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
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.
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
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.
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?
