Cisco based Networking Questions part xiii

Your time is limited, so don’t waste it living someone else’s life.

 –Steve Jobs

Random Cisco based networking questions and answers to help with accreditation or just for fun :-)

1. What is the function of asymmetric switching?

A) To prioritise bandwidth to nodes that need it
B) To prevent bottlenecks on the port a server is connected to
C) To allow RAS clients to connect to the network

2. What Cisco IOS command executes the configuration stored in NVRAM.

A) config t
B) config mem
C) config net
D) config start

3. How would you disable an interface (Cisco command)?

A) Router(config-if)#shutdown
B) Router(config-if)#disconnect
C) Router(config-if)#disable
D) Router(config-if)#close
E) Router(config-if)#stop

4. What will be the IP address of the second subnet given the following?

172.16.0.0
255.255.224.0
(Assume ip subnet-zero is enabled)

A) 172.16.0.0
B) 172.16.8.0
C) 172.16.16.0
D) 172.16.32.0
E) 172.16.64.0

5, Given the IP address 192.168.10.0 
What subnet mask should you use to create 16 subnets?
(Assume ip subnet-zero is enabled)

A) 255.255.255.240
B) 255.255.240.0
C) 255.240.0.0
D) 255.255.255.248
E) 255.255.248.0

6. What is the Spanning Tree forward delay?

A) The time that is spent in the Listening and Learning states
B) 50 seconds
C) Time taken for a switch to go from Listening to Forwarding
D) Time taken for a switch to go from Blocking to Forwarding

Bonus Question

IGRP advertises routes to interior, system and exterior routes

A) True
B) False









1. Correct Answer: B
An asymmetric switch provides switched connections between ports of different bandwidths.
Asymmetric switching is optimized for client-server traffic where multiple clients simultaneously communicate with a server, requiring more bandwidth dedicated to the server port to prevent a bottleneck at that port.

2. Correct Answer: B
config mem executes configuration commands stored in NVRAM by copying startup-config to the running-config

3. Correct Answer: A
The interface command shutdown disables an interface.

4. Correct Answer: D
The subnet block size is 256 - 224 = 32
The first subnet will be subnet zero 172.16.0.0
The second subnet will be 172.16.32.0

5. Correct Answer: A
This is a class C IP address, so octets 1-3 cannot be used for subnetting.
24 = 16 subnets, which means we need to borrow 4 bits.
The fourth octet value should therefore be 240.

6. Correct Answer: A
Forward delay — The time that is spent in the listening and learning state, 15 sec by default, but you can tune the time to be between 4 and 30 sec

Bonus Question. Correct Answer: A
IGRP advertises three types of routes:

Interior routes are routes between subnets in the network attached to a router interface.
System routes are routes to networks within an autonomous system.
Exterior routes are routes to networks outside the autonomous system.

How did you go? let me know,,

Cisco Based Networking Questions part xii

Strive not to be a success, but rather to be of value. 

–Albert Einstein.

More Random Cisco Based networking Questions for you to ponder.

1, In a local broadcast all bits set to 1 received by all hosts on local and remote broadcast domains?

A) True
B) False

2. Which protocol is used to determine the IP address if the MAC address is already known?

A) ARP
B) RARP
C) IP
D) IPX
E) TCP

3. What is the invalid timer set to by default when you have a router running the Interior Gateway Routing Protocol?

A) 3 times the update period
B) 270 seconds
C) 3 times the update period + 10 seconds
D) Answer A and B
E) 7 times the update period

4. The startup-config (Cisco) is found in the ...

A) FLASH
B) DRAM
C) NVRAM
D) ROM

5. What component of a router holds the routing tables and the software that allows the router to function?

A) Bootstrap
B) POST
C) ROM monitor
D) RAM
E) Configuration register

6. Which switching mode has the highest degree of error checking?

A) Fragment-Free
B) Fast-Forward
C) Cut-Through
D) Store-and-Forward
E) FIFO

1. Correct Answer: B
Routers don't forward broadcasts so local broadcasts will stay on the broadcast domain from which they originated.

2. Correct Answer: B
Reverse Address Resolution Protocol (RARP) is a networking protocol used by a host computer to request its IP address from an administrative host, when it knows its MAC address.

3. Correct Answer: D
IGRP sends its routing table to its neighbors every 90 seconds. IGRP uses an invalid timer to mark a route as invalid after 270 seconds (three times the update timer). IGRP uses a flush timer to remove a route from the routing table (default flush timer is 630 seconds, seven times the update period).

