Network Layer Notes PDF

the network layer what does the network layer do transport segment from sending to recievinghost on the sendingside encapsulates segment into datagrams on the reciever side delivers segm...

the network layer what does the network layer do transport segment from sending to recievinghost on the sendingside encapsulates segment into datagrams on the reciever side delivers segments to transport layer What are the two keys for network layerfunctions forwarding moves packets from router's input to routers output route taken bypackets from determine sourceto destination routing routing algorithms What is data plane thedataplane also known as theforwardingplane it is responsible forthe actual movement of data packets through a network device such as a router switch what are the keyfunctions of data plane Packet forwarding determines how to forward incomingdata packets to the correct estimation based on forwarding tables and routingrules Router Architecture Router input ports these are theinterfaces through which packets enter the ater and what do this inputports do converts incoming signals into digital packets  g handles operation like error detection and MAC address processing as well as temporarily holds packets before forwardingthem to the switching fabric high speed switching fabric it interconnects the input and output ports it is esponsible for transferring packets from the correct input port to the appropriate utputport Louter output ports these arethe interfaces where packets leave therouter toreach heir destination Routing Processor runs routing protocols and updates the forwardingtable decides how packets should be forwarded by computingroutes and disseminatingthese ales to the data plane what are line Cards line cards connect the router to physical network they handlethe reception and transmission of data atthe hardwarelevel line cards also determine how and where packets should be sent based on forwardin ables decrement time tolive adjusts the time to live value ofpackets as required bythe IPprotocol this insures packets that live endlessly are eventually iscarded temporarily stores packets in memorywhile they are queued forprocessing r transmission to avoid data loss what doesthe switching fabricdo Deliver packets inside the router from incoming interface to outgoinginterface Mustoperate very quickly multipate packets to same outgoing interface going switch scheduling to match inputs to outputs implementation techniques Bus cross  g g abs What is packet switching backet switchingis amethod used to transmit packets from one link ingress to another egress based on their destination Ingress links are the input ports through which packets enter the system Egress links these are the output ports where packets are sent out after being rocessed What is the process backet arrival a packet enters through an ingress each packet contains information ach as a destination identifier which indicates its intended output port hoosing egress the system preforms a lookup Basedon the destination information in he packet the system determines the appropriate egresslink fter the egress is determined the switchingfabric connects the ingress port tothe orrect egress port once the switching fabric directsthe packet tothe destinationpo is sentout ow do loss anddelay occur Packet queueing inRouter when packets arrive they are stored inbuffers while aiting to be processed and transmitted tothe next link ifthepacket arrivalrate exceeds the output link capacitypacketswill startqueuing inthepuffer What is the router processor it is responsible for the  y gg control plane the Loopback interface is a virtual network interface assigned an IP address theIP addressidentifies the router's CPU Control plane implementation of the routingprotocols creation of forwarding able for the line cards interfaces to network administrators the router processorprovides interfaces for etwork administrators to manage and monitor the router Command line allows administrators to configure the router transmission ofmeasurements collects and reports preformance metric handles packets that arespecial what is Per router control plane describes how each router independetly manages routing decisions and forwardingwithin a network the control plane is responsible for decision makeingin eachrouter the data plane handles theactual packetforwardingbased on each what is Longest prefixMatching it is a keyalgorithm used in routersto ecide the correct output interface for a packet therouteruses thelongest address prefix in the forwardingtablethatmatches the destination header inthe acket header what is IP addressing connection between hostrouter andphysicallink  What are subnets a subnet is a logically defined portion of a network dividing a larger network intosmaller segments subnets are created defined by by heir IP addresses range andsubnetmask which determines the number of hosts thatcan exist within thesubnet What is a subnet mask a subnet mask is used to identifywhichportion an IP address represents the network and which portion represents the host forexample IPaddress 192.168 1.10 subnetmask 255.255.25500 124 which means thefirst 24bits the network and the last represents I represen the host and there can be 28 2 hosts on the network NetworkAddress and Broadcast address Network Address Thefirst IP address in asubnet usedto identifythe subnetitself Broadcast address thelast IP address usedto senddata to all devices in thatsubne What is subnetting subneting isthe process of dividing alarger networkinto smaller subnetworks Dividing 192.168 0.0 116 into multipate smallersubnets 192.1681.01 192.168 2.0 124 Special IPAddresses Loopback interfaces all addresses 127 0.0.1 127.255.255.25 are reserved