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154 Cards in this Set
- Front
- Back
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What are the layers of the OSI model? (Number and Name)
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7 - Application
6 - Presentation 5 - Session 4 - Transport 3 - Network 2 - Data Link 1 - Physical |
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What is the function of the Application layer?
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The Application layer serves as an entry-point for data from an application.
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What is a redirector?
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A redirector is a part of network client software installed on a workstation.
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What does a redirector do?
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A redirector passes data from applications to the Application layer, and from the Application layer to the appropriate applications.
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What is the function of the Presentation layer?
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The function of the Presentation layer is to free network communication from the limitations imposed by differences in data representation methods.
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How does the Presentation layer serve its function?
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The Presentation layer serves its function by translating, converting, encrypting and decrypting, and compressing and decompressing data.
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What are the tasks of the Session layer?
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The Session layer handles the initiation of communication connections, session maintenance, and bidirectional acknowledgment of communication.
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What is a bidirectional acknowledgment of communication referred to as?
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A bidirectional acknowledgment of communication is referred to as a handshake.
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What responsibilities are met by the Transport layer?
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The Transport layer provides optional error detection and correction and end-to-end (host-to-host) error recovery and it controls the flow of packets.
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Why must the flow of packets be controlled?
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If packets are sent more quickly than the recipient can process them, they will be dropped.
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What two protocols are employed at the Transport layer?
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The Transport layer uses the Transmission Control Protocol, or TCP, and the User Datagram Protocol, or UDP.
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What is the difference between TCP and UDP?
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TCP ensures data delivery by resending dropped packets. UDP maximizes speed by not resending packets.
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What happens to data passed to the Transport layer from the Session layer?
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Data passed down to the Transport layer is broken down into pieces.
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What are the data pieces generally referred to as?
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The general name for the data pieces is Data Protocol Units, or DPUs.
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What are DPUs also called at the Transport layer?
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At the Transport layer, DPUs are also called segments.
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What does the Network layer handle?
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The Network layer is tasked with packet addressing, path determination, and packet forwarding.
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What else are DPUs referred to as at the Network layer?
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At the Network layer, DPU's are also referred to as datagrams or packets.
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What is packet addressing?
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Packet addressing is encapsulating a packet with an IP header containing the source and destination network addresses.
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What is path determination?
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Path determination is determining how to get to the destination network.
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What is packet forwarding?
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Packet forwarding is sending the packet towards its destination.
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What else does the Network layer determine, which it then passes to the Data Link layer?
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The Network layer also determines the source and destination MAC (or data link) addresses then passes it to the Data Link layer.
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In a TCP/IP environment, which protocols are responsible for which tasks?
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The IP protocol handles packet addressing and path determination.
The ARP protocol takes care of MAC address determination. |
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What does the Network layer do on behalf of the network technology?
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The Network layer ensures that the datagrams passed down to the Data Link layer are not too large for the network technology to handle.
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What does MTU stand for, and what is the significance?
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MTU stands for Maximum Transmission Units, and it represents the largest packet size the network technology can handle.
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What defines the Data Link layer in a network?
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The Data Link layer is defined by the network technology.
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What protocol is most common for LANs?
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The protocol for LANs is most often the 802.3 protocol, better known as Ethernet.
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What other name do DPUs have at the Data Link layer.
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At the Data Link layer, DPUs are also called frames.
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What's contained in a frame?
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At the Data Link layer, a packet is wrapped in headers containing the source and destination MAC addresses, some network protocol specific info, and an added checksum for error checking, then called a frame.
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What is a MAC address?
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MAC (Media Access Control) addresses are the unique identifying address burned into every network interface card and NIC-less computer.
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What else are MAC addresses known as?
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MAC addresses are known as physical addresses, because they're permanently tied to their NIC. They are also known as data link addresses in the OSI model.
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How many bits are in a MAC address, and how is it represented?
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A MAC address is 48 bits represented by 6 pairs of hexadecimal digits.
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How are the parts of a MAC address divided?
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The first 3 pairs in a MAC address dfenote the manufacturer, and the last 3 are unique to the NIC.
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What is the Data Link layer responsible for on the local network only?
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Just on the local network, the Data Link layer also takes care of delivery and error detection.
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What happens to the data if it must be routed to another network?
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If the data must be routed to another network, the router strips the frame off the packet and applies a new one depending on the network protocol at the packet's next hop.
