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# IT0013 – MODULE 4 SUBTOPIC 1 & 2 ## EXAM REVIEWER FOR NETWORKING ### TOPIC: ETHERNET SWITCHING - Ethernet operates in the **data link** layer and the **physical** layer. - It is a family of networking technologies defined in the IEEE 802.2 and 802.3 standards. - What are the two sublayers of dat...

# IT0013 – MODULE 4 SUBTOPIC 1 & 2 ## EXAM REVIEWER FOR NETWORKING ### TOPIC: ETHERNET SWITCHING - Ethernet operates in the **data link** layer and the **physical** layer. - It is a family of networking technologies defined in the IEEE 802.2 and 802.3 standards. - What are the two sublayers of data link layer which is used to operate? **LLC** and **MAC** - This sublayer places information in the frame to identify which network layer protocol is used for the frame. **LLC** - What does LLC stand for? **Logical Link Control** - This sublayer is responsible for data encapsulation and media access control, and provides data link layer addressing. **MAC** - What does MAC stand for? **Media Access Control** - Data Encapsulation includes 3 things which are? - **Ethernet frame** - **Ethernet Addressing** - **Ethernet Error detection** - This is the internal structure of the Ethernet frame. **Ethernet frame** - The Ethernet frame includes both a source and destination MAC address to deliver the Ethernet frame from Ethernet NIC to Ethernet NIC on the same LAN. **Ethernet Addressing** - The Ethernet frame includes a frame check sequence (FCS) trailer used for error detection. **Ethernet Error detection** - What does FCS stand for? **Frame Check Sequence** - This sublayer includes the specifications for different Ethernet communications standards over various types of media including copper and fiber. **MAC Sublayer** - using a bus topology or hubs, is a shared, half-duplex medium. **Legacy Ethernet** - Ethernet over a **half-duplex** medium uses a contention-based access method, carrier sense multiple access/collision detection (CSMA/CD). - Ethernet LANs of today use switches that operate in **full-duplex**. - **Full-duplex** communications with Ethernet switches do not require access control through CSMA/CD. - The minimum Ethernet frame size is **64** bytes and the maximum is **1518** bytes. The preamble field is not included when describing the size of the frame. - Any frame less than 64 bytes in length is considered a **collision fragment** " " or " " and is automatically discarded. - Frames with more than 1500 bytes of data are considered" **jumbo** " or " **baby giant frames** " " - If the size of a transmitted frame is less than the minimum, or greater than the maximum, the receiving device **drops** the frame. - **Dropped frames** are likely to be the result of collisions or other unwanted signals. They are considered invalid. - **Jumbo Frames** are usually supported by most Fast Ethernet and Gigabit Ethernet switches and NICs. - An Ethernet MAC address consists of a **48**-bit binary value, expressed using **12** hexadecimal values. ### 00 to FF - Given that 8 bits (one byte) is a common binary grouping, binary 00000000 to 11111111 can be represented in hexadecimal as the range **00 to FF** - When using **hexadecimal** to leading zeroes are always displayed to complete the 8-bit representation. For example the binary value 0000 1010 is represented in hexadecimal as OA. - Hexadecimal numbers are often represented by the value preceded by **0x** to distinguish between decimal and hexadecimal values in documentation. (e.g., 0x73) to - Hexadecimal may also be represented by a subscript **16** , or the hex number followed by an H (e.g., 73H). ### 16 - In an Ethernet **LAN** , every network device is connected to the same, shared media. - addressing provides a method for device identification at the data link layer of the OSI model. **MAC** ### 48; 12; 6 - An Ethernet MAC address is a **48**-bit address expressed using **12** hexadecimal digits. - Because a byte equals 8 bits, we can also say that a MAC address is **6** bytes in length. - All MAC addresses must be **unique** to the Ethernet device or Ethernet interface. To ensure this, all vendors that sell Ethernet devices must register with the to obtain a unique 6 hexadecimal (i.e., 24-bit or 3-byte) code called the **IEEE; OUI** ### ΙΕΕΕ; ### OUI; - What does OUI stand for? **Organizationally unique identifier** - An Ethernet MAC address consists of a 6 hexadecimal vendor **code** followed by a 6 hexadecimal **code**-assigned value. ### NIC; ### Destination MAC - When a device is forwarding a message to an Ethernet network, the Ethernet **NIC** include a Source MAC address and a Destination MAC address. - When a **NIC** receives an Ethernet frame, it examines the **MAC address** to see if it matches the physical MAC address that is stored in RAM. If there is no match, the device discards the frame. If there is a match, it passes the frame up the OSI layers, where the de-encapsulation process takes place. - Ethernet NICs will also accept frames if the destination MAC address is a **unicast** or a **multicast group** of which the host is a