Chapter 4 - Network Layer

What is the function of the routing processor in traditional routers?

- Executing routing protocols - Maintaining routing tables and attached link state information - Computing the forwarding table for the router

What are the key components of a router?

- Input ports - Switching fabric - Output ports - Routing processor

What are the three types of switching fabrics?

- Switching via memory - Switching via a bus - Switching via an interconnection network

What are the Advantages of SDN?

1- Network is programmable, making it easy to modify via the controller 2- Switch hardware becomes cheaper as each switch only needs a data plane 3- Hardware is abstracted, allowing applications to be written on top of the controller that are independent of switch vendor 4- Provides better security through the ability to monitor traffic and deploy security policies

What does the DHCP process involve?

1- The host broadcasts a "DHCP discover" message (optional) 2- The DHCP server responds with a "DHCP offer" message (optional) 3- The host requests an IP address with a "DHCP request" message 4- The DHCP server sends the requested address with a "DHCP ack" (acknowledgment) message.

What are some solutions to the NAT traversal problem?

1. Statically configure NAT to forward incoming connection requests at a given port to a server 2. Use the Universal Plug and Play (UPnP) Internet Gateway Device (IGD) Protocol to allow a NATed host to learn its public IP address and add or remove port mappings with lease times 3. Use relaying, where a NATed client establishes a connection to a relay and an external client connects to the relay, which then bridges packets between the two

What is a SDN?

A SDN (Software-Defined Networking) is a new approach to building and managing networks in which the control plane (i.e., the logic that directs traffic to its destination) is separated from the data plane (i.e., the physical devices that transmit the traffic). In a SDN, a central controller is used to program the data plane devices (e.g., switches and routers) to forward traffic in a desired way, rather than having each device make forwarding decisions based on its own local routing table.

How do crossbar switches work, and what advantages do they offer over other types of switching fabrics?

A crossbar switch is an interconnection network consisting of 2N buses that connect N input ports to N output ports. Each vertical bus intersects each horizontal bus at a crosspoint, which can be opened or closed by the switch fabric controller. When a packet arrives from a specific input port and needs to be forwarded to a specific output port, the switch controller closes the crosspoint at the intersection [Switching via an interconnection network]

How many interfaces does a host typically have?

A host typically has a single interface.

How does a router forward a packet, and what role does the forwarding table play in this process?

A router forwards a packet by examining the value of one or more fields in the arriving packet's header, and then using these header values to index into its forwarding table. The value stored in the forwarding table entry for those values indicates the outgoing link interface at that router to which the packet is to be forwarded. The forwarding table is a key element in every network router.

How many interfaces does a router typically have?

A router has multiple interfaces, one for each of its links. Because every host and router is capable of sending and receiving IP datagrams, each host and router interface must have its own IP address. Thus, an IP address is technically associated with an interface, rather than with the host or router containing that interface.

What is the "security" service that the network layer could provide?

A service that provides confidentiality to all transport-layer segments by encrypting all datagrams at the source and decrypting them at the destination, thereby providing confidentiality to all transport-layer segments.

What is a subnet in IP networking?

A subnet is a network that interconnects multiple host interfaces and one router interface. It is also called an IP network or simply a network in the Internet literature.

What is the Internet's network-layer packet referred to as? A) Datagram B) Datapacket C) Netpacket D) Networkgram

A) Datagram

If a host is attached to the 223.1.1.0/24 subnet, what must its address be in the form xxx.xxx.xxx.xxx? A. 223.1.1.xxx B. 223.1.2.xxx C. 223.1.3.xxx D. 223.1.4.xxx

A. 223.1.1.xxx

How does an ISP obtain a block of IP addresses?

An ISP obtains a block of IP addresses through the Internet Corporation for Assigned Names and Numbers (ICANN), a nonprofit organization that is responsible for the allocation of IP addresses and the management of the Domain Name System (DNS). ICANN also assigns domain names and resolves disputes related to these functions.

What is an alternative approach to implementing routing functionality?

