Home

This is an intuitive blog on Network Principles and Case Studies. This is a place for learning, helping and sharing networking knowledge.

Our initiative is to provide large scale knowledge-base on TCP/IP, BGP, OSPF, IS-IS, MPLS, Traffic Engineering. This a one of the very few places where you can find a integrated learning materials with hand on lab. Also the virtual appliances you can download from here to use in different network simulators like GNS-3 and EVE-NG.

DHCP Operation
DHCP is a client/server protocol used to assign configuration(ip, gateway, dns, options etc.) to hosts dynamically. It is an extension of BOOTP protocol and backward compatibility is maintained. DHCP essentially uses BOOTP message format added with some options filed using UDP(Port 67 & 68). Clients/Hosts send request to DHCP servers for IP address and Server respond with a free IP address from it’s IP pool. A IP Pool is a contiguous range of IPs allocated for DHCP use. Server/Client perform the sanity check for the IP offered/allocated by sending a ARP request. Server also inform the client about how much time it can use the allocated IP, it’s called lease duration. Once the lease duration is expired, a client can extend the lease by requesting a renew of that address from the server. DHCP Message Formats In a general scenario DHCP mainly uses Discover, Offer, Request and Acknowledge messages, it’s […]
Tags   dhcp dhcp ack dhcp discover dhcp lease dhcp offer dhcp reuest dhcp transaction id dhcpdecline dhcpinform dhcpnak dhcprelease dora 
Gratuitous ARP & Proxy ARP
Remember OLD DR
Introduction - Preemption vs Remember OLD DR. Remembering old DR is an optimization of DR/BDR election process. It's a Cisco proprietary and use to enable fast DR recovery in a multi-access network.
Tags   dr ospf remember old dr 
BGP Stuck in ACTIVE & IDLE
BGP Neighbor States – IDLE – CONNECT – ACTIVE From this explanation we might understand that a BGP process remains in ACTIVE state is due to TRANSPORT ERROR means the BGP process is unable to initiate a TCP Connection to the Neighbor. Refer the below flow chart where it explains the FSM transitions of three states IDLE, CONNECT and ACTIVE. In real-time BGP never remain in an particular state other than ESTABLISHED. Actually it flaps between IDLE, CONNECT and ACTIVE. BGP Stuck in IDLE Input Events 1 & 13 causes the IDLE state remain in IDLE state. IE1 is BGP START event and IE13 is BGP Notification Received. Also IE 2, 4, 6, 8, 9, 13 causes other BGP states to transit back to IDLE. So the possible reason for a BGP router remain in IDLE is mentioned below. BGP Stuck in ACTIVE Input Event 5 cause the ACTIVE state […]
Tags   bgp bgp-fsm bgp-stuck-in-active bgp-stuck-in-idle 
BGP Message Types & FSM
In this tutorial we will discuss about different message types of BGP, BGP Peer Connection, BGP Finite State Machine. Before establishing BGP Peer Connection, two neighbor must perform TCP Three-Way-Handshake and open a connection to Port number 179. BGP is a Transport Layer Protocol, hence TCP provides fragmentation, acknowledgement, sequencing functions necessary for reliable connection. BGP Peer must be statically configured and a route must present in the routing table. All the BGP Messages are unicast over TCP Connection. BGP Uses five basic message. BGP Messages All BGP Messages have a common header and encapsulated into a TCP Fragment. Header consists of Marker, Length and Type of the BGP Messages. A Keepalive message is nothing but a BGP Header. Open Message consists of version number of bgp, autonomous system number of the originating router, hold time, bgp identifier and optional parameters for capabilities negotiation. A Update Message consists of withdrawn […]
Tags   bgp-fsm bgp-input-events bgp-message-types bgp-stuck-in-active 
BGP Path Selection Algorithm
In this discussion we will dive into the BGP Path Selection Algorithm. There are 3 (Rejection, Selection, Tie-Break) rounds of BGP Path Selection which involve 18 different steps. The first round is Rejection where any route matching certain condition will be rejected. The second Round is Selection where BGP Best Path Compiler will choose a path matching certain conditions. The last round is Tie-Break where the BGP Best Path Compiler will make the final decision based on certain criteria. Rejection Round Any roues matching the following conditions will be rejected by default. The above behavior can be changed with explicit configuration. We will discuss each with an example in another tutorial. Selection Round In this steps one route will be preferred over another in case it fulfill the any of the below conditions which include certain Path Attributes and other constraints. You can further remember the steps with the following […]
Tags   bgp-pa bgp-path-attribute bgp-path-selection path-attribute 
Selection of iBGP & EBGP Paths
In a situation where a route coming from both ebgp and ibgp peer, the best path election will takes place in two different way. If the rote is locally originated then it will prefer ibgp path, otherwise it will chose ebgp path.
Tags   BGP Distance bgp-path-selection iBGP over EBGP prefer iBGP over EBGP 
BGP Prefix Independent Convergence
Attribute Flag & Affinity Bit – MPLS Traffic Engineering

