1
Q
What is the “nuts and bolts” view of the Internet?
A
It is a “network of networks” consisting of billions of connected computing devices called hosts or end systems1111.
2
Q
How are computing devices connected on the Internet?
A
They are connected via communication links (fiber copper radio satellite) and packet switches such as routers and switches2.
3
Q
What is the “service” view of the Internet?
A
It is an infrastructure that provides services to applications and a programming interface for distributed applications3333.
4
Q
What is a protocol?
A
A protocol defines the format and order of messages sent and received among network entities and the actions taken on message transmission or receipt4.
5
Q
What is the network edge?
A
The network edge consists of hosts such as clients and servers which often reside in data centers5.
6
Q
What is the network core?
A
The network core is a mesh of interconnected routers that use packet-switching to forward data6666.
7
Q
What are the three main types of access networks?
A
They include residential access institutional access (school/company) and mobile access networks7.
8
Q
What is Digital Subscriber Line (DSL)?
A
DSL uses existing telephone lines to a central office DSLAM to transmit data and voice at different frequencies8888.
9
Q
What is Hybrid Fiber Coax (HFC)?
A
HFC is an asymmetric cable-based access network where homes share access to a cable headend999999999.
10
Q
What is a packet?
A
A packet is a smaller chunk of an application message created by a host for transmission10.
11
Q
How is transmission delay calculated?
A
It is calculated as the packet length in bits (L) divided by the link transmission rate in bits per second (R) or $L/R$11111111.
12
Q
What is store-and-forward transmission?
A
It is a mechanism where the entire packet must arrive at a router before it can be transmitted on the next link12.
13
Q
When do packet queuing and loss occur?
A
They occur if the arrival rate to a link exceeds the transmission rate of the link for a period of time causing buffers to fill up13.
14
Q
What is the difference between forwarding and routing?
A
Forwarding is a local action moving packets from input to output links while routing is a global action determining the paths taken by packets14141414.
15
Q
What is Wireshark?
A
Wireshark is a packet analyzer that uses packet capture (pcap) to provide a copy of all Ethernet frames sent or received15151515.
16
Q
What is circuit switching?
A
It is an alternative to packet switching where end-to-end resources are allocated to and reserved for a “call” between source and destination.
17
Q
1What are the characteristics of dedicated resources in circuit switching?
A
There is no sharing of resources which results in guaranteed circuit-like performance but means segments remain idle if not used.
18
Q
2What is Frequency Division Multiplexing (FDM)?
A
It is a method where optical or electromagnetic frequencies are divided into narrow bands and each call is allocated its own band.
19
Q
3What is Time Division Multiplexing (TDM)?
A
It is a method where time is divided into slots and each call is allocated periodic slots to transmit at the maximum rate of a wider frequency band.
20
Q
4What is a major advantage of packet switching over circuit switching?
A
Packet switching allows more users to use the network; for example a 1 Gbps link can support 35 users with a very low probability of congestion compared to only 10 users in circuit switching.
21
Q
5Why is packet switching great for “bursty” data?
A
It allows for resource sharing and is simpler because it requires no call setup.
22
Q
6What are the drawbacks of packet switching?
A
Excessive congestion is possible which can lead to packet delay and loss due to buffer overflow.
23
Q
7How is the Internet structured as a “network of networks”?
A
Hosts connect via access ISPs which are then interconnected through a complex global hierarchy driven by economics and policy.
24
Q
8What is a Tier-1 ISP?
A
These are large commercial ISPs with national and international coverage like AT&T or Sprint that sit at the center of the Internet structure.
25
9What is a Point-of-Presence (POP)?
It is a location within a Tier-1 provider network that contains links to peering networks and customer networks.
26
10What are Internet Exchange Points (IXPs)?
They are points where multiple ISPs interconnect to exchange traffic.
27
11What are the four sources of packet delay?
The sources are nodal processing delay ($d_{proc}$) queueing delay ($d_{queue}$) transmission delay ($d_{trans}$) and propagation delay ($d_{prop}$).
28
12How is propagation delay calculated?
It is the length of the physical link (d) divided by the propagation speed (s) or $d_{prop} = d/s$.
29
13What is traffic intensity?
It is defined as $La/R$ where L is packet length a is the average arrival rate and R is bandwidth; as it approaches 1 average queueing delay becomes large.
