1.1- OSI VS. TCP/IP models

OSI Model- Reference model- Defines what occurs during network communications but can be applied to any protocol model

All People Seem To Need Data Processing

1. Physical(Physical Topology)- Turns the encapsulated packet into transmit-able data. Moves bits between devices, specifies voltage, wire speed, and pinout of cables.
   • Sends and recieves bits. Binary.
   • DCE(Data communication equipment)- Located at the service provider
   • DTE(Data termination equiptment)- ussally accessed by a modem CSU/DSU(Channel service unit/data service unit)
2. Data Link(Framing)- Physical addressing- Mac Address. Combines packets into bytes, and bytes into frames, provides access to media using MAC address, performs error detection not correction.
   • Formats the messages into a "Data Frame". Adds a customized header containing the hardware destination and source address
   • IEEE Etherenet data link layers
     1. Media Access control(MAC)- How packets are placed on the media. First come/first served access wherever bandwidth is shared. Logical topology- signal path through the physical topology- Line discipline, error notification, ordered delivery of frames and option flow control can all be added.
     2. Logical Link Control(LLC)- Identification of network layer protocols. LLC header tells the data link layer what to do with a packet once a frame is recieved. Can provide flow control and sequencing of control bits.
3. Network(Routing)- Logical Addressing is assigned here. IP Address
   • Data Packets- Used to transport user data through the internetwork. Uses routed protocols- IP, IPv6
   • Route update packets- Update neighboring routers about the networks connected to all routers within the internetwork. Used to help build and update routing tables.
   • Network Address- A router must maintain a routing table for each specific protocol, IP, IPv6
   • Interface- The exit interface a packet will take when destined for a specific port
   • Metric- The distance to a remote network. Different routing protocols calculate this differently.
4. Transport(End to end connection)- Breaks data down and assigns appropriate port number. What application makes the request. Service receives the request. Provides reliable or unreliable delivery, performs error correction before transmit
   • Connection- oriented communication- Call setup or three-way handshake. Fully establishes connection with host before data transfer can begin. Syn- Syn/Ack- Ack
   • Syn- Request for synchronization
   • Syn/ack- acknowledge the receivers connection is synchronized so that bidirectional can be formed. Also established connection parameters and rules.
   • Ack- Acknowledges the connection agreement has been accepted and establishes the connection.
   • Flow control- Ensures Data integrity, Segments delivered are acknowledged back to the sender, Segments not acknowledged are retransmitted, segments are sequenced back in proper order upon arrival, a managable flow is maintained in order to avoid congestion, overloading or data lose.
   • Windowing- Allows the sending of multiple data segments without acknowledgment of each one being received. TCP/IP uses bytes for windows size.
5. Session(Dialog Control)- Keeps different applications data separate
6. Presentation(Data encryption, compression, translation services)- Presents data, Handles processing such as encryption
7. Application(File, Print, Message, DataBase, and applications services)- Provides a user interface

Process/application layer

• Telnet- Remote access, No encryption, Data sent in clear text, Uses 8 bit byte oriented data connection over TCP
• SSH(Secure shell)-Similar to telnet but encrypted
• FTP(File Transfer protocol)- program acting as a protocol, used to move files, requires authentication to use usually, can list directories
• TFTP(Trivial File Transfer Protocol)- Stripped down version of FTP, doesn't display directories, gives files that are asked for
• SNMP(Simple Network Management protocol)- Collects and manipulates valuable network information, polls from Network Management Station(NMS) at fixed intervals,
• HTTP(Hypertext Transfer Protocol)- used to manage communications between web browsers and web servers
• HTTPS(Hypertext Transfer Protocol Secure)- Uses SSL(Secure Socket Layers), Secure version of HTTP
• NTP(Network Time protocol)- Used to synchronize clocks
• DNS(Domain Name Service)- Resolves hostnames, converts requests from hostname to IP, First request is UDP to DNS server, If the DNS server doesn't know the address it forwards a TCP request to it's root DNS server, FQDN(Fully Qualified Domain Name)
• DHCP(Dynamic Host Configuration Protocol)- Assigns IP addresses to Host, Server can provide IP address, subnet mask, Domain Name, Default Gateway, DNS Server Address, WINS Server Address, Client sends out DHCP discover message (Braodcast) at both layer 2 and layer 3, Uses UDP
  1. DHCP client broadcasts a DHCP Discover message looking for a DHCP server(Port 67)
  2. Server responds and sends a Layer 2 unicast DHCP offer message back to the host
  3. Client broadcasts to the server a request message for the offered IP address and possibly other information
  4. Server finalizes the exchange with a unicast DHCP acknowledgement(ACK)
• DHCP Confilicts- DHCP Server checks for conflicts prior to assigning the address, Client uses gratuitous ARP to check, Sends out a broadcast on the local lan or VLAN, If a conflict occurs the IP address will be removed from the pool until manually resolved.
• APIPA(Automatic Private IP Addressing)- Microsoft automatic addressing if no DHCP server is available, Range- 169.254.0.1 -169.254.255.254 Subnet-255.255.0.0

