What are Azure availability sets?

An availability set is a logical grouping of two or more VMs that helps to keep the application hosted in the Azure cloud, available during planned or unplanned maintenance.

Planned events such as patch security vulnerabilities, improve performance, and add or update features can be considered as a Planned Maintenance. Where as, an unplanned maintenance are events that involves a hardware failure in the data center, or a power outage or a disk failure etc. On such events, cloud providers needs to ensure that their customers are not affected by any of these events. To achieve this in the Azure cloud, one of the method is to use availability sets. VMs that are part of an availability set automatically switch to a working physical server so the VM continues to run. The group of virtual machines that share common hardware are in the same fault domain. A fault domain is essentially a rack of servers. It provides the physical separation of your workload across different power, cooling, and network hardware that support the physical servers in the data center server racks. In the event the hardware that supports a server rack becomes unavailable, only that rack of servers is affected by the outage.

For example, during the monthly patching activity, the VMs are required to reboot. Using Availability Sets, one VM can be rebooted at a time and the other will be up achieving fault tolerance and zero downtime.

Preparing for Azure Cloud Certifications? Browse my related posts.

Cisco ASA: Disable SSLv3 and configure TLSv1.2.

For configuring TLS v1.2, the ASA should run software version 9.3(2) or later. In earlier versions of ASA, TLS 1.2 is not supported.If you are running the old version, it's time to upgrade. But before that i will show you the config prior to the change. I am running ASA version 9.6.1 Now ,set the server-version to tlsv1.2, though ASA supports version tlsv1.1, its always better to configure the connection to more secure. Server here in the sense, the ASA will be act as the server and the client will connect to the ASA. #ssl server-version tlsv1.2 set the client-version to tlsv1.2, if required. #ssl client-version tlsv1.2 ssl cipher command in ASA offers 5 predefined security levels and an additional custom level. #ssl cipher tlsv1.2 high we can see the setting of each cipher levels using #show ssl cipher command. Now set the DH group to 24, which is the strongest offered as of now in the ASA. #ssl dh-group group24 An

RUST error: linker `link.exe` not found

While compiling Rust program in a windows environment, you may encounter the error : linker `link.exe` not found. This is because of the absence of the C++ build tools in your machine. For compiling Rust programs successfully, one of the prerequisites is the installation of the Build Tools for Visual Studio 2019. Download the Visual Studio 2019 Build tools from the Microsoft website. After the download, while installing the Build tools, make sure that you install the required components (highlighted in Yellow) This will download around 1.2GB of required files. Once everything is successfully installed, reboot and re-run your rust program and it will compile successfully. Read More on RUST Hello World Rust Program : Code explained RUST Cargo Package Manager Explained Data Representation in Rust.

How to Install Netmiko on Windows?

Netmiko, developed by kirk Byers is an open source python library based on Paramiko which simplifies SSH management to network devices and is primarily used for network automation tasks. Installing Netmiko in linux is a matter o f one single command but if you need to use Netmiko in your Windows PC, follow this process. 1) Install the latest version of Python. 2) Install Anaconda, which is an opensource distribution platform that you can install in Windows and other OS's (https://www.anaconda.com/download/) 3) From the Anaconda Shell, run “ conda install paramiko ”. 4) From the Anaconda Shell, run “ pip install scp ”. 5) Now Install the Git for Windows. (https://www.git-scm.com/downloads) . Git is required for downloading and cloning all the Netmiko library files from Github. 6) From Git Bash window, Clone Netmiko using the following command git clone https://github.com/ktbyers/netmiko&#8221 7) Once the installation is completed, ch

What is a Gratuitous ARP? How is it used in Network attacks?