30
14What does the traceroute program do?
It provides delay measurements from a source to all routers along an end-to-end Internet path by sending three probes to each hop.
31
15What is a bottleneck link?
It is the link on an end-to-end path that constrains the overall end-to-end throughput.
32
16What is the Internet protocol stack?
It consists of five layers: application transport network link and physical.
33
17What is encapsulation in networking?
It is the process where each layer adds a header ($H$) to the message ($M$) as it moves down the stack from source to destination.
34
18How does the ISO/OSI reference model differ from the Internet stack?
The OSI model includes seven layers adding presentation and session layers which are not found in the standard Internet stack.
35
19What was the first host-host protocol on ARPAnet?
It was the Network Control Protocol (NCP) introduced in 1972.
36
20What are Cerf and Kahn's internetworking principles?
They include minimalism/autonomy a best-effort service model stateless routing and decentralized control.
37
21What is DoS (Denial of Service)?
It is an attack where an attacker overwhelms a resource like a server or bandwidth with bogus traffic to make it unavailable to legitimate users.
38
What is the primary goal of network application software?
To run on end systems and communicate with each other over the network rather than on network-core devices like routers1111.
39
What characterizes the server in a client-server architecture?
It is a permanent host that is always on with a fixed IP address and often resides in data centers for scaling2222.
40
What is the peer-to-peer (P2P) architecture?
An architecture where arbitrary end systems communicate directly without a central server offering self-scalability3333.
41
How do processes on different hosts communicate?
They communicate by exchanging messages over the network through a software interface called a socket4444.
42
What are the two components of a process identifier?
A 32-bit IP address to identify the host and a port number to identify the specific process on that host555.
43
Which transport protocol is used for 100% reliable data transfer?
TCP (Transmission Control Protocol) which provides a connection-oriented service and reliability6666.
44
What are the characteristics of UDP (User Datagram Protocol)?
It is an unreliable "no-frills" data transfer service that lacks connection setup and congestion control7777.
45
Which port is typically used for HTTP (Web) traffic?
Port 808.
46
What does it mean that HTTP is a stateless protocol?
The server maintains no information about past client requests9999.
47
What is the difference between non-persistent and persistent HTTP?
Non-persistent sends at most one object per TCP connection while persistent allows multiple objects over a single connection10101010.
48
What are the four common requirements of transport services?
Data integrity timing throughput and security.
49
What is the primary goal of network application software?
To run on end systems and communicate with each other over the network rather than on network-core devices like routers1111.
50
What characterizes the server in a client-server architecture?
It is a permanent host that is always on with a fixed IP address and often resides in data centers for scaling2222.
51
What is the peer-to-peer (P2P) architecture?
An architecture where arbitrary end systems communicate directly without a central server offering self-scalability3333.
52
How do processes on different hosts communicate?
They communicate by exchanging messages over the network through a software interface called a socket4444.
53
What are the two components of a process identifier?
A 32-bit IP address to identify the host and a port number to identify the specific process on that host555.
54
Which transport protocol is used for 100% reliable data transfer?
TCP (Transmission Control Protocol) which provides a connection-oriented service and reliability6666.
55
What are the characteristics of UDP (User Datagram Protocol)?
It is an unreliable "no-frills" data transfer service that lacks connection setup and congestion control7777.
56
Which port is typically used for HTTP (Web) traffic?
Port 808.
57
What does it mean that HTTP is a stateless protocol?
The server maintains no information about past client requests9999.
58
What is the difference between non-persistent and persistent HTTP?
Non-persistent sends at most one object per TCP connection while persistent allows multiple objects over a single connection10101010.
59
What are the four common requirements of transport services?
Data integrity timing throughput and security11111111.
60
What are the four components of the cookie system?
Cookies consist of a header line in the HTTP response message; a header line in the next HTTP request; a cookie file kept on the user's end system; and a back-end database at the Web site. 1
61
What is a common use for cookies in Web applications?
They are used for authorization; shopping carts; recommendations; and maintaining user session state. 2
62
How does a Web cache (proxy server) improve network performance?
It satisfies client requests without involving the origin server; which reduces response time for the user and decreases traffic on an institution's access link. 3
63
What is the purpose of the HTTP Conditional GET?