for loopbackinterfaces IP address of a network host number is all zeros 128.143.0 0 Broadcast address hostnumber is all ones 128.143.255.255 Basic idea of subnetting split the host number portion of an IP address into a subnet number and a smaller host number  How toget an IP address DHCP IP datagram format Whatis an Autonomous system an autonomous system is a larger collection of networks under a single by an ASN dmistrative domain identified Tample of As ISP Routingwithin As is referred to as Intra As Routing whilerouting between Asesis referred to as inter As routing Intra As routing refers to routing within a single Autonomous system EachAs has it's own IntraAs routing setup private IP vs public IP private IP address scope is local topresent network  no is used to communicate withinthe network public IP addressscope isglobal and s used to communicate outside the network NAI network address translation localnetwork usesjust one IP address as far as outside world is concerned can change address of devices in local network without notifyingoutside world whatisNAT it is a techniqueused routers to allow multiple devices in aprivate by etwork to share a single public IP address for internet access is a process where the router modifies the IP addressandportnumber inthe headers of network packets as they pass through Handling outgoing datagrams the router replaces thesource IP addressandport number in each outgoing datagram the privateIP address and port are replaced with the NAT router's public IP address and a newport number theNATkeeps rack of each translation in a NAT translation table it records the mapping between the private IP andport and the public IP andport Handlingincoming datagrams the router the replaces destinationIP andport with the correspondingprivate IP andport from theNAT translation table Multiple devices in a household or business canshare one publicIP address each differentiated by a unique part key challenges ofNAT Breaks end to end connectivity Limits on portnumbers complexity in Application Design  linklayer where is the link layer implemented it is implemented in each and everyhost link layer is implemented in adaptor network interface card it is a compination of hardware software firmware how does communication happens between adaptors each host has a network adaptor that handles the communication the adaptor contains a controller which managestheframing and processing of data a frame is a datagram plus additional information such as error checking and control data On the sendingside the sending adaptor performs two keytasks Incapsulation It wraps the datagram in a frame byaddingheaders trailers For checking and Control On the recievingside Error Detecation andControl Datagram extraction what is MAC it is used locally toget frame from one interface to anth interface hysicaly connected WhatisARPI it is used to map an IPaddress to aMAC address within a local Area Network What is the ARPprocess IP address to MAC addressMapping Devices on a LAN communicate using MAC addresses if a device knows theIP address of another device butnotits MACaddress it uses ARP tofind the correspond MAC address each device maintains an ARP table How ARP works f a device e.g 137.196 7.78 wants to send data to another device 137.196.7 check its ARPtable for the MAC address correspondingto 137.1967.23 f the MAC address is found it uses it to send theframe f not it broadcasts an ARP request tothe entire LAN askingwhohas IP 37.196.7 23 the device with IP 137.196.723 responds withits mac address her the sender stores this mapping in its ARP table What is Ethernet 7 am bus allnodes in same collision domain star active switchin center sender Adaptor encapsulates IP datagram inEthernetFrame Preamble safety data CRC preamble usedto synchronize recieversender clockrates Abytes addresses 6 bytesource destination MAC addresses if adaptor recieves frame with matching destination address or with broadcast address it passesdata in frame tonetwork layer protocol otherwise adaptor discardsframe indicates type higher layerprotocol CRC cyclic redundancy check atreciever Ethernet is unreliable and connectionless connectionless No handshakingbetween recievingandsending Nic  g g g unreliable recievingNIC does not send ack or nacks to sendingNIC What is anEthernet Switch An ethernet switch is a networking device that connects devices within alocalArea Network it operates on the link stores and forwards Ethernet frames layer ExaminestheMAC address in incomingframes and selectivelyforwardsthem to the appropriate outgoinglink uses ad CSMA tomanage access to network segments It is transparent hosts connected to the networkare unaware of the switch's resence slug andplay self learning each switch has a switch table each entry MAC address of host interface reach host time stamp switch is self learning switch learns which hosts can be reached through hich interface Switch frame filtering forwarding switches vs routers both are store and forward network routers layer devices switches link layer devices both have forwardingtables routers compute tables algorithms IPaddresses usingrouting switch learn forwarding table usingflooding learningMAC addresses  g g What is a vlan a logical segmentation of a physical network into multiple solated networks devices within a Vlan can communicate as iftheyare onthe same physical LAN even if theyare connected to different switches How VLANS work switch ports are assigned to specificVLANS EachVlan has its own broadcast omain and devices on another VLAN can not communicate with devices inanother VLAN without a router or a layer 3switch DHCP allow host to dynamically obtain its IP address from networkserver when it joins network DHCP overview DHCI discover