MikroTik on GNS3
Follow the article to Simulate a mikrotik router in GNS3. Download the appliances from our database and using QEMU on GNS3 you can easily start the MikroTik Router. You have to simply configure the QEMU and import the iso/img file onto it. Refer to the following sections for further details.
Tags   download mikrotik image gns3 mikrotik-6.15.iso mikrotik-6.28.iso mikrotik.img mikrotrik simulation 
Running Cisco Switches on GNS3
Running Cisco Catalyst Switch(CLI) on GNS3 using IOU (IOS on Unix) and VirtualBox Downlaods File Name Download  CiscoKeyGen.py GNS3 IOU VM 1.3.1rc4.ova GNS3 IOU VM_1.2.3.ova GNS3 IOU VM-disk1.vmdk GNS3 IOU VM.vbox GNS3 IOU VM.vbox-prev iourc.txt Cisco IOU Virtualbox and GNS3.zip   Cisco IOU Compaitable Images.zip   Import IOU in VirtualBox The IOU Vmware zip file contains a full load of stuffs. You need only one. VirtualBox IOU VM Host Settings  After that open the vmdk file in VirtualBox and do some little changes in settings. Set the memory requirement as 256MB and it is enough to open the IOU VM. Before you start the VM, do not forget to set the Virtual Network Adapter settings as Host Only. Now time to fire up the VM and after successful booting the VirtualBox console will come up with a login prompt with a notification to browse the VM through browser to upload […]
Tags   cisco iou download iou images gns3 i86bi-linux-l2-adventerprisek9 i86bi-linux-l3-adventerprisek9 iou 
ASA in GNS3
Install ASA in GNS3  – Integrate ASDM to ASA  Downloads Step 1: Extract ASA zip file. It contains the  two image file ‘asa842-vmlinuz.kernel’ & ‘asa842-initrd’. Now you need to open GNS3.  Go to preferences in the edit tab.  Then go to Quemue VM. Opne a new Quemue VM by clicking new. Now set the name and type of the Quemue VM  ‘ASA8.4(2)‘. Step 2: Set the Quemue Binary executable path and RAM size. Step 3: Choose initrd and kernel image into proper boot specific location. Please note that at the time of importing do not make these image as default for this platform.     Now ASA rendering to GNS is complete. Its time to explore the rest of the ASA magic. Before that please take a look of my network diagram(physical and virtual) and how I actually implemented in my virtual platform.   Now to implement in my system I did the following […]
Tags   asa asa firewall asa in gns3 gns3 
Juniper Tutorial
 Import a Juniper Vmware VirtualBox Host in GNS3  – Run Juniper  in GNS3 
Tags   
Fortigate VM (v5.0) on VMware
Installation of Fortigate VM version 5.0 in VMware and initial setup. Download Fortigate VM(v5.0):arrow:  for VMware. This version is more faster than Fortigate VM version 4.0 and performance is better.
Tags   
Juniper Legacy vMX on GNS3
This discussion is regarding what all it takes to get the legacy single-VM versions of vMX to run via GNS3. Since they are far more lightweight (resource-wise) than the split VM public releases of vMX, you might want to consider tracking these down. Sure, they are missing features, but they’re perfect if you want to dip your toes in Juniper’s “water”, and you can easily use multiple instances in a topology.
Tags   legacy vmx vfp vmx 
EVE-NG in the Cloud I have been running GNS3 since last couple of years but when it comes to a large scale network simulation with high end devices my Laptop, the resources doesn’t support. This brought me to seeking a way to run EVE-NG on scalable and expandable resources. Configuring Eve-NG on Google Compute Engine In this tutorial I will walk-through on how to deploy Eve-NG on the cloud and more specifically on Google Compute Engine. I’ve tried Eve-NG on AWS and Azure but neither of them actually worked since nested virtualization isn’t supported. Google Compute Engine was also the cheapest option. It provide $300 free credit during registration which is valid for 12 Months. If you use the GCP VM only once required, the approximate uptime with variable resources are estimated below. Go to https://cloud.google.com/products/calculator/ to estimate the cost. Step 1: Connect to Google Cloud Platform (GCP) https://console.cloud.google.com/getting-started Step 2: […]
Tags   
Begin With Checkpoint
Get started with most powerful network security appliance Checkpooint and most popular security management system GAiA
Tags   
Checkpoint Part 2
We have ended up with the VMware setup to launch the Checkpoint (GAiA Virtual Edition) 💡  Begin With Checkpoint. We will now begin the procedure of installing GAiA(R76).
Tags   
Running FortiOS (Fortigate VM) in VMware

