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1.TCP/IP basic knowledge Ethernet | IP | ICMP | ARP | TransportPs |…

- - - - TCP Encapsulation
        Data(Application Layer)
        [TCP | Data]Segment (Transport Layer)
        [IP | TCP | Data]PacketDatagram (Network Layer) > Path Discovery (RoutingTable) (Host must have knowledgeof a path to the destination)
        [Ethernet | IP | TCP | Data | FCS] Frame(DataLink Layer)(Destination mac address is the Gateway mac address )ARP cache to discover dataLink Next hop | unkown next hop > ARP request
      - Frame Forwarding
        Data link layer uses CS to detect for existing traffic
        Preambule and SFD used to synchronize with forwarded frame
        SFD StartFrameDelimiter make the recver know what is the start of the frame
      - Frame Processing
        After recving the frame > to Router > Router see the Source Mac Addresss and then the Destination mac address which is matter > compares it with its own interfaces addresses > if its equal the frame is for him | if its not for him > he drops it
        
        Packet Processing
        (Destination IP is checked against the address of the gateway ) after Router accept it > drop the ethernet header " look into IP header > using the destination IP to look into the Routing table for the next hop > before sending to the next hop Router checks the Arp cache for the destination mac address matching the next hop > if it exists then it encapsulate back the packet with ethernet frame to be sent
        if dosent exist a new frame header is constructed following discovery process
        Proceess Repeated for all Hops
      - Frame Decapsulation
        Frame is forwarded with Destination MAC address of Server A
        Server A compares interface MAC to frame destination MAC
        Decapsulation (Stripping Ethernet / IP headers)
        depending on the Destination Port in TCP for example > if its HTTP port > then The TCP header is stripped and forwarded into HTTP process
- - - - Application
        Presentation >> Data
        Session
      - Transport >> header + Data = segment
      - Network > header(ip) + segment = packet
      - Data link >> header(destina+surc) + Data + FCS = frame
      - Physical > signal transmission
    - - Data link layer frames are used to govern transmission over the communications medium.
      - Frame formats
        
        Ethernet ll >
        Field value > 1536
        associated with protocols with type value greater than 1536
        
        D.MAC - 6B
        determines a frame should be processed or discarded upon being recved by an end device
        
        Type - 2B > identify type of protocol > 0x600
        
        0x0800 (2048) > IP
        
        0x0806 (2054) > ARP
        
        Data > 46-1500
        
        FCS
        
        S.MAC - 6B
        
        IEEE802.3
        Field value > 1500
        
        S.MAC
        
        Length
        
        D.MAC
        
        LLC
        
        D.SAP
        
        S.SAP
        
        Control
        
        SNAP
        
        Type > identify type of protocol > 1500 0x05DC
        
        0x03 > STP
        
        Org Code
        
        Data > 38-1492 bytes
        
        FCS
  - - - reference models
        
        Novell > IPX/SPX
        
        TCP/IP + Ethernet
        
        Transport
        
        Network
        
        Application
        
        Ethernet > Network interface
        
        IBM > SNA
        
        OSI
        
        Session Layer
        
        Network layer > packet
        
        Physical layer
        
        Data link layer > frame :
        
        Transport layer > segment
        
        Presentation layer > certain file format
        
        Application
      - Nets
        
        WANs
        
        PPP
        
        HDLC
        
        Ethernet
        
        LANs > IEEE 802
  - - - Unicast frame forwarding
        1 sendor > 1 recver
        D.MAC > even number (8th bit is 0)
      - MultiCast Frame Forwarding
        1 sendor > multi recvers
        D.MAC > odd number (8th bit is 1)
      - Broadcast Frame forwarding
        1 sendor > all recv
        EthernetFrame (FF FF FF...) all 0s
- - - - Half Duplex
        only one side can send data at one time
      - Full Duplex
        both sides can send data at same time
  - - - Ethernet - Twisted pair cable - RJ-45 connection
        The Primary Physical medium used in enterprise Networks
        Standard>PhysicalMedium>Distance
        10Base-T>2 pais of category 3/4/5 twisted pair cables>100m
        100Base-TX>2 pais of category 5 twisted pair cables>100m
        100Base-T>2 pais of category 5e twisted pair cables>100m (can supp Gigabit Ethernet)
        
        STP - Shielded Twisted Pair
        covered by aliminium foil > more robust to the magnetic interference
        