member. - Any device that is the source or destination of an Ethernet frame, will have an Ethernet NIC and therefore, a **MAC** address. This includes workstations, servers, printers, mobile devices, and routers. ### TRUE - [T/F] In Ethernet, different MAC addresses are used for Layer 2 unicast, broadcast, and multicast communications. **TRUE** - A **unicast** MAC address is the unique address that is used when a frame is sent from a single transmitting device to a single destination device. - The process that a source host uses to determine the destination MAC address associated with an IPv4 address known as **Address Resolution Protocol (ARP)** - What does ARP stand for? **Address Resolution Protocol** - The process that a source host uses to determine the destination MAC address associated with an IPv6 address is known as **Neighbor Discovery (ND)** - What does ND stand for? **Neighbor Discovery** - [T/F] The source MAC address must always be a unicast. **TRUE** - An Ethernet **broadcast** frame is received and processed by every device on the Ethernet LAN. It has a destination MAC address of FF-FF-FFFF-FF-FF in hexadecimal (48 ones in binary). - It is flooded out all Ethernet switch ports except the incoming port. It is not forwarded by a router. - If the encapsulated data is an IPv4 broadcast packet, this means the packet contains a destination IPv4 address that has all ones (1s) in the host portion. This numbering in the address means that all hosts on that local network (broadcast domain) will receive and process the packet. - An Ethernet **multicast** frame is received and processed by a group of devices that belong to the same **group**. - There are other reserved multicast destination MAC addresses for when the encapsulated data is not IP, such as - **Spanning Tree Protocol (STP)** - What does STP stand for? **Spanning Tree Protocol** ### NONE - Note: It is flooded out all Ethernet switch ports except the incoming port, unless the switch is configured for multicast snooping. It is not forwarded by a router, unless the router is configured to route multicast packets. - Because multicast addresses represent a group of addresses (sometimes called a **host group** ), they can only be used as the destination of a packet. The source will always be a unicast address. ### multicast - As with the unicast and broadcast addresses, the multicast IP address requires a corresponding **MAC** address. - A Layer 2 Ethernet switch uses Layer 2 MAC addresses to make **forwarding** decisions. It is **completely unaware** of the data (protocol) being carried in the data portion of the frame, such as an IPv4 packet, an ARP message, or an IPv6 ND packet. - An Ethernet **switch** makes its forwarding decisions based solely on the Layer 2 Ethernet MAC addresses. - When a switch is turned on, the MAC address table is **empty** - Unlike legacy Ethernet, that repeat bits out all ports except the incoming port when a switch **examines** its MAC address table to make a forwarding decision for each frame. ### switch; hub ### Content Addressable Memory (CAM) - What does CAM stand for? **Content Addressable Memory** - The MAC address table is sometimes referred to as a **table**. ### Source MAC address does not does - Every frame that enters a switch is checked for new information to learn. It does this by examining the **MAC address** of the frame and the port number where the frame entered the switch. If the BLANK 1 MAC address **does not** exist, it is added to the table along with the incoming port number. If the BLANK 1 MAC address **does** exist, the switch updates the refresh timer for that entry. ### Source MAC address - We examine the **Source MAC address** (Learn) ### 5 Minutes - By default, most Ethernet switches keep an entry in the table for **5** minutes. ### new entry - If the source MAC address does exist in the table but on a different port, the switch treats this as a **new entry**. The entry is replaced using the same MAC address but with the more current port number. ### Unicast - If the destination MAC address is a **unicast** address, the switch will look for a match between the **MAC address** of the frame and an entry in its MAC address table. If the BLANK 2 address is **in** the table, it will forward the frame out the specified port. If the BLANK 2 address is **not in** the table, the switch will forward the frame out all ports except the incoming port. This is called an unknown unicast. ### Destination MAC address - We find the **Destination MAC address** (Forward) - If the **destination MAC address** is a broadcast or a multicast, the frame is also flooded out all ports except the incoming port. - As a switch receives frames from different devices, it is able to populate its MAC address table by examining the **MAC address** of every frame. - When the MAC address table of the switch contains the **MAC address**, it is able to filter the frame and forward out a single port. - Use one of the following forwarding methods for switching data between network ports which are? - **Store-and-forward switching** - **Cut-through switching** ### Store-and-forward