive SPF hold time
• Adjacent area information (CCNP)
Displaying OSPF interface information
Router# show ip ospf interface
Displays:
• Router-ID
• Process-ID
• Interface cost
• DR and BDR of this network if applicable
• Hello and Dead timer intervals
Displaying OSPF adjacent neighbor information
Router# show ip ospf neighbor
Displays neighbors’:
• Router-ID
• IP address
• Interface state
o “Full” when fully adjacent
o “Full” or “2-way” for multi-access networks
• Interface priority
o Default = 1
Debug Commands
Displays OSPF adjacency processing
Router# debug ip ospf adj
• Adjacency information
• Hello processing
• DR/BDR election
• Authentication
• Steps to OSPF operations
Router# debug ip ospf events
• Adjacency information
• Hello processing
• DR/BDR election
• Authentication
• Steps to OSPF operations
Displays OSPF event processing
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CED255 INTERNETWORKING III, Ver. 3.0
MODULE 3 STUDY GUIDE
1. What is the difference between IGRP and EIGRP?
EIGRP supports VLSM and CIDR, it has faster convergence times, it’s more
scalable, and handles routing loops better than IGRP does.
2. Why is EIGRP referred to as a hybrid protocol?
Because it primarily is a distance vector protocol, but also has some
characteristics of a link state protocol, such as sending hello packets,
sending only partial updates (instead of entire table exchanges), and using
neighbor discovery. However, it’s easier to configure than OSPF.
3. Can IGRP and EIGRP routers “talk” to each other? Why or why not?
Yes, they can talk because EIGRP is simply an enhancement of IGRP;
they’re still basically the same protocol.
4. List the three tables that EIGRP maintains and briefly describe each one.
Topology – lists all routing tables in the AS; all learned routes are in this
table
Neighbor – lists adjacent routers, their addresses and interfaces
Routing – lists best route to each destination network
5. List the five pieces of information found in the topology table and briefly describe
each one.
•
•
•
•
•
Feasible distance – The feasible distance (FD) is the lowest calculated
metric to each destination.
Route source – The source of the route is the identification number of the
router that originally advertised that route. This field is populated only for
routes learned externally from the EIGRP network. Route tagging can be
particularly useful with policy-based routing.
Reported distance – The reported distance (RD) of the path is the distance
reported by an adjacent neighbor to a specific destination.
Interface information – The interface though which the destination is
reachable
Route status – Routes are identified as being either passive (P), which
means that the route is stable and ready for use, or active (A), which means
that the route is in the process of being recomputed by DUAL.
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6. What is DUAL?
The EIGRP distance vector algorithm is called the Diffusing Update
Algorithm (DUAL). DUAL tracks all the routes advertised by neighbors.
Composite metrics of each route are used to compare them. DUAL also
guarantees that each path is loop free. DUAL inserts lowest cost paths into
the routing table. These primary routes are known as successor routes. A
copy of the successor routes is also placed in the topology table.
7. What is the difference between a “feasible successor” route and a :successor”
router?
The successor route is the route in the routing table; in other words, the
route considered the best to the destination. The feasible successor is the
back-up route, or the next-best route.
8. What makes EIGRP able to support IP, IPX, and AppleTalk?
It uses PDMs (protocol dependent modules). Also, for AppleTalk, it can
actually act as the primarily protocol and AppleTalk doesn’t even have to
be running.
9. What is RTP? What does it do?
Reliable Transport Protocol is a transport-layer protocol that can guarantee
ordered delivery of EIGRP packets to all neighbors. This means EIGRP
does not rely on TCP/IP to exchange routing information the way that RIP,
IGRP, and OSPF do. To stay independent of IP, EIGRP uses RTP as its own
proprietary transport-layer protocol to guarantee delivery of routing
information.