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How is the data passed to the Physical layer?
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The Data Link layer converts frames to bit streams to pass to the Physical layer.
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What are the sub-layers of the Data Link layer, in order?
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The upper sub-layer of the Data Link Layer is the Logical Link (LLC) layer. The lower sub-layer is the MAC layer.
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What defines the LLC sub-layer?
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The LLC sub-layer is defined by the IEEE 802.2 standard.
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What does the LLC sub-layer do with packets?
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The LLC sub-layer frames packets by applying the MAC address and checksum headers.
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What are the LLC sub-layer's session-related capabilities?
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The LLC sub-layer can establish a connection-based or connection-less session with the next node in the path.
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What else is handled by the LLC sub-layer?
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The LLC sub-layer is also responsible for frame synchronization, flow control, and error correction.
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What is an 802.2 frame good for?
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An 802.2 frame allows for identification of the transport protocol in use.
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What networking standards is the MAC sub-layer associated with?
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The MAC sub-layer is associated with various networking standards such as 802.3 and 802.5.
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What are the names for protocols 802.3 and 802.5?
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802.3 is CSMA/CD or Ethernet, and 802.5 is Token Ring.
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What does the MAC sub-layer handle?
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The MAC sub-layer takes care of communication with the network adapter and arbitrates shared access to the media.
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What is defined by the Physical layer?
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The Physical layer defines the electrical, mechanical, functional, and procedural characteristics used to access and send a stream of bits over a physical medium.
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How does the Physical layer prepare bits for transmission?
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The Physical layer converts bits to electrical, light, or radio signals for transmission across a physical medium,
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What is encapsulation?
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Encapsulation is the process of wrapping data in headers as it is passed down the layers.
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What headers are applied at each layer?
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No headers are applied in the upper layers (Application to Session).
A TCP or UDP header is applied at the Transport layer. The Network layer encapsulates DPUs with an IP header. The Data Link layer adds a MAC header, as well as an 802.2, LLC, and/or SNAP header. The Physical layer does not contribute any headers. |
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What basic information is stored in the TCP/UDP header?
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Both TCP and UDP headers contain the source and destination port numbers and a checksum.
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Describe the layers of the TCP/IP networking model.
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The TCP/IP networking model is separated into the Application layer, Transport layer, Internet layer, and Network Interface layer.
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Match up the layers of the TCP/IP model to the layers of the OSI model.
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The Application layer in the TCP/IP model represents the Application, Presentation, and Session layers of the OSI model, the Transport layer is the Transport layer, the Internet layer is equivalent to the Network layer, and the Network Interface layer corresponds to the Data Link and Physical layers together.
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Which TCP/IP protocols are associated with the Application layer of the TCP/IP model?
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HTTP, TELNET, FTP, SMTP, DNS, and SNMP all correspond to the TCP/IP Application layer.
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Which protocols are associated with the Transport layer?
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TCP and UDP are associated with the Transport layer.
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Which protocols are associated with the Internet layer?
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IP, ARP, IGMP, and ICMP are associated with the Internet layer.
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What are the individual merits of the OSI and the TCP/IP models.
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The OSI model is embedded in the lexicon as the model most used for describing networking. The TCP/IP model best reflects the actual protocols in use.
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Describe the encapsulation state of a DPU as it passes through a router.
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A DPU enters a router as a layer 2 frame and moves through it as a layer 3 datagram.
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What layer of the OSI model are repeaters associated with?
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Repeaters are associated with the Physical layer, as they are unable to examine the content of frames.
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What do repeaters do, in detail?
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Repeaters receive a frame, regenerate an exact copy of it, and send the copy on its way.
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What is the primary use of repeaters?
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Repeaters are used only for intranetwork communication, mostly to extend the maximum length of cable runs.
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What effect has fiber optics had on the usefulness of repeaters?
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Repeaters are hardly seen used specifically for networking anymore, as fiber optics have extended maximum cable run length without need for repeaters.
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What are hubs?
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Hubs are essentially multiport repeaters, with 24+ ports instead of 2.
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How does a hub work?
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It forwards packets received in any port out through all other ports.
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What layer does a hub operate on?
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Hubs, like repeaters, operate on the Physical layer, as they cannot scrutinize the bits received in any way.
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What is a collision domain?
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A collision domain is a section of a network where packets may collide with one another.
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What is packet collision?
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If two signals are on the same wire at the same time they collide.
