HW #16 Flashcards
Recall that the name of a transport-layer packet is segment and that the name of a link-layer packet is frame. What is the name of a network-layer packet?
Answer: A network layer packet is a datagram
What are the two most important network-layer functions in a datagram network?
Two important network-layer functions in a datagram are forwarding and routing.
What is the difference between routing and forwarding?
Forwarding is when the router needs to move the packet to the appropriate output link after it arrives at a router’s input link. Routing is for the network layer to determine the route or path taken by packets as the flow from a sender to a receiver.
We saw that a router typically consists of input ports, output ports, a switching fabric, and a routing processor. Which of these are implemented in hardware and which are implemented in software?
Input ports, output ports and switching fabric are implemented in hardware, routing processors are implemented in software. Those implemented in hardware are done so because
their datagram-processing functionality is too fast for software implementation. Software is used for routing processors(in a traditional router) to execute routing protocols, to maintain routing tables and attached link state information, and to compute the forwarding table of a router.
Three types of switching fabrics are discussed in class. List and briefly describe each type. Which, if any, can send multiple packets across the fabric in parallel?
Switching via memory: Fabric switching with the use of CPU Switching via a bus: Fabric switching via shared buses on input and output port Switching via interconnection network: fragmenting datagrams into fixed length cells, switch cells through fabric
Describe how packet loss can occur at input ports. Describe how packet loss at input ports can be eliminated (without using infinite buffers).
Answer: Packet loss occurs if the queue size at the input port grows large because of slow switching fabric speed and thus exhausting router’s buffer space. It can be eliminated if the switching fabric speed is at least n times as fast as the input line speed, where n is the number of input ports.
Describe how packet loss can occur at output ports. Can this loss be prevented by increasing the switch fabric speed?
Answer:If the queue size at the input port grows large because of slow switching fabric speed and thus exhausting the router’s buffer space. It can be eliminated if the switching fabric speed is not smaller than the speed of the number of input ports time.
What is HOL blocking? Does it occur in input ports or output ports?
HOL blocking - a queued packet in an input queue must wait for transfer through the fabric because it is blocked by another packet at the head of the line. It occurs at the input port.
Do routers have IP addresses? If so, how many?
Yes, one per router interface.
What is the 32-bit binary equivalent of the IP address 223.1.3.27?
According to Quizlet, the 32-bit binary equivalent of the IP address 223.1.3.27 is 11011111.00000001 00000011 00011011.
Visit a host that uses DHCP to obtain its IP address, network mask, default router, and IP address of its local DNS server. List these values
Students will get different correct answers for this question.
Suppose there are three routers between a source host and a destination host. Ignoring fragmentation, an IP datagram sent from the source host to the destination host will travel over how many interfaces? How many forwarding tables will be indexed to move the datagram from the source to the destination?
(Number of routers) * (2 per router) + 2 = 6 + 2 = 8
3 routers means three forwarding tables will be indexed