10. What are the five EIGRP packet types? Briefly describe each one.
•
•
•
•
•
Hello - discover, verify, and rediscover neighbor routers
Acknowledgement - to indicate receipt of any EIGRP packet during a
reliable exchange
Update - used when a router discovers a new neighbor. An EIGRP router
sends unicast update packets to that new neighbor, so that it can add to its
topology table
Query - uses query packets whenever it needs specific information from
one or all of its neighbors
Reply - used to respond to a query
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11. What are the commands used to start EIGRP running on a router?
router(config)# router eigrp [autonomous-system-number]
router(config-router)# network [network number]
router(config)#int [type] [number]
router(config-if)# bandwidth [kilobits]
router(config-if)# eigrp log-neighbor-changes
12. If you do not want to summarize routes, what is the command to turn it off? Why
might you not want to summarize (aggregate) routes?
router(config-router)#no auto-summary
If you have discontiguous subnets (subnets not right beside each other in
the numbering scheme), route summarization probably won’t work right.
13. List some of the show commands you can use to verify that EIGRP is running
correctly.
show ip route
show ip eigrp
show ip protocol
show ip eigrp neighbor [details]
show ip eigrp interface
show ip eigrp topology
show ip eigrp traffic
14. Which table built by EIGRP is considered the most important? List the fields of
information contained in this table and briefly describe each one.
•
•
•
•
•
The neighbor table.
Neighbor address –network layer address of the neighbor router
Hold time –interval to wait without receiving anything from a neighbor
before considering the link unavailable. Originally, the expected packet was
a hello packet, but in current Cisco IOS software releases, any EIGRP
packets received after the first hello will reset the timer.
Smooth Round-Trip Timer (SRTT) –average time that it takes to send and
receive packets from a neighbor; used to determine the retransmit interval
(RTO).
Queue count (Q Cnt) –number of packets waiting in a queue to be sent.
Sequence Number (Seq No) –number of the last packet received from that
neighbor; used to acknowledge a transmission of a neighbor and to
identify packets that are out of sequence.
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15. What is the most common problem that keeps RIP tables from updating?
The use of VLSM and RIP v. 1, which doesn’t support it.
16. What is the most common type of networking problem?
Layer 1 issues (cabling is the most prevalent)
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CED255 INTERNETWORKING III, Ver. 3.0
MODULE 4 STUDY GUIDE
1. Why is Ethernet described as a collision-prone network?
Because of the nature of Ethernet. It is a broadcast technology, which
means that it is a shared technology where every packet is broadcast to
every device on the segment. It is also non-deterministic, which means any
device can transmit at any time. This makes it prone to collisions.
2. What networking device can help cut down or even eliminate collisions on an
Ethernet network? Why?
A switch because every port on a switch acts like a mini-bridge, making it a
separate collision domain. Only those devices that are on that port of the
switch will be in the same collision domain. If each port goes to a separate
workstation or printer, then you basically will eliminate all collisions.
3. What does the term “microsegmentation” mean?
It is segmenting a network into point-to-point collision domains using
switches, which gives maximum usage of bandwidth.
4. Fill in the following table:
Item
Router
Switch
Bridge
Passive hub
Active hub
Transceiver
IP address
MAC address
Packets
Frames
Data segments
Repeater
3
2
2
1
1
1
3
2
3
2
4
1
Layer
5. What is the most common LAN architecture used today?
Ethernet
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6. Explain CSMA/CD. What does it stand for and how does it apply to Ethernet
networks?
Carrier Sense Multiple Access/Collision Detect: this is the technology that
Ethernet is built on. Since Ethernet devices can transmit at will, CSMA/CD
has been built into them so that they will listen to the media first to see if
there is any traffic on it before transmitting. This is how Ethernet tries to
avoid collisions. However, if a collision occurs, it is detected very quickly
and all devices are told not to transmit for the back-off time to avoid more
collisions.
7. What is meant by “half-duplex” technology?
A device can either transmit or receive, but not both at the same time.
8. What does the term “latency” mean?
It is the delay the time a frame or a packet takes to travel from the source
station to the final destination. Latecncy is is inherent in different types of
networks and networking devices.
9. What are the three sources of latency on an Ethernet network?
•
•
•
First, there is the time it takes the source NIC to place voltage pulses on
the wire and the time it takes the receiving NIC to interpret these pulses.
This is sometimes called NIC delay, typically around 1 microsecond for a
10BASE-T NIC.