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What problem arises with large single collision domains?
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As more hosts enter a collision domain, collisions become more frequent, and communication must be reattempted so often as to impede performance.
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What is a bridge?
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A bridge is a repeater with the ability to examine the outer layer of frames and thus make intelligent forwarding decisions.
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What layer does a bridge serve at?
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Bridges are associated with the Data Link layer, as they can examine the headers applied at that layer.
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How does a bridge know which direction to forward DPUs?
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Bridges build an internal table that records every node attached to either port, and so learns which nodes are connected to which port.
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What is the primary benefit of bridges over repeaters?
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Since bridges don't forward DPUs the wrong direction, they limit wasted network communication and they split collision domains.
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What is a switch?
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Switches are to bridges what hubs are to repeaters.
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How are collision domains determined by a switch?
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Each port on a switch forms a collision domain.
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What is wire speed technology and what is its significance?
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Wire speed technology is a firmware based code that mitigates the delay arising form the switch examining every packet's MAC addresses.
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In what form do switches often appear in when in a home?
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In homes, switches are often employed within 4 port switch/Internet/router combo boxes.
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What is the primary benefit of a switch with only 4 nodes on the network?
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Having each node on a switched port makes eavesdropping more difficult, enhancing security.
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What's the basic purpose of routers?
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Routers are generally required to forward packets from one network to another.
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Which OSI layer are routers associated with?
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Routers are Network layer devices, as they read the IP (network) addresses of DPUs to determine where to send them.
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What type of domain do routers isolate?
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Routers isolate broadcast domains as well as collision domains.
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What are the basic attributes of any router?
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A router has a processor, an OS, 2+ network interfaces to forward packets through, a route table indicating which interface the packets should be forwarded through, and some type of memory to store the OS, route table, and config info.
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What does one need to use a general purpose computer as a router?
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To use a general purpose computer as a router, just install 2+ network interface cards and configure for packet forwarding.
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What is a computer with 2+ NICs referred to as?
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A computer with 2+ NICs is referred to as a multi-homed computer or a multi-homed system.
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What types of memory are employed by routers?
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Routers use non-volatile memory, such as ROM, Flash/EEPROM, and NVRAM, and volatile memory, like RAM.
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What are the differences between volatile and non-volatile memory?
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Volatile memory is faster, but non-volatile memory isn't lost when power is shut off.
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What do routers typically use each type of memory for?
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Routers typically store a stripped down OS in ROM, the full OS in Flash/EEPROM, and start up config in NVRAM. Information is copied to RAM on boot up for faster operation, and RAM also stores the running config, route tables, etc.
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What are the two traditional interface types in routers?
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Each router traditionally has a LAN interface and a WAN interface.
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Throw out some details about WAN interfaces.
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WAN interfaces allow connections to a WAN link, such as a modem or digital line (such as T1 or 56K). A Data Terminal Equipment / Data Circuit-terminating Equipment cable connects a WAN interface to a Channel Service Unit / Data Service Unit.
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Throw out some details about LAN interfaces.
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A LAN interface connects a routers to one or more local networks. It can be either an RJ-45 jack (100base-T) or a DB-15 female connector.
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What was the DB-15 connector designed for?
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The DB-15 connector was designed to connect to the now-obsolete 10base-2 (coax) networks.
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What series of Cisco router still uses a DB-15 connector?
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The Cisco 2500 series routers still use DB-15 connectors.
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What does NAT device stand for?
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Network Address Translation device.
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What does a NAT device do?
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NAT devices translate a private address to a public address when communicating with outside networks.
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Most consumer networking devices which incorporate NAT are labelled as what?
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Most consumer networking devices label NAT-incorporating devices as routers, despite NAT devices not performing any actual routing.
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What is a layer 3 switch?
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A layer 3 switch combines switch and router functions. It can read layers 2&3 headers and so can forward data either across the local network or to a separate network.
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What is a public IP address?
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A public IP address is a number assigned to a host that uniquely identifies them both on the local network and all public IP networks.
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What is a private IP address?
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A private IP address can't be used on public IP networks (including the Internet) and so can be reused by many people in private networks.
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What is the purpose of private IP addresses?
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Private IPs allow many hosts to use one public IP, thereby saving many.
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How large is an IP address and how is it expressed?
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IP addresses are 128 bits as of IPv6, and are often expressed as groupings of 8 bits each then converted to decimal.