It allows a cache to verify if its stored copy of an object is still up-to-date with the origin server. 4
64
Which HTTP header is used to implement a Conditional GET?
The cache includes the "If-modified-since: " header in its request to the origin server. 5
65
What HTTP status code does a server return if a cached object has not been modified?
The server returns "304 Not Modified;" which contains no entity body to save bandwidth. 6
66
What is the difference between the HTTP GET and POST methods?
POST sends user input via an entity body; while GET typically sends input by including a query string in the URL. 7
67
What does the HTTP HEAD method do?
It requests only the header of a response (no entity body); often used by developers for debugging or checking if an object exists. 8
68
What is the primary function of the Domain Name System (DNS)?
DNS acts as a distributed database that translates human-readable hostnames into IP addresses. 9
69
Why is FTP considered an "out-of-band" protocol?
Because it uses two separate parallel TCP connections: one for control commands (port 21) and a different one for actual data transfer (port 20). 10
70
What is the difference between non-persistent and persistent HTTP connections?
Non-persistent HTTP sends at most one object per TCP connection; whereas persistent HTTP allows multiple objects to be sent over a single connection. 11
71
What is the primary function of the Domain Name System (DNS)?
DNS is a distributed database that acts as a directory service to translate human-readable hostnames into IP addresses. 111
72
What are the four main services provided by DNS?
DNS provides hostname-to-IP translation; host aliasing; mail server aliasing; and load distribution for replicated servers. 2
73
What are the levels of the DNS hierarchy?
The hierarchy includes Root Name Servers; Top-Level Domain (TLD) Servers; Authoritative DNS Servers; and Local DNS Name Servers. 3
74
What are the three major components of the Internet electronic mail system?
The system consists of user agents; mail servers; and the Simple Mail Transfer Protocol (SMTP). 4
75
Which protocol is used for the reliable transfer of email messages from server to server?
SMTP (Simple Mail Transfer Protocol) is used; typically over TCP port 25. 5
76
What are the three phases of an SMTP transfer?
The phases are Handshaking (greeting); the Transfer of messages; and the Closure of the connection. 6
77
Why are mail access protocols like IMAP needed?
Since SMTP is a "push" protocol; access protocols like IMAP or HTTP are required for a user to "pull" or retrieve mail from a server to a local device. 7
78
What is the main advantage of the IMAP protocol?
IMAP provides more features than earlier protocols; such as the ability to manipulate messages and manage folders directly on the mail server. 8
79
What does DASH stand for in the context of video streaming?
DASH stands for Dynamic; Adaptive Streaming over HTTP. 9
80
How does DASH handle varying bandwidth levels?
The server divides video into chunks encoded at different rates; the client then measures current bandwidth and requests the specific chunk rate that fits its connection. 10
81
What is the goal of a Content Distribution Network (CDN)?
The goal is to store copies of content at multiple geographically distributed sites to bring content "closer" to users and improve throughput. 11
82
What is the "stateless" nature of HTTP?
HTTP is considered stateless because the server maintains no information about the past requests of a specific client. 12121212
83
What is the difference between non-persistent and persistent HTTP?
Non-persistent HTTP sends a maximum of one object per TCP connection; while persistent HTTP allows multiple objects to be sent over a single connection. 13
84
What are the common port numbers for Web
Mail; and File transfer?; HTTP (Web) typically uses port 80 2; SMTP (Mail) uses port 25 3; and FTP (File Transfer) uses port 21 for control and port 20 for data4.
85
How does the port number function within a process identifier?
The port number specifically identifies a unique process running on a host; complementing the 32-bit IP address that identifies the host machine itself5.
86
What port is used by DNS for its directory services?
DNS name servers generally listen for queries on port 536.
87
Which protocols are considered "out-of-band" and why?
FTP is considered out-of-band because it uses a dedicated control connection on port 21 that is separate from the data connection on port 207.
88
What is the difference between a "push" and a "pull" email protocol?
SMTP is a "push" protocol used to send mail to a server 8; while IMAP and HTTP are "pull" protocols used by clients to retrieve mail from a server9.
89
How do Web caches (proxy servers) reduce delay?
Caches satisfy requests locally using stored copies of objects; which avoids the delay of traveling to the origin server and reduces traffic on the access link10.