        UTP - Unshielded Twisted Pair
        
        Croise - Crossover
        câble Ethernet utilisé pour connecter directement des périphériques informatiques. Contrairement aux câbles droits, les câbles croisés utilisent deux normes de câblage différentes : une extrémité utilise la norme de câblage T568A et l’autre extrémité utilise la norme de câblage T568B.souvent utilisé pour connecter deux périphériques du même type
        
        normes de cablage
        
        T568A
        
        Green Pair
        
        WhiteOrange
        
        Blue Pair
        
        Orange
        
        Brown Pair
        
        T568B
        
        Orange Pair
        
        White Green
        
        Blue Pair
        
        Green
        
        Brown Pair
        
        Droit - Straight Through
        utilisé dans les réseaux locaux pour connecter un ordinateur à un concentrateur de réseau tel qu’un routeur.
        norme de câblage : les deux extrémités utilisent la norme de câblage T568A ou les deux extrémités utilisent la norme de câblage T568B.
      - Fiber Optic - SC/LC connectors
        Standard > Physical Medium > Distance
        10Base-F>2 strand fiber>2000m
        100Base-FX>2 strand multi-mode fiber>2000m
        (1G)1000Base-LX>Single-mode fiber or multi-mode fiber>316-5000m
        (10G)1000Base-SX>multi-mode fiber>275-550m
      - Coaxial
        Copper Coaxial Cabling commonly used to support users as part of a shared Network
        Standard>Cable>MaxTransmissionDistance
        10Base2>thinCoaxial>185m
        10Base5>thickCoaxial>500m
      - Serial
        Serial represent a legacy form of data transmission
        Standards continue to evolve as in forms such as USB
        Standard>Speed
        RS-232> Standards defince up to 20000bps but can reach 1Mbit/s
        RS-422> 100Kbit/s - 10Mbit/s+
- - - - ICMP (Routing )
        in a scenarion where we have 2 routers > Nets > 2 Gateways
        and one host in iddle >> which of these Routers should the be configured in the Host (host can configure only one gateway address) >> soo we just specify that in the gateway of the host > should match up with one of routers address
        soo if we wana send packet to a host that behind the other Net (That host dont know about) soo it sends its packet to the Gateway (router configured) and the router do the rest of the job sending the packet to the targetted router that it know all about it and the Network behind it >>
        
        NOT BEST SOLUTION >> thats why we have the ICMP protocol
        
        Router configured in our host that know about the other Router >> sends an ICMP message >> ICMP redirect message
        informing our Host that this was the wrong gateway for this Network and specify in it which Gateway we should instead forward to soo that next time it will directly sent to right Gateway
      - ICMP (Diagnostics)
        2 separate messages are used for the request and reply
        ICMP ECHO Request and ICMP ECHO Reply
        when host want to ping another host > it uese ICMP 2 messages for the request and reply (network only forward)
        if there was no ICMP ECHO Reply > then server is down or host not connected
      - ICMP (errors)
        maybe if packet is destroyed when forwarding
        ICMP notifies that packet source of problems with packet forwarding > Uses the Source IP address in the ip Header
        Example > ICMP Destination Unreachable
  - - - Type - 1B
        (0 > no need for code)... formatof a message
        
        0x00> Echo Reply
        0x03> Destination inaccessible
        0x04> Limitation de production a la source
        0x05> Redirecction (changement de route)
        0x08> Echo Request
        0x09> Router Announcement
        0x0a> Router Solicitation
        0x0b> Expired TTL
        0x0c> Prameter problems of packet
        0x0d> Demande d'horodatage
        0x0e> Rep a une Demande d'horodatage
        0x11> Rep a une demende de masque de Sous-Reseau
        0x02> demande de masque de sous-reseau
      - Code - 1B
        more specific message description
      - Checksum - 2B
      - Var Parameters
        Dep on ICMP Type Field
      - Internet Header - 64 bits of org datagram
        Dep on ICMP Type Field
  - - - only uses ECHO request and ECHO reply
      - On VRP platform, -a can be used together with the "ping"
        command to specify the source address of an echo request message
    - - traceroute list all the hops that the packet will pass through
        the work process is based on the TTL value,
        displays hop by hop limit for each set of results
        the packet goes out of the TTL (set it to 1 in case of just 2 routers existing )
        then each router will minus the TTL by one (then TTL on Next Router Will be 0) >> TTL = 0 >> TTL will drop this packet > and send back to the source the ICMP message that packet is dropped
        3 probe packets are sent for each TTL value by default when "tracert" is used to detect the path along which packet is sent from source to destination
- - - - Flags - 3 bits - B1>always 0
        B2(DF) > 0>fragment | 1>do not fragment
        B3(MF) > 0>last fragment | 1>otherFragments
      - Fragment Offset - 1B+5 bits
        fragment position in the original packet (devisible by 8)
      - Identification - 2B (0>65535)
        used by the sender to facilitate the fragments assembling of a packet
      - Total Frame Length > = HeaderLength + Data < MTU
        Data devisible by 8
      - TTL TimeToLive - 1B
      - Reserved + Protocole - 1B
        
