Learning Linux – bookmarks and commands I forget :)

This post is for my self-learning and I’ll be updating it with all the handy docs/blogs I come across over the internet.

Linux Directory Structure

How to Use Fdisk to Manage Partitions on Linux

sudo lsblk - Check file system
sudo vmblank_mode=0 vmware - to start vmware as root and for some reason I have to set the vmblank




Dynamic Multipoint VPN (CCIE Notes)

Disclaimer: These are my rough cut notes for CCIE Security studies! Not a detailed explanation of DMVPN.

Three components that make up DMVPN:

1. Mulitpoint GRE (mGRE)

  • Tunnel interface having multiple tunnel destinations unlike a point-to-point GRE tunnel that has a single tunnel destination.

2. Next-Hop Resolution Protocol (NHRP)

  • Each router in an NHRP topology acts as either a NHC or a NHS.
  • mGRE uses NHRP for mapping logical/tunnel IP address to physical/real IP addresses.
  • NHC registers its physical-to-tunnel mapped IP address to the NHS and the NHS acts as a database agent which stores all registered mappings and replying to NHC queries.
  • If a NHS does not have a requested entry in its database, it can forward packet to another NHS to see if it has the requested association.

3. Cisco Express Forwarding (CEF)

  • Cisco Express Forwarding (CEF) is a packet-switching technique which provides the ability to switch packets through a device in a very quick efficient way while also keeping the load on the router’s processor low.
  • CEF is made up of two different main components: the Forwarding Information Base (FIB) and the CEF Adjacency Table.

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TCP Intercept for DoS Attack Prevention (CCIE Notes)

TCP Intercept

  • It protects a TCP server from TCP SYN-flooding attacks (DoS) attacks.
  • It intercepts and validates TCP connection requests.
  • Establishes connection with the client on behalf of the destination server, and if successful, establishes a connection with the server on behalf of the client and knits the two half connections transparently.
  • Either all requests can be intercepted or those coming from specific networks or destined for specific servers.

Modes of Operation:

Intercept Mode

  • This is the default mode.
  • Performs a three-way handshake with the client, if successful, sends the original SYN packet to the destination server and performs a three-way handshake with the server.
  •  When this is completed, the two half connections are joined.

Watch mode

  • Connection requests are allowed to pass through the router to the server but are watched until they become established.
  • If requests fail to establish within 30 seconds (default), the software sends a reset request to the server to clear up its state.

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Analyzing FW Monitor Output in CLI

If you understand the inspection points in Check Point and can use FW Monitor to get the required logs/captures then you can read further on how how to analyze those logs.

Click to enlarge

So to start off with, lets see what the different fields are in the above picture of a sample log from the console;

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