SemSim CCNA Cram Sheets

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OSI Reference Model OSI Reference Model The OSI model is a layered model to define the standards for network communications. The control is passed from one layer to the next, starting at the application layer in one station, and proceeding to the bottom layer over the media to the next station. This model contains 7 layers: -Application Layer: Provides network access for applications. Defines processes for user authentication. Devices: Gateways Data Unit: Data Protocols: HTTP, POP3, SMTP, FTP, SNMP, Telnet. -Presentation Layer: Determines the form used to exchange data between networked computers (ASCII or EBCDIC). Performs protocol conversion, encryption and data compression. Ensures that data from one system is compatible with another system. Devices: Gateways and Redirectors Data Unit: Data -Session Layer: Allows applications to communicate with each other over a network by establishing a communication session, synchronizing the involved computers, and terminating the session. Devices: Gateway Data Unit: Data -Transport Layer: Manages and optimizes the transfer of data from the source to the destination, transforms messages into smaller formats, provides error free delivery and error handling functions. Device: Gateway Data Unit: Segment Protocols: NetBEUI, TCP, UDP, SPX, and NWLink -Network Layer: Provides connectivity and path selection between two end systems. Handles addressing, translates logical addresses and names to physical addresses, performs routing and traffic sequencing and congestion control. Devices: Router and Brouter Data Unit: Packet Protocols: IP, IPX, NWLink, and NetBEUI. -Data Link Layer: Broken down into two sublayers. The Logical Link Control (LLC) (LLC ) frames messages for transmission, performs error detection and correction, checks the integrity of received messages, and ensures pr oper sequencing of transmitted data. Defines a sub layer, the Media Access Control (MAC) that appends the MAC address of the next hop to the frame header and controls protocol access to the physical layer. Devices: Switch, Bridge, and Brouter Data Unit: Frame -Physical Layer: Provides electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems. Consists of the cables, connectors and associated hardware to implement a network. Devices: Multiplexer and Repeater, Physical Media Data Unit: Bit

Network Design EthernetEthernet is typically a Local Area Network (LAN) technology covered by the IEEE 802.3 standards providing transmission speeds of 10 megabits to 1000 megabits megabits per second. The standards also differ as far as the type of cabling and the allowed length of the cabling.

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Ethernet Network Elements: The network nodes are of two types: -Data Terminal Equipment (DTE): Define either the source or the destination of data frames. Defines devices such as PCs, workstations, file servers, or print servers. -Data Communication Equipment (DCE): Defines intermediate network devices that receive and forward frames across the network, such as repeaters, and routers, or communications interface units such as network interface cards and modems. -The Ethernet MAC Sublayer: The MAC sublayer communicates with the Logical Link Control sub-layer above it allowing it to access and speak to the upper layer network protocols. -Ethernet Frame Format: Ethernet defines following basic data frame format required for all MAC implementations: Preamble (PRE)- 7 bytes, informs stations about arrival of frames. State-of-frame Delimiter (SOF)- 1 byte, indicates that the next bit is the left-most bit in the left-most byte of the destination address. Destination Address- 6 bytes, defines the identification of the stations that should receive the frame. Source Address- 6 bytes, identifies the sending station. The left-most bit is always 0. Length/Type- 4 bytes, indicates the number of MACclient data bytes. DataData- Defines sequence of n-bytes of data where n is less than or equal to 1500. 1500. If it is too small (< 46, the field must be padded t o equal 46. Frame Check Sequence (FCS ))- 4bytes, contains a 32-bit Cyclic Redundancy Check (CRC) value to check the accuracy of data. -Frame Transmission: Half Duplex Transmission (CSMA/CD access Mode): Defines a method for stations to share a common media over the network. The CSMA/CD access rules are governed by following protocol’s acronym: Carrier sense: Stations continuously check the availability of the carrier. Multiple access: Stations begin transmission any time when the carrier is free. Collision detection: Stations may begin transmission at any time. But they should be able to detect collision, if any, and retransmit the data. Full Duplex Transmission: Allows simultaneous bothways transmission over point-to-point links. Contains no media issues, no collisions, and no retransmissions. -Frame Reception: Reception is same for Full-duplex and Half-duplex transmissions. CSMA/CD Algorithm If two or more electrical signals were sent at the same time, they would overlap and collide, making both signals meaningless. To handle this situation Ethernet defined a specification known as carrier sense multiple access with collision detection (CSMA/CD). CSMA/CD ensures that only one device sends traffic on the network at a time. This is accomplished via the asymmetric sending of information at random times and detection of collions. Fast Ethernet Fast Ethernet, also known as 100BASE-TX, is a networking standard that supports 100 Mbps Data transfer rate. It is based on the Ethernet standard. Fast Ethernet is covered by the IEEE 802.3u

standards. Fast Ethernet is based on CSMA/CD LAN ACCESS methods. Cable Type: Copper with maximum length 100 m Gigabit Ethernet Gigabit Ethernet, also known as 1000BASE-LX or 1000BASE-SX, defines a networking standard that supports 1Gbps Data transfer rate. It retains the CSMA/CD access methods same as original Ethernet. It supports both full-duplex and halfduplex operations. Cable Type: Fiber with maximum length 550m (SX) 5 km (LX) -Physical Layer: Uses the combination of original Ethernet technologies and ANSIX3T11 Fiber channel specifications. Supports following media: -1000Base: SX850 nm laser on multi mode fiber -1000Base: LX1300 nm laser on both single and multi mode fiber -1000Base: CX Short haul copper “twinax” STP cable -MAC Layer: The MAC layer uses CSMA/CD protocol. The length of the cable is limited by the CSMA/CD protocol. -Carrier Extension: Defines a means of supporting 802.3 minimum and maximum frame sizes.

-Packet Bursting: Defines an extension of Carrier Extension. Adds a burst of packets to the Carrier Extension.

Wireless Basics: Wireless works through radio signals to transmit data from one point to another. -An ad-hoc or peer-to-peer wireless network consists of a number of computers each equipped with a wireless networking interface card. -IEEE 802.11: A standard defining all aspects of Radio Frequency Wireless networking. -Makes provisions for data rates of 1,2,5,and 11 Mbps. -Calls for operation in the 2.4 - 2.4835 and the 5 GHz range. -Specifies a carrier sense multiple access with collision avoidance (CSMA/CA) protocol. IEEE Max Speed Frequency Standard 802.11a 54 Mbps 5 GHZ 802.11b 11 Mbps 2.4 GHZ 802.11g 54 Mbps 2.4 GHZ Cabling: The types of cables used in networks are Twisted Pair Cable, Coaxial Cable, Fiber Optic Cable, Wireless LANs, Cable Installation Guides -EIA/TIA-568 STANDARD: The EIA/TIA-568 Standard specifies generic telecommunication cabling system. It provides standard for the following: -Building Entrance: Provide the point at which outside cabling interfaces with the intra-building backbone cabling often called Point of Presence.