Tags   
Getting Started with HP
This discussion covers HP router and Switch Simulations 💡 
Tags   
Juniper Tutorial
 Import a Juniper Vmware VirtualBox Host in GNS3  – Run Juniper  in GNS3 
Tags   
Packet Capture and Analyze
In this tutorial I will demonstrate how to capture packets using Wireshark and export captures in a web compatible format to view outputs in a user friendly environment. Exporting Data Wireshark provides a variety of options for exporting packet data. This section describes general ways to export data from the main Wireshark application. We will only use XML format and a script(in XSLT) to customize outputs. After you have loaded a capture file into Wireshark, choose File → Export Packet Dissections → as XML PDML and save the new file. How to convert PDML to HTML You can convert such a PDML file into HTML to view in a web browser. This is done with a XSLT (EXtensible Stylesheet Language) file called pdml2html.xsl.You can download the file from the below link. If you want to use the PDML file on a web server, all that is required is to place the pdml2html.xsl file in the same directory where the PDML […]
Tags   packet capture wireshark 
Search & Download
Appliances for more than 10 Hardware Vendors like Cisco, Juniper, Huawaei, HP, Palo-Alto, F5, Checkpoint, Alcatell-Lucent, Erricson, Riverbed etc.
Tags   asa commware csr dsl linux ensp fortios ftos gaia hp ns ios iou ltm mikrotik nexus olive srx pa-vm srcpe timos veos vios vmx vsr vsrx vxr 
EVE-NG in the Cloud I have been running GNS3 since last couple of years but when it comes to a large scale network simulation with high end devices my Laptop, the resources doesn’t support. This brought me to seeking a way to run EVE-NG on scalable and expandable resources. Configuring Eve-NG on Google Compute Engine In this tutorial I will walk-through on how to deploy Eve-NG on the cloud and more specifically on Google Compute Engine. I’ve tried Eve-NG on AWS and Azure but neither of them actually worked since nested virtualization isn’t supported. Google Compute Engine was also the cheapest option. It provide $300 free credit during registration which is valid for 12 Months. If you use the GCP VM only once required, the approximate uptime with variable resources are estimated below. Go to https://cloud.google.com/products/calculator/ to estimate the cost. Step 1: Connect to Google Cloud Platform (GCP) https://console.cloud.google.com/getting-started Step 2: […]
Tags   
MikroTik on GNS3
Follow the article to Simulate a mikrotik router in GNS3. Download the appliances from our database and using QEMU on GNS3 you can easily start the MikroTik Router. You have to simply configure the QEMU and import the iso/img file onto it. Refer to the following sections for further details.
Tags   download mikrotik image gns3 mikrotik-6.15.iso mikrotik-6.28.iso mikrotik.img mikrotrik simulation 
Running Cisco Switches on GNS3
Running Cisco Catalyst Switch(CLI) on GNS3 using IOU (IOS on Unix) and VirtualBox Downlaods File Name Download  CiscoKeyGen.py GNS3 IOU VM 1.3.1rc4.ova GNS3 IOU VM_1.2.3.ova GNS3 IOU VM-disk1.vmdk GNS3 IOU VM.vbox GNS3 IOU VM.vbox-prev iourc.txt Cisco IOU Virtualbox and GNS3.zip   Cisco IOU Compaitable Images.zip   Import IOU in VirtualBox The IOU Vmware zip file contains a full load of stuffs. You need only one. VirtualBox IOU VM Host Settings  After that open the vmdk file in VirtualBox and do some little changes in settings. Set the memory requirement as 256MB and it is enough to open the IOU VM. Before you start the VM, do not forget to set the Virtual Network Adapter settings as Host Only. Now time to fire up the VM and after successful booting the VirtualBox console will come up with a login prompt with a notification to browse the VM through browser to upload […]
Tags   cisco iou download iou images gns3 i86bi-linux-l2-adventerprisek9 i86bi-linux-l3-adventerprisek9 iou 
ASA in GNS3
Install ASA in GNS3  – Integrate ASDM to ASA  Downloads Step 1: Extract ASA zip file. It contains the  two image file ‘asa842-vmlinuz.kernel’ & ‘asa842-initrd’. Now you need to open GNS3.  Go to preferences in the edit tab.  Then go to Quemue VM. Opne a new Quemue VM by clicking new. Now set the name and type of the Quemue VM  ‘ASA8.4(2)‘. Step 2: Set the Quemue Binary executable path and RAM size. Step 3: Choose initrd and kernel image into proper boot specific location. Please note that at the time of importing do not make these image as default for this platform.     Now ASA rendering to GNS is complete. Its time to explore the rest of the ASA magic. Before that please take a look of my network diagram(physical and virtual) and how I actually implemented in my virtual platform.   Now to implement in my system I did the following […]
Tags   asa asa firewall asa in gns3 gns3 
Getting Started with HP
This discussion covers HP router and Switch Simulations 💡 
Tags   
Getting Started With Huawei
Simulate Huawei Router and Switches and connect them to GNS3
Tags   
Begin With Checkpoint
Get started with most powerful network security appliance Checkpooint and most popular security management system GAiA
Tags   
Checkpoint Part 2
We have ended up with the VMware setup to launch the Checkpoint (GAiA Virtual Edition) 💡  Begin With Checkpoint. We will now begin the procedure of installing GAiA(R76).
Tags   
Cisco IOS Upgrade Using USB Flash
Cisco IOS Upgrade 3 Easy steps to upgrade the software version of a Cisco ASR Series Router.
Tags   
Juniper Tutorial
 Import a Juniper Vmware VirtualBox Host in GNS3  – Run Juniper  in GNS3 
Tags   
JunOS Upgrade Using USB Flash
Upgrade JunOS ↗ in ACX2200 through USB stick
Tags   
Fortigate VM (v5.0) on VMware
Installation of Fortigate VM version 5.0 in VMware and initial setup. Download Fortigate VM(v5.0):arrow:  for VMware. This version is more faster than Fortigate VM version 4.0 and performance is better.
Tags   
Running FortiOS (Fortigate VM) in VMware