90
What status code confirms a successful HTTP request?
The status code "200 OK" indicates that the request was successful and the requested object is included in the response11.
91
What is the status code for an unsuccessful search where the server cannot find the requested resource?
The status code "404 Not Found" is returned when the server cannot find the requested URL12.
92
What are the common port numbers for Web
Mail; and File transfer?; HTTP (Web) typically uses port 80 2; SMTP (Mail) uses port 25 3; and FTP (File Transfer) uses port 21 for control and port 20 for data4.
93
How does the port number function within a process identifier?
The port number specifically identifies a unique process running on a host; complementing the 32-bit IP address that identifies the host machine itself5.
94
What port is used by DNS for its directory services?
DNS name servers generally listen for queries on port 536.
95
Which protocols are considered "out-of-band" and why?
FTP is considered out-of-band because it uses a dedicated control connection on port 21 that is separate from the data connection on port 207.
96
What is the difference between a "push" and a "pull" email protocol?
SMTP is a "push" protocol used to send mail to a server 8; while IMAP and HTTP are "pull" protocols used by clients to retrieve mail from a server9.
97
How do Web caches (proxy servers) reduce delay?
Caches satisfy requests locally using stored copies of objects; which avoids the delay of traveling to the origin server and reduces traffic on the access link10.
98
What status code confirms a successful HTTP request?
The status code "200 OK" indicates that the request was successful and the requested object is included in the response11.
99
What is the status code for an unsuccessful search where the server cannot find the requested resource?
The status code "404 Not Found" is returned when the server cannot find the requested URL12.
100
What is the goal of reliable data transfer (rdt)?
The goal is to provide a reliable service over an inherently unreliable channel; ensuring data arrives without errors; in order; and without gaps1.
101
What mechanisms does rdt use to handle channel unreliability?
It uses checksums for error detection; acknowledgments (ACKs) for feedback; timeouts for retransmission; and sequence numbers to handle duplicates and ordering2.
102
What are the components of a TCP segment header?
A TCP segment header includes source and destination port numbers; a sequence number; an acknowledgment number; and a receive window3.
103
What is the purpose of the "receive window" in a TCP header?
The receive window is used for flow control to ensure the sender does not overflow the receiver's buffer4.
104
How is a TCP connection established?
It is established using a 3-way handshake: the client sends a SYN; the server responds with a SYN-ACK; and the client finishes with an ACK5.
105
What is network congestion?
Congestion occurs when too many sources send too much data too fast for the network to handle; leading to long delays and packet loss6.
106
How does TCP detect and respond to congestion?
TCP limits its sending rate based on perceived congestion using a method called Additive Increase; Multiplicative Decrease (AIMD)7.
107
What is the AIMD mechanism in TCP?
The sender increases its window size gradually until loss occurs (additive increase) and then cuts the window size in half (multiplicative decrease) to alleviate congestion8.
108
What is the difference between flow control and congestion control?
Flow control matches the sender's rate to the receiver's drain rate; while congestion control matches the sender's rate to the network's carrying capacity9.
109
Why is pipelining used in TCP?
Pipelining allows a sender to have multiple transmitted but unacknowledged packets "in the pipe" to increase the utilization of high-speed links10.
110
What is the congestion window (CongWin) in TCP?
It is a variable used by the TCP congestion control algorithm to limit the amount of data a sender can have in flight to match the network's carrying capacity. 1
111
How does the "Additive Increase" part of the AIMD mechanism work?
The sender increases the congestion window by 1 Maximum Segment Size (MSS) every Round Trip Time (RTT) until a loss event is detected. 2
112
How does the "Multiplicative Decrease" part of the AIMD mechanism work?
Upon detecting a loss event; the sender immediately cuts its congestion window size in half to reduce network pressure. 3
113
What occurs during the TCP "Slow Start" phase?
When a connection begins; the congestion window starts at 1 MSS and doubles every RTT; allowing the rate to grow exponentially until it reaches a threshold or loss is detected. 4
114
What are the three steps of the TCP 3-way handshake?
The client sends a SYN segment; the server responds with a SYN-ACK; and the client completes the connection with an ACK. 5
115
How is a TCP connection formally closed?
Both the client and server must send a segment with the FIN bit set and receive an acknowledgment from the other side. 6
116
What is the principle of "Fairness" in TCP?