-Equipment Room: The specifications are in the EIA/TIA 569 standard. -Backbone Cabling : The available options for backbone cabling with maximum distances are: >100 ohm UTP cable (800 meters maximum) -24 AWG solid conductors -25 pair binder groups >150 ohm STP cable (700 meters maximum) >62.5/125 um multimode optical fiber cable (200 meters maximum) >Single mode optical fiber cable (3000 meters maximum) -Horizontal Cabling: Three media types are recognized as options for horizontal cabling: 1. Four-pair 100 ohm UTP cable 2. Two-pair 150 ohm STP cables 3. Two fiber 62.5/125 um optical fiber cable

Network Devices HubA hub is a hardware device that connects multiple nodes of a network and internetworking equipment. It repeats (broadcasts) signals received on each port to all the other connected ports. A Hub is defined by the following points: -Works on Physical layer of OSI model. -Defines number of UTP ports. -Defines cascading to create desired layout. -Can cause problems with network congestion RepeatersRepeaters connect two or more segments of the network. It receives, amplifies, and retransmits signals in both directions. -Works on physical layer of OSI model. -Two network segments with a single repeater will allow a connection up to 370 meters with 58 devices. -Work on 5-4-3 rule: Defines that not more than 5 segments using not more than 4 repeaters with not more than 3 occupied segments.

BridgeA bridge connects different network types or networks of the same type. It maps the Ethernet addresses of the nodes and allows only the required traffic to pass through the bridge. Bridges are often being replaced by switches due to better performance. -Works on Data-link layer of OSI model. -Can be programmed to reject packets from particular networks. -Cannot read IP addresses, but only the outermost MAC address of the packet. -Can read the Ethernet data, which gives the hardware address of the destination. -Forwards all broadcast messages. To resolve the network segment that the MAC address belongs to, bridges use one of the following: -Transparent Bridging: Builds a table of addresses each time they receive packets. If the address does not appear in the bridging table, the packet is forwarded to all segments other than source segment. Ethernet networks use this type of bridging. -Source route bridging: The source computer provides path information inside the packet. Token

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Ring networks use this bridging. SwitchSwitches are used to connect networks together. Switches allow s egmentation and segregation of data. Switches allow heavily loaded networks to isolate data flow and improve performance. The key difference between hubs and switches is the fact that switches direct traffic by MAC address whereas hubs do not. -Works on the Data link layer of the OSI model. -Cut-through switching runs faster because when a packet arrives, it forwards the packet to the destination address after reading the destination frame instead of waiting for the entire packet to arrive. -Store-and-forward switch examines the entire packet before forwarding. Switches are dedicated devices as they utilize close to 100% of the bandwidth for each given connection. Switches use a hardware switch fabric and software to handle its functions. RoutersRouters are used to segment LANs. Routers also connect remote LANs together using different WAN technologies. The Router forwards data packets along networks. The Routers use headers and forwarding table information to calculate the shortest path for forwarding the packets. -Works on the Network layer of OSI model. -Divides LAN into Subnets. -Uses routing protocols to communicate with each other and calculate the best route between any two hosts. -Divides network using a logical addressing scheme. -Forwards data that is meant only for particular subnets. BrouterA Brouter is a combination of bridge and router providing the functionality of both devices Sometimes referred to as a Layer-3 Switch. A brouter routes specific types of packets, such as TCP/IP packets. Any other in coming packets are simply forwarded to other networks connected to the device, which is the function of a bridge. -Works on Data link and Network layer of OSI model. -Offers routing of a restricted number of protocols, operating by routing where possible and bridging the remaining protocols. -Bridges some packets (based on data link layer information) and routes other packets (based on network layer information). -The bridge/route decision is based on configuration information. GatewaysA Gateway is an internetworking system that joins two dissimilar networks together. A Gateway can be implemented completely in software, completely in hardware, or as a combination of both. -Operates at any level of the OSI model from application protocols to low-level signaling depending on the implementation. -Uses a router that use headers and forwarding tables to determine destination address, and a switch that to find actual path for the packet in and out of the gateway. -Compatible with AUI, BNC, IEEE 1394, GBIC, MIC, RJ-45, SC, serial, ST, ISDN BR S/T, ISDN BRI U, and USB ports.

-Provides functionalities for integrated firewalls, and Virtual Private Networks. -Allows IPX/SPX clients to use a TCP/IP uplink to an internet connection. Converts TCP/IP to IPX/SPX.

Virtual LAN (VLAN) Virtual Local Area Network is a logical group of user stations, servers, and network devices that appear to be on the same LAN, irrespective of their physical location. In VLAN, switches need to use trunking on network segments between the switches. In VLAN trunking, sending switches add another header to the frame before sending it over the trunk. This extra header includes a VLAN identifier field so that the sending switch can list the VLAN ID. The receiving switch also knows in what VLAN each frame belongs. This process is known as VLAN tagging. The reasons for separating hosts into different VLANS are: • To create flexible network designs • To fragment the network devices into smaller LANS • To increase the security • To reduce the workload for the Spanning Tree Protocol • To segregate network traffic by an IP phone from network traffic sent by PCs A created VLAN is unused until it is assigned to a switch port. Inter Switch Link (ISL): It is defined by Cisco. It supports normal range (1-1005) and extended range (1006 -4094) VLANS and allows multiple spanning trees. It can be used only between Cisco switches which supports ISL .ISL encapsulates each data in a header and trailer. The header has several fields including a VLAN field. ISL uses MAC address of the sending and receiving switch as the source and destination address in the header frame. IEEE 802.1Q: It is defined by IEEE. It has all the features of ISL. It is most popular trunking protocol as some of the new Cisco switches is not supporting ISL. ISL encapsulates each data in a header and trailer. It inserts another 4-byte header instead of completely encapsulating the original frame. It uses a native VLAN. It uses MAC address of the sending and receiving switch as the source and destination address in the header frame. VLAN Trunking Protocol (VTP): It helps the switches to exchange VLAN configuration information. It defines a layer 2 messaging protocol. When a VLAN os modified or added or deleted then VTP helps all the switches to synchronize their VLAN configuration information Command Description vlan vlan_id Is a global configuration command that creates the VLAN and also puts the CLI into VLAN configuration mode vtp domain Is a global configuration domain_name command which defines the VTP domain name vtp password Is a global configuration password command which defines the vtp password Shutdown vlan Is a global configuration vlan_id command which disables a VLAN Vtp {server| Is a global configuration client| command that defines the transparent} VTP mode