4. Correct Answer: C
The startup configuration is stored in NVRAM

5. Correct Answer: D
The running-config is stored in RAM and allows the router to function.

6. Correct Answer: D
Store and forward switching method is known as store and forward because the switch will store the incoming data frame in its internal buffer, then when the complete frame has been received the switch will then run a Cyclic Redundancy Check (CRC) against the frame. If the CRC passes, the switch will then look up the destination MAC Address in its MAC filter table to forward it on to its destination.

More to come - stay tuned...

Cisco Based Networking questions - part xi

Another set of 6 random IT questions to active your grey matter :-)

1. Hosts on one VLAN that want to communicate with another VLAN need to go through a router.

A) True
B) False

2. Triggered updates are used to speed the network convergence process?

A) True
B) False

3. What process is used to check whether packets have been received when using IP?

A) Acknowledgments
B) CRC
C) Windowing
D) Flow control
E) None

4. What is the administrative distance of RIP?

A) 110
B) 1
C) 120
D) 90
E) 100

5. What Cisco IOS command executes the configuration stored in NVRAM.

A) config t
B) config mem
C) config net
D) config start

6. Where would you place extended access lists?

A) As close to the destination as possible
B) As close to the source as possible





1. Correct Answer: A
VLANs act as if they are different networks.  So communication between VLANs require routers.

2. Correct Answer: A
A triggered update is sent immediately in response to a change in the network (e.g. A link going down). The router detecting the change immediately sends an update message to its adjacent routers, which then generate their own triggered updates. This process continues until the network converges. Triggered updates occurs independently from the regular routing updates and are intended to speed the convergence process.

3. Correct Answer: E
Trick question. IP provides NO form of error correction/acknowledgements.

4. Correct Answer: C
Here in the question the A is administrative distance 110 for OSPF, B is 1 for Static Route, D is 90 for Internal EIGRP, E is 100 for IGRP so the last C is 120 for RIP.

5. Correct Answer: B
config mem executes configuration commands stored in NVRAM by copying startup-config to the running-config

6. Correct Answer: B
Extended access lists are much more granular than standard ACLs, you can block specific ports or protocols. To avoid unnecessary traffic on your network place them as close to the source as possible.

Cisco based exam questions - part x

Part 10 of random Cisco CCNA based questions to stimulate some thought or just refresh - enjoy


1. What command would you use to erase the startup config of a router?

A) erase nvram
B) erase flash
C) delete startup
D) erase startup
E) delete run

2. HDLC is ISO standard WAN protocol which means you don't need Cisco routers at both ends of a WAN connection, a router from any vendor that supports HDLC will work.

A) True
B) False

3. When you connect to a remote router "out-of-band", via what port would you connect with?

A) Console port
B) Auxiliary port
C) Ethernet port
D) Serial port

4. What is the IEEE standard describing VLANs called?

A) IEEE VLAN
B) 802.3
C) 802.1q
D) 802.11b
E) 802.3q

5. PPP can be used over what types of serial connections?

A) Synchronous
B) Asynchronous
C) Both
D) Neither

6. What do asymmetric switches require?

A) memory buffers
B) extra ports
C) statically assigned ports only
D) high speed CAM







1. Correct Answer: D
To erase the startup configuration use the following command:

Router#erase startup-config
or
Router#erase startup

2. Correct Answer: B
Even though HDLC is an ISO standard, each vendor has their own implementations of HDLC.

3. Correct Answer: B
When a router is out-of-band (out of the network) you would connect remotely via a modem attached to the auxiliary port.

4. Correct Answer: C
The IEEE 802.1Q standard specifies a standard method for inserting virtual LAN (VLAN) membership tags into Ethernet frames.

5, Correct Answer: C
Point-to-Point Protocol (PPP) can be used over ISDN (synchronous) and dial-up (asynchronous) connections.

6. Correct Answer: A
With ability for support of high bandwidth ports Asymmetric Switches require more Buffer memory for storing & forwarding of packets for fast processing. 

How did you go? couple of tricky ones there huh :-)

More coming, stay tuned!

Subnets and subnet masks

One of the most complex tasks TCP/IP has to perform is to determine whether or not a given IP address exists on the same subnet. The task isn’t really that complicated once you understand how TCP/IP uses its IP address and subnet mask, here's a very basic rundown.

An IP address looks something like this: 192.168.10.52. IP addresses always contain four numbers from 0–255, separated by periods. A portion of the IP address is called the network ID and acts as a unique identifier for a particular subnet.