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What's the general rule regarding IP address validity?
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If the network or host section of an IP address is all 1s or 0s, then the address is invalid.
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Why are all 0 and all 1 host addresses invalid?
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All 0s in the host section of an address represents the network number itself. All 1s represents the broadcast address for the network.
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Why was the classful addressing system replaced with the classless?
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With the classful addressing system, many IP addresses were wasted as network addresses were distributed. With the classless, requesters get the exact number of addresses they need.
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How is it ensured that all public IP addresses are unique?
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A central assigning authority allocates all public IP addresses.
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What are the ranges of public IP addresses?
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1.0.0.0 - 9.0.0.0
11.0.0.0 - 126.0.0.0 128.0.0.0 - 172.15.0.0 172.32.0.0 - 191.255.0.0 192.0.0.0 - 192.167.255.0 192.169.0.0 - 223.255.255.0 |
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What are the ranges of private IP addresses?
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10.0.0.0
172.16.0.0 - 172.31.0.0 192.168.0.0 - 192.168.255.0 |
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What is RFC 1918 and when was it done?
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In the mid-90's, RFC 1918 allocated a range of IP addresses for use by private networks, never to be used online.
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The use of which devices was fueled by the implementation of private addresses?
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The use of proxy servers, NAT boxes, and gateways has been fueled by the implementation of private addresses, as they substitute a public IP for the private when communicating with the internet.
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Most consumer internet routers, which incorporate NAT devices for internet access, default to what private address?
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Most consumer routers default to a class C private address, usually 192.168.(0-2).0.
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What was the method of determining the network portion of an address in the classful system?
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The First Octet rule was used with the classful system; the first octet was examined to determine class and so length of network portion in the address.
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What is used in a classless environment to distinguish the network portion of an IP address?
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In a classless environment, subnet masks and/or prefix numbers are used to distinguish the network portion of an IP address.
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Subnet Time! Express subnet masks in dotted decimal.
a. The first one and a half octets are in the network portion of the address. b. The first two octets and one bit more are in the network portion of the address. |
a. 255.240.0.0
b. 255.255.128.0 |
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Prefix Notation Time! Translate these dotted decimal subnet masks to prefix notation.
a. 172.0.0.0 b. 255.224.0.0 |
a. /2
b. /11 |
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How is a subnet mask applied by a router?
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A router applies a subnet mask to an IP address (both as 32-bit binary numbers) by ANDing them.
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Which method of distinguishing network portions of IPs is commonly used by public WAN carriers?
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Public WAN carriers often use prefix notation.
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What is subnetting?
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Subnetting is the act of taking a single IP network ID and subdividing it to create 2+ network IDs, by relocating the network/host division towards the right.
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What are Variable Length Subnet Masks?
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VLSMs allow subnets to be further subnetted.
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What is supernetting?
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Supernetting is the act of combining sequential IP network IDs into one network ID.
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What is CIDR?
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Classless Inter Domain Routing is the sub-/supernetting and VLSM techniques applied at the address assignment level.
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How does CIDR work, basically? Generic example works.
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ISP A receives an allotment of addresses with the subnet mask 240.0.0.0. ISP A subnets their addresses then gives ISP B an allotment with the subnet mask 255.255.0.0.
ISP B subnets and gives a network address to a small group with the subnet mask 255.255.255.240 |
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What benefit does CIDR hold for route tables?
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The CIDR address allotment system lends well to route summarization, limiting the entries in tables for backbone routers.
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What are some important steps to take before you subnet a network ID?
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Before subnetting a network ID...
1. Determine the total number of subnets needed, accounting for future networks. 2. Determine the total number of hosts that each subnet must support, accounting for the future. 3. Define a custom subnet mask that will support the required number of hosts per subnet. 4. Derive the subnet IDs, then the host IDs and broadcast address for each subnet. |
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Give the formula(s) for finding the number of valid subnet addresses created by subnetting and calculating how many valid host addresses are in a subnet.
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2^n-2=number of viable addresses
For number of network addresses, n is the number of bits borrowed from the host portion. For host addresses, n is the number of bits left in the host portion. |
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What is the original network address useful for after subnetting? What's that use referred to as, and why is it good?
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The original network address can represent the collection of subnets in route tables of certain routers. This is called route summarization, and it minimizes route table entries.
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If one subnets a network address, what does one need hardware-wise?