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Command vtp pruning

shutdown

show vlan vlan_id show vtp status vtp password password

Description Is a global configuration command that informs the VTP server to inform all switches to use VTP pruning Is a VLAN subcommand which prevents a switch from forwarding traffic in the VLAN Displays information about the VLAN Displays configuration and status information about VTP Is a global configuration command which defines the vtp password Displays administrative settings abd operational state information for the interface Displays all operational trunks information

Show interfaces interface_id switchport Show interfaces interface_id trunk VLSM: Variable-Length Subnet Masks (VLSM) allows an administrator to use more than one subnet mask within the same network address space. It also helps to reduce the wastage of IP address in each subnet. The following example shows the commands needed to configure a router, named ROUTER1, with a 28-bit mask on its Ethernet port and a 26-bit mask on its serial port: ROUTER1(config)#interface e0 ROUTER1 (config-if)#ip address 201.21.24.30 255.255.255.240 ROUTER1 (config-if)#interface s0 ROUTER1 (config-if)#ip address 207.21.20.193 255.255.255.192

Route summarization: It helps to reduce the size of the routing tables but it maintains all the destination routes in the network. With route summarization you can Improve the routing performance • Save memory • Improve convergence time • There are two ways of route summarization, manual summarization and autosummarization. Manual summarization occurs when an administrator configures it manually using one or more command. Autosummarization occurs automatically without any specific configuration command. The following routing protocols supports autosummarization: RIP-1 • RIP-2 • EIGRP • OSPF do not supports autosummarization. Difference between VLAN and subnetting: VLAN is a layer 2 concept and a subnet is Layer 3 concept. The devices in a VLAN need to be in the same subnet.

Bridging/Switching Switch Concepts Switching refers to the process of connecting LAN segments using a table of MAC addresses to resolve the segment to transmit datagrams. Bridges are no longer manufactured and can be characterized as LAN switches that used software instead of hardware LAN Switching -A Switch is similar to a bridge with more than two ports. -Switching is done by examining the contents of a frame to resolve the MAC address to the destination port. -A Switch determines the interface for the destination address and establishes a hardware connection to it

interface and forwards the frame to proceed to its destination. -Switches allow high-speed data exchange, low latency & high frame forwarding rates, full-duplex, media rate adaptation (10/100 Mbps). The figure shows an example of switching:

The two types of switching are: Port Switching: port assigned to a physical network by software. Frame Switching : increases bandwidth on the network. Allows multiple transactions in parallel. Common commands for the Catalyst series Switches(Top-level commands): clear Commands: clear alias: Clears aliases of commands. clear arp: Clears ARP table entries. clear cam: Clears CAM table entries. clear config: Clears the configuration and resets system. clear counters: Clears MAC and port counters. clear filter: Clears custom filtering configuration. configure: Downloads a configuration batch file from a TFTP server and then execute the commands in the file. copy: copies data movement processor (DMP) or network management processor (NMP) image files between the network host and Flash memory using the TFTP protocol. disable: Turns off enable mode. disconnect: Temporarily disconnects the FDDI port from the FDDI ring temporarily without disconnecting the FDDI cables. download: Downloads code to the network management processor (the default) or the data movement processor. enable: Turns on privileged mode. Certain commands are available, and certain displays have extra information in privileged mode. help: Displays the help information in normal mode. ping: Send Internet Control Message Protocol (ICMP) echo packets to another node on the network. quit: Quits the current admin. reset: Resets the system. set Commands: set alias: Sets an alias for a command. set arp: Sets an ARP table entry. set bridge help: Shows the set bridge help screen. set bridge ipx: Sets the default mode for translating IPX packets. set bridge vlan: Groups ports into bridge VLANs. set fddi cam: Sets FDDI CAM mode set filter: Sets custom filtering set interface: Sets the network interface configuration set ip alias: Sets an alias for an IP address set ip forwarding: Sets the router IP forwarding enable/disable set ip fragmentation: Sets the bridge IP fragmentation enable/disable set ip vlan: Sets the IP VLAN set length: Sets terminal display line, 0 to disable set mac: Sets the MAC address set password: Sets the console password

set port disable: Disables a port set port enable: Enables a port set port name: Sets the port name set prompt: Sets a prompt you designate set snmp community: Sets a SNMP string set snmp help: Shows the SNMP help screen set snmp rmon: Sets an SNMP RMON enable/disable set snmp trap: Sets a SNMP trap receiver address set span: Sets switch port analyzer set spantree disable: Disables a spanning tree set spantree enable: Enables a spanning tree set trunk: Configures ports to perform as links show commands: show arp: Displays the ARP table show bridge: Displays bridge information show cdp: Displays CDP2 configuration slip: Attaches or detach a SLIP interface. test Command: test online: Runs a diagnostic test on the system test snmp: Tests the SNMP upload: Uploads the Flash memory image file from the catalyst to a network host to create a backup file. wait: Pauses the console output for the number of seconds indicated. write: Writes the Catalyst 1200 series switch configuration either to an existing file in a network host tftpboot directory or to the terminal screen display Spanning Tree Protocol: Spanning-Tree Protocol (STP) defined in the IEEE 802.1D is a link management protocol that provides path redundancy while preventing undesirable loops. STP is a technology that: -Uses the Spanning Tree Algorithm (STA) to ensure that only one path exists between any two stations. -Allows bridges to communicate with each other to discover physical loops in the network. -Specifies an algorithm that bridges use to create a loop-free logical topology. -Creates a tree structure of loop-free leaves and branches that spans the entire Layer 2 network. -5 states of switches in STP: Listening, Learning, Forwarding, Blocking, Disabled.

-Root Switch Variables Affecting STP: -Maximum Age Timer: Measures and discards the received protocol information for a port when its age limit exceeds the value to the maximum age parameter. -Forward Delay Timer: Examines the time spent by a port in the learning and listening states. -Bridge Protocol Data Units(BPDU):The active topology of a switched network is determined by the following: -The unique switch identifier, port identifier (MAC address) associated with each switch. -The path cost to the root associated with each switch port. Each configuration BPDU contains the following information: -The unique identifier of the switch that the transmitting switch takes as root switch. -The cost of the path to the root from the transmitting port. -The identifier of the transmitting port.