An alternative approach is to have a physically separate, remote controller compute and distribute the forwarding tables to be used by each and every router.

What is an interface in IP networking?

An interface is the boundary between a host or router and the physical link over which it is connected to the network.

How is the payload of an IP datagram passed to the transport layer at the destination?

At the destination, the payload of the datagram is passed to the transport layer only after the IP layer has fully reconstructed the original IP datagram. If one or more of the fragments does not arrive at the destination, the incomplete datagram is discarded and not passed to the transport layer.

Which of the following is NOT a layer in a typical SDN architecture? A) Application layer B) Data plane layer C) Control layer D) Infrastructure layer

B) Data plane layer

What is the format of an IP address in CIDR notation? A. a.b.c/x, where x is the number of bits in the subnet portion of the address B. a.b.c.d/x, where x is the number of bits in the subnet portion of the address C. a.b.c, with no indication of the length of the subnet portion of the address D. a.b.c.d, with no indication of the length of the subnet portion of the address

B. a.b.c.d/x, where x is the number of bits in the subnet portion of the address

What does a router use to forward a packet? A) The packet's header values B) The router's forwarding table C) Both A and B D) None of the above

C) Both A and B

Where do packet queues form in a router? A) At the input ports B) At the output ports C) Both A and B D) Neither A nor B

C) Both A and B

What is Classless InterDomain Routing (CIDR)?

CIDR is a method of allocating IP addresses and routing Internet Protocol packets that allows for a more flexible allocation of IP addresses than the original system of IP address classes.

What is the "guaranteed minimal bandwidth" service that the network layer could provide? A) A service that guarantees that a packet sent by a source host will eventually arrive at the destination host. B) A service that guarantees delivery of a packet within a specified host-to-host delay bound. C) A service that guarantees that packets arrive at the destination in the order that they were sent. D) A service that emulates the behavior of a transmission link of a specified bit rate between sending and receiving hosts. As long as the sending host transmits bits (as part of packets) at a rate below the specified bit rate, then all packets are eventually delivered to the destination host. E) A service that provides confidentiality to all transport-layer segments by encrypting all datagrams at the source and decrypting them at the destination.

D) A service that emulates the behavior of a transmission link of a specified bit rate between sending and receiving hosts. As long as the sending host transmits bits (as part of packets) at a rate below the specified bit rate, then all packets are eventually delivered to the destination host.

Which of the following is NOT a characteristic of software defined networking (SDN)? A) Separates the control plane from the data plane B) Allows for centralized control of the network C) Involves the use of flow tables to forward packets D) Requires access to individual switches to configure the network

D) Requires access to individual switches to configure the network

Why must each interface on every host and router in the global Internet have a globally unique IP address? A. To ensure that every device on the network can be uniquely identified and properly addressed B. To allow for easy identification of devices on the network C. To make it easier for network administrators to configure devices D. All of the above

D. All of the above

What is the Dynamic Host Configuration Protocol (DHCP)?

DHCP is a network protocol that allows a host to obtain (be allocated) an IP address automatically, without the need for manual configuration. This makes it easier for network administrators to manage large networks, as they do not need to manually configure the IP addresses of every host.

How do destination-based forwarding and generalized forwarding differ?

Destination-based forwarding involves forwarding packets based only on the destination IP address, while generalized forwarding involves forwarding packets based on any set of header field values. Destination-based forwarding is the traditional approach used by routers, while generalized forwarding is used in software-defined networking (SDN).

What is the "guaranteed delivery" service that the network layer could provide? A) A service that guarantees delivery of a packet within a specified host-to-host delay bound. B) A service that guarantees that packets arrive at the destination in the order that they were sent. C) A service that emulates the behavior of a transmission link of a specified bit rate between sending and receiving hosts. D) A service that provides confidentiality to all transport-layer segments by encrypting all datagrams at the source and decrypting them at the destination. E) A service that guarantees that a packet sent by a source host will eventually arrive at the destination host.

E) A service that guarantees that a packet sent by a source host will eventually arrive at the destination host.