The rest of the IP address is called the host ID and identifies a particular computer or network device on that subnet uniquely. How can you tell which part of the IP address is which? By using the subnet mask. A subnet mask looks a lot like an IP address, with four groups of numbers: 255.255.255.0. Remember, computers are binary machines that can understand only in zeros and ones. For the subnet mask to make sense, you have to translate it and the IP address into binary.
 

TIP: You can switch the Windows Calculator into Scientific view, which enables you to convert numbers from decimal to binary.


Convert all the four groups (octets) of numbers into binary code. For example, an IP address of 192.168.10.41 and a subnet mask of 255.255.255.0 look like this in binary:


Address or Mask 1st octet 2nd octet 3rd octet 4th octet

192.168.10.41 11000000 10101000 00001010 00101001

255.255.255.0 11111111 11111111 11111111 00000000



Everyplace you see a “1” in the subnet mask corresponds to the portion of the IP address that is the network ID. Everyplace you see a “0” in the subnet mask corresponds

to the portion of the IP address that is the host ID. Here, the network ID is 192.168.10, and the host ID is 41.TCP/IP treats everything with an IP address that starts with 192.168.10 as if it were on the same subnet. Any IP address that starts with something other than 192.168.10 is treated as if it existed on another subnet. 

 
Basic TCP/IP Services

A number of the protocols in the TCP/IP suite are considered core protocols, which means they are usually present on any network that uses TCP/IP. The core protocols provide basic services that no network can do without. These services include

_ Data transmission. Is handled by more than one protocol: the User Datagram Protocol (UDP) and the Transport Control Protocol (TCP). Computers use UDP when they need to send a small packet of data and don’t care if the remote computer actually receives the data. Computers use TCP when loads of data needs to be transmitted because TCP allows the remote computer to reply, confirming its receipt of the data.

_ Name resolution. Provided by the Domain Name System, or DNS, protocol. DNS enables people to use easy-to-remember names like www.microsoft.com and allows computers to translate those names to numeric IP addresses.

_ Windows Internet Name System (WINS). Prior versions of Windows also use WINS to convert computer names into IP addresses. Windows Server 2003 is compatible with WINS.


   “ We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths.”

― Walt Disney
 
References:
Sybex(2003): Mastering Windows Server 2003

Understanding Engineers

 The following is a collection of quotes gleaned from the pages of pprune.org replicated here for your enjoyment :-)

Understanding Engineers #1
Two engineering students were biking across a university campus when one said, "Where did you get such a great bike?" The second engineer replied, "Well, I was walking along yesterday, minding my own business, when a beautiful woman rode up on this bike, threw it to the ground, took off all her clothes and said, "Take what you want." The first engineer nodded approvingly and said, "Good choice: The clothes probably wouldn't have fit you anyway."

Understanding Engineers #2
To the optimist, the glass is half-full. To the pessimist, the glass is half-empty.
To the engineer, the glass is twice as big as it needs to be.

Understanding Engineers #3
A priest, a doctor, and an engineer were waiting one morning for a particularly slow group of golfers. The engineer fumed, "What's with those guys? We must have been waiting for fifteen minutes!"
The doctor chimed in, "I don't know, but I've never seen such inept golf!"
The priest said, "Here comes the greens-keeper. Let's have a word with him."
He said, "Hello George, What's wrong with that group ahead of us? They're rather slow, aren't they?"
The greens-keeper replied, "Oh, yes. That's a group of blind firemen. They lost their sight saving our clubhouse from a fire last year, so we always let them play for free anytime!."
The group fell silent for a moment.
The priest said, "That's so sad. I think I will say a special prayer for them tonight."
The doctor said, "Good idea. I'm going to contact my ophthalmologist colleague and see if there's anything she can do for them."
The engineer said, "Why can't they play at night?"

Understanding Engineers #4
What is the difference between mechanical engineers and civil engineers?
Mechanical engineers build weapons . Civil engineers build targets .

Understanding Engineers #5
The graduate with a science degree asks, "Why does it work?"
The graduate with an engineering degree asks, "How does it work?"
The graduate with an accounting degree asks, "How much will it cost?"
The graduate with an arts degree asks, "Do you want fries with that?"

Understanding Engineers #6
Three engineering students were gathered together discussing who must have designed the human body. One said, "It was a mechanical engineer . Just look at all the joints".
Another said, "No, it was an electrical engineer. The nervous system has many thousands of electrical connections".
The last one said, "No, actually it had to have been a civil engineer. Who else would run a toxic waste pipeline through a recreational area?"

Understanding Engineers #7
Normal people believe that if it ain’t broke, don't fix it.
Engineers believe that if it ain’t broke, it doesn't have enough features yet.