EtherChannel EtherChannel allow you to group multiple Ethernet ports into a single logical transmission path between the switch and a router, host, or another switch. -Port Aggregation Protocol: Exchanges packets between channel-capable ports. -Channel Modes: -on: Forces the port to channel without negotiation. -of: Prevents the port from channeling. -auto: Places a port into a passive negotiating state. -desirable: Places a port into an active negotiating state. -silent: When you are connecting to a "silent partner" -non silent: When you are connecting to a device that will transmit BPDUs or other traffic Portfast: The Portfast setting allows you to immediately convert a port to the forwarding state from a blocking state, bypassing the listening and learning states. Portfast is used on ports connected to a single workstation or server to allow those devices to immediately connect to the network, instead of waiting for the spanning tree to converge. -Prevents the ports connected to a single workstation or server from receiving BPDUs. -Minimizes the time taken by ports to wait for the spanning tree protocol to converge. The commands to set port fast from privileged mode on a Cisco 2950 switch are: config t interface fastethernet0/1 spanning-tree portfast end IEEE 802.1w: Rapid Spanning Tree Protocol This defines a supplementary to ISO/IEC 158023:1998 (IEEE Std 802.1D-1998) that defines the changes required for the operation of a MAC Bridge in order to provide rapid reconfiguration capability. - Defines required improvements in Spanning Tree performance through manipulation of the existing default parameter values. -Changed semantics for RFC 1493 Bridge MIB: 1. Bridge Id / Priority, Port Id / Priority, 2. Time since t opology change, Topology Changes 3. Hold Time not applicable to RSTP -Included in RSTP-MIB: 1. Force Version 2. Protocol Migration check 3. Point-to-point link -Not included in new MIBs: 1. Transmission Limit txHoldCount constant, not configurable 2. MAC Enabled, MAC Operational uses ifAdminStatus and ifOperStatus

LAN Protocols TCP/IP Protocol Suite The TCP/IP suite is the set of communications protocols that implement the protocol stack on which the Internet runs. It is a combination of Transmission Control Protocol (TCP) and the Internet Protocol (IP). TCP: Defines a connection-oriented transport protocol that transmits data with error correction and guaranteed delivery to a stream of bytes. It uses sequence numbers and acknowledgment m essages to provide a sending node with delivery information about packets transmitted to a destination node. If the data is lost in transit from source to destination, TCP retransmits the data until either a timeout condition is reached or until successful delivery has been achieved. -Can also recognize duplicate messages and will discard them appropriately.

-Provides flow control mechanisms to slow data transfer. TCP can also communicate delivery information to the upper-layer protocols and applications it supports. IP: Defines a primary layer 3 protocol in the Internet suite. IP is a connectionless protocol used for besteffort delivery of information over the network. IP provides error reporting and fragmentation and reassembly of information units called datagrams for transmission over networks with different maximum data unit sizes along with network routing information. -Defines a unique 32-bit number for the node on the network recognizable by all devices on the network for forwarding information between stations and the Internet. -An IP address is divided into three parts. The first part designates the network address, the second part designates the subnet address, and the third part designates the host address. IP Configuration: Every IP address consists of 2 portions, the Network ID (netid) and the Host ID (hostid). Each host on the same network must have the same netid. Each of these hosts contains a hostid that is unique with combination of the netid. IP addresses are divided into 4 octets with each having a maximum value of 255. We analyze IP addresses in decimal notation such as 124.35.62.183, but it is actually in the form of binary data. IP addresses are divided into following classes: Total Total Class Range number of number of Network Host 7

A

1-126

B

128-191

2 – 2 =126 2

24

2 -2 = 16,777,214

14

=16384

21

16

=2097152 2 -2=254

2 -2=65534 8

C

192-223

2

D

224-239 Multicasting

NA

NA

E

NA 240-255 Experimental

NA

Class A defines addresses for networks with a large number of hosts. The first octet defines the netid and the 3 remaining octets define the hostid. Class B addresses are used in medium to large networks with the first 2 octets defining the netid and the remaining 2 are the hostid. A class C is for relatively smaller networks with the first 3 octets making up the netid and the last octet comprising the hostid. Subnetting: Subnetting is the process of subdivision of a CIDR block into smaller CIDR blocks. A subnet mask is a 32-bit number that determines how an IP address is split into network and host portions, on a bitwise basis. A subnet mask blocks out a portion of an IP address and is used to differentiate between the hostid and netid. The default (classified)subnet masks are as follows: Default # of # of Hosts Per Subnet Subnets Subnet 255.0.0.0

126

16,777,214

255.255.0.0

16,384

65,534

255.255.255.0 2,097,152 254 To determine number of hosts or subnets, use the formula 2^n – 2. n is the number of bits being used for either the host portion or network portion of the address. In these cases, the part of the IP address blocked out by 255 is the netid.

The decimal numbers in a subnet mask are as follows: Subnet Masks’s Binary Binary 1s / Decimal Octet Equivalent Binary 0s 0

00000000

0/8

128

10000000

1/7

192

11000000

2/6

224

11100000

3/5

240

11110000

4/4

248

11111000

5/3

252

11111100

6/2

254

11111110

7/1

255 11111111 8/0 TCP/IP Ports: Ports are what an application uses while communicating between a client and the server. Following are a sample of some common TCP/IP ports: FTP - 21 TELNET - 23 SMTP - 25 TFTP - 69 HTTP - 80 POP3 - 110 NetBIOS - 139 SNMP - 161 ICMP: Internet Control Message Protocol (ICMP) is an extension to the Internet Protocol (IP) defined by RFC 792. Some of ICMP's functions are: -Announce network errors: Announces network errors if a host or entire portion of the network face an error. -Announce network congestion: Generates ICMP Source Quench messages. The message causes the rate of packet transmission to be slowed. -Assist Troubleshooting: Supports an Echo function (ping) to send a packet on a round--trip between two hosts using. -Announce Timeouts: Makes announcement if a router discards a packet. CIDR: CIDR is an addressing scheme for the Internet which allows for more efficient allocation of IP addresses than the old Class A, B, and C address scheme. You need CIDR if you are: 1. Running out of IP addresses 2. Running out of capacity in the global routing tables >A CIDR network address looks like: 192.30.250.00/18 >In CIDR, each IP address contains a network prefix to identify an individual gateway. >The length of the network prefix is given as part of the IP address. >A destination IP address, which describes various possible destinations, has a shorter prefix and is said to be less specific. >A longer prefix describes a destination gateway more efficiently. >Routers use the most specific or longest network prefix in the routing table while forwarding packets. NAT (Supernetting): Network Address Translation (NAT) defines an Internet standard that allows a LAN to use one set of IP addresses for internal traffic and a second set of addresses for external traffic. NAT box is located at the place where the LAN meets the Internet. NAT makes all necessary IP address translations. NAT serves the following purposes: >Hides internal IP addresses. 10.0.0.0, 172.16.0.0


>Allows more internal IP addresses usages that avoid possibility of conflict with IP addresses used by other companies and organizations. >Allows combining multiple ISDN connections into a single Internet connection. NAT Address Terms Terms Meaning Inside Local

Name of inside source host address before translation. A more descriptive term is inside private.

