| OSI model | TCP/IP model | Protocol data unit (PDU) | Example | Equipment operating on given layer | Domain |
|---|---|---|---|---|---|
| Application | Application | HTTP | Firewall | ||
| Presentation | |||||
| Session | |||||
| Transport | Transport | segment | TCP, UDP | Router w/NAT, firewall | |
| Network | Network | packet | IP | router | Subnet |
| Data-link | Data-link | frame | Ethernet, 802.11 | switch | Broadcast domain |
| Physical | Physical | bit/symbol | UTP, single-mode fiber, multimode fiber | hub | Collision domain |
P, D, N, T, S, P, A … Please Do Not Throw Sausage Pizza Away!
- Provides network services to the applications of the user and does not provide services to any other OSI layer.
- Establishes the availability of intended communication partners.
- Synchronizes and establishes agreement on procedures for error recovery and control of data integrity.
- Ensures that the information that is sent at the application layer of one system is readable by the application layer of another system.
- Translate among multiple data formats using a common format (e.g. computers with different encoding schemes).
- Establishes, manages and terminates sessions between two communicating hosts.
- The session layer also synchronizes dialog between the presentation layers of the 2 hosts and manages their data exchange.
- Offers efficient data transfer, CoS (Class of Service) and exception reporting of upper layer problems.
- TCP (Transport Control Protocol) / UDP (User Datagram Protocol)
- Port Number
- Defines services to segment, transfer and reassemble for individual communications between the end devices.
- Breaks down large files into smaller segments that are less likely to incur transmission problems.
| Description | Value | Additional Description |
|---|---|---|
| Protocol | 0x0006 + | 06 |
| Source Address (IP) | 0x0a0a + 0x0a02 + | 10.10.10.2 |
| Destination Address (IP) | 0x0a0a + 0x0a01 + | 10.10.10.1 |
| TCP length (including the data part) in byte (no actual header field, has to be counted!) | 0x0014 + | 20 bytes (= 14 in hex) |
| Source + Destination Port | 0x3039 + 0x0050 + | 1234 and 80 |
| Sequence Number | 0x0000 + 0x0000 + | 00 00 00 00 |
| Acknowledgement Number | 0x0000 + 0x0000 + | 00 00 00 00 |
| Data Offset, Reserved, Flags, Window Size | 0x5002 + 0x7110 + | 0101 000 000000010 and 71 10 |
| Checksum (set to 0x0000 in calculation), Urgent Pointer | 0x0000 + 0x0000 = | |
| Subtotal | 0x119cc | |
| Removing the carryover | 0x19cc + 0x0001 = 0x19cd | |
| Negation with 0xffff | 0xffff – 0x19cd = | |
| Checksum | 0xe632 |
- The TCP Three-Way Handshake
[SYN][SYN, ACK][ACK]
- Provides transparent layer of data between host and is resonsible for end-to-end error recovery and flow control
- Flow control is the process of adjusting data from the sender to ensure effective delivery
- The process by which a host is able to support multiple sessions simultaneously and manage the individual traffic streams over a single link
- Source and Destination IP Address.
- Provides connectivity and path selection between 2 host systems that may be located on geographically separated networks,
- Manages connectivity of hosts by providing logical addressing.
- Responsible for routing packets to their destination and for Quality of Service
- Internet Protocol is the most well known layer 3 protocol
- A connectionless protocol with no acknowledgements at layer 3
- Other layer 3 protocols include: ICMP (Internet Control Message Protocol / Ping) and IPSec
- Layer 2 uses MAC Addresses and the logical seperation between networks is done at layer 3 i.e. subnetting
- 32-bits, 4 octets in dotted-decimal format, each octet is 8 bits long
- bytes = b'...' literals = a sequence of octets (integers between 0 and 255)
| Description | Value | Additional Description |
|---|---|---|
| Version, IHL, Type of Service + Total Length | 0x4500 + 0x0028 + | – |
| Identification + Flags, Fragment Offset | 0xabcd + 0x0000 + | – |
| TTL, Protocol + Header Checksum (0x0000 in calculation) | 0x4006 + 0x0000 + | – |
| Source Address (IP) | 0x0a0a + 0x0a02 + | 10.10.10.2 |
| Destination Address (IP) | 0x0a0a + 0x0a01 = | 10.10.10.1 |
| Subtotal | 0x15912 | |
| Removing the carryover | 0x5912 + 0x0001 = 0x5913 | |
| Negation with 0xffff | 0xffff – 0x5913 = | |
| Header Checksum | 0xa6ec |
ipconfig --ip address, subnet mask and default gateway
--windowsifconfig --ip address and subnet mask
--linuxip route --default gateway --linux
CISCO IOS:
Router> enable
Router# show ip interface brief
Router# show interface
- Dynamic Host Configuration Protocol (DHCP) assigns IP addresses automatically to client machines
- IP Addresses are usually set manually on servers, printers and network devices; routers and switches
- IP Range: 1.0.0.0 to 126.0.0.0
- First octet value range from 1 to 127
- Subnet Mask: 255.0.0.0 (8 bits)
- Number of Networks: 126
- Number of Hosts per Network: 16,777,214
- Range: 128.0.0.0 to 191.255.0.0
- First octet value range from 128 to 191
- Subnet Mask: 255.255.0.0 (16 bits)
- Number of Networks: 16,382
- Number of Hosts per Network: 65,534
- Class B Private APIPA Range: 169.254.0.0 to 169.254.255.255
Automatic Private IP Addressing (APIPA) is a feature on Microsoft Windows-based computers to automatically assign itself an IP address within this range if a Dynamic Host Configuration Protocol (DHCP) server is not available. A DHCP server is a device on a network that is responsible for assigning IP address to devices on the network.