Second, there is the actual propagation delay as the signal takes time to
actually travel along the cable. Typically, this is about .556 microseconds
per 100 m for Cat 5 UTP. Longer cable and slower nominal velocity of
propagation (NVP) results in more propagation delay.
Third, latency is added according to which networking devices, whether
they are Layer 1, Layer 2, or Layer 3, are added to the path between the two
communicating computers. The actual transmission time, the duration of
time to actually send the bits, must also be included in understanding
timing on networks.
10. What is meant by “bit time” in Ethernet networks?
It is defined as the basic unit of time in which one bit can be sent.
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11. What is meant by the term “attenuation” when talking about data networks? What
causes it?
Attenuation means that the signal weakens as it travels through the
network. The resistance in the cable or medium through which the signal
travels causes the loss of signal strength.
12. What is meant by “full duplex” technology? Which Ethernet connections can take
advantage of it? What does it take in order to create a full duplex network?
It means that a device can both send and receive at the same time.
Ethernet 10BASE-T, 100BASE-TX, or 1000BASE-Fx can use full duplex.
A dedicated port on a switch that can support full duplex is required for
each node
13. How many wires does it take to make a full-duplex cable? How much of the
bandwidth is available on a full-duplex network?
it takes two pairs for full duplex. 100% of the bandwidth in both directions
is available on full duplex because there is one pair of wires for sending
and another for receiving data.
14. Is there an advantage of segmenting a network using switches instead of routers?
Disadvantages?
Yes, switches introduce less latency onto the network. They only add 1030% latency; routers add 20-30% latency. However, switches only can
segment at Layer 2 to create separate collision domains; routers can
segment at Layer 3 (networks) and can subnet in separate networks.
15. What is the main reason for LAN segmentation?
It improves the performance of shared media (cuts down on collision
domain size)
16. Are there more or fewer collision domains in a microsegmented LAN? Why?
There are more collision domains in a microsegmented LAN because
switches break a LAN down into smaller “LANs” by segmenting them. This
makes smaller—but more—collision domains.
17. What are the two main functions of switching devices?
•
•
Switching data frames
Maintaining switching operations
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18. What type of circuits does a switched LAN create? What is one advantage of using
switches on a LAN?
virtual circuits. Switches create many small collision domains so collisions
are almost totally avoided, thus speeding up transmission.
19. What is the difference between a symmetric and asymmetric switch?
symmetric switches switch between like media (same bandwidth);
asymmetric switches switch between unlike media (different bandwidths).
20. Where does a switch store destination and transmission data? Describe the
difference between the two main types.
In memory buffers in queues. In port-based memory buffering, packets are
stored in queues that are linked to specific incoming ports. Shared memory
buffering deposits all packets into a common memory buffer which all the
ports on the switch share.
21. What are the two switching methods? What are the main differences between the
two?
store-and-forward switching, cut-through switching. The main difference is
that store-and-forward waits until the entire frame has been received before
it sends it on its way; cut-through switching reads the destination MAC
address on the incoming frame and immediately begins sending it on
through (before the entire frame is received).
22. What are the two sub-types of cut-through switching?
Fast Forward – only reads the destination MAC address and immediately
starts forwarding the frame
Fragment Free – makes sure there area at least 64 bytes of data to send
before forwarding the frame (anything less than 64 bytes is a fragment)
23. What are the two main reasons to use of Ethernet switches in a network?
•
•
Isolate traffic among segments
Achieve greater amount of bandwidth per user by creating smaller collision
domains
24. What are the three main frame transmission modes used by Ethernet switches?
•
•
•
Cut Through
Store and Forward
Fragment Free
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25. What is the fourth mode? What is different about it?
Adaptive cut-through – With this mode, the switch uses cut-through until it
detects a given number of errors. Once the error threshold is reached, the
switch changes to store and forward mode. This method is sometimes
referred to as Error sensing
26. What does a bridge use to forward data packets? How does it learn this information?
They use MAC address to forward/not forward data packets to another
segment. They learn new MAC addresses from the source address in the
header of a packet and add this info to a MAC table they build.
27. How does a switch learn MAC addresses? What happens when a switch adds a new
MAC address to its table?