Outside Local

Name of destination host before translation. A more descriptive term is outside private.

Inside Global

Name of the inside host after translation. A more descriptive term is inside public..

Name of outside destination host Outside Global after translation. A more descriptive term is outside public. Static NAT: In static NAT a private IP address is mapped to a public IP address, where the public address is always the same IP address. Dynamic NAT: In Dynamic NAT a private IP address is mapped to a public IP address drawing from a pool of registered public IP addresses. Command Description ip nat {inside | Is an interface subcommand outside} which enables NAT and identify whether the interface is in the inside or outside of the network ip nat inside Is a global command which source {list enables NAT globally, {access-listreferencing the ACL that number | accessdefines which source list-name}} addresses to NAT and (interface type interface or pool from which number | pool to find global addresses pool-name} [overload] ip nat pool name Is a global command which start-ip end-ip defines a pool of NAT {netmask address netmask | prefixlength prefixlength} show ip nat Is a EXE command which statistics lists counters for packets, NAT table entries and configuration information show ip nat Is a EXE command which translations displays the NAT table [verbose] Debug ip nat Is a EXE command which issues a log message describing each data packet whose IP address is translated with NAT IP version 4: IP Version 4 (IPv4) is version 4 of the Internet Protocol. It is described in IETF RFC 791. IPv4 provides the basic datagram delivery capabilities for TCP/IP. IPv4 uses 32-bit addresses, limiting it to 4,294,967,296 unique addresses. -Address Notation: IPv4 addresses are written in dot-decimal notation, like: 207.142.131.235. Other formats are: >Dotted Decimal (normal) 207.142.131.235 >Dotted Hexadecimal 0xCF.0x8E.0x83.0xEB >Dotted Octal 0317.0216.0203.0353 >Decimal 3482223595 >Hexadecimal 0xCF8E83EB


IP version 6: IP Version 6 (IPv6) is version 6 of IP, initially known as IP Next Generation (IPng). -IPv6 is supposed to replace the IPv4 standard. -IPv6 supports up to about 3.4 × 1038 (3.4 duodecillion) addresses. Equivalent of 4.3 × 1020 (4.3 quintillion) addresses per inch² (6.7 × 1017 (6.7 quadrillion) addresses/mm²) of the Earth's surface. -Address Notation: IPv6 addresses are 128 bits long but are written in eight groups of 4 hexadecimal digits. > An example: 2001:0db8:85a3:08d3:1319:8a2e:0370:7344 Categories of IPV6 Unicast:Sending of data packets to a single destination. Multicast: Delivery of data packets simultaneously to a group of destinations Anycast: Forwarding data packets to the nearest server Command Description ipv6 unicastIs a global command routing which enables IPv6 routing on the router ipv6 router rip tag Is a global command which enables RIPng ipv6 rip name Is a interface command enable which enables RIPng on the interface ipv6 address {ipv6 Is a global command to address/prefix create a static host length| prefix name name definition sub bits/prefix length} eui-64 show ipv6 route Is a EXEC command which displays ipv6 routes show ipv6 route ip Is a EXEC command address which displays the routes this router would match for packets sent to the given ip address show ipv6 Is a EXEC command interface brief which displays interface status and IPv6 addresses for each interface show ipv6 Is a EXEC command interface [type which displays IPv6 number] settings on an interface, including link local and other unicast Ip addresses show ipv6 route Is a EXEC command [prefix/prefixwhich displays the route length] for the given prefix IPX: Internetwork Packet Exchange (IPX) defines a networking protocol used by the Novell NetWare operating system. Similar to UDP/IP, IPX is a datagram protocol for connectionless communications. The IPX Network address contains two parts: the Network ID and the Host ID. The first 8 hex digits represent the network ID, and the remaining hex digits represent the host ID, -Uses services of a dynamic distance vector routing protocol called Routing Information Protocol (RIP). SPX: Sequenced Packet Exchange (SPX) protocol operates at the transport layer providing connection oriented communication on top of IPX.

-Creates virtual circuits between hosts, and that each host is given a connection ID in the SPX header for identifying the connection. -Service Advertisement Protocol (SAP) is used by NetWare servers to advertise network services via broadcast at an interval of every 60 minutes by default.

Wide Area Network Wide Area Network (WAN) defines a computer network that spans over large geographical area. -Consists of two or more LANs. -Connected through public networks, such as PSTN. -Can also be joined using leased lines or satellites. The largest WAN is Internet. PPP configuration & concepts: Point-to-Point Protocol (PPP) defines a method of connecting a computer to the Internet. -Provides a single, pre-established two-way transmission path from a local location through a carrier network, such as PSTN to a remote network. -Works as an encapsulation protocol for transmitting IP traffic over point-to-point communication paths. -Defines standards for assignment and management of IP addresses, network protocol multiplexing, link designing, link quality testing, and error recognition. -Provides an extensible Link Control Protocol (LCP) and Network Control Protocols (NCPs) to maintain optional configuration parameters and facilities. -Supports other protocols, such as Novell's Internetwork Packet Exchange (IPX) and DECnet.

Physical Layer Requirements: PPP requires existence of a duplex circuit, dedicated or switched, which can operate in asynchronous or synchronous bit-serial mode, and transparent to PPP link layer frames. It operates across any DTE/DCE interface, such as EIA/TIA-232-C, EIA/TIA-422, EIA/TIA-423, and ITU-T V.35. PPP Link Layer: PPP follows the standards, terminology, and frame structure of ISO HDLC procedures -PPP control procedures use the definitions and control field encodings standardized of ISO 43351979 and ISO 4335-1979/Addendum 1-1979. The PPP frame format : 1

1

1

2

Flag

Address

Control

Protocol

Variable

2 or 4

Data

FCS

-Flag: 1 byte, Defines the start or end of a frame. -Address: 1byte, Defines the binary sequence 11111111 for standard broadcast address. It does not assign address to individual station. -Control: 1byte, Defines the binary sequence 00000011 that triggers the transmission of user data in a no sequenced fr ame. -Protocol: 2 bytes, Identifies the protocol summarized in the information field. -Data: Zero or more bytes of information enclosed in the datagram for the protocol defined in the protocol field. -Frame check sequence (FCS)—16 bits (2 bytes). Components of PPP: HDLC(High-level Data Link Control): Defines a data link layer protocol. The Cisco implementation of HDLC includes a Protocol type field that identifies the type of packet inside the frame. Cisco uses the same values in its 2-byte HDLC Protocol Type field.