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When subnetting a network address, one needs a router for each subnet and another router to forward packets between the subnets.
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The introduction of what led to supernetting becoming unnecessary?
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The introduction of CIDR removed need for supernetting, as old class limitations no longer applied.
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What is the central internet agency responsible for assigning network addresses?
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The internet agency responsible for assigning network addresses is called the Internet Network Information Center, InterNIC, or just NIC.
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With regards to allocation of network addresses, what has come of the internet growing so large?
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As the internet has grown larger, allocation of public IPs has been delegated to private regional entities,
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What is the American agency for allocating network addresses?
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The American Registry for Internet Numbers (ARIN) allocates network addresses in America.
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What is a domain?
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A domain is defined as a network or networks under a single administrative control.
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What problems were solved by CIDR?
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CIDR solved the problem of wasted IP addresses and the sheer enormity of backbone route tables.
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What's the difference between IPv4 and IPv6?
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IPv4 IP addresses are 32 bits; IPv6 addresses are 128 bits.
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What does a port number indicate?
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A port number indicates which application is to be used to process a packet.
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How does the recipient computer use the port number of packets?
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A recipient computer reads the port number of packets and sends the packets to the application listening on that port.
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What ports do web servers and FTP servers listen on?
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Web servers listen on TCP port 80; FTP servers listen on port 20.
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What is the range of ports?
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Both UDP and TCP protocols have their own 0-65,535 range of ports.
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What range of ports is reserved?
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The range of ports from 0-1023 are reserved, and used by server-based applications.
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What is a socket and how is it displayed?
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A socket is an IP address and port combination, and is displayed IPaddress:port (ie 192.164.0.2:80).
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What series of port numbers do web clients make use of?
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Web clients make requests using any of a series of sequential port numbers between 1024 and 4096, order wrapping.
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What is a connection-oriented protocol? Give an example.
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Connection-oriented protocols, such as TCP, establish a connection between the source and destination hosts before transferring data packets.
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What is a connection-less protocol? Give an example.
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A connection-less protocol, such as UDP or IP, does not create an initial connection between the source and destination hosts before sending packets.
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Which layer header contains the source and destination port numbers?
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The source and destination port numbers are contained in the Transport layer (4) header.
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What is TFTP?
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TFTP stands for Trivial File Transfer Protocol, and is used when assured delivery is not required, as it utilizes UDP.
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What does Cisco use TFTP for?
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Cisco uses TFTP to upload IOS and config files to routers, as that often happens over a local network, a relatively reliable medium.
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What does the TFTP application use for error detection and correction?
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The TFTP application uses checksums for error detection and correction.
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Do broadcast packets use TCP or UDP?
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Broadcast packets use UDP, because broadcasts are sent to all hosts on a subnet and are usually responded to by one host, if that, making it pointless to ensure delivery of all broadcast packets.
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What does TCP do first, before sending data packets?
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Before actual communication begins, TCP sends a SYN packet, and waits for an ACK packet reply so it knows the connection has been established.
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What is the sequence number in TCP communications?
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The sequence number is used in TCP communications to ID packets and ensure that each packet arrives at the destination.
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How do two hosts synchronize TCP sequence numbers?
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Two hosts synchronize the sequence number in the initial SYN and ACK packets.
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What does the sending host do when it receives the ACK packet?
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When the sending host receives the ACK packet, it sends one additional packet to indicate to the other host that it received the ACK and synched to the given sequence number.
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What is the TCP communication preparation called?
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The 3-way handshake is the name given to the TCP process for initializing communication.
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How does TCP decide when to resend packets?
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For every packet sent out, TCP notes the sequence number and starts a timer. If the ACK with that sequence number is not received before the timer expires, the packet is resent.
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What is a sliding window?
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The sliding window is TCP's method of flow control. It's a buffer in memory that stores a number of outbound packets to be sent in a burst, after which no more packets will be sent until the packets in the burst have been ACKd.
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What happens if the TCP sliding window is too large?
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If the sliding window is too large, flow is too high and packets are dropped, and TCP responds by narrowing the window.
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How is the initial size of a TCP sliding window determined?
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The initial size for the sliding window is determined in the 3-way handshake.
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What is the Internet Protocol (IP) responsible for?
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IP is responsible for logical packet addressing and forwarding datagrams.
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What must be done if reliable communication is required when using IP?
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If reliable communication is required, the layer 4 TCP protocol must be invoked by the sending application.
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