Host to Host or Transport Layer Protocols

• Transmission Control Protocol(TCP)- Breaks down large segments of information from an application, breaks them into segments, numbers the sequences, after they are sent it waits for acknowledgement the segments are received, then re transmits any segments that aren't acknowledged.
  1. Connection oriented- the connection is negotiated by the sender and receiver before transmission begins. Amount of data sent is agreed upon.
  2. Full Duplex, connection-oriented, reliable, accurate protocol- very complicated and costly to overhead.
• User Datagram Protocol(UDP)- Does same as TCP but with less overhead and doesn't require a reliability check, Does not sequence segments and does not care the order they arrive at the destination, Sends segments and forgets about them, referred to as an unreliable protocol,
  1. Connectionless- Does not create or negotiate connection prior to sending.

TCP Segment Format(Picture above)

• Source Port- Port number of the application on the host
• Destination Port- Port number of the application requested on the destination host
• Sequence Number- Number used to put transmitted data back in the correct order
• Acknowledgment Number- TCP Octet that is expected next
• Head Length- The number of 32 bit words in the header- Specifies where the data begins
• Reserved- Always set to zero
• Code bits/flags- Controls functions used to set up and terminate a session
• Window- The window size the sender is willing to accept in octets
• Checksum- Cyclical redundancy check(CRC) used because TCP doesn't trust the lower layers and checks everything
• Urgent-
• Options-
• Data- Handed down to the TCP protocol from the transport layer.

UDP Segment Format

• Source port- Port number of application sending data
• Destination Port- Port number of requesting host
• Length- Length of UDP header and Data
• Checksum- Checksum of both UDP header and UDP data fields
• Data- Upper Layer data

TCP- Telnet(23), SMTP(25), HTTP(80), FTP(20,21), DNS(53),HTTPS(443),SSH(22), POP3(110), IMAP4(143)

UDP- SNMP(161),TFTP(69), DNS(53), BooTPS/DHCP(67), NTP(123)

Port Numbers-

• Numbers below 1024 are considered well know port numbers and defined by RFC 3232
• Numbers 1024 and above are used by upper layers to set up sessions with other hosts.

Internet Layer Protocols

Only layer that handles routing.

Internet Protocol(IP)

IP looks at the packet addresses and uses the routing table to send the packet where it needs to go on the network.

This requires the following two questions to be answered

1. Which network is it on? Software address or logical address
2. What is it's ID on that network? Hardware address

• IP recievees segments from the host to host layer and fragments them into datagrams if necessary.
• It reassembles them back into datagrams on the receiving side.

IP Header Parts-

• Version- Which version of IP is used
• Header Length- 32 bit words?
• Priority or Type of service- Tells how the datagram should be handled
• Total length- Length of the packet including header and data
• Identification- Unique IP-packet value used to differentiate fragmented packets from different datagrams
• Flags- Specifies whether fragmentation should occur
• Fragment offset- Provides fragmentation and reassembly if the packet is too large to put in a frame. also allows a different MTU
• Time to Live(TTL)- generated with the original packet, if it doesn't get to where it is suppose to before the TTL expires it dies.
• Protocol- Port of the upper layer protocol
• Header checksum- Cyclical redundancy check on the header only
• Source IP address- 32 bit address of the sending station
• Destination IP address- 32 bit address of the receiving station
• Options- Used of testing, debugging, security and more
• Data- Upper layer data

IP protocols- ICMP(1), IP in IP(4), TCP(6), UDP(17), EIGRP(88), OSPF(89), IPv6(41), GRE(47), Layer 2 tunnel(115)

Internet Control Message(ICMP)

• Can provide hosts with information about network problems
• Encapsulated within IP datagrams
• Common events or messages
  1. Destination unreachable- If a router can't send an IP datagram any further it responds with this
  2. Buff Full/Source squelch- Routers memory buffer is full, it will send this till congestion abates
  3. Hops/time exceeded- The packet has run out of total hops and will die.
  4. Ping- ICMP echo used to check physical and logical connectivity
  5. Traceroute- Uses ICMP timeouts to discover the path a packet takes.

Address resolutution Protocol(ARP)-

• Finds the hardware address of a host from a known IP address.
• ARP interogates the network by sending a broadcast out asking with the machine with the specified IP to respond.
• ARP translates IP to a hardware address.

INSERT ETHERNET FRAME INFORMATION

Encapsulation

PDU(Protocol data unit)- Application, Presentation, Session- This is the data in the packet

Segment- Transport- Port address- Source port and destination port- TCP or UDP

Packet- Network - IP- Source address and Destination Address

Frame- Data Link Layer- Ethernet(Mac Address)- Source address and Destination address

Sources-

https://www.youtube.com/watch?v=Pje0l5r7_lk

http://www.electronicdesign.com/what-s-difference-between/what-s-difference-between-osi-seven-layer-network-model-and-tcpip