What is First-in-First-Out (FIFO) in packet scheduling?

FIFO selects packets for link transmission in the same order in which they arrived at the output link queue. If there is not sufficient buffering space to hold the arriving packet, the queue's packet-discarding policy then determines whether the packet will be dropped (lost) or whether other packets will be removed from the queue to make space for the arriving packet.

True or False: A subnet consists only of host interfaces and no router interfaces.

False. A subnet consists of multiple host interfaces and one router interface.

What are the 3 packet scheduling algorithms used?

First-in-First-Out (FIFO) Priority Queuing Round Robin and Weighted Fair Queuing (WFQ)

What is head-of-the-line (HOL) blocking and how does it occur?

Head-of-the-line (HOL) blocking occurs when a queued datagram at the front of a queue prevents other datagrams in the queue from moving forward. This can happen if two packets at the front of two input queues are destined for the same output queue, and the switching fabric can only transfer one packet to a given output port at a time.

What is the Internet Control Message Protocol (ICMP)?

ICMP is a network-level protocol used by hosts and routers to communicate network-level information, such as error reporting (e.g., unreachable host, network, port, or protocol) and echo request/reply (used by the ping command). ICMP operates "above" IP, meaning that ICMP messages are carried in IP datagrams. An ICMP message consists of a type, a code, and the first 8 bytes of the IP datagram that caused the error.

How are IP addresses typically written?

IP addresses are typically written in so-called dotted-decimal notation, in which each byte of the address is written in its decimal form and is separated by a period (dot) from other bytes in the address.

How is an IP address assigned to a subnet?

IP addressing assigns an address to a subnet using the notation xxx.xxx.xxx.xxx/yy, where the /yy notation, sometimes known as a subnet mask, indicates that the leftmost yy bits of the 32-bit quantity define the subnet address.

What is IPv6 and what was the motivation for its development?

IPv6 is a new version of the Internet Protocol (IP) designed to address the increasing demand for IP addresses. One of the main motivations for the development of IPv6 was the realization that the 32-bit address space of the original IP protocol (IPv4) was running out, as more and more devices were being connected to the Internet and being assigned unique IP addresses. IPv6 uses a larger 128-bit address space to provide a virtually unlimited number of unique addresses.

What can happen if the packet queues in a router grow too large?

If the packet queues in a router grow too large, the router's memory can eventually be exhausted and packet loss will occur when there is no memory available to store arriving packets. These queues within the router are where packets are dropped and lost when they are "lost within the network" or "dropped at a router."

What happens if the switch fabric in a router is not fast enough relative to the input line speeds?

If the switch fabric in a router is not fast enough relative to the input line speeds, packet queuing can occur at the input ports. Packets must join input port queues to wait their turn to be transferred through the switching fabric to the output port.

How is the subnet portion of an IP address represented in CIDR?

In CIDR, the subnet portion of the address can be of arbitrary length.

What is the function of the routing processor in SDN routers?

In SDN routers, the routing processor communicates with the remote controller to: - Receive forwarding table entries computed by the remote controller - Install these entries in the router's input ports - Perform other activities as needed - Perform network management functions

How is control-plane routing functionality separated from the physical router in a SDN?

In a SDN, control-plane routing functionality is separated from the physical router by having the routing device perform forwarding only, while a remote controller computes and distributes forwarding tables. The remote controller might be implemented in a remote data center with high reliability and redundancy, and might be managed by the ISP or some third party.

How do the interfaces in a typical SDN architecture communicate?

In a typical SDN architecture, the application layer communicates with the control layer via northbound APIs, while the control layer communicates with the infrastructure layer via southbound APIs. These interfaces allow the layers to exchange information and instructions in order to shape traffic and manage the network.

What additional information can be returned by DHCP besides the allocated IP address on a subnet?

In addition to the allocated IP address, DHCP can return the following information to a client: 1- The address of the first-hop router for the client 2- The name and IP address of the DNS server 3- The network mask, which indicates the network versus host portion of the address.

