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# System prepended metadata

title: Lecture 03B Network Protocols
tags: [School, NETF, Notes, DISM]

---

---
title: 'Lecture 03B Network Protocols'
disqus: hackmd
---

:::info
ST1010 Networking Fundamentals
:::

Lecture 03B Network Protocols
===

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## Table of Contents

[TOC]

Telnet
---
- allow user to login remotely to another system
- port 23
- old protocol - data not encrypted
    - use SSH (secure shell)

Secure Shell (SSH)
---
- popular for remote login
- port 22
- data encrypted

Email Protocols
---
### Simple Mail Transport Protocol (SMTP)
- to transmit emails between computers
    - server to server or client to server

### Post Office Protocol (POP3)
- emails stored in mail server
    - users use own client comps to retrieve emails from server
- POP3 used to retrieve these emails
- POP3S - secured

![](https://i.imgur.com/63oz4Gh.png)

### Internet Message Access Protocol (IMAP4)
- alt to POP3
- IMAPS - secured


Address Resolution Protocol (ARP)
---
- when device has packet to send, will look at dest ip
    - determines if dest ip on same local network
        - look at net part of ip addr
    - if dest not local, packet sent to gateway
    - if dest local, send packet to dest
- MAC needed to send packet to dest on local network

#### To Find MAC Addr of IP Addr
- sender look at ARP table
- if ip not in arp table, sender send arp broadcast to all devices in local network to ask who has that ip addr
- device with ip addr send arp reply to sender with its mac
- sender send packet to the mac addr
- sender update arp table with the mac in case need to send more packets again

#### Find MAC Addr on Different Network
- src comp uses arp to retrieve mac addr of router configed as default gateway
- packet delivered to router
    - router determine whr packet shld go next
- when packet gets to dest network, router on dest network use arp to get dest comp's mac
- packet delivered to dest comp

### ARP Poisoning/Spoofing
- atker poison arp table
    - cause devices to send packets to him

#### Normal Scenario
![](https://i.imgur.com/Z0Wrqfc.png)

#### Attack Scenario
![](https://i.imgur.com/8lvlhtl.png)


Domain Name System (DNS)
---
- dns server translate fully qualified domain names (Eg. www.yahoo.com) to IP addr (Eg. 72.30.38.140)
- dns is distributed db system running on internet
- ea domain have 1 or more dns servers
- dns server (AKA nameserver) contain db holding section of domain names mapped to IP addr

![](https://i.imgur.com/OAFUhr4.png)

#### How it Works
![](https://i.imgur.com/Dnt5G8M.png)

### DNS Poisoning/Spoofing
- atker edit dns db/cache
    - direct users to his own website
- proper config of dns can reduce risks of this atk

#### Example
![](https://i.imgur.com/BAGvN5G.png)


Simple Network Management Protocol (SNMP)
---
- for remote monitoring & management of network nodes
- snmp manager monitors set of snmp agents installed on network nodes
    - check perf of monitored nodes
    - make changes in config of monitored nodes
- snmp agent can send warning to snmp manager of unusual situations

### Ping Sweeps
- ping sweep sends ping packets to range of IP addr to see which system will reply
- used to see which system is alive
- AKA ICMP sweep

### Basic Port Scan
- when send SYN packet to web server on port 80, it send back SYN/ACK packet as 3 way handshake

![](https://i.imgur.com/yGRpmAm.png)

- if port 80 not opened, no packet sent back

![](https://i.imgur.com/13YGYjF.png)

- firewalls can be configed to blk such port scans

![](https://i.imgur.com/Rdq1E0R.png)


Banner Grabbing
---
- many services return info like ver num when client connects to it
    - AKA banner
- banner grabbing - method to find more info abt running service
    - usually telnet/netcat used for banner grabbing

Summary
---
![](https://i.imgur.com/X41FXoy.png)



###### tags: `NETF` `DISM` `School` `Notes`