DHCP offer DHCP request DHCPACK Hcp can return defult getaway name and IP address ofDNS servernetworkmask Each subnet will have a DHCP server if not thenDHCPrelay agent thatknows the address of a DHCP serverforthat network is needed port for DHCP client68 andserver67 if a Host has more than a networkinterface it will have multiple MAC and IP addresses ARP works in the same subnet outsides the subnet requires the defult communication getawayto resolve  ay addresses What is CDN store multiple copies of videos at multiple geographically distribut ites What is cloud computing cloud computing is the deliveryof computing servers storage network software overthe internet it enables organizations and individuals to access these resources on demand without owning or managing he underlying physical infrastructure Delievery models software as a service uses provider's application over a etwork platform as a service deploy customer created application to a cloud infrastructure as a Service Rent processing storage network capacity questions What are the main responsability of the network layer transfer packages between different networks What is the difference between forwarding and the network layer routing in forwarding how to move packages from inputports to outputport route from one router to another using routing algorithm ating deciding the data plane and control plane in the router data plane is responsible for the forwarding of packets based on forwarding  g g ables control plane Manages the routing logic updatingrouting tables and running routing protocols What is the longest prefix matching algorithm andwhy is it used in routing Matching determines the correct output interface for a packet by matchingthe destination address in the packet header with the most specific entryin the orwarding table what is asubnet mask and how does it determine the network and hostportions ofanIP address provide an example a subnet mask specifies which portion of an IP address represents the network nd which representsthe host example forIP 192.168 1.10 andsubnet mask 55.255.2550 network portion 192.168 1.0 and host portion 10 What are the key differences between a public IPand aprivateIP Sublic IP used to communicate with external networks rivate IP used within local networks not routable onthe internet Explain how NAT works whatare it's benefits and challenges AT allows multiple devices in a private network to share a singlepublicIP hallenges withNAT Breaks end to end connectivity limited port number for translatio What is a broadcast address and how is it used with in a subnet The broadcast address is the last IP address in a subnet usedtosenddata to all evices for a subnet 192.168 1.0 24 the broadcast is 192.168.1255  Whyis subnetting important in network design traffic segregation upnetting improves resource management securityand Dividing 192.168 0.0 24 into two subnets abnet 1 192.168 0.0 25 abnet 2 192.168 0.128 25 0 What are the functions of the routing processor with in a router runs routing protocols updates forwarding tables computes and dismantles routes 1 Describe the purpose of line cards and what keytasksthey preform connect the router to physical networks reform data reception transmission and temporary packet storage ecrement the time to live value of packets 2 How does the link layer handle erron detection and control during communication uses error checking codes ncapsulates data inframes with headers and trailers forcontrol Whatis ARP and how does it map an IP to aMAC address ARP broadcasts a request on the local network tofind theMAC addressof a givin IP the device with the matching IP replies with itsMACaddress 4 Explain the process of ethernet communication between two devices whaterole doMAC addresses play  ay enderencapsulates theIP datagram in an Ethernet frame usesMACaddress to entify the source and destination devices Ethernet switches forward frames basedo estination MACaddress 5 What is the difference between an Ethernet switch and a router when weuse ach switches operate at the link layer forwards frames within the same network outer Operates at the network layer forwards packetsbetween different netwo What is cloud computing andwhat are three primary delivery models Cloud computing delivers computingresources over the internet Models IaaS Infrastructure as a service PaaS Platform as a service SaaS software as a service 7 What is a CDN and how does it improve the preformance of websites DN stores content on geographically distributed servers to reducelatency improves performance by delieviring content from the serverclosest to the user 8 Explain the four keysteps in the DHCP HCP discover offer request ACK 9 What is Vlan and how does it isolate traffic within a physical network VLANs segment a physical network into logical networks Devices in one VLAN can not communicate with another VLAN without a router What isthe purpose of the checksum in the VDP protocol  he checksum ensures the integrity of the data by veryfing the recieved ata matches the sent data it helps detect error during transmission Multiple subnets DHCP discover the broadcast cannot cross subnet oundaries A DHCP rely agent forwards the Discover to the DHCPserver message The DHCP responds with an IP address from the appropriate subnet he relay agent relays the response back to the client Advanced DHCP Parameters Default the router to send to destination outside getaway specifies packets he subnet DNS server Resolves domain name to IP addresses for the client Order DHCP first assigns the IP ARP thenresolves MAC addressesfor ommunication Cloud models laas provides virtualized computingresources use cases hosting web application where full control over the infrastructure is required aas offers a