LCP(Link Control Protocol): Creates, tests and configures the data link connection. NCPs(Network Control Protocols: Configures various protocols, allowing them to operate on the same line simultaneously. Frame Relay: Frame Relay is a WAN protocol that operates at the physical layer and data link layer of the OSI model. Frame Relay operates on packetswitched technology. Frame Relay switch transfer data in Committed Information Rate (CIR), bits per second. If a Cisco router and a non-Cisco router are connected with a serial connection, one must configure PPP or any encapsulation method, such as Frame Relay. Frame Relay Assembler/Disassembler (FRAD): A FRAD is networking equipment that assembles and disassembles data frames. Example: DCB SR and SRX series of multiplexers assemble asynchronous data into frame relay frames. FRAD encapsulates Ethernet MAC layer protocol, TCP/IP protocol, IPX protocol, IBM SDLC protocol, bisync protocol, and Poll/Select polling protocols. Permanent Virtual Circuits (PVC): PVC defines a software-based logical connection in the network. You can customize logical connections and desired bandwidth between end points. Data Link Connection Identifier (DLCI): Defines a number that identifies a virtual circuit. Frame Relay has following features: -Speed ranges between 56 Kbps to 45. Mbps. -Uses Data Link Connection Identifiers (DLCI) to identify the virtual circuit -Uses Local Management Interfaces (LMI) to provide information on the DLCI values. Cisco routers support Cisco (Default), ANSI and Q933a formats. Inverse ARP (IARP) is used to map a known DLCI to an IP address. Remote Access concepts: Remote Access defines a method logoff logging onto a network from a remote location. This requires a computer, a modem and remote-access software to allow the computer to dial into the network over a telephone line and connect remotely. -Remote access defines that the remote computer works as a full-fledged host on the network. -The access software at the remote location dials in directly to the network server. -Remote Access Server: A remote access server is the combination of computer and software that handles users seeking access to network remotely. The remote access server work in combination with a firewall to provide security and a router that can forward the remote access request to another part of the network. ISDN: The Integrated Services Digital Network defines an international communications standard for transmission of voice, video, and data over digital telephone lines or normal telephone wires. ISDN supports data transfer rates of 64 Kbps. ISDN provides two levels of services: -Basic Rate Interface (BRI ) -- Contains two 64-Kbps B-channels and one 16kbps D-channel for transmitting control information. Primary Rate Interface (PRI) -- Contains 23 Bchannels and one D-channel or 30 B-channels and one D-channel Following are the protocols used in various layers: 2B1Q(Two Binary, One Quaternary Line Encoding): Used in the physical layer. Link Access Protocol: Used in data link layer. SPIDs (Service Profile Identifier): Used in the network layer.


connection-oriented switching technology that arranges digital data into 53-byte cell units.

ATM Reference Model: Physical layer: Manages the medium-dependent transmission. ATM layer: Allows simultaneous sharing of virtual circuits over a physical link. adaptation layer (AAL): Isolates higher-layer protocols from the details of the ATM processes . Command Description show ip nat Displays the NAT/PAT translations translation table entries show dhcp Displays information learned server from a DHCP server clear ip nat Clear the NAT table by translation * removing the dynamic entries Show Displays the status of cable controllers connectivity and also states serial number whether it is DTE or DCE cable

Network Management CDP: Cisco Discovery Protocol (CDP) obtains protocol addresses of neighboring devices and discovers the platform of those devices. CDP also informs about the interfaces your router uses. -CDP is media and protocol independent and runs on all Cisco based equipments, such as routers, bridges, access servers, and switches. -Configuring CDP: Use following commands to configure CDP: no cdp run: Disables CDP. no cdp enable: Disables CDP on an interface. cdp timer seconds: Defines interval between CDP advertisements cdp holdtime seconds : Defines hold time before information should be discarded. clear cdp counters: Resets traffic counters. clear cdp table: Purges the table. Managing configuration files: -Configuring a Static IP Route: Commands to configure a Static IP route: ip route prefix1 mask2 [ethernet0 | atm0][.subinterface]: Configures a static IP route on the Ethernet interface or ATM subinterface of the processor. end : go back to privileged EXEC mode. copy system:running-config nvram:startup-config: Saves the configuration to NVRAM. - Maintaining Configuration Files: The following are the tasks performed to maintain configuration files: - Copy configuration files from the router/switch to a network server. -Copy configuration files from the network server to the router/switch. -Maintain configuration files that are bigger than NVRAM. -Copy configuration files between different locations. -Again execute the configuration commands in startup configuration. - Maintaining System Images: Following are the tasks performed to maintain system image files: -Copy images from flash memory to a network server. -Copy images from a network server to Flash memory.

-Copy images within local Flash memory devices. IP Access control list security: Access Control Lists (ACLs) defines a security feature. ACLs increases security on Cisco routers by protecting the router from unwanted and potentially harmful traffic. -Allows us to apply some level of security on the network by examining and filtering traffic when it enters or exits an interface. -Every router may contain several access lists of the same or different types. -Access Lists come in three types: Standard that filers based on IP address, Extended that can filter based on application or port and named which is the same as standard or extended but use plain English for labeling. -Access Lists should be applied nearest the interface where the traffic is to be filtered. -Access Lists can be used on both LAN and WAN interfaces - Access Lists are bi-directional and can be used on any router after the 11.0 IOS release. IP Access Lists: 1-99: IP standard lists (use source IP) 100-199: IP extended (Use src, dest IP, protocol and port no. ) Command Description access-list Is a global command used access-lst-number for standard numbered {deny|permit} access lists. It uses a source [sourcenumber between 1 & 99 or wildcard][log] 1300 & 1999, inclusive. access-list Is a global command used access-lst-number for extended numbered {deny|permit} access lists. It uses a protocol source number between 100 and [source-wildcard 199 or 2000 and 2699, destination inclusive. destinationwildcard][log] access-list Is a global command used access-lst-number with specific TCP-IP {deny|permit} tcp source sourcewildcard [operator [port]] destination destinationwildcard [operator [port]] [log]

Routing IP Static Routing: In static routing, the route is explicitly configured and fed into the routing table. Static routes are given priority over the routes defined by dynamic routing protocols. -Uses a pre-configured route developed by network administrator. -Provides a means for controlling security and reducing traffic. -Has lowest administrative distance (cost/metric) Dynamic Routing: In dynamic routing, the route is automatically adjusted to the changes in network topology and traffic. -Also known as adaptive routing. -Uses a route that a network routing protocol dynamically defines automatically for topology or traffic changes. -More successful than static routing because: >Auto maintenance of a routing table. >Distributes knowledge as routing updates to other routers for end to end connectivity. >A disadvantage is the increased traffic on the