It is the goal that if K TCP sessions share the same bottleneck link of bandwidth R; each session should receive approximately R/K of the throughput. 7
117
Why is UDP considered potentially "unfair" to TCP?
UDP does not use congestion control and can send data at high constant rates regardless of network state; which can starve competing TCP connections. 8
118
What are the three major components of the Internet email system?
The system consists of user agents; mail servers; and the Simple Mail Transfer Protocol (SMTP). 9
119
What is the difference between an iterative and a recursive DNS query?
In a recursive query; the queried server takes on the task of resolving the name; while in an iterative query; the server replies with the address of the next DNS server to contact. 10
120
How does DASH (Dynamic
Adaptive Streaming over HTTP) work?; The server stores video chunks encoded at different rates; and the client requests the specific rate that fits its current measured bandwidth. 11
121
What is the purpose of a Content Distribution Network (CDN)?
CDNs store copies of content at geographically distributed nodes to bring data closer to users and improve throughput. 12
122
What is the primary difference between the network layer's data plane and control plane?
The data plane consists of local per-router functions that determine how datagrams are forwarded from input to output ports 1; while the control plane is network-wide logic that determines the end-to-end paths taken by datagrams2.
123
What is the definition of forwarding in a router?
Forwarding is the data plane action of moving a packet from a router's input link to the appropriate output link3.
124
What is the definition of routing in the network layer?
Routing is the control plane action of determining the source-to-destination paths taken by packets using routing algorithms4.
125
What are the four main components inside a router?
A router consists of input ports; a switching fabric; output ports; and a routing processor5.
126
What functions do input ports perform?
They perform physical layer termination; link-layer processing; and look up the forwarding table to determine the appropriate output port6.
127
What is the role of the switching fabric?
The switching fabric connects the router's input ports to its output ports and acts as the "network within the router"7.
128
When is buffering required in a router?
Buffering is required when datagrams arrive from the switching fabric faster than the transmission rate of the outgoing link8.
129
What is the "best-effort" service model of IP?
It means the Internet Protocol does not guarantee that datagrams will be delivered; nor does it guarantee specific timing or order of delivery9.
130
What is a subnet in IP addressing?
A subnet is a group of device interfaces with the same network portion of an IP address that can physically reach each other without an intervening router10.
131
What is CIDR (Classless Inter-Domain Routing)?
CIDR is an addressing scheme where an address is formatted as a.b.c.d/x; with x representing the number of bits in the subnet portion of the address11.
132
How do hosts typically obtain an IP address?
Hosts usually get an IP address automatically using DHCP (Dynamic Host Configuration Protocol)12.
133
Which organization is responsible for allocating blocks of IP addresses to ISPs?
ICANN (Internet Corporation for Assigned Names and Numbers) allocates address blocks13.
134
What is "match-plus-action" in generalized forwarding?
It is a process where a router matches bits in various layer headers (Link; Network; or Transport) and performs a specific action such as forwarding; dropping; or modifying the packet14.
135
What is OpenFlow?
OpenFlow is a standard protocol used in Software Defined Networking (SDN) to define match-plus-action rules for routers15.
136
What is the primary function of Network Address Translation (NAT)?
It allows all devices in a local network to share a single public IPv4 address by using different source port numbers to identify internal hosts1.
137
What are the private IP address prefixes typically used in local networks?
The standard prefixes are 10/8; 172.16/12; and 192.168/162.
138
What is the size of an IPv6 address?
IPv6 addresses are 128 bits long to ensure a virtually inexhaustible supply of unique addresses3.
139
Why was the checksum removed from the IPv6 header?
It was removed to reduce processing overhead at each router hop as the packet moves through the network4.
140
What is tunneling in the context of IPv6?
It is a transition mechanism where an IPv6 datagram is encapsulated as the payload of an IPv4 packet to travel across portions of the Internet that have not yet been upgraded5.
141
How does a router handle an IPv6 packet that is too large for a link?
It drops the packet and sends an ICMPv6 "Packet Too Big" message back to the sender because routers no longer perform fragmentation in IPv66.
142
What are middleboxes?
They are intermediary devices other than standard IP routers that perform functions such as NAT; firewalls; or load balancing7.
143
What is the goal of DHCP (Dynamic Host Configuration Protocol)?