platform for application development use case Rapidlydeveloping and deploying apps without managing infrastructure Tas focuses on runningcode without managing servers Event triggering pplications like triggering actions on file upload  gg key Difference Faas is stateless andeventdriven scalling automaticallybasedon he number of function calls whereas laas andPaas involve presistentresource routing management control plane operates in millisecond software forwarding data plane hardware operttes in nanosecond timeframe routing processor I high speed router inputports switching routeroutput ports fabric a line card is a physical compotent hardware that typicallycontains both input andoutput ports along with processing capabilities Where is thedataplane and control plane located plane in the processor control data plane in the switching fabric andlinecards Implementation technique for switching fabrics in routers include Busi single shared path between input and output ports only one packet can transfer  a time simple but limited throughput Crossbars Grid like structure with input output intersections multiple simultaneous transfer sossible Better preformancethanBus more complex scheduling needed interconnectionNetwork Multiple stages of smaller switching elements Provides multiple parallel paths Better scalability than simple crossbar can hand multiple transfer simutaneously LAN use OSI Layer1 and Layer2 data connection equipment for transmission WAN use Layer 1,2 and 3 network devices for data transmission NATtypes StaticNAT Dynamic NA ort Addresstranslation NAT range of addresses not needed fromISP just one IP address for all devices NAT router must replace source IP address port ofeveryoutgoingdatagram NAT IP address new port remote clients willrespond using NAT IP address w port as destination address remember every soure IPaddress port to NAT IPaddress newport translation air incomingdatagrams replace NAT IP address new part in destfield of every incoming datagram with corresponding source IP NATTable addresspart storedin  g g g what is a frame a frame is a digital data transmission unit in a network atthe data linklayer it includes Header Mac addresses payload the actual databeingtransmited Frames are essential for communication within ocal network adaptor is network interface card How the link layer operates the controler handles link layer tasks like framing error detection and MAC The NIC serves as the bridge between the computer andthe network What is host bus pathawaythat the CPU connects a is a communication nd main memory to peripherl devices like network interface cards storage devices important when a NIC sends or recieves data the CPU instructstheNICvia the host bus the NIC accesses or sends data to from memorythrough bus host bus like PSI Impeyortant the higher layers reside in the CPU and memory of the system where data is generated or processed the link layer is software implemented partly in and partly in hardware Network adaptor card this hardware ethernet or Wificard is responsible for converting digital signals into physical signal for transmission over the network components ofNIC Controller implements link layerfunctions such as framing errordetectionand  y g MAC physical transmission functions of MAC usedlocally a MACaddress is primarilyused within a localnetwork to transfer rames between devicesthat are directlyconnected or reachable without routing ameNetwork Mac addresses work within the same IPsubnet communication between differentsubnets requires routing where MAC address is no longer used asthe identifier MAC addresses operate withinthe boundaries of asingleNetwork ahomeWifi office LAN by IEEE MAC allocation administered IIiiiff.li g 1iI he sender device only needsthe MAC address ofit's default gatewayto communicate ith devices outside itsLAN ARPhappens at each router andLAN boundarytoresolve e MAC addresses required forlocal delievery ÉÉTÉ IP 192 168 1.10 MAC AA AA AAAAAAAA onLAN1 Device B IP 10 0.0.20 MAC 1 BB BB BB BB BB BB on LAN2 a router connects thetwo IANS LAN 1 Routers CC Cc MAC  LAN2 RoutersMAC DDDD Device A sends Data DeviceA determines that Device B is on a different subnet Device A usesARP to find theMAC address of therouter on LAN1 Device A sends the packet tothe router Router Processes the packet 0.240 the router recieves the packet and examinesthe destination IP 10.0 determines the packet needs to be forwarded to LAN2 outer Resolve destinationMAC ONLAN 2 the router uses ARP tofind the MAC address of DeviceB itforwards hepacket to deviceB Device β recievesthe frame withits MAC addressandprocesses he data Ethernet frame structure ethernet frame sending adaptor encapsulates IP datagram in Preamble dest source CRC add type data address address if adaptor recievs frame with matching destination duress or with broadcast address it passes data in frame to network layer otherwise daptor discardsframe type indicator higher layer protocol CRC error detectedframe is dropped Ethernet is connectionless and unaliable Ethernet MAC protocol he Ethernet MACprotocol is responsible formanaging access totheshared communicat edium to avoid collisions andensure successful datatransmission nslotted CSMACD carriersense SC devices listen to the medium before attemptingto send data Multiple Access MA multiple devices can access the shared medium CD coulision detection stoptransmitingand take stepsto recover Unslotted there is no predefined time slot for devicestotransmit Devices can ransmit as soon as the medium is idle what is BinaryBackoff If a collision occursboth devicesinvolved stoptransmitting nowaitfora random amountof time before tryingagain how it works in Ethernet A device listens tothe medium if the medium isidle it startstransmitting