Understanding Engineers #8
An engineer was crossing a road one day, when a frog called out to him and said, "If you kiss me, I'll turn into a beautiful princess".
He bent over, picked up the frog, and put it in his pocket.
The frog spoke up again and said, "If you kiss me, I'll turn back into a beautiful princess and stay with you for one week".
The engineer took the frog out of his pocket, smiled at it and returned it to the pocket.
The frog then cried out, "If you kiss me and turn me back into a princess, I'll stay with you for one week and do anything you want".
Again, the engineer took the frog out, smiled at it and put it back into his pocket.
Finally, the frog asked, "What is the matter? I've told you I'm a beautiful princess and that I'll stay with you for one week and do anything you want. Why won't you kiss me?"
The engineer said, "Look , I'm an engineer. I don't have time for a girlfriend, but a talking frog - now that's cool".

Networking Questions - Cisco based

Another interesting set of Questions to help you on your way to certification - or as a refresh - enjoy.

1. How many access control lists can you apply to an interface?

A) Unlimited
B) One ACL per port per direction
C) 10
D) You do not apply ACL to interfaces

2.  IGRP advertises routes to interior, system and exterior routes

A) True
B) False

3. What class of routing protocol is EIGRP?

A) Link state
B) Distance vector
C) Hybrid

4. Where would you place standard access lists?

A) As close to the destination as possible
B) As close to the source as possible

5. With full-duplex Ethernet no collisions can occur.

A) True
B) False







1. Correct Answer: B
Cisco routers only allow you to place one access control list (ACL) per direction. One inbound ACL and one outbound ACL. However you can add multiple statements to these access lists.

2. Correct Answer: A
IGRP advertises three types of routes:

Interior routes are routes between subnets in the network attached to a router interface.
System routes are routes to networks within an autonomous system.
Exterior routes are routes to networks outside the autonomous system. 

3.  Correct Answer: C
EIGRP is a hybrid routing protocol which uses a combination of distance vector and link state methods to determine the best path.

4. Correct Answer: A
Standard access lists only filter based on source address so they have to be placed as close to the destination as possible.

5. Correct Answer: A

How did you go? More Questions coming, stay tuned...

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Cisco based exam questions part ix

Random networking questions for those curious, wanting to refresh or studying for Cisco certification.




1. In a local broadcast all bits set to 1 received by all hosts on local and remote broadcast domains?

A) True
B) False

2. What is the invalid timer set to by default when you have a router running the Interior Gateway Routing Protocol?

A) 3 times the update period
B) 270 seconds
C) 3 times the update period + 10 seconds
D) Answer A and B
E) 7 times the update period 

3. What are the 3 ways of assigning a switched port to VLANs?

A) Switch-centric, Port-centric, Dynamic VLANs
B) Port-centric, Static VLANs, Dynamic VLANs
C) Interface-based, Static VLANs, Dynamic VLANs

 4. What OSI layer does the following refer to?

"Establishes availability of intended communication partners, establishes agreement on procedures regarding error recovery and data integrity and synchronizes networked applications"

A) Transport layer
B) Session layer
C) Datalink layer
D) Application layer
E) Presentation layer

5. Which of the following protocols do not form part of the TCP/IP Internet Layer?

A.) IP
B.) ICMP
C.) FTP
D.) ARP
E.) RARP

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1. Correct Answer: B

Explanation
Routers don't forward broadcasts so local broadcasts will stay on the broadcast domain from which they originated.

2. Correct Answer: D

Explanation
IGRP sends its routing table to its neighbors every 90 seconds. IGRP uses an invalid timer to mark a route as invalid after 270 seconds (three times the update timer). IGRP uses a flush timer to remove a route from the routing table (default flush timer is 630 seconds, seven times the update period).

3. Correct Answer: B

Explanation
3 ways of assigning a switched port to VLANs:

1.Port-Centric - All nodes connected to ports in the same VLAN are assigned to the same VLAN ID.
2.Static VLANs - Statically assign ports to a VLAN.
3.Dynamic VLANs - Ports that can automatically determine their VLAN assignments based on MAC addresses.

4. Correct Answer: D

Explanation
The Application layer of the OSI model (layer 7) establishes availability of intended communication partners, establishes agreement on procedures regarding error recovery and data integrity and synchronizes networked applications.

5. Correct Answer C

Explanaition
FTP is an application layer protocol and not part of the TCP/IP suit.

Cisco exam questions part viii

Another set of mixed up networking questions to get the grey matter ticking - enjoy.