switching - This frame forwarding method receives the entire frame and computes the Cyclic redundancy check (CRC). If the CRC is valid, the switch looks up the destination address, which determines the outgoing interface. Then the frame is forwarded out of the correct port. ### Cut-through switching - This frame forwarding method forwards the frame before it is entirely received. At a minimum, the destination address of the frame must be read before the frame can be forwarded. ### store-and-forward switching; bandwidth - A big advantage of **FORWARDING METHOD - store-and-forward switching** is that it determines if a frame has errors before propagating the frame. When an error is detected in a frame, the switch discards the frame. Discarding frames with errors reduces the amount of consumed by corrupt data. - switching is required for quality of service (QoS) analysis on converged networks where frame classification for traffic prioritization is necessary. For example, voice over IP (VoIP) data streams need to have priority over web-browsing traffic. **Store-and-forward Switching** ### Store-and-forward Switching - In switching, the switch acts upon the data as soon as it is received, even if the transmission is not complete. The switch buffers just enough of the frame to read the destination MAC address so that it can determine to which port it should forward out the data. The switch does not perform any error checking on the frame. **cut-through Switching** ### Fast-forward switching; Fragment-free switching - What are the two variants of cut-through switching? ### Fast-forward switching - This type of cut-through switching offers the lowest level of latency by immediately forwarding a packet after reading the destination address. Because fast-forward switching starts forwarding before the entire packet has been received, there may be times when packets are relayed with errors. The destination NIC discards the faulty packet upon receipt. Fastforward switching is the typical cut-through method of switching. ### Fragment-free switching - This type of cut-through switching is a compromise between the high latency and high integrity of store-and-forward switching and the low latency and reduced integrity of fast-forward switching, the switch stores and performs an error check on the first 64 bytes of the frame before forwarding. Because most network errors and collisions occur during the first 64 bytes, this ensures that a collision has not occurred before forwarding the frame. ### buffering - An Ethernet switch may use a **buffering** technique to store frames before forwarding them or when the destination port is busy because of congestion. ### Port-based memory - A buffering method where frames are stored in queues that are linked to specific incoming and outgoing ports. **Port-based memory** ### Port-based memory - A buffering method where a frame is transmitted to the outgoing port only when all the frames ahead in the queue have been successfully transmitted. **Port-based memory** ### Port-based memory - A buffering method where it is possible for a single frame to delay the transmission of all the frames in memory because of a busy destination port. **Port-based memory** ### Port-based memory - A buffering method where this delay occurs even if the other frames could be transmitted to open destination ports. ### Shared memory - A buffering method where deposits all frames into a common memory buffer shared by all switch ports and the amount of buffer memory required by a port is dynamically allocated. - A buffering method where the frames in the buffer are dynamically linked to the destination port enabling a packet to be received on one port and then transmitted on another port, without moving it to a different queue. ### Shared memory - memory buffering also results in larger frames that can be transmitted with fewer dropped frames. This is important with asymmetric switching which allows for different data rates on different ports. Therefore, more bandwidth can be dedicated to certain ports (e.g., server port). ### Shared memory - Two of the most basic settings on a switch are the ("speed") and settings for each individual switch port. It is critical that the two settings match between the switch port and the connected devices. **Bandwidth and Duplex** ### Full and Hald Duplex - What are the two types of duplex? - **Full-duplex** - **Half-duplex** ### Full-duplex - A duplex where both ends of the connection can send and receive simultaneously. ### Half-duplex - A duplex where only one end of the connection can send at a time. ### Autonegotiation - is an optional function found on most Ethernet switches and NICs. It enables two devices to automatically negotiate the best speed and duplex capabilities. **Autonegotiation** ### Full - Gigabit Ethernet ports only operate in -duplex. **Full-duplex** ### Duplex mismatch - mismatch is one of the most common causes of performance issues on 10/100 Mbps Ethernet links. **Duplex mismatch** ### Duplex mismatch - It occurs when one port on the link operates at halfduplex while the