Switches learn MAC addresses from incoming packets. They add these
addresses to their MAC tables so they can remember which segment hosts
which nodes. Each new address is time stamped so the switch can
determine which address are still good and which are old.
28. What is Content-Addressable memory (CAM) used for in switch applications?
•
•
To take out and process the address information from incoming data
packets
To compare the destination address with a table of addresses stored within
it
29. What do switches/bridges use to filter frames?
They can filter frames based on any Layer 2 fields
30. Can switches filter broadcast or multicast frames? Why or why not?
Most Ethernet switches can filter broadcast and multicast frames, because
today, they are able to filter according to the network-layer protocol.
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31. What are the three ways of communicating on a data network? Briefly describe each
one.
•
•
•
Unicast – one transmitter tries to reach one receiver
Multicast –one transmitter tries to reach only a subset, or group, of the
entire segment broadcasting
Broadcast – one transmitter tries to reach all the receivers in the network.
The server station sends out one message and everyone on that segment
receives the message.
32. What is the MAC address for a broadcast message?
FF:FF:FF:FF:FF:FF
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MODULE 5 STUDY GUIDE
33. What are the four components that make up a successful network design? Briefly
describe each one.
•
•
•
•
Functionality – The network must work. The network must allow users to
meet their job requirements. The network must provide user-to-user and
user-to-application connectivity with reasonable speed and reliability.
Scalability – The network must be able to grow. The initial design should
grow without any major changes to the overall design.
Adaptability – The network must be designed with a vision toward future
technologies. The network should include no element that would limit
implementation of new technologies as they become available.
Manageability – The network should be designed to facilitate network
monitoring and management to ensure ongoing stability of operation.
34. To maximize bandwidth and availability of resources, what should you consider
when designing a LAN?
•
•
•
•
The function and placement of servers
Collision detection issues
Segmentation issues
Broadcast domain issues
35. What are the two main groups of servers? Give some examples of each would do
and would be located.
Enterprise – DNS, e-mail, DHCP; located in Distribution Facilities (either
MDF or IDFs)
Application – applications used by workers (Word, Excel, Accounting, etc.);
located close to the users
36. What are the steps you should follow in order to create a successful network
design?
•
•
•
•
Gather requirements and expectations
Analyze requirements and gathered data
Design the Layer 1, 2, and 3 LAN structure, or topology
Document the logical and physical network implementation
37. What is meant by “availability”? Give some examples.
Availability measures the usefulness of the network; it includes
throughput, response time, and access to resources
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38. What layers of the OSI model are you primarily working with when you’re designing
a network? What is involved at each layer?
•
•
•
Layer 1 – what type of media will be used in the network
Layer 2 – how will the network be segmented at this layer; where will
switches be placed in the network?
Layer 3 – how will the network be subnetted (or will it be) and how
should those subnets be allowed to communicate; where should
routers be injected into the network?
39. What are MDFs and IDFs? What would you find in them?
They are wiring rooms (telecommunication rooms/distribution facilities).
This is where all the networking devices (routers, switches, hubs, patch
panels, telephone connections, etc.) should be located. This is the endpoint of your horizontal cabling.
40. What is the difference between horizontal cabling and vertical cabling?
Horizontal cabling runs from the workareas to the DF; backbone cabling is
the main cable running from floor-to-floor carrying the majority of the data
to the major networking devices (switches and routers).
41. List some of the documents you should create as you design and build your network.
•
•
•
•
•
•
The exact locations of the MDF and IDF wiring closets
The type and quantity of cabling used to interconnect the IDFs with the
MDF, along with how many spare cables are available for increasing the
bandwidth between the wiring closets.
Detailed documentation of all cable runs, the identification numbers, and
which port on the HCC or VCC the run is terminated on
List of devices and their locations
The IP addressing should be documented by site and by network within the
site. A standard convention should be set for addressing important hosts
on the network. This addressing scheme should be kept consistent
throughout the entire network. Addressing maps provide a snapshot of the
network.
Physical maps of the network (helps to troubleshoot the network)
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42. What is the hierarchical design model? Why would you want to use it? What are the
three layers of this design model? Briefly describe each one.