ATM: The Asynchronous Transfer Mode (ATM) is a distance-vector protocol based on a 1970s Xerox design. Features of RIP are: Width restriction: A RIP network contains less than 15 hops. If number of hop is elevated on slow or less reliable links, this can become a problem. Subnet support : Was introduced previous to subnetting and doesn’t directly support it. It can be used in subnetted environments but with restrictions. Bandwidth consumptive: After every 30 seconds, the RIP protocol transmits the lists of networks and subnets. Depending on the size of the network, bandwidth usage can become unaffordable on slow links. Difficult diagnosis: Like any distance-vector protocol, RIP sometimes is difficult to debug because the routing algorithm is distributed over various routers. Weak security: Version 1 Contains no security features, but Version 2 RIP implementations have been introduced that will only recognize updates from configured hosts. Interior Gateway Routing Protocol (IGRP): IGRP is a network protocol that is designed to work on autonomous systems and developed by Cisco Systems. IGRP is a distance-vector routing protocol. - Each router sends information of its routing table in a routing message update at regular intervals to each of its neighboring routers. - A router calculates the best path between the source and destination. As each path can contain several links, the system needs a method to compare the links to find the best path. A system such as RIP uses sole criteria i.e. the number of hops to calculate the best path. This gives IGRP a unique advantage over RIP as a protocol that can develop and identify better routes. - IGRP uses five criteria to resolve the best path i.e. the speed of the link, delay, packet size, loading and reliability. Network administrators may set the weighting factors for each of these metrics. The features of IGRP are: Stability: >Holddowns: Prevents regular update messages from inappropriately reinstating a route that might have faced some errors. >Split horizons: Doesn’t send information about a route back in the direction from which it has arrived. Timers: Specifies the frequency for sending routing update Open Shortest Path First (OSPF): OSPF is a routing protocol developed for IP networks that works on basis of the shortest path first or link-state algorithm. -Operates on the basis of link-state algorithms to transmit routing information to all nodes in the network -Calculates the shortest path for each node based on topography. -Each router sends that portion of the routing table describing the status of its own links, and it also sends the complete routing structure. -When changes are detected, only the changed portion of the routing table is sent, rather than the entire routing table. Enabling OSPF: To configure OSPF on the router: -Enable an OSPF process using the router ospf command. -Assign areas to the interfaces using the network command. Administrative Distance: A number (0 255)indicating route trust level of route/routing protocol (255 = lowest trust , 0 = highest trust) Enhanced IGRP (EIGRP): EIGRP is a network protocol that allows routers to exchange information more efficiently than with earlier network protocols.


-Doesn’t make periodic updates. Sends partial updates only when the metric for a route changes. -Supports AppleTalk, IP, and Novell NetWare. -Underlying Processes and Technologies: >Neighbor discovery/recovery mechanism: enables routers to dynamically learn about other routers on the network. >Reliable Transport Protocol (RTP): responsible for guaranteed, ordered delivery of Enhanced IGRP packets to all neighbors. >DUAL(Diffusing-Update Algorithm) finite-state machine: incorporates the decision process for all route calculations by tracking all routes advertised by all neighbors. Comparision between OSPF and EIGRP: Both the protocols: Unite quickly • Has built-in loop prevention • Sends routing updates when it is changed • or new Supports VLSM and manual • summarization Uses IP multicast on LANs to send routing • information Features of EIGRP but not OSPF: Manual Summarization at any router • Supports flexible network design without • areas Supports equal-metric and unequal-metric • load balancing Can advertise IP, IPX, and AppleTalk • routes Features of OSPF but not EIGRP: Uses the concept of a designated router on • LAN Public standard • Command Description show ip eigrp Displays the EIGRP-enabled interfaces interfaces excluding the passive interfaces show ip ospf Displays the OSPF-enabled interface brief interfaces including the passive interfaces Show ip Displays the contents of the protocols network configuration commands for each routing protocol. Classful Routing protocols: Routing protocols do not advertise mask. They do not support VLSM and route summarization. Example: RIP-1 and IGRP. Classless Routing protocols: Routing protocols do advertise mask. They also support VLSM and route summarization. Example: RIP-2, OSPF and EIGRP Classless routing: The packet is forwarded through default route only when it’s destination matches a router’s default route and do not match with any other route. Classful routing: The packet is forwarded through default route only when it’s destination matches a router’s default route and do not match with any other route and of this router do not know any other routes in the classful network in which the destination IP address resides. Command Description show ip route Displays the router’s entire routing table show ip route Displays detailed information ip-address about the route that a router matches for the given IP address ping {hostTests IP routes by sending an name| ipICMP packet to the given ipaddress} address

network due to the routing updates. Routing Information Protocol (RIP): RIP is a Command Description traceroute Used to determine the route {host-name| taken by packets across an IP ip-address} network

Cisco IOS Cisco routers use the Internetworking Operating System (IOS) that stores the configuration information in Non-Volatile RAM (NVRAM). The IOS itself is stored in flash. The IOS can be accessed through Telnet, console connection or dial-up connection. You can also configure the router in the form of a web server and then access a web-based configuration panel using http. You need to inform the router to boot from the specified configuration source (file/network).Basic configuration for CISCO devices: You can perform booting using Flash memory, TFTP and ROM. -Load new image of IOS on a TFTP server first; and copy the image from the TFTP server to the flash memory in the form of a backup mechanism. -You can use copy command such as "copy tftp flash" to copy the IOS image from TFTP. Specify the following to boot from flash: > boot system flash {filename} > boot system tftp {filename} {tftp server IP address} > boot system rom To login: >The User EXEC is the first mode. It provides us a prompt of "Router>". To exit this mode makes you log out completely, you can use logout command. >If you want to proceed to the Privileged EXEC, you need to enable (type ENABLE ) EXEC command. After enabling it, the prompt will be changed to ‘Router#". >To go back to user EXEC mode, use the disable command. Some of the editing commands are: Crtl-P: Recalls commands in the history buffer starting with the most recent command. Crtl-N: Returns to more recent commands in the history buffer. Crtl-B: Moves the cursor back one character Crtl-F: Moves the cursor forward one character Crtl-A: Moves the cursor to the beginning of the command line Crtl-E: Moves the cursor to the end of the command Esc B: Moves the cursor back one word Esc F: Moves the cursor forward one word Crtl-R: Redisplays the current command line Router components: ROM: Stores the router's bootstrap startup program, operating system software, and poweron diagnostic tests programs. Flash Memory: Contains operating system image(s). Flash memory is erasable, reprogrammable ROM. -Flash content is preserved when you switch off or restart the router. RAM: Store operational information such as routing tables, router's running configuration file. Also provides caching and packet buffering capabilities. Contents are retainable when you switch off or restart the router. Nonvolatile RAM (NVRAM): Store the router's startup configuration file. The contents of the startup configuration file are preserved even if you