other port operates at full-duplex. **Duplex mismatch** ### Duplex mismatch - This can occur when one or both ports on a link are reset, and the autonegotiation process does not result in both link partners having the same configuration. **Duplex mismatch** ### Duplex mismatch - It also can occur when users reconfigure one side of a link and forget to reconfigure the other. Both sides of a link should have autonegotiation on, or both sides should have it off. Best practice is to configure both Ethernet switch ports as full-duplex. ### NONE - Note: Connections between devices once required the use of either a crossover or straight-through cable. The type of cable required depended on the type of interconnecting devices. A direct connection between a router and a host requires a connection. **cross-over connection** ### Automatic Medium-Dependent Interface Crossover (auto-MDIX) - Most switch devices now support the feature. When enabled, the switch automatically detects the type of cable attached to the port and configures the interfaces accordingly. **Automatic Medium-Dependent Interface Crossover** ### auto-MDIX - The feature is enabled by default on switches running Cisco IOS Release 12.2(18)SE or later. However, the feature could be disabled. For this reason, you should always use the correct cable type and not rely on the auto-MDIX feature. **auto-MDIX** ### mdix auto - Auto-MDIX can be re-enabled using the interface configuration command. **mdix auto** ### TOPIC: NETWORK LAYER - This layer provides services to allow end devices to exchange data. - Principle network layer communication protocols are? - IP version 4 (IPv4) and - IP version 6 (IPv6) - The four (4) basic operations of the network layer are? - Addressing end devices, - Encapsulation, - Routing, and - De-encapsulation - IP encapsulates the **data link** layer segment. - IP can use either an IPv4 or IPv6 packet and not impact the **network** segment. - IP packet will be examined by all layer devices as it traverses the network. - [T/F] The IP addressing does not change from source to destination. **TRUE** ### Connectionless - IP is meant to have low overhead and may be described as things which are? - IP does not establish a connection with the destination before sending the packet. - There is no control information needed (synchronizations, acknowledgments, etc.). - The destination will receive the packet when it arrives, but no pre-notifications are sent by IP. - If there is a need for connection-oriented traffic, then another protocol will handle this (typically TCP at the transport layer). ### Best Effort - IP is **Best Effort**: - IP will not guarantee delivery of the packet. - IP has reduced overhead since there is no mechanism to resend data that is not received. - IP does not expect acknowledgments. - IP does not know if the other device is operational or if it received the packet. ### unreliable - IP is **unreliable**: - It cannot manage or fix undelivered or corrupt packets. - IP cannot retransmit after an error. - IP cannot realign out of sequence packets. - IP must rely on other protocols for these functions. ### media independent - IP is **media independent**: - IP does not concern itself with the type of frame required at the data link layer or the media type at the physical layer. - IP can be sent over any media type: copper, fiber, or wireless. ### Maximum Transmission Unit (MTU) - The network layer will establish the where the Network layer receives this from control information sent by the data link layer and where the network then establishes the MTU size. ### Maximum Transmission Unit (MTU) - What does MTU stand for? **Maximum Transmission Unit** ### Fragmentation - is when Layer 3 splits the IPv4 packet into smaller units. **Fragmentation** ### Latency - Fragmenting causes **Latency**. ### IPv6 - The does not fragment packets. **IPv6** ### IPv4 - The is the primary communication protocol for the network layer **IPv4** - It ensures the packet is sent in the correct direction (to the destination). **IPv4** - It contains information for network layer processing in various fields. **IPv4** ### Network Header - contains information for network layer processing in various fields.). - The information in the header is used by all devices that handle the packet **Network Header** ### Layer 3 - The IPv_network header characteristics: - It is in binary. - Contains several fields of information - Diagram is read from left to right, 4 bytes per line - The two most important fields are the source and destination. - Layer 3 hop count. When it becomes zero the router will discard the packet. - ### Time to Live (TTL) - IPv4 has three major limitations which are? - **IPv4 address depletion** - **Lack of end-to-end connectivity** - **Increased network complexity** - This IPv4 major limitations states that we have basically run out of IPv4 addressing. **IPv4 address depletion** ### IPv4 address depletion - This IPv4 major limitations states that to make IPv4 survive this long, private addressing and NAT were created. This ended direct communications with public addressing. **IPv4 