It allows a host to dynamically and automatically obtain an IP address from a network server when it joins a network8.
144
How does NAT handle outgoing datagrams?
It replaces the private source IP address and port number of an outgoing datagram with the NAT IP address and a new port number; then indexes this mapping in a NAT translation table9.
145
What is the main advantage of the fixed-length 40-byte header in IPv6?
It allows for faster processing of datagrams by routers compared to the variable-length header in IPv410.
146
What are the two primary approaches to structuring the network control plane?
The two approaches are per-router control; where each router runs a routing algorithm; and logically centralized control; where a separate controller computes and distributes forwarding tables to routers. 1
147
How do per-router control planes operate?
Individual routing algorithm components in every router interact with each other in the control plane to calculate local forwarding tables. 2
148
What is the goal of a routing algorithm?
The goal is to determine "least-cost" paths through a network from a source router to a destination router. 3
149
How are network topologies represented for routing algorithms?
They are typically represented as a graph G = (N; E); where N is a set of nodes (routers) and E is a set of edges (links) with associated costs. 4
150
What is the difference between static and dynamic routing algorithms?
Static algorithms change slowly over time; often through manual configuration; while dynamic algorithms change routes more quickly in response to periodic updates or topology/link cost changes. 5
151
What is a Link State (LS) routing algorithm?
It is a "global" algorithm where all routers have a complete map of the network topology and link costs before running the calculation. 6
152
What is Dijkstra's algorithm used for in networking?
It is an iterative link-state algorithm that computes the least-cost path from one source node to all other nodes in the network. 7
153
What is the complexity of Dijkstra's algorithm for n nodes?
It has a complexity of $O(n^2)$ because each of the n iterations must check all nodes not yet in the set of confirmed shortest paths; though efficient implementations can achieve $O(n \log n)$. 8
154
Why might oscillations occur with Link State algorithms?
Oscillations can occur if link costs are based on traffic volume; causing the algorithm to constantly switch paths as traffic shifts toward lower-cost (less-congested) links. 9
155
What is a Distance Vector (DV) routing algorithm?
It is a decentralized; iterative algorithm where nodes only know the costs of links to their direct neighbors and exchange best-path estimates (distance vectors) with them. 10
156
What is the Bellman-Ford equation in the context of DV routing?
it is the mathematical basis for the algorithm; stating that the shortest path to a destination is the minimum of the cost to a neighbor plus that neighbor's shortest path to the same destination. 11
157
What is an Autonomous System (AS)?
An AS is a group of routers under the same administrative control (like an ISP); which allows for scalable routing through hierarchical structures. 12
158
What is the difference between Intra-AS and Inter-AS routing?
Intra-AS routing handles paths within a single autonomous system; while Inter-AS routing handles paths between different autonomous systems. 13
159
What is OSPF (Open Shortest Path First)?
OSPF is a popular intra-AS routing protocol that uses a link-state algorithm (Dijkstra's) and is often organized hierarchically within an AS. 14
160
What is BGP (Border Gateway Protocol)?
BGP is the "glue" that holds the Internet together; serving as the inter-AS routing protocol that allows autonomous systems to advertise their existence and reachable prefixes to the rest of the Internet. 15
161
What is the role of ICMP (Internet Control Message Protocol)?
ICMP is used by hosts and routers to communicate network-layer information; such as reporting errors (host unreachable) or performing diagnostics (ping and traceroute). 16
162
What is SNMP (Simple Network Management Protocol)?
It is a protocol used for network management that allows a managing server to query and configure network devices (agents) and receive asynchronous trap messages about events. 17
163
What is the purpose of YANG in network management?
YANG is a data modeling language used to define the structure; syntax; and semantics of network management data; often used in conjunction with protocols like NETCONF. 18
164
What is the primary difference between the network layer's control plane and data plane?
The data plane consists of local per-router functions that determine how datagrams are forwarded from input to output ports 1; while the control plane is network-wide logic that determines the end-to-end paths taken by datagrams2.
165
What are the two primary approaches to structuring the network control plane?
The two approaches are per-router control; where each router runs a routing algorithm 3; and logically centralized control (SDN); where a separate controller computes and distributes forwarding tables to routers4444.
166
What is the goal of a routing algorithm?