•
•
•
It is a design model that breaks a network into three distinct layers. It is a
good idea to use a hierarchical design because this will make it easier to
make changes to the network as the organization grows. The three layers
are:
The Access Layer – provides users in workgroups access to the network
The Distribution Layer – provides policy based connectivity
The Core layer – provides optimal transport between sites. The core layer
is often referred to as the backbone
43. What layer of the OSI model do access switches run at? What are they designed to
do? List a few of the Cisco models.
They run at Layer 2 (although they have some Layer 3 characteristics) and
their main purpose is to allow end users into the network. Some of the
Cisco models are 1900 series, 2950 series, 4000 series, and 5000 series.
44. What layer of the OSI model do distribution switches run at? What are they designed
to do? List a few of the Cisco models.
Switches in this layer operate at Layer 2 and Layer 3 and they aggregate the
wiring closet connections, define broadcast/multicast domains, allow Virtual
LAN (VLAN) routing, create any media transitions that need to occur, and add
security to the network. Some of the models are 2926G, 5000 series, and 6000
series.
45. What layer of the OSI model do core switches run at? What are they designed to
do? List a few of the Cisco models.
Core switches are designed to use Layer 2 or Layer 3 switching and switch
packets as fast as possible and do not perform any packet manipulation, such
as access list filtering, which would slow down the network. An example of a
core switch is an ATM switch. Some of the models include Catalyst 6500
series, Catalyst 8500 series, IGX 8400 series, and Lightstream 1010.
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MODULE 6 STUDY GUIDE
1. What types of ports/interfaces does a configurable switch normally have?
Ports (10/100/1000Mpbs) to connect devices; console port; higher speed
ports for backbone cables.
2. What do the LEDs on the switch do?
•
•
•
•
Alert you as to whether or not ports are working correctly
Whether power is being received into the switch from the power
connection
Whether a remote power source is being used or not
Current mode being used by switch
3. What is a POST? When is it performed?
Power On Self-Test. It is performed by the device upon power-up.
4. What kind of cable is required to access the console port on a switch or router?
Which port do you use? How do you know what’s going on on the device?
Roll over cable into the console port. You normally use a HyperTerminal or
Telnet session from a PC to see what is happening on the device.
5. Where is the power switch on a Cisco switch?
There is none. You simply plug in the switch to the power source.
6. What does CLI stand for? How does it differ on a Cisco switch from a router?
Command line interface. It doesn’t differ very much—they both use the
Cisco IOS; the only thing that’s a little different is the particular command
set available on each.
7. List (in order) the EXEC modes on the Cisco switch.
•
•
•
•
User EXEC
Enable/privileged EXEC
Global configuration EXEC
Particular configuration EXEC (e.g., interface, line, etc.)
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8. What are the steps you should follow in order to completely configure a switch that
may already have a configuration on it?
•
•
•
Remove any existing VLAN information by deleting the VLAN database file
VLAN.dat from the flash directory
Erase the back up configuration file startup-config
Reload the switch
9. List some of the things you should configure on a switch to ensure it is secure, yet
easy to access for those authorized to do so.
•
•
•
•
switch should be given a hostname
passwords should be set on the console and vty lines
IP addresses and a default gateway should be set
In a switch-based network, all internetworking devices should be in VLAN
1, the management VLAN
10. Identify what the following commands will do on the switch:
Command
Switch#show mac-address-table
Switch#clear mac-address-table
Switch(config)#mac-address-table static
[mac address of host] interface
[type][number] vlan [number or name]
Switch#show port security
Purpose
Displays the MAC table
Clears all entries out of the MAC table
and forces it to rebuild itself
To set a static MAC address in the MAC
table
Display switch security on ports
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MODULE 7 STUDY GUIDE
1. What is meant by “redundant technologies” when talking about networks? Why or
why not is this a good thing?
Redundancy means to be in excess or exceeding what is usual and natural.
Fault tolerance is achieved by redundancy. Normally, this is a good thing
for a network.
2. What is a drawback of having a redundant switched topology?
It may cause broadcast storms, multiple frame copies, and MAC address
table instability problems. It is possible for switches to learn the wrong
information. A switch can learn that a MAC address is on a port when it is
not really on that port.