        6 > TCP
        
        17 > UDP
        
        1 > ICMP
      - TOS - Type Of Service - 1B
        
        Precedence > packet priority (0>7)
        
        0 > unitilise
        
        T > highThroughPut
        si > ThroughPut must be maxmized
        
        D > Delai > delai de propagation
        si 1 > fault minimiser le delai en passant par n cable sous marine
        
        R > highReliability
        si 1 > routers must favor reliable links
        
        C > transmissionCost
        si 1 > cost must be minimised
      - Checksum - 2B
      - Header Length - 4 bits > ip header length = 20 B
        5 words of 32 bits > 20 B
      - Address IP source - 4B
      - Version - 4 bits > Protocol version
      - Address IP destination - 4B
  - - - Diagnostic > 127.0.0.0-127.255.255.255 loopback address
      - Any Network > 0.0.0.0
      - Network Broadcastst > 255.255.255
    - - A > 10.0.0.0-10.255.255.255
        B > 172.16.0.0-172.31.255.255
        C > 192.168.0.0-192.168.255.255
  - - - Subnet masks destinguish between the binary of values that reporesent each (sub)Networj and those that represent each host.
      - Default Subnet Mask
        A > 255.0.0.0
        B > 255.255.0.0
        C > 255.255.255.0
        D > 255.255.255.0
    - - Subnet (C) > 255.255.255.0
      - Network Address > 192.168.1.0
      - possible host addresses (8bits) > 2^8
        valid host addresses > 2^8 - 2
    - - VLSM case Scenario
        192.168.1.0/24
        1st Net (30 hosts) > 2^5-2 (5bits host)
        255.255.255.(11100000)
        2nd Net (20 hosts) > 2^5-2
        255.255.255.(11100000)
        2nd Net (10 hosts) > 2^4-2
        255.255.255.(11110000)
    - - IP Gateways
        
        computers to communicate within same Net (have same Net part) they only need source and destination in ip address
        if they are not in same Net > source and dest ip + host does not now other comp not in same Net >> soo host search for Gateway (the exit Net of the Net) like door pf separate rooms
        if gateway cannot be found then they cannot communicate
      - IP Fragmentation
        
        in the ip format
        we have the indentification / flags / fragment offfset
        Are Concerned about the IP packet Fragmentation
        identification >> when fragmenting we need it to identify the fragmentation has happened and what is sequence of each fragment
        flags > fragments are from same packet
        fragment offset >> first fragment offset is 0 (1st byte) by how my bytes we offset to get to the current fragment
      - TTL TimeToLive < oncce packet passed number of hps >> TTL reach 0 down from a max value > gets dropped >> prevent Net Loops
        reduced by one each packet pass a hop
      - Protocol
        
        0x06/0x11 > TCP/UDP
        0x01 >> ICMP
- - - - TCP
        Connection is established before data is sent
        TCP ports represent individual services such as those listed above | sourcr port number is randmly chosen | destination port number dependson Application layer protocol
        TCP one transport layer protcol can support multiple application layer protocol > FTP-20/21 HTTP-80 TELNET-23 SMTP-25
        
        Flags
        
        FIN > disconnect the connection
        
        Ack > Confirm How many bytes i have recved
        
        SYN > to synchronize the sequence number and the Window size Btw S and D
        
        RST >disrupt and reset the connection
        
        Ack Number
        
        Window - Recver does not need to confirm each packet > improve speed
        
        Sequence Number
        
        Destiantion Port - 2B
        
        Source Port - 2B
        
        Checksum
        
        Urgent Pointer
        
        Options
        
        Padding
        
        Header Length
        
        Reserved
      - TCP Connection Establichment
        HostA <> ServerA
        a TCP connction is established after a three-way handshake
        a,b are integers
        HostA > senc SYN (seq=a, CTL=SYN)(req to establish connction)
        ServerA > send SYN,Ack (seg=b, ack=a+1,CTL=SYN,ACK) meaning server is saying i have recved data of eg:a=2000 and want data that begins as 2001
        Host A > Send ACK (seq=a+1,ack=b+1,ACL=ACK)
        meaning server is saying i have recved data of b and want data that begins as b+1
        After theese 3 packets >> CONNECTION ESTABLISHED
      - After Connction Establish >> TCP Transmission Process
        Host can send multiple packets at time depending on window size
        lets say windowSize = 3
        Host A > send 1,2,3
        Server > Aknowledge it and demand for next packets that begins at 4
        Host A > send 4,5,6
        When A packet is not recved for example packet 4 > what will we put in the Ack Number > Server Will Still Ack 4
        Server reAck 4
        Host A > reSend 4,5,6
      - TCP Flow Control
      - TCP Connction Termination
        Host A will ensure ACK is received by Server A before closing
        Host A > FIN
        Server A > ACK
        FIN
        Host A > ACK
        Connection Closed
        State of Conneciton in both Sides will be deleted
    - - UDP
        UDP Based data is sent without establishing a connection
        