The goal is to determine the "least-cost" paths through a network from a source router to a destination router5555.
167
How does the Distance Vector (DV) routing algorithm function?
It is a decentralized; iterative algorithm where nodes only know the costs of links to their direct neighbors and exchange best-path estimates (distance vectors) with them666.
168
What is the Bellman-Ford equation in the context of DV routing?
It is the mathematical basis for the algorithm; stating that the shortest path to a destination is the minimum of the cost to a neighbor plus that neighbor's own shortest path to the same destination7.
169
How does the Link State (LS) routing algorithm differ from Distance Vector?
In Link State; all routers have a complete map of the network topology and link costs before running calculations 88; whereas Distance Vector nodes only share path estimates with direct neighbors999.
170
What is Dijkstra's algorithm used for in networking?
It is an iterative link-state algorithm that computes the least-cost path from one source node to all other nodes in the network1010.
171
What are the two types of routing used for scalability in the Internet?
Routing is divided into Intra-AS routing (handling paths within a single autonomous system like OSPF) 111111and Inter-AS routing (handling paths between different autonomous systems like BGP)121212.
172
What is the role of the Border Gateway Protocol (BGP)?
BGP is the inter-AS routing protocol that acts as the "glue" holding the Internet together by allowing different autonomous systems to exchange reachability information131313.
173
Why is policy important in BGP routing?
Because BGP connects different commercial and private entities; routing decisions are often based on business agreements and administrative policies rather than just the shortest physical path14.
174
What is Software Defined Networking (SDN)?
SDN represents a shift to a logically centralized control plane where a central controller (like OpenDaylight or ONOS) maintains a global view of the network and computes forwarding tables for all routers15151515.
175
What is ICMP (Internet Control Message Protocol)?
ICMP is used by hosts and routers to communicate network-layer information; such as reporting errors like "host unreachable" or performing diagnostics via ping and traceroute16161616.
176
What is the purpose of SNMP (Simple Network Management Protocol)?
It is a protocol used by administrators to monitor and configure network devices by querying agents and receiving asynchronous trap messages about events17171717.
177
What are NETCONF and YANG?
NETCONF is a protocol and YANG is a data modeling language that together provide a modern framework for managing and modeling network configurations18181818.
178
What is the responsibility of the link layer?
It is responsible for transferring datagrams from one node to a physically adjacent node over a communication link1.
179
What are "nodes" and "links" in link-layer terminology?
Hosts and routers are referred to as nodes; while the communication channels that connect adjacent nodes are called links2.
180
What is a link-layer packet called?
A link-layer packet is called a frame; which encapsulates a network-layer datagram3.
181
What is framing in the context of the link layer?
Framing is the process of encapsulating a network-layer datagram into a link-layer frame before transmission4.
182
How does the link layer handle bit-level errors?
It uses error detection and correction services to identify and sometimes fix bit-level errors caused by signal attenuation or noise5.
183
What is a multiple access protocol?
It is a protocol that coordinates access to a single shared broadcast communication channel to prevent signal collisions6.
184
What is the difference between an IP address and a MAC address?
An IP address is a 32-bit logical identifier for a host's network interface; while a MAC address is a permanent 48-bit physical identifier assigned to a network interface card (NIC)7.
185
What is the purpose of the Address Resolution Protocol (ARP)?
ARP is used to translate a known IP address into its corresponding MAC address so a frame can be delivered on a local network8.
186
How does an Ethernet switch determine where to send a frame?
It uses a switch table to learn which MAC addresses are reachable through which of its ports; allowing for private and collision-free communication9.
187
What is a Virtual LAN (VLAN)?
A VLAN allows a single physical switch to be partitioned into multiple virtual networks to improve security and manage broadcast traffic10.
188
What are Top-of-Rack (ToR) switches in a data center?
They are switches that connect all the servers in a single rack to the rest of the data center network11.
189
What are the steps in a "day in the life of a web request"?
It involves getting an IP address via DHCP; using ARP and DNS to find addresses; and establishing a TCP connection to send an HTTP request12.
190
How is the efficiency of Pure ALOHA calculated?
The efficiency is determined by the probability that a node transmits successfully; which requires that no other node transmits during the same time interval13.
191
What are the primary elements of a wireless network?
