Computer Networks Exam 2 Q&A
Datagram - =the name of a network-layer packet
What is the difference between a router and a link-layer switch? - =Router uses IP (layer 3) address of
the packet to forward it.
Switch uses MAC (layer 2) address of packet to forward it.
Two most important network-layer functions in a datagram network? - =Forwarding and routing
Forwarding - =process of moving the packet that arrives at the input link of the router to a correct
output link. Done by using forwarding tables.
Routing - =route in which the packet flows from sender to receiver, calculated by routing algorithm.
Determines end-to-end paths that packet takes
Important network-layer functions in a virtual-circuit network - =Forwarding, routing, connection setup
Connection setup - =three-way handshake is required before data flows from source to destination.
Routers along the chosen path handshake with each other to set up connection
What are some services that network layer provides to a single packet? - =Guaranteed delivery,
guaranteed delivery with bounded delay
Applications that would benefit from ATM's CBR service model - =Telephone companies, audio/video
traffic, live multimedia apps
What are the three types of switching fabrics? Which can send multiple packets across the fabric in
parallel? - =Via memory, via bus, via interconnected network.
Switching via interconnected network, allows packets from different input ports to the same output
port.
, Do routers have IP addresses? How many? - =Every router has an IP address for each interface.
What is the 32-bit binary equivalent of the IP address 223.1.3.27? - =Each decimal number represents a
byte (8 bits).
11011111 00000001 00000011 00011011
What is DHCP? - =Dynamic Host Configuration Protocol. Allows the host in obtaining the IP address
automatically. Client-server protocol.
When one host sends a TCP segment encapsulated in an IP datagram, how does the receiving host
network layer know it should pass the segment to TCP rather than UDP or something else? - =The IP
datagram consts of an 8-bit field called Protocol, which gives info about which transport layer protocol
the segment is to be passed to.
What are the differences/similarities between the IPv4 and IPv6 headers? - =IPv6 consists of minimum
number of fields, rather than a lot of optional fields.
IPv6 has a FIXED header size (40 bytes), IPv4 header is TYPICALLY 20-bytes.
IPv6 src/dest address: 128 bits.
IPv4 src/dest address: 32 bits.
Compare/contrast link-state and distance-vector routing algorithms - =Both find best path from src
router to dest router. Both compute least-cost path.
LS computes least-cost path from src to dest with complete knowledge on network, DV computes least-
cost path in an iterative/distributed manner
LS shortest path found with Dijkstra, DV found with Bellman Ford
Open Shortest Path First (OSPF) is LS, Routing Information Protocol (RIP) is DV
LS is global, DV is decentralized (exchange info with neighbors)
Broadcast routing - =network layer provides a service of delivering a packet sent from a source node to
all other nodes in the network
Datagram - =the name of a network-layer packet
What is the difference between a router and a link-layer switch? - =Router uses IP (layer 3) address of
the packet to forward it.
Switch uses MAC (layer 2) address of packet to forward it.
Two most important network-layer functions in a datagram network? - =Forwarding and routing
Forwarding - =process of moving the packet that arrives at the input link of the router to a correct
output link. Done by using forwarding tables.
Routing - =route in which the packet flows from sender to receiver, calculated by routing algorithm.
Determines end-to-end paths that packet takes
Important network-layer functions in a virtual-circuit network - =Forwarding, routing, connection setup
Connection setup - =three-way handshake is required before data flows from source to destination.
Routers along the chosen path handshake with each other to set up connection
What are some services that network layer provides to a single packet? - =Guaranteed delivery,
guaranteed delivery with bounded delay
Applications that would benefit from ATM's CBR service model - =Telephone companies, audio/video
traffic, live multimedia apps
What are the three types of switching fabrics? Which can send multiple packets across the fabric in
parallel? - =Via memory, via bus, via interconnected network.
Switching via interconnected network, allows packets from different input ports to the same output
port.
, Do routers have IP addresses? How many? - =Every router has an IP address for each interface.
What is the 32-bit binary equivalent of the IP address 223.1.3.27? - =Each decimal number represents a
byte (8 bits).
11011111 00000001 00000011 00011011
What is DHCP? - =Dynamic Host Configuration Protocol. Allows the host in obtaining the IP address
automatically. Client-server protocol.
When one host sends a TCP segment encapsulated in an IP datagram, how does the receiving host
network layer know it should pass the segment to TCP rather than UDP or something else? - =The IP
datagram consts of an 8-bit field called Protocol, which gives info about which transport layer protocol
the segment is to be passed to.
What are the differences/similarities between the IPv4 and IPv6 headers? - =IPv6 consists of minimum
number of fields, rather than a lot of optional fields.
IPv6 has a FIXED header size (40 bytes), IPv4 header is TYPICALLY 20-bytes.
IPv6 src/dest address: 128 bits.
IPv4 src/dest address: 32 bits.
Compare/contrast link-state and distance-vector routing algorithms - =Both find best path from src
router to dest router. Both compute least-cost path.
LS computes least-cost path from src to dest with complete knowledge on network, DV computes least-
cost path in an iterative/distributed manner
LS shortest path found with Dijkstra, DV found with Bellman Ford
Open Shortest Path First (OSPF) is LS, Routing Information Protocol (RIP) is DV
LS is global, DV is decentralized (exchange info with neighbors)
Broadcast routing - =network layer provides a service of delivering a packet sent from a source node to
all other nodes in the network