How does an SDN switch forward packets?

In an SDN network, a switch's forwarding behavior is determined by entries in its flow table. Each entry in the flow table consists of match fields (such as the input port number and packet header) and instructions for how to handle packets that match those fields. When a packet enters a switch, it is matched against the match fields of the flow table entries. If a match is found, the instructions of the corresponding flow entry are executed (e.g., forwarding the packet via one or multiple ports, dropping the packet, or adding headers to the packet). If no match is found, the switch sends a query to the SDN controller, which sends a new flow entry to the switch. The switch then forwards or drops the packet based on this flow entry.

How do first generation routers implement switching?

In first generation routers, switching is implemented by traditional computers with switching under the direct control of the CPU. When a packet arrives, it is copied to the system's memory. The speed of this type of switching is limited by the memory bandwidth, as each datagram requires two bus crossings. [Switching via memory]

How do routers that use a shared bus for switching work, and what is bus contention?

In routers that use a shared bus for switching, an input port transfers a packet directly to the output port over the shared bus, without intervention by the routing processor. This is done by having the input port pre-pend a switch-internal label (header) to the packet indicating the local output port to which the packet is being transferred and transmitting the packet onto the bus. Only the output port that matches the label will keep the packet, and the label is then removed at the output port. If multiple packets arrive at the router at the same time, each at a different input port, all but one must wait since only one packet can cross the bus at a time. This is known as bus contention, and it means that the switching speed is limited by the bus bandwidth. [Switching via bus]

What happens if a packet is temporarily blocked from entering the switching fabric in a router?

In some router designs, a packet may be temporarily blocked from entering the switching fabric if packets from other input ports are currently using the fabric. If this happens, the packet will be queued at the input port and scheduled to cross the fabric at a later point in time.

What is the function of input ports in a router?

Input ports in a router perform several key functions, including: - Terminating incoming physical links - Performing link-layer functions needed to interoperate with the link layer at the other side of the incoming link - Performing a lookup function using the forwarding table to determine the router output port to which an arriving packet will be forwarded via the switching fabric

How much buffering is recommended for a network link with N flows?

It is recommended that the amount of buffering be equal to the RTT (Round Trip Time) times the link capacity C, divided by the square root of N. RTT*C/sqrt(N)

How is the process of longest prefix matching typically performed in routers?

Longest prefix matching, which involves finding the forwarding table entry for a given destination address by using the longest address prefix that matches the destination address, is often performed using ternary content addressable memories (TCAMs).

What is Network Address Translation (NAT)?

NAT is a technique that allows multiple devices on a local network to share a single registered (public) IP address when connecting to the Internet. It is used to conserve IP addresses and is commonly implemented in home and small office networks. NAT translates the local (private) IP addresses of devices on the local network into the registered IP address, and uses port numbers to distinguish the traffic from different devices.

What are the motivations for using Network Address Translation (NAT)?

NAT is used to conserve IP addresses and is commonly implemented in home and small office networks. Some of the motivations for using NAT are: - To allow a local network to use just one IP address as far as the outside world is concerned - To minimize the range of addresses needed from an ISP, by using just one IP address for all devices on the local network - To be able to change the addresses of devices on the local network without having to notify the outside world - To be able to change ISPs without changing the addresses of devices on the local network - To make devices inside the local network not explicitly addressable or visible by the outside world, which provides an added security benefit.

What is IP fragmentation and reassembly?

Network links have a maximum transfer size, known as the MTU (maximum transmission unit), which is the largest possible link-level frame that can be transmitted over that link. Different link types may have different MTUs. If an IP datagram is too large to fit within the MTU of the link over which it is being transmitted, it must be divided into smaller pieces, known as fragments.

How are IP addresses typically assigned to host and router interfaces in an organization?

Once an organization has obtained a block of IP addresses, it can assign individual addresses to the host and router interfaces in its network. The IP addresses of routers are typically configured manually by a system administrator, while the IP addresses of hosts can be configured manually or automatically.

How does a packet enter the switching fabric in a router?