1. By default is CDP enabled or disabled on compatible devices?

A) Enabled
B) Disabled

2. What is the default setting on a router for the invalid timer if you are using IGRP?

A) 90 seconds
B) 30 seconds
C) 280 seconds
D) 270 seconds
E) 180 seconds

3. What are the default metrics of IGRP?

A) Delay, Bandwidth
B) Load, Reliability
C) Reliability, Bandwidth
D) Delay, Reliability

4. What WLAN standard operates in the 5GHz band with a data rate of up to 54Mbps?

A) 802.11a
B) 802.11b
C) 802.11g
D) 802.11h
E) 802.11n

5. Where is the best position to place an Extended ACL?

A) As close to the destination as possible
B) As close to the source as possible

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1. Correct Answer: A

Explanation
CDP is enabled on Cisco routers by default. To disable CDP use the no cdp run command.

2. Correct Answer: D

Explanation
IGRP sends its routing table to its neighbors every 90 seconds. IGRP uses an invalid timer to mark a route as invalid after 270 seconds (three times the update timer). IGRP uses a flush timer to remove a route from the routing table (default flush timer is 630 seconds, seven times the update period).

3. Correct Answer: A

Explanation
IGRP and EIGRP use multiple metric parameters to calculate their composite metric.  These are bandwidth, delay, load, and reliability. By default, IGRP chooses a route based on bandwidth and delay.

4. Correct Answer: A

Explanation
802.11a operates in the 5GHz band with a data rate of up to 54Mbps and is immune to interference from other devices operating in the 2.4GHz spectrum.

5, Correct Answer: B

Explanation
The general rule is to place standard ACLs as close to the destination as possible and to position extended ACLs as close as possible to the source of the traffic that will be denied. This is because extended ACLs can take in to account source and destination addresses as well as port numbers.

How TCP and UDP work

Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)is a transportation protocol that is one of the core protocols of the Internet protocol suite. Both TCP and UDP work at transport layer TCP/IP model and both have very different usage.

Lets imagine, that we need to transfer certain amount of data. You may transfer only certain amount at the time (you have limitation on the packet size, which is below TCP/UDP).

In case of TCP, first you should establish connection (you may read about "3-Way handshake"). During this you agree on the "TCP Window Size" (explained  below). Then you start actual data transfer...

You transfer a packet, and then you wait for a confirmation, that the packet received. If you didn't receive confirmation within certain amount of time, you transmit the same packet again (Retransmission occured). If you agreed on certain "TCP Window Size", you may transmit multiple packets without waiting for a confirmation, and then you receive one confirmation for all these packets (not many, usually a few, just "more than one"). If you sent 3 packets, but only two confirmed, you will send that missing packet, if no confirmation was received at all, then you send all 3 packets again. But the bottom line is - each and every packet should be confirmed.

TCP has tweaked for performance over the years. ACKs are often piggy-backed with replies to messages so there is no extra packet or waiting. It can also dynamically adjust to changing network performance with features like slow start and congestion avoidance. TCP optimizes the amount of data sent per packet to avoid IP fragmentation. With UDP, if you send a message greater than 1472 bytes (for 'normal' Ethernet) the IP layer will fragment it into multiple datagrams and it will buffered and re-assembled in the receiving stack.


In case of UDP, you just blindly split your data into packets, and transfer them without any care, if they were received or not. You may do it "at the wire speed". And if you need some kind of control over the data, this should be taken care on higher layers of OSI model (for example, you should implement transfer verification at the Application Layer).

So, in theory, TCP actual performance is at least twice slower (for example, your one-way-trip time is 100ms, you sent a packet, and wait for a response), plus depends on receiver (how long it takes to prepare and send a confirmation), while UDP may send packets "as a stream" without any delay.

That said, there are many case where UDP may be a better choice. there isn't much use for retransmissions with applications like VOIP. For a simple exchange where you don't need the overhead of establishing and tearing down a connection UDP is likely the way to go, DNS being a perfect example. Note that even DNS will switch to TCP when the server sees that the reply will be lengthy due to multiple addresses and/or MX records.

If you are creating a VoIP application, there is no need constantly to check if the other end is on-line, so you can use UDP to transfer the main payload (voice) and a second TCP connection to handle connection/disconnection at a lower speed (once a second is ok).

If you are transmitting a public radio station over IP, you need only to enable your players to join one multicast channel. In the latest case, UDP is far more effective and is causing less overhead, since all the network balancing is handled by the multicast enabled routers.

In areas of video streaming and VoIP the overhead of TCP would be intolerable, so they use UDP and they work pretty well- mainly because the network infrastructure and the protocols have "matured" to the extent where reliability is largely taken for granted.

Clear as mud?