3. What is the answer to this problem?
To create a logical loop-free topology, which is called a tree. The Spanning
Tree Algorithm is used to span all the trees, thus creating a loop-free
logical topology.
4. What is the IEEE standard for Spanning Tree? What does it specify
802.1d; It specifies that the STP (spanning tree protocol) use the Spanning
Tree Algorithm (STA) to construct a loop free shortest path network.
Shortest path is based on cumulative link costs. Link costs are based on
the speed of the link.
5. What are BPDUs? What information contained in these BPDUs allow the switch to
create the loop-free topology?
The message that a switch sends allowing the formation of a loop free
logical topology is called a Bridge Protocol Data Unit (BPDU).
•
•
•
•
•
Select a single switch that will act as the root of the spanning tree
Calculate the shortest path from itself to the root switch
For each LAN segment, designate one of the switches as the closest one to
the root. This bridge is called the “designated switch.” The designated
switch handles all communication from that LAN towards the root bridge.
Each non-root switch chooses one of its ports as its root port. This is the
interface that gives the best path to the root switch.
Select ports that are part of the spanning tree, the designated ports. Nondesignated ports are blocked.
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6. What are the four elements that must exist on every switch in a spanned, switched
network?
•
•
•
•
One root bridge per network
One root port per non root bridge
One designated port per segment
Non designated ports are unused
7. Which switch will become the root bridge in a network running STP?
The switch with the smallest BID (bridge ID) number.
8. How often are BPDUs sent out by default?
Every 2 seconds
9. What are the five STP states? Briefly describe each one.
•
•
•
•
•
blocking state - ports can only receive BPDUs; data frames are discarded
and no addresses can be learned
listening state - switches determine if there are any other paths to the root
bridge (called the forward delay)
learning state - user data is not forwarded, but MAC addresses are learned
from any traffic that is seen (also called the forward delay)
forwarding state - user data is forwarded and MAC addresses continue to
be learned; BPDUs are still processed
disabled state - occurs when an administrator shuts down the port or the
port fails
10. What is the definition of a converged switched internetwork?
When all the switch and bridge ports are in either the forwarding or blocked
state
11. What does the 802.1w standard define?
Rapid Spanning Tree Protocol
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MODULE 8 STUDY GUIDE
1. What is the definition of a VLAN?
A VLAN is a group of network services that is not restricted to a physical
segment or switch. VLANs logically segment switched networks based on
an organization'
s functions, project teams, or applications as opposed to a
physical or geographical basis.
2. Is a VLAN able to contain broadcasts?
Yes, a VLAN may be thought of as a broadcast domain that exists within a
defined set of switches
3. How does a switch that has multiple VLANs on it switch frames that come into it?
•
•
•
•
The switch maintains a separate bridging table for each VLAN, so if a frame
comes in on a port in VLAN 1 the switch searches the bridging table for
VLAN 1
When the frame is received, the switch adds the source address to the
bridging table if it is currently unknown.
The destination is checked so a forwarding decision can be made.
For learning and forwarding the search is made against the address table
for that VLAN only.
4. What are the three main ways that VLANs are organized?
Port-centric, statically, dynamically
5. List some of the advantages of VLANning a network.
•
•
•
•
•
Easily move workstations on the LAN.
Easily add workstations to the LAN.
Easily change the LAN configuration.
Easily control network traffic.
Improve security.
6. What are the three basic models for determining and controlling how a packet gets
assigned to a VLAN?
•
•
•
Port-based VLANS.
MAC address based VLANs.
Protocol based VLANs
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7. What happens to the frame header when using any of the above models?
A VLAN ID is inserted into it before the frame is transmitted onto the link
between the VLANs.
8. What is the most used frame tagging option used in switching? What is special
about this?
Inter-Switch Link (ISL); it’s a Cisco-proprietary protocol that maintains
VLAN information as traffic flows between switches and routers.
9. How can you make an ATM network look like an Ethernet network?
LAN emulation (LANE) is a way to make an Asynchronous Transfer Mode
(ATM) network simulate an Ethernet network
10. What type of address must be assigned to each VLAN?
A unique Layer 3 network address
11. What characteristics should an end-to-end VLAN network comprises?
•
•
•
•
Users are grouped into VLANs independent of physical location, but
dependent on group or job function.