Tags   
Juniper Legacy vMX on GNS3
This discussion is regarding what all it takes to get the legacy single-VM versions of vMX to run via GNS3. Since they are far more lightweight (resource-wise) than the split VM public releases of vMX, you might want to consider tracking these down. Sure, they are missing features, but they’re perfect if you want to dip your toes in Juniper’s “water”, and you can easily use multiple instances in a topology.
Tags   legacy vmx vfp vmx 

DHCP Operation

DHCP is a client/server protocol used to assign configuration(ip, gateway, dns, options etc.) to hosts dynamically. It is an extension of BOOTP protocol and backward…
Read More

BGP Message Types & FSM

In this tutorial we will discuss about different message types of BGP, BGP Peer Connection, BGP Finite State Machine. Before establishing BGP Peer Connection, two…
Read More

Search & Download

Appliances for more than 10 Hardware Vendors like Cisco, Juniper, Huawaei, HP, Palo-Alto, F5, Checkpoint, Alcatell-Lucent, Erricson, Riverbed etc.
Read More

EVE-NG

EVE-NG in the Cloud I have been running GNS3 since last couple of years but when it comes to a large scale network simulation with…
Read More

MikroTik on GNS3

Follow the article to Simulate a mikrotik router in GNS3. Download the appliances from our database and using QEMU on GNS3 you can easily start…
Read More

ASA in GNS3

Install ASA in GNS3  – Integrate ASDM to ASA  Downloads Step 1: Extract ASA zip file. It contains the  two image file ‘asa842-vmlinuz.kernel’ & ‘asa842-initrd’. Now you…
Read More

Checkpoint Part 2

We have ended up with the VMware setup to launch the Checkpoint (GAiA Virtual Edition) 💡  Begin With Checkpoint. We will now begin the procedure…
Read More

Fortigate VM (v5.0) on VMware

Installation of Fortigate VM version 5.0 in VMware and initial setup. Download Fortigate VM(v5.0):arrow:  for VMware. This version is more faster than Fortigate VM version 4.0 and…
Read More

Remember OLD DR

Introduction – Preemption vs Remember OLD DR. Remembering old DR is an optimization of DR/BDR election process. It’s a Cisco proprietary and use to enable…
Read More