        UDP Format - 8B
        UDP Acheives minimal overhead for each datagram
        Datagram Delivery is not guarenteed with UDP
        
        Length - 2B > data + headerLength
        
        Checksum - 2B
        
        Destination Port - 2B
        
        Source Port - 2B
        
        UDP Forwarding Behavior
        UDP susceptible to the possiblity of datagram duplication or non-orderly delivery of datagrams
        UDP packets can take diffrent paths than each other packets and recved in nonOrderly way > and it cannot recover from the NonOrderly delivery bicuz it just does not know
        There is no Acks Therfore lost packets are not retransmitted > this hoever is benificial to delay sensitive data
- - - - Hrdware Type - 2B
        indical physical Net Type Concluding the Searched Physical address
        
        0x0001 > Ethernet (10 Mbit/s)
        
        0x0007 > ARCNET
      - Operation Code - 2B
        
        0x0001 > ARP request
        
        0x0002 > ARP reply
        
        0x0003 > RARP request
        
        0x0004 > RARP reply
      - Protocol Length - >1B
        
        0x0004 > ipv4
        
        0x0010 > ipv6
      - Hardware Length - <1B
        physical address length
        
        0x0006 > Ethernet
        
        0x0001 > TokenRing
      - Source Hardware Address - 4B(varies)
      - Protocol Type - 2B > (0x0800 > IP)
      - Source P Address - 4B(varies)
      - Destinnation Hardware Address - 4B(varies)
      - Destination P Address - 4B(varies)
    - - ARP Cache Loockup
        1st Host A will check its Cache
        manually HostA>arp -a
        Internet Address | Phyysical Address | Type
        if there us nothing when the Host A will send the request out
      - ARP Request Process (ARP enc with Layer 2 Frame )
        D.MAC (FF-FF-FF-FF-FF-FF (Broadcast)) | S.MAC | ARP (DestMAC > 00-00-00-00-00-00 () , SourceMAC > HostA, Operation Code > Request)
      - ARP Reply Process
        host recv the basic information and search and its ARP cache to find the right address with the matching MAC address
        D.MAC (HostA ) | S.MAC > (ReqMAC)| ARP (DestMAC > HostA () , SourceMAC, Operation Code > Reply)
        HostA recv the Arp reply and and accept the info and add it to its cache
        in Arp Cache Type >> Dynamic/Static
        Dynamic >> arp cache item learned using the Arp resolution (item will be deleted after a fixed period of time )
        Static >> added manually
      - Proxy ARP
        Host A LANG0/0/0<Proxy-R>G0/0/1LAN Host B
        Proxy ARP enables data link discovery between networks
        Proxy replies with own (G0/0/0) address on behalf of Host B
        ARP request is sent by broadcast which exist only inside one LAN soo the Router will not forward the ARP request > it just drops it >> soo in such scenario we need to give attention to the SubnetMask (when Host A pings Host B it will just regard the NetPart of HostB>10 and think its the same Net > so it just send ARP request in the same Net )
        But in the True Scenarion Host A and B are not in same Net >> Arp Request Cannot cannot Be recved >
        But if This Router > enables Proxy ARP > Router recv ARP request in G0/0/0 if himself dosent have it >> then Releases it to the Net
        HostA > ARP request to HostB passing by RouterProxyARP
        HostB > ARP Reply > RouterRecv Reply and Reply to Host A(but in this Reply its not HostB mac address > its G0/0/0 mac address )
        soo after learning this when sending a packet >> Destination MAC is Router G0/0/0 when Router Recved it >> seees the IP dest address which is actual Host B ip address >> Router forwards it to host B
      - Gratuitous ARP
        its purpose is just to detect if there is a collision in the IP address >> that means > detecting duplicate IPs > there is another deivce using the same ip address in this Net > Change IP address
        Duplicate IP addresses may be assigned in a single IP Net
        ARP can be used to discover IP address conflicts
        A gratuitous ARP packet uses the same format as an ARP request packet