address depletion** - This IPv4 major limitations states that NAT was meant as temporary solution and creates issues on the network as a side effect of manipulating the network headers addressing. NAT causes latency and troubleshooting issues. **Lack of end-to-end connectivity** ### Increased network complexity - IPv6 was developed by . **Internet Engineering Task Force (IETF)** - Improvements that provides: - Increased address space - based on 128 bit address, not 32 bits - Improved packet handling - simplified header with fewer fields - Eliminates the need for NAT - since there is a huge amount of addressing, there is no need to use private addressing internally and be mapped to a shared public address ### IPv6 - There are billion IPv4 address while there are undecillion IPv6 address. **4; 340** - The IPv6 header is simplified, but not smaller and the header is fixed at **40** Bytes or octets long . ### Flag, Fragment Offset, and Header Checksu, Hop Limit - Some IPv4 fields were removed to improve performance are? - Replaces TTL field Layer 3 hop count ### extension headers (EH) - IPv6 packet may also conatin which provide optional network layer information, are optional, are placed between IPv6 header and the payload, and may be used for fragmentation, security, mobility support, etc. **extension headers (EH)** ### routers - Unlike IPv4, do not fragment IPv6 packets. **routers** ### Source Routing - Packets are always created at the table. **Source Routing** - Each host devices creates their own table. **Source Routing** ### Itself, Local, and Remote Hosts - A host can send packets to the three following which are? - **127.0.0.1 (IPv4), ::1 (IPv6)** - destination is on the same LAN - devices are not on the same LAN **Itself, Local, and Remote Hosts** ### Source IPv4 - The device determines whether the destination is local or remote. **Source IPv4** ### IPv6 - This method of determination is where source uses its own IP address and Subnet mask, along with the destination IP address Source uses its own IP address and Subnet mask, along with the destination IP address. **IPv6** ### Local traffic - This method of determination is where source uses the network address and prefix advertised by the local router. **Local traffic** ### Remote traffic - A traffic is dumped out the host interface to be handled by an intermediary device. **Remote traffic** - A traffic is forwarded directly to the default gateway on the LAN. **Remote traffic** ### router or switch - A or layer 3 can be a default-gateway. **router or switch** - It must have an IP address in the same range as the rest of the LAN. - It can accept data from the LAN and is capable of forwarding traffic off of the LAN. - It can route to other networks. ### TRUE - [T/F] If a device has no default gateway or a bad default gateway, its traffic will not be able to leave the LAN. **TRUE** ### DHCP in IPv4 - The host will know the default gateway (DGW) either statically or through or can be configured manually. **DHCP in IPv4** ### Router Solicitation (RS) - IPv6 sends the DGW through a or can be configured manually. **Router Solicitation (RS)** ### DGW - A is static route which will be a last resort route in the routing table. **DGW** ### DGW - All device on the LAN will need the of the router if they intend to send traffic remotely. **DGW** - On Windows, route print or netstat -r to display the PC routing table - Three sections displayed by these two commands: - Interface List - all potential interfaces and MAC addressing - IPv4 Routing Table - IPv6 Routing Table ### NOTE - There three types of routes in a router's routing table which are? ### Directly Connected ; Remote; Default Route - **Directly Connected** routes are automatically added by the router, provided the interface is active and has addressing. - These are the routes the router does not have a direct connection and may be learned in two ways which are? - **Manually and Dynamically** - **Manually** - **Dynamically** ### Manually - A remote route learned with a static route. **Manually** ### Dynamically - A remote route learned by using a routing protocol to have the routers share their information with each other. **Dynamically** ### Default Route - this forwards all traffic to a specific direction when there is not a match in the routing table. - Must be configured manually. - Good for small non-redundant networks. - Often used in conjunction with a dynamic routing protocol for configuring a default route. ### Dynamic - Routes Automatically: - Discover remote networks - Maintain up-to-date information - Choose the best path to the destination - Find new best paths when there is a topology change Dynamic routing can also share static default routes with the other routers. ### show ip route - The command shows the following route sources: - L - Directly connected local interface IP address - C- Directly connected network - S - Static route was manually configured by an administrator - O-OSPF - D - EIGRP - This command shows types of routes: - Directly Connected - C and L - Remote Routes - O, D, etc. - Default Routes - S*