Once the output port for a packet has been determined via the lookup performed at the input port, the packet can be sent into the switching fabric.

What is the function of output ports in a router?

Output ports in a router store packets received from the switching fabric and transmit these packets on the outgoing link by performing the necessary link-layer and physical-layer functions. When a link is bidirectional, an output port is typically paired with the input port for that link on the same line card.

Under what circumstances can queueing occur at a switch's output ports?

Queueing can occur at a switch's output ports if packets arriving at each of the N input ports are destined to the same output port, and the output port is not able to transmit the packets fast enough. The packets will have to queue (wait) for transmission over the outgoing link. If the number of queued packets grows large enough, it can exhaust available memory at the output port.

How does routing work at the network level?

Routing algorithms are used to calculate the paths used. Every router has a forwarding table, and when a router receives a packet, it extracts a value from a specific field in the header and searches for that value in the forwarding table. The procedure used to set up and update the table depends on the protocol used. However a router receives and sends routing protocol messages to configure its forwarding table.

What is routing?

Routing is the process of determining the path that packets should take as they flow from a sender to a receiver. Routing algorithms are used to calculate these paths. Every router has a forwarding table, and when a router receives a packet, it extracts a value from a specific field in the header and searches for that value in the forwarding table.

What is software defined networking (SDN)?

Software defined networking (SDN) is an approach that separates the control plane (which determines how packets are forwarded through the network) from the data plane (which actually forwards the packets). In an SDN network, the control plane is centralized in a unit called the SDN controller, while the data plane remains in the network switches. This allows a network administrator to shape traffic and configure the network from a centralized console without needing to access the individual switches.

What are some differences between the IPv4 and IPv6 datagram formats?

Some differences between the IPv4 and IPv6 datagram formats include: 1- Fragmentation/Reassembly: this field is not present in the IPv6 datagram format 2- Header checksum: this field is not present in the IPv6 datagram format 3- Options: this field is not present in the IPv6 datagram format 4- ICMPv6: a new version of ICMP with additional message types (e.g., "Packet Too Big") and multicast group management functions has been developed for IPv6.

What are some possible services that the network layer could provide?

Some possible services that the network layer could provide include: - Guaranteed delivery - Guaranteed delivery with bounded delay - In-order packet delivery - Guaranteed minimal bandwidth - Security (e.g., encryption of datagrams) This is only a partial list of services that a network layer could provide there are countless variations possible.

What are the advantages of using TCAMs in routers?

TCAMs are content addressable, meaning that the address can be presented to the TCAM and the address can be retrieved in one clock cycle, regardless of the size of the table. For example, Cisco Catalyst routers can store up to around 1 million routing table entries in TCAM.

What is the "guaranteed delivery with bounded delay" service that the network layer could provide?

The "guaranteed delivery with bounded delay" service is a service that not only guarantees delivery of a packet, but also guarantees delivery within a specified host-to-host delay bound (for example, within 100 msec).

What is the "in-order packet delivery" service that the network layer could provide?

The "in-order packet delivery" service is a service that guarantees that packets arrive at the destination in the order that they were sent.

What is the IPv4 datagram format?

The IPv4 datagram format is the structure used by the Internet Protocol (IP) to encapsulate data for transmission over an IP network. It consists of a header and a payload, with the header containing information about the datagram such as the source and destination IP addresses, the protocol being used, version of the protocol, time to live, datagram length, upper layer, fragment offset, fls, 16-bit identifier, header length, type of service, and other optional fields. The payload is the actual data being transmitted. The header and payload are combined to form a single unit called a datagram, which is then transmitted over the network.

What is the NAT traversal problem?

The NAT traversal problem refers to the difficulty of establishing a connection through a NAT router, which translates the local (private) IP addresses of devices on a local network into a single registered (public) IP address when connecting to the Internet.

What is the purpose of the "Type of Service" (TOS) field in the IPv4 header?