- Range: 192.0.0.0 to 223.255.255.0
- First octet value range from 192 to 223
- Subnet Mask: 255.255.255.0 (24 bits)
- Number of Networks: 2,097,150
- Number of Hosts per Network: 254
- Not allocated to hosts and are used for multicasting
- Range: 224.0.0.0 to 239.255.255.255
- First octet value range from 224 to 239
- Number of Hosts per Network: Multicasting
- Reserved for research purposes
- Range: 240.0.0.0 to 255.255.255.255
- First octet value range from 240 to 255
- IP Range: 127.0.0.1 to 127.255.255.255
| CLASS A | CLASS B | CLASS C |
|---|---|---|
| 10.0.0.0 - 10.255.255.255 | 172.16.0.0 - 172.31.255.255 | 192.168.0.0 - 192.168.255.255 |
| 255.0.0.0 | 255.240.0.0 | 255.255.0.0 |
- Assigned to hosts and not routable on the internet
- Most enterprises today use RFC 1918 addresses and NAT
| Destination MAC Address | Source MAC Address | Protocol Type |
|---|---|---|
| 00 0c 29 d3 be d6 | 00 0c 29 e0 c4 af | 08 00 (= IPv4) |
- Source and Destination MAC Address (layer 2 address)
- How data is formatted for transmission and how to access to physical media is controlled.
- Includes error detection and correction to ensure reliable delivery of data.
- Frames are encoded and decoded into bits at Layer 2
- Error detection and correction for the physical layer
- Ethernet is the layer 2 medium used on LAN networks
The 48-bit hexadecimal MAC address has two parts:
- The first 24 bits is the OUI (Organizationally Unique Identifier) and identifies the manufacturer of the Ethernet Port, assigned by the IEEE
- The last 24 bits are vendor assigned The burned in MAC address on every NIC port in the world is globally unique e.g. 00:50:56:C0:00:08
Cisco IOS: show interface
Windows: ipconfig /all
Linux: ifconfig
- Enables bit transmission between end devices.
- Defines the specification needed for activating, maintaining and deactivating the physical link between end devices.
- Voltage levels, physical data rates, maximum transmission distances, physical connectors etc.
- OSI Layer 1 conveys the bit stream, electrical impulse, light or radio signals, though the network at the electrical and mechanical level
- Provides the hardware means of sending and receiving data, including defining cables, interface cards and physical aspects
- Coaxial cable (no longer used)
- Twisted copper pair cable
- Fiber cable
- Wireless
RJ-45 max length = 100m
- Cat 5 / 5e - Gigabit Ethernet
- Cat 6 - 10 Gigabit Ethernet
- Copper UTP (Unshielded Twisted Pair) cables are commonly used to connect desktop computers to switches
- Straight-Through connect end device of different types eg. PC or router to a switch
- Crossover connect devices of the same type eg. 2 computers/2 switches
- Modern switches support Auto MDI-X; receive and transmit signals are reconfigured automatically to yield the expected result
- Support longer distances or higher bandwidth requirements i.e. between separate buildings in a campus
- Switch to switch connections in a building
- Single-mode fiber optic cables: more expensive, long distances
- Multi-mode fiber: less expensive
- Port at the back of the Switch > Transceiver > Fiber Optic Cable connector
- PoE Switch: use a power injector
Cisco devices do not have a default IP address, so we need to set one up before we can connect to it over the network. We need a console connection to make the initial configurations including adding IP addresses.
Use “Ctrl-A” to move back to move back to the start of the line
Cisco IOS CLI:
Router> (The User Exec prompt)
Router> ? (Ask for help :-\)
Router> enable (Privileged Exec mode) /disable (to esc.)
Router# show ?
Router# show ip interface brief
Router# show running config
Router# show run int fast0/0
Router# show run | begin hostname (case sensitive regular expression)
Router# show run | include/exclude interface
Router# show run | section bgp
Router# configure terminal (Global Configuration)
Router(config)# ?
Router(config)# hostname Router1
Router(config)# do show ip interface brief (Show cmd at global config mode)
Router(config)# interface fastEthernet 0/0
Router(config-if)# exit (takes you back to global config)
Router(config-if)# end (takes you back to Privileged Exec mode)
Router# conf t
Router(config)# hostname Router1
Router1(config)# do show startup-config
Router1(config)# do show running-config
Router1(config)# end
Router1# copy run startup-config (Privileged Exec mode)
Router1# copy run flash:my-config
Router1# show flash
Router1# write erase start
Router1# copy flash:my-config start
Router1# copy run tftp
Router1# more flash:myconfig
- The IOS image is stored in flash
- The startup configuration is stored in NVRAM
- The running configuration is stored in RAM
- Running config is loaded into RAM from the startup config when the device boots up