All users in a VLAN should have the same 80/20 traffic flow patterns.
As a user moves around the campus, VLAN membership for that user
should not change.
Each VLAN has a common set of security requirements for all members.
12. What does standard 802.1q pertain to?
Fast Ethernet Inter-Switch Link (ISL), which is used to carry multiple VLAN
information between the wiring closets and the distribution layer switches.
13. What is meant by a static VLAN? What are some advantages/disadvantages of this
method?
Ports on a switch are manually assigned to a VLAN by using a VLAN
management application or by working directly within the switch.
Advantage is that they’re very secure and easy and straightforward to
configure; disadvantage is that they must be configured and updated
manually by an administrator.
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14. What is meant by a dynamic VLAN? What are some advantages/disadvantages of
this method?
Do not rely on ports assigned to a specific VLAN. Instead, VLAN
assignment is based on MAC addressing, logical addressing, or protocol
type. Advantage is that the switch takes care of VLAN switching and
tagging based on the protocols being used. Disadvantage is that the
protocol must be robust enough to maintain the switched network.
15. Complete the table for the commands used to configure a VLAN on a 2900 series
Catalyst switch.
Command
Switch#show version
Switch#vlan database
Switch(vlan)#vlan [vlan number]
Switch(config)#interface [type] [port]
Switch(config-if)#switchport access vlan
[vlan number]
Switch#show vlan [brief]
Switch#show vlan id [vlan number]
Switch#show running-config
Switch(vlan)#no vlan [vlan number]
Switch#show spanning-tree
Switch#debug sw-vlan packets
Purpose
Displays the version of IOS running on the
switch
Enter the VLAN configuration mode
Assign a number to the VLAN to create
Identify which interface to assign VLAN to
Assign VLAN to one or more interfaces
Verify VLAN assignment(s)
Verify VLAN assignment
Display the switch’s configuration file
Delete a VLAN
Display the spanning tree topology known
to the router
Display general information about VLAN
packets that the router received but is not
configured to support
16. What are the steps you should follow to troubleshoot problems with your VLANs?
1.
2.
3.
4.
5.
Check the physical indications, such as LED status.
Start with a single configuration on a switch and work outward.
Check the Layer 1 link.
Check the Layer 2 link.
Troubleshoot VLANs that span several switches.
17. What is a broadcast storm?
A broadcast storm occurs when a large number of broadcast packets are
received on a port. Forwarding these packets can cause the network to
slow down or to time out. Storm control is configured for the switch as a
whole, but operates on a per-port basis. By default, storm control is
disabled.
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18. How can they be prevented?
By the use of high and low thresholds to discard excessive broadcast,
multicast, and unicast MAC traffic. Also the switch can be set to shut down
the port when the rising threshold is reached.
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MODULE 9 STUDY GUIDE
1. What is the definition of a trunk in a switched network?
A physical and logical connection between two switches across which
network traffic travels. A trunk is a single transmission channel between
two points that are usually switching centers.
2. What is a trunk designed to do if there are multiple VLANs in a network?
The purpose of a trunk is to save ports when creating a link between two
devices implementing VLANs, typically two switches.
3. What are trunking protocols designed to do? What are the two types of trunking
mechanisms? Which has become the standard? Why?
To effectively manage the transfer of frames from different VLANs on a
single physical line. The trunking protocols establish agreement for the
distribution of frames to the associated ports at both ends of the trunk.
Trunking mechanisms: frame filtering and frame tagging
Frame tagging has been adopted as the standard trunking mechanism by
IEEE because it is more scalable than frame filtering.
4. How does frame tagging work?
Frame tagging places a unique identifier in the header of each frame as it is
forwarded throughout the network backbone. The identifier is understood
and examined by each switch before any broadcasts or transmissions are
made to other switches, routers, or end-station devices. When the frame
exits the network backbone, the switch removes the identifier before the
frame is transmitted to the target end station. Frame identification
functions at Layer 2 and requires little processing or administrative
overhead.
