Networking

IMAGE GALLERY (1)

netfilter¹

Netfilter is a framework provided by the Linux kernel that allows various networking-related operations to be implemented in the form of customized handlers. Netfilter offers various functions and operations for packet filtering, network address translation, and port translation, which provide the functionality required for directing packets through a network and prohibiting packets from reaching sensitive locations within a network.

How to find out Wireless Networking info?

1. command-line tool for controlling NetworkManager
2. Show radio switches status
3. List all visible wifi SSID with signal strength, and bars
4. COnneccting to wifi using cli
5. Manage network

Who are connect to my wifi?

xerosploit

Effcient and advanced man in the middle framework

Inject HTML

Inject javascript

DoS attack

> sudo xerosploit
> scan

Opensource Firewalls

Very important when exposed to external world

iptables

baked into linux

ufw

uncomplicated firewall

ufw --dry-run status verbose
ufw --dry-run enable/disable
ufw --dry-run reset
ufw show raw

ufw --dry-run default deny incoming
ufw --dry-run default allow outgoing

ufw --dry-run allow/deny ssh/22/tcp/udp

ufw --dry-run allow from 192.168.1.1                    # default gateway
ufw --dry-run allow from 192.168.1.1 to any port 22
ufw --dry-run allow from 192.168.1.1/24
ufw --dry-run status numbered

ufw --dry-run delete 1/deny 80/tcp
ufw logging on/off

Types

• Instant virtual network with mininet²

  Bridges

Used a lot with virtualization

• Divide LAN into multiple segments
• works under Data link layer
  • works with MAC address of device

• Any request is first sent to bridge, then bridge decides which segment to broadcast the data to

• Home router IPs are always 192.168.*.*

• ISP provided IP address 24.*.*.*

  brctl
  networkctl list
  networkctl status
  

Troubleshooting Network

• Analysize communication using tcpdump
  • -A - print in ASCII

How do I add eth2 to my linux machine?

On Linux machines, eth0 and eth1 correspond to real network ports. To add an eth2, you’ll need to add another NIC, either by adding an internal PCI(e) network card, or by adding a USB network adapter.

• How do I create virtual ethernet devices in linux?
• TUN and TAP virtual network interfaces

Networking tasks

1. check interface status and IP
2. Release and renew IP from DHCP server
3. eth0 is the first netwrok card in system
4. Internet routung is self-healing. Whst if we nuke a router?
5. VPN - uses Tunneling Protocol, encryption
   1. Tunnel can recreate itself in case of Man-in-the-middle-attack
6. interface eth0.1 is a virtual interface with VLAN ID 1 having eth0 as its parent interface.
7. A Linux bridge behaves like a network switch. It forwards packets between interfaces that are connected to it. It’s usually used for forwarding packets on routers, on gateways, or between VMs and network namespaces on a host. It also supports STP, VLAN filter, and multicast snooping.

8. DHCP 4 step protocol stages

   1. DHCPDISCOVER
   2. DHCPOFFER
   3. DHCPREQUEST

   4. DHCPACK 9.

      # Release and renew DHCP client
      dhclient
      /etc/init.d/networking
      

Footnotes