The TOS bits were included in the IPv4 header to allow different types of IP datagrams to be distinguished from each other. For example, it might be useful to distinguish real-time datagrams (such as those used by an IP telephony application) from non-real-time traffic (e.g., FTP). The specific level of service to be provided is a policy issue determined and configured by the network administrator for that router. Two of the TOS bits are also used for Explicit Congestion Notification.

What is the application layer in a typical SDN architecture?

The application layer in a typical SDN architecture contains network applications such as intrusion detection, firewall, and load balancing.

What is the control layer in a typical SDN architecture?

The control layer in a typical SDN architecture consists of the SDN controller, which acts as the brain of the network and allows hardware abstraction to applications written on top of it.

How is the forwarding table in a router computed and updated, and what is its function?

The forwarding table in a router is either computed and updated by the routing processor using a routing protocol to interact with the routing processors in other network routers, or it is received from a remote software-defined networking (SDN) controller. The lookup performed in the input port of the router is central to the router's operation, as it uses the forwarding table to look up the output port to which an arriving packet will be forwarded via the switching fabric.

How are fragments handled during transmission?

The fragments are transmitted separately and reassembled at the final destination to form the original, larger IP datagram. The IP header includes bits that are used to identify and order the related fragments.

What is the infrastructure layer in a typical SDN architecture?

The infrastructure layer in a typical SDN architecture consists of physical switches which form the data plane and carry out the actual movement of data packets.

What are the main fields in the IPv6 datagram format?

The main fields in the IPv6 datagram format are: 1- Version: a 4-bit field that identifies the IP version number 2- Priority: used to identify the priority among datagrams in a flow 3- Flow Label: used to identify datagrams in the same "flow" 4- Next Header: identifies the upper layer protocol for the data 5- Hop Limit: decremented by one by each router that forwards the datagram. If the hop limit count reaches zero, the datagram is discarded. 6- Payload Length: a 16-bit value indicating the number of bytes in the IPv6 datagram following the fixed-length, 40-byte datagram header 7- Source and Destination Addresses: the 128-bit IPv6 addresses of the source and destination nodes.

What service does the network layer of the Internet provide, and what are the guarantees offered by this service?

The network layer of the Internet provides a single service known as best-effort service. With best-effort service, packets are neither guaranteed to be received in the order in which they were sent, nor is their eventual delivery even guaranteed. There is no guarantee on the end-to-end delay nor is there a minimal bandwidth guarantee.

What are the primary data-plane and control-plane roles of a router?

The primary data-plane role of a router is to forward datagrams from its input links to its output links. The primary role of the network control plane is to coordinate these local, per-router forwarding actions so that datagrams are ultimately transferred end-to-end, along paths of routers between source and destination hosts.

What is the primary function of a switching fabric in a router?

The primary function of a switching fabric in a router is to transfer packets from the input buffer to the appropriate output buffer.

What is the primary function of output port processing in a router?

The primary function of output port processing in a router is to take packets that have been stored in the output port's memory and transmit them over the output link. This includes selecting (i.e., scheduling) and de-queueing packets for transmission, and performing the necessary link-layer and physical-layer transmission functions.

What is the role of the network layer?

The role of the network layer is deceptively simple: to move packets from a sending hosts to a receiving host. It does 2 main functions, forwarding and routing

How does traceroute work?

The source sends a series of User Datagram Protocol (UDP) segments to the destination, with each set having a different Time to Live (TTL) value. When the nth set of datagrams arrives at the nth router, the router discards the datagrams and sends the source an ICMP message (type 11, code 0) with the name and IP address of the router. The source records the Round Trip Times (RTTs) when the ICMP messages arrive.

What is the function of the switching fabric in a router?

The switching fabric in a router connects the router's input ports to its output ports. It is a network inside of the router.

How is the switching rate typically measured in a router?

The switching rate, which is the rate at which packets can be transferred from inputs to outputs, is often measured as a multiple of the input/output line rate. For example, if a router has N inputs, it may be desirable for the switching rate to be N times the line rate.

Which of the following is NOT a layer in a typical SDN architecture?