The elements include wireless hosts (devices); base stations (Access Points or cell towers); wireless links; and the wired network infrastructure.
192
What are three major challenges unique to wireless links?
Wireless links face decreasing signal strength (attenuation); interference from other radio sources; and multipath propagation (signals reflecting off objects).
193
What is the difference between infrastructure mode and ad hoc mode?
In infrastructure mode; hosts connect to the wider Internet via a base station; in ad hoc mode; hosts have no fixed infrastructure and communicate directly with each other.
194
What multiple access protocol does 802.11 (WiFi) use?
WiFi uses CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) because it is difficult to detect collisions in the wireless medium while transmitting.
195
What is a Basic Service Set (BSS) in WiFi?
A BSS is the fundamental building block of a WiFi LAN; consisting of wireless hosts and typically a central Access Point (AP).
196
How has the core architecture changed in 4G and 5G cellular networks?
These generations have moved to an all-IP core network; integrating more closely with the standard Internet protocol stack and utilizing SDN principles.
197
What is the distinction between a mobile user's home network and a visited network?
The home network is the permanent "home" of the device; while the visited network is the one the user is currently attached to while roaming.
198
What is a "handover" in cellular networks?
A handover is the process of changing the association of a mobile station from one base station to another as the user moves; ideally without dropping the connection.
199
How does "indirect routing" work for mobile users?
Datagrams are first sent to the home network's home agent; which then encapsulates and tunnels them to the foreign agent in the user's current visited network.
200
How does mobility impact TCP performance?
TCP interprets packet loss due to wireless bit-errors or handovers as network congestion; causing it to unnecessarily decrease its congestion window and reduce throughput.
201
Why is bandwidth considered a "scarce resource" in wireless networks?
Wireless spectrum is limited and shared among many users; and signal quality can vary significantly; making high-speed transmission more difficult than in wired links.
202
What are the 4G roles for the HSS and MME?
The HSS (Home Subscriber Server) manages user data in the home network; while the MME (Mobility Management Entity) handles signaling and mobility management tasks like handovers.
203
What are the four key dimensions of network security?
Network security involves confidentiality (only sender and receiver understand content); authentication (confirming identity); message integrity (ensuring no alteration); and access/availability.
204
What is the difference between symmetric and public key cryptography?
Symmetric key cryptography uses the same secret key for both encryption and decryption; while public key cryptography uses a pair of keys: a public key for encryption and a private key for decryption.
205
Why is the RSA algorithm considered secure?
RSA's security is based on the mathematical difficulty of factoring very large numbers.
206
What is a "session key" and why is it used?
A session key is a symmetric key used for a single communication session; it is used because symmetric encryption is significantly faster (at least 100 times) than public-key encryption like RSA.
207
What is a "nonce" in authentication protocols?
A nonce is a "number used once-in-a-lifetime" sent by a server to a user to prove the user is "live" and to prevent playback attacks.
208
What occurs in a "playback attack"?
An attacker records a legitimate user's transmitted credentials (like a password) and later "plays them back" to the server to gain unauthorized access.
209
What is a Man-in-the-Middle attack?
An attack where an intruder (Trudy) intercepts communication by posing as the sender to the receiver and as the receiver to the sender; effectively controlling the conversation.
210
How does a digital signature ensure message integrity?
The sender creates a hash of the message and encrypts it with their private key; the receiver uses the sender's public key to decrypt the hash and verify it matches the message's actual hash.
211
What are the common cryptographic hash functions mentioned?
Common examples include MD5 and SHA-1; which produce a fixed-size "fingerprint" of a message.
212
What is the goal of an authentication protocol?
The goal is for one party (e.g.; Bob) to have the other party (e.g.; Alice) prove their identity over a network.
213
What is IP spoofing?
It is a failure scenario where a user creates a packet with a false source IP address to impersonate another host.
214
Ethernet
"D; Wired. Up to 100's Gbps per link. +"
215
802.11 WiFi
"G; Wireless. 10’s to 100’s of Mbps per device. +"
216
Cable access network
"A; Wired. Up to 10’s to 100’s of Mbps downstream per user. +"
217
Digital Subscriber Line
"E; Wired. Up to 10’s of Mbps downstream per user. +"
218
4G cellular LTE
"B; Wireless. Up to 10’s Mbps per device. +"
PJATK
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