f a collision is detected it stops transmitting immediatly andsends a jam signalt alert other devices the device waits for arandom back offtime before tempting to retransmit switch selective forwarding Instead of broadcastingframes to all ports like a hub a witch forwards framesto specific outgoinglinks based onthe destinationMACaddress hisprocess reduces network congestion and improves efficency Transparent hosts are unaware of switches Ethernet switches are intelligent link layer devices that actively manageframe  g ay o manual orwarding based onMAC addresses configuration switcheswork theyare transparent tonetwork devicesand require at the datalink layer managingcommunication etween devices within the same LAN each switch has a switch table eachentry MAC address of host interface to reach host timestamp interface refers to the specificport onthe switch that connects to a articular device orhost each port on device is considerd an interface nd it is used to send and recieve ethernetframes between the switchand evices connected to it or example the interface number 1 unique identifies the port on the switch hrough which a device is reachable A VLAN is about creating smaller isolated networks within a single shysical network VLAN divides a single switch into virtual switches to control which devices can communicate with eachother VLANS operate at layers frames are forwarded between devices on aswitch They control how ethernet VLANS are based onswitch ports andMAC addresses the switch learns the sourceMAC address  CDN is a network of servers distributed geographically to efficiently eliverweb content to users whatis the impact that CDN have CDNS enhance web preformence by reducing latencyand improving page load imesforusers globally What is the purpose of CDN The primaryfunction ofCDN is to cache content and distribute it closerto sers enhancing speed and reliability what Does CDN Do Manage servers in multiple geographically distributed locations store copies of videos and other webcontent to a CDN location thatwill provide the best Direct each user request ser experience CDN can be aprivate or a third party CDN What happens in DNS Routing we send a DNS query to local DNS ocal DNS queries the authortative for youtube which notices the watch in he hostname andsends a hostname for a server in google.video.com a content erver in google's CDN INS sends another for the hostrecieved earlier andgetstheIPfor it  qy DNS gives IP to the host ost establishes a Tcp connection and sendsHTTP get request cluster selection strategy real time measurment cast Geographically any Routing Dash a video streaming technology that allows high quality media streaming ver the internet by adaptingthe vedio quality automatically based onthe viewer's ternet speedand device preformance What DASH does Dash breaks video content intosmall chunks or segments ole ofCDN CDN play a critical role in ensuringDashworkseffectivelyby israbuting content efficiently acrosstheglobe CDNs cache the Dash video segment totheirservers located in different egions when a user requests a video they are served from the nearest DN server reducing latency and improvingplaypack preformence Load balancing CDNs distributethe load by balancing requests Bandwidth optimization captive streaming support Dash player frequentlyrequestsegments based on real time network conditions CPNshelp serve the right video segment at the requested bitrate or resulation  g q tore and deliver multiple versions of the same content CDN L v enterdeep bring home push CDN servers deep into many smaller number oflarger clustersin access networks POPs near access network close to users used by Limelight used by Akamai SOP point of presence contains router switches servers andother networking quipment serves as a hub formanaging internet traffic Tample when you stream videofrom a CDN you are connecting to a popclose to your geographic location an ISP's PoP is where your internet traff entersthier network a PoP refers to where cached content is stored andserved to users whatis over the top refers to services that deliver video or othermedia directly over theinternet without requiringtraditional cable or sateliate infrastructure what is the cloud it refers to servers that are accessed overthe internet  nd the software and databases thatrun on those servers where are cloudservers Cloud servers are in data centers all over the world Byusingcloud computing users and companies do nothave themselves or run software applications on Thierown manage physical servers achines What is cloud computing on demand delivery of ITresources and via the internet with pplications pay as you gopricing Whatis the AWS it is designed to provide highly scalable reliable and globally istributed cloud computingservices Global infrastructure ws global infrastructure is divided into several layersto provide highavailabilty w latency and resilience Regions ws regions are geographicareas where AWS operates cloud infrastructure ach region consists of multiple availability zones ach region operates independently to ensure data sovereigntyand low latencyforuser that area Availabiltyzones An Az is a physically distinct datacenterwithin a region withindependentpower ooling and networking allregions have 2 or more Azs  Each Az is 1 or more Data center Nodata center is in two Azs Data centers in Az less than 0.25ms apart what do we mean by eat time measurment this strategy measures real time networkconditions to determine the best performing clusterforthe user at themoment nycast routing Anycastrouting is a routing method where a single IP is advertised rom multiple locations the network automaticallyroutes the user'srequest to the losestor most optimal cluster basedon routing policies