---
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


### 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

#### Attack Scenario

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


#### How it Works

### 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

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


- if port 80 not opened, no packet sent back


- firewalls can be configed to blk such port scans


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
---

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