- Router running EIGRP stores all its neighbors' routing tables to quickly adapt to alternate routes LAN Concepts for CISCO IOS: -Broadband: Cisco delivers Broadband Aggregation capabilities on a comprehensive set of routers. -High Availability: Defines a technology, delivered in Cisco IOS Software that enables network-wide resilience to increase IP network availability. -IP Routing: Defines Cisco IOS Software that supplies IP intelligence to the Cisco product-based networks. -IP Services: Defines Cisco IOS Software that contains number of critical network services to solve the most difficult network related problems. -IPv6: Cisco IOS uses IPv6 that is a new IP protocol intended to replace IPv4. -MPLS: Cisco IOS MPLS allows various enterprises service providers to construct next-generation intelligent networks -IP Multicast: Defines is a bandwidth-conserving technology used by Cisco IOS that minimizes traffic and simultaneously transmitting a single stream of information to various recipients.

Dynamic Host Configuration Protocol DHCP: DHCP stands for 'Dynamic Host Configuration Protocol '. It is an IP standard used to automatically allocate reusable network addresses and configuration options to hosts on a TCP/IP network. It is based on the Bootstrap Protocol (BOOTP). DHCP is built on a client/server model, where the DHCP server allocates IP addresses and other parameters such as the default gateway, subnet mask, DNS Server, NIS Server and NTP Server to the dynamically configured host computers. • Benefits of DHCP Server: Implementing DHCP can provide the following benefits: Reliable network configuration: Minimizes configuration errors caused by manual IP address configuration. • Reduced cost: Using automatic IP address assignment at each remote site substantially reduces Internet access costs. Static IP addresses are more costly compared to automatically allocated IP addresses. Since DHCP is easy to configure, it minimizes operational costs associated with device configuration tasks. • Reduced administration: Since DHCP server automatically dispenses IP addresses and other configuration information to the client, the process of connecting a new client to the network is easy and simpler. DHCP is very flexible and allows the network administrator to centrally define global and subnet-specific TCP/IP configurations to serve thousands of clients. DHCP Server: DHCP Server manages a pool of IP addresses and information about client configuration parameters such as the subnet mask, default gateway, DNS servers and other servers. It ensures that all IP addresses that are distributed to the clients are unique. It assigns IP addresses to clients that are connecting to the network for the first time. DHCP Client: DHCP Client receives network address dynamically from the DHCP server to access the network resources. A DHCP client can receive offers from multiple DHCP servers at a time but it can accept only one of the offers. It generally accepts the first offer it receives. DHCP Relay Agent: DHCP Relay Agent forwards the packets between the DHCP client and server. IP address allocation: DHCP supports three mechanisms for IP address allocation depending on implementation:


Dynamic allocation: In dynamic allocation, DHCP server assigns a network address to a client for a limited period of time. It is the only method which provides dynamic re-use of IP addresses. • Automatic allocation: In automatic allocation, DHCP server assigns a permanent IP address to a requesting client. • Manual allocation: In manual allocation, the DHCP server provides the IP address to a requesting client based on a table with MAC address. How DHCP works: The following steps describe the process of acquiring an IP address by a DHCP client from a DHCP server: 1. A DHCP client sends DHCPDISCOVER broadcast message to locate a DHCP server. 2. A DHCP server receives the DHCPDISCOVER broadcast message and sends a DHCPOFFER packet to a client. 3. The DHCP client receives the DHCPOFFER packet and a DHCPREQUEST packet to the server. 4. The DHCP server receives the DHCPREQUEST packet and sends a DHCPACK packet to the client to assign a lease of IP address. 5. The DHCP client requests to extend the lease by sending a DHCPREQUEST packet to the server. 6. The server sends a DHCPACK packet to update and extends the lease time. 7. The DHCP server sends a DHCPACK packet to extend the lease on the IP address

Domain Name Service DNS: DNS stands for ‘Domain Name System’. It is used to translate hostnames to IP addresses and vice versa. It is a hierarchical database where the. root domain, ".", is at the top, and various sub domains are under. .(root domain)

.org .edu .gov

.ca

.com

semsim.com

.net

semsim.co.uk

DNS Domains: • Root Domain: Represented by period (.). It is the top of the DNS structure • Top Level Domain: Indicates a country/region or the type of organization using a name. For example, .com • Second Level Domain: Indicates an individual or organization using a name. For example, cisco.com • Sub Domain: Indicates additional names that an organization can create. For example, tools.cisco.com • Host or resource name: Indicates a specific computer on the network. For example, hosta.tools.cisco.com. Difference of DHCP for IPv4 and IPv6: In IPv6 • A host sends multicast to search a DHCP Server. IPv6 multicast addresses have a prefix of FF00::/8..

switch off or restart the router. Router Architecture:

Difference between stateful mode and Stateless mode: DHCP servers have two operational modes, • stateful and stateless. In stateful mode the server tracks the information, such as leased IP address and leased time period. In stateless mode the server does not tracks state information. • In stateful mode the server retain information of clients, assigns IP address to a client, and supplies useful information like DNS server IP address. • In stateless mode the server do not retain information of clients, do not assign IP address to a client. It supplies useful information like DNS server IP address and is useful in combination with stateless auto configuration. DNS Record: DNS Description Record Start of Stores information about DNS Authority itself for the domain. It is (SOA) mandatory for every record. Stores information used to Name identify the name servers in Server the domain that store (NS) information for that domain. Stores the host name and IP Address address of individual hosts in (A) the domain. Canonica Stores additional host names, l Name or aliases, for hosts in the (CNAME) domain. Mail Stores information about Exchang where mail for the domain e (MX) should be delivered. Stores the IP address and host Pointer name of individual hosts in the (PTR) domain. Host Stores information about the Informati hardware for specific hosts. on (HINFO) Well Stores information about the Known various network services Services available from hosts in the (WKS) domain. Text Stores up to 256 characters of Informati text per line. on (TXT) Responsi Stores information about the ble person responsible for the Person domain. (RP) Starting, Stopping, and Restarting the DNS Server: To start the DNS server : Start the Cisco Service Manager (CSM). The CSM is a graphical utility that allows a user to start, stop, configure, and monitor services. Select DNS from the Available Services list. Click Start. To stop the DNS server : Start the CSM. Select DNS from the Available Services list. Click Stop. To restart the DNS server : Start the CSM. Select DNS from the Available Services list. Click Restart.


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SemSim CCNA Cram Sheets

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