The three layers of a typical SDN architecture are the application layer, the control layer, and the infrastructure layer.

What is the traditional approach to implementing routing functionality?

The traditional approach to implementing routing functionality has been to have each router have a routing component that communicates with the routing component of other routers.

What are the two main functions of the network layer?

The two main functions of the network layer are forwarding and routing.

What are the two types of forwarding that can be performed at the input port of a router?

The two types of forwarding that can be performed at the input port of a router are: 1- Destination-based forwarding 2- Generalized forwarding

What are the challenges in transitioning from IPv4 to IPv6?

There are several challenges to transitioning from IPv4 to IPv6, including the fact that not all routers can be upgraded simultaneously and the need to support a mixed network with both IPv4 and IPv6 routers. One solution to these challenges is tunneling.

What are the steps involved in the implementation of Network Address Translation (NAT)?

To implement NAT, a NAT router must perform the following tasks: 1- For outgoing datagrams, replace the (source IP address, port number) of every outgoing datagram with the (NAT IP address, new port number) 2- Remember, in the NAT translation table, every (source IP address, port number) to (NAT IP address, new port number) translation pair 3- Remote clients and servers will respond using the (NAT IP address, new port number) as the destination address 4- For incoming datagrams, replace the (NAT IP address, new port number) in the destination fields of every incoming datagram with the corresponding (source IP address, port number) stored in the NAT table.

What is Traceroute?

Traceroute is a utility that allows a user to track the route that a packet takes from a source to a destination.

When does Traceroute stop?

Traceroute stops when the User Datagram Protocol (UDP) segment eventually arrives at the destination host and the destination returns an Internet Control Message Protocol (ICMP) "port unreachable" message (type 3, code 3). Or when the source stops.

True or False: The data plane components of per-router (traditional network) and SDN are identical.

True.

True or False: The forwarding table is a key element in every network router.

True.

What is tunneling and how does it work?

Tunneling is a method of transmitting IPv6 packets over an IPv4 network. It is used when two IPv6 nodes want to communicate using IPv6 datagrams, but are connected to each other by intervening IPv4 routers. In this case, the IPv6 node on the sending side of the tunnel puts the entire IPv6 datagram in the data (payload) field of an IPv4 datagram and sends it through the tunnel (consisting of the intervening IPv4 routers). The IPv6 node on the receiving side of the tunnel extracts the IPv6 datagram from the payload of the received IPv4 datagram and processes it as a normal IPv6 datagram.

What is Priority Queuing in packet scheduling?

Under priority queuing, packets arriving at the output link are classified into priority classes upon arrival at the queue. Each priority class typically has its own queue. When choosing a packet to transmit, the priority queuing discipline will transmit a packet from the highest priority class that has a nonempty queue (that is, has packets waiting for transmission). The choice among packets in the same priority class is typically done in a FIFO manner.

What is Round Robin in priority scheduling?

Under the round robin queuing discipline, packets are sorted into classes as with priority queuing. However, rather than there being a strict service priority among classes, a round robin scheduler alternates service among the classes. A work-conserving round robin discipline that looks for a packet of a given class but finds none will immediately check the next class in the round robin sequence. A generalized form of round robin queuing that has been widely implemented in routers is the so-called weighted fair queuing (WFQ).

What is weighted fair queuing (WFQ) in priority scheduling?

Weighted fair queuing (WFQ) is a generalized form of round robin queuing that has been widely implemented in routers. It is designed to allow multiple packet streams sharing the same link to achieve an equitable share of the link's bandwidth. WFQ works by assigning a weight to each active packet stream and using these weights to determine the sequence in which packets are transmitted. This allows each stream to receive a fair share of the link bandwidth, proportional to its weight. WFQ also has the ability to provide low delay to delay-sensitive traffic (such as real-time audio or video) by giving these streams a higher weight.

What is forwarding?

When a packet arrives to a router's input link, the router must move the packet to the appropriate output link. It is an action local to the router.

Can queueing occur at a switch's output ports?

Yes, queueing can occur at a switch's output ports.