CompTIA Network+ certification course sum up. Oriented for cybersecurity later courses.
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7
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Application
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Data
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6
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Presentation
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Data
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5
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Session
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Data
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4
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Transport
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Segments/Datagram
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3
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Network
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Packets
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2
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Data-Link
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Frames
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1
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Phyiscal
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Bits
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Function
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transmission of bits across network
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Representation
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Electrical voltage on wires -> 1 or 0
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- NRZ
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0 volt = 0, +/-5 volts = 1
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- Transition Modulation
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during a clock cycle, no change = 0, change = 1
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Topology
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see cheatsheet 1/20
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Async comm.
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use of start bits and stop bits to indicate when transm. occurs
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Sync comm.
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use of a reference clock to coordinate transm.
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Broadband bandwith
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divides bw into separate channels (ex Cable TV)
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Baseband bandwith
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uses different freqs on a cable & a ref clock to coordinate transm.
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Baseband Multixplexing
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TDM, StatTDM, FDM are ways to allocate time slots and freqs over channels
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ex
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cables, radio freqs, devices (hubs, WAP, converters, ...)
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MAC
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48-bit -> Network Interface Card (NIC) / 1st 24bits : manufacturer, 2nd 24bits : unique device value
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LLC
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Logical Link Control
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Reliable transmission of data
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Segmentation & addressing
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Flow and Error control (checksum)
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Syncro
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Isochronous, Syncronous or Asyncronous
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Devices
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NIC, bridges, switches
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Function
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forwards traffic with logical adress
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Logical adress
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IPv4, IPv6, IPX, AppleTalk
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Packet switching
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divides data into packets and forward
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Circuit switching
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dedicated comm link
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Message switching
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divides data into storable messages which can be stored and forwarded later
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Routers
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routing table based on IP adress, static or dynamic route
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protocol RIP, OSPF, EIGRP
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Flow control
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regulates data flow/speed
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Packet reordering
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thanks to numbering and sequencing, packets can be sent across multiple routes
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ICMP
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Internet Control Message Protocol
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send error msg & ops info about an IP, uses ping and traceroute
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ex:
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routers, multilayer switches, IPv4, IPv6, ICMP
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TCP
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Transmission Control Protocol
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connection oriented
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reliable, resend lost segments, acknowlege (3-way handshake)
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UDP
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User Datagram Protocol
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connectionless
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ureliable, no retransmission, faster due to low overhead
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Windowing
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adjust amount of data, based on retransmission reception quantity
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Buffering
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router allocates memory to store segments
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buffer overflow = segments dropped
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ex:
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TCP, UDP, WAN accelerators, load balancers, firewalls
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Function
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setup a conversation
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Setting up
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check credentials, session id, services needed and who starts
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Maintaining
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transfer data, reestablish connection, acknowledge data recept°
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Tearing Down
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on mutual agreement or other party disconnecting
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ex:
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H.323/264 (voice/video streaming), NetBIOS (file exchange)
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Function
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format data for readability, encrypt and secure data
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Data Formating
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for compatibility purposes, readability (ASCII, JPG, etc)
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compression, conversion
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Encryption
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scrambles data, provide confidentiality (TLS)
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ex:
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programmation languages, text formats, pict extentions, protocols like TLS, SSL
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Function
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interface user <-> computer
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App. Services
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File transfer, sharing, email, remote access, NW mgmt, cl/srv processes
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Advertisement
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service initiating a service offer to a NW
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ex :
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POP3, IMAP, SMTP / HTTP-S / DNS / FTP-S / Telnet, SSH / SNMP
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Function
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"envelopping" data with headers
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PDU
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Protocol Data Unit. ex: L3PDU->Packet
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Flags
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SYN
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initiates synchronization of connection
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ACK
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acknowledges during 3-WSH and packet reception
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FIN
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initates termination of connection
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RST
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when client or server receives a non expected packet
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PSH
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gives priority to data (for sender)
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URG
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gives priority to data (for recipient)
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MAC
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phyiscal adress of a NIC
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EtherType
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identify the protocol used (IPv4/v6)
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from L7 to L1
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at L4
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+TCP/UDP header (source & dest ports)
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at L3
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+IP header (source & dest adresses)
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at L2
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+MAC+LLC ---- +FCS
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at L1
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transmit L2 in bits (0 and 1)
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