Networking Overview: Difference between revisions

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= Intro =
= Intro =
== Network Layers ==
<blockquote>
The network layers used depend on the networking ''model'' used.
Most networks use the IP model with 4x layers (physical, datalink, network, transport),
the other populare model is OSI with 6x layers
(physical, datalink, network, transport, session, presentation).
The combination of these layers is referred to as the '''networking stack'''.
{| class="wikitable"
|-
! Layer
! Unit
! Debug Tools
! Description
|-
|-
| 1) Physical Layer ||        || linklight, ipconfig/ifconfig, replace-cable ||
ethernet, arp (address resolution protocol), the cord
|-
| 2) Datalink Layer || frames || arp, nd, tcpdump ||
The protocol used to transmit frames over the wire.
The Datalink layer is designed to fire frames at a target MAC addr (Media Access Control)
using ARP (Address Resolution Protocol).
|-
| 3) Network Layer || packets || ping, traceroute ||
The network layer answers 'how do i get this to the target host?'.
Unlike the physical/datalink layers which get stripped off and replaced
as the information passes through different networks, the network layer
always stays the same.
The network layer speaks a specific protocol. The internet (the one that serves you websites)
uses TCP/IP. All nodes in a TCP/IP network are assigned a globally unique address
(within that network) so that other hosts can find it.
|-
| 4) Transport || segments || netstat, netcat, tcpdump ||
Low level connectivity between hosts happens here. This is the languages that carry
the data. Examples of transport layer protocols are HTTP, DHCP, BGP, SSH, LDAP, POP, XMPP, ...
This is also the layer that carries ICMP error messages.
|-
|}
</blockquote>
== Example Transaction ==
== Example Transaction ==
<blockquote>
<blockquote>

Revision as of 01:45, 8 August 2021

TODO:

this page is abysmal. fix.

Resources

router overview https://www.uhcl.edu/computing/information-security/tips-best-practices/routers

Tutorials

code a TCP/IP stack https://www.saminiir.com/lets-code-tcp-ip-stack-1-ethernet-arp/

5-layer TCP/IP model

- layer protocol unit address
1 physical 10 Base T, 802.11 Bits n/a
2 datalink Ethernet, WiFi Frames MAC addr
3 network IP Datagram IP addr
4 transport TCP, UDP Segment Ports
5 application HTTP, SMTP, .. Messages n/a

Intro

Example Transaction

An example might help this sink in. 

visit a website: #(GET request on server's port 80)

transport (HTTP)
   request is sliced into segments(transport) of 536 bytes or smaller

network (TCP/IP)
   if network knows how to reach destination, each segment is wrapped in
   TCP/IP info, and handed off to the datalink layer.

datalink (MAC,ARP)
   Adds information about the physical protocol (ethernet, token-ring, ...) 
   and fires the data to a target MAC address.

---

physical
   the information is sent over the wire

--- 

On the receiving end, datalink, and network layers are stripped off, and all 
segments (transport) are re-assembled to form the request. This is handed to
the web-server, which then repeats the above with a reply.

Layers

Physical

coax
optical

Datalink

protocols
ethernet most commonly used protocol for the datalink layer


terminology
routing schemes broadcast, unicast, multicast, ...
duplex If traffic can be sent/received at the same time
MTU the largest allowed frame-size (datalink) on a network.
Network Configurations
vlan using one NIC/cord to share multiple connections to separate networks (ex: WAN/LAN on firewall)
Datalink Errors
frame errors Frames received with an invalid checksum.
drops Frames that were discarded by the netwk iface. unexpected VLAN tags, ipv6 packets when iface is not configured for ipv6.
overruns Too much data received too quickly (before kernel can handle them). The buffer is full, so packets are dropped.
collisions On half-duplex netwk, when 2x sides of a connection are talking at the same time.

finding datalink errors 

netstat -i

## Windows does not officially support viewing datalink errors. check the switch

TX-     ## packets sent
RX-     ## packets received


*-OK   ## correctly recceived frames
*-ERR  ## incorrect packets received
*-DRP  ## packets dropped at this interface
*-OVR  ## packets this interface was unable to receive

Network

Protocols
ipv4
ipv6


Transport

Protocols
tcp
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