5. What is the first step you must perform on a switch before starting trunking?
Configure the port first as a trunk and then specify the trunk encapsulation
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6. Complete the following table:
Command
Switch(config-if)#switchport mode trunk
Switch(config-if)#switchport trunk
encapsulation [dot1q | isl]
Switch#show port capabilities
Switch#show trunk [mod_num/port_num]
Switch#erase startup-configuration
Switch(vlan)#vtp v2-mode
Switch(vlan)#vtp domain [name]
Switch#show vtp status
Switch(vlan)#vtp [client | server | transparent]
Switch#show vtp counters
Router(config)#interface fastethernet [portnumber.subinterface-number]
Router(config-if)#encapsulation dot1q [vlannumber]
Router(config-if)#ip address [ip-address]
[subnet-mask]
Purpose
Turns on trunking mode
Specifies encapsulation type on port with
either 802.1a or ISL
Displays what the port can do, including
what encapsulation the port can support
Displays if trunking has been configured
and the settings
Clears NVRAM of any saved configuration
files
Sets the VTP version to Version 2
Creates a management domain
Displays VTP configuration and status
Sets the correct mode of the switch
Displays statistics about advertisements
sent and received on the switch
Identifies which port and/or subinterface
you wish to configure
Set encapsulation for 802.1q on an
interface
Sets the IP address on an interface
7. What does it mean if the trunking mode has been set to “negotiate”?
Puts the port into permanent trunking mode but prevents the port from
generating Dynamic Trunking Protocol (DTP) frames. You must configure
the neighboring port manually as a trunk port to establish a trunk link.
8. What is VTP? Why should it be used on a VLAN’ed network?
VLAN Trunking Protocol (VTP) was created to solve potential operational
problems in a VLANs network switched environment. The role of VTP is to
maintain VLAN configuration consistency across a common network
administration domain. VTP is a messaging protocol that uses OSI Layer 2
trunk frames to manage the addition, deletion, and renaming of VLANs on a
single domain. Further, VTP allows for centralized changes that are
communicated to all other switches in the network.
9. What is a VTP domain?
A VTP domain is made up of one or more interconnected devices that
share the same VTP domain name.
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10. What are the four items found in a VTP message?
•
•
•
•
VTP protocol version: Either Version 1 or 2
VTP message type: Indicates one of four types
Management domain name length: Indicates size of the name that follows
Management domain name: The name configured for the management
domain
11. What are the three modes that switches can work in when running VTP? Briefly
describe each one.
•
•
•
Server - can create, modify, and delete VLAN and VLAN configuration
parameters for the entire domain. VTP servers send VTP messages out to
all trunk ports.
Client - cannot create, modify, or delete VLAN information. VTP clients do
process VLAN changes and send VTP messages out to all trunk ports.
Transparent - forward VTP advertisements such as version 2, but ignore
information contained in the message. A transparent switch will not modify
its database when updates are received, nor will the switch send out an
update indicating a change in its VLAN status. Except for forwarding VTP
advertisements, VTP is disabled on a transparent switch.
12. What are the two types of VTP advertisements?
•
•
Requests from clients that want information at bootup
Response from servers
13. What are the three types of VTP messages?
•
•
•
Advertisement requests
Summary advertisements
Subset advertisements
14. What kinds of activities can trigger a VTP advertisement?
Creating or deleting a VLAN, suspending or activating a VLAN, changing
the name of a VLAN, changing the maximum transmission unit (MTU) of a
VLAN
15. What are the two versions of VTP available now? Which is the default version? Are
they interoperable?
Version 1 and Version 2. Version 1 is the default; they are not
interoperable.
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16. Can VLANs communicate directly with one another? Why or why not?
No, they must still go through a router to communicate. Routers are
designed to connect networks, which is what VLANs are.
17. What is meant by “a router on a stick”?
A trunk line, which can support multiple VLANs, is the physical connection
to a router. This topology is called a router on a stick because there is a
single connection to the router. However, there are really multiple logical
connections between the router and the switch, based on how many
VLANs run through the trunk.
18. What is a “subinterface”? How are they used on a switch?
The logical division of a physical interface into several logical interfaces.
Each subinterface of a port can support a separate VLAN and is assigned a
different IP address.
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