Many of us encountered the word "Gratuitous" while exploring the network topic on ARP, The Address Resolution Protocol. Before explaining Gratuitous ARP, here is a quick review on how ARP works. ARP provides IP communication within a Layer 2 broadcast domain by mapping an IP address to a MAC address.For example, Host B wants to send information to Host A but does not have the MAC address of Host A in its ARP cache. Host B shoots a broadcast message for all hosts within the broadcast domain to obtain the MAC address associated with the IP address of Host A. All hosts within the same broadcast domain receive the ARP request, and Host A responds with its MAC address. We can see the ARP entries on our computers by entering the command arp -a . So, back to the topic on what is a Gratuitous reply, here is a better explanation. Gratuitous arp is when a device will send an ARP packet that is not a response to a request. Ideally a gratuitous ARP request is an ARP request packe

Google Cloud : Basic Cloud Shell commands

Google Cloud resources can be managed in multiple ways. It can be done using Cloud Console, SDK or by using Cloud Shell. A few basic Google Cloud shell commands are listed below. 1) List the active account name gcloud auth list 2) List the project ID gcloud config list project 3) Create a new instance using Gcloud shell gcloud compute instances create [INSTANCE_NAME] --machine-type n1-standard-2 --zone [ZONE_NAME] Use gcloud compute machine-types list to view a list of machine types available in particular zone. If the additional parameters, such as a zone is not specified, Google Cloud will use the information from your default project. To view the default project information, use gcloud compute project-info describe 4) SSH in to the machine gcloud compute ssh [INSTANCE_NAME] --zone [YOUR_ZONE] 5) RDP a windows server gcloud compute instances get-serial-port-output [INSTANCE_NAME] --zone [ZONE_NAME] 6) Command to check whether the server is ready f

Recovery Procedure: Alcatel-Lucent Omni-Switch not booting AOS: Going to Mini-boot prompt.

Problem: Switch not booting AOS; Going to Mini-boot prompt. Model: Alcatel-Lucent OS6850 [Note:The same procedure might be applicable for different models of Omni-Switches, However, for this illustration, i have used OS-6850 ] Reason: This problem may occurs due to corrupt AOS image files or misconfigured boot parameters. Hence switch cannot boot the images properly and will go to Mini-boot prompt. Work Around: [Note: This zmodem procedure consumes a lot to time to finish the process.] 1.) Power off your OS6850 2.) When you switched it back on, stop it before the Miniboot (there is some counter counting down from 4). Press Enter to break. 3.) You will have the following prompt " => " 4.) Enter " setenv baudrate 115200 ”. Increasing baudrate helps to increase the data transfer speed using zmodem. 5.) Enter " saveenv " 6.) Enter " boot " 7.) The switch should run now in baud rate 115200 (so you have to change your clients ter

PrintNightmare (CVE-2021-1675) PoC exploit Walkthrough

I am not an exploit developer but was interested to see how this vulnerability can be exploited. So i tried to replicate the infamous PrintNightmare vulnerability using the following PoCs ( https://github.com/cube0x0/CVE-2021-1675 ) and ( https://github.com/rapid7/metasploit-framework/pull/15385 ) However i had trouble with the new metasploit module (auxiliary/admin/dcerpc/cve_2021_1675_printnightmare) and i couldn't able to exploit the machine successfully. So i tried the second PoC from cube0x0. This one has done the magic. I just followed the guidelines with couple of tweaks. First of all, i installed the impacket (cube0x0 version) which will install the required modules and files. After that i set up a samba share with an anonymous login. This is required for hosting the dll file. I edited the smb.conf with the following settings. [global] map to guest = Bad User server role = standalone server usershare allow guests = yes idmap config * : backend = tdb s

Cisco Modular Policy Framework (MPF) : A brief Introduction

Modular Policy Framework (MPF) configuration defines set of rules for applying firewall features, such as traffic inspection, QoS etc. to the traffic transiting the firewall There are 3 main components in creating a MPF. 1) Class Map Class map is used to identify the type of traffic. This can be done by creating an ACL. 2) Policy Map Policy Map specifies what action the ASA should take against the traffic identified by the Class Map. 3) Service Policy Finally Service policy specifies where to apply it. The policy is applied to an interface or Globally. Udacity has special offers worldwide to help anyone learn important, higher-paying job skills during this challenging time. Click here to get your offer and start learning now! Sample Illustration Consider the following Command lines. access-list OUTSIDE-TO-INSIDE permit tcp any any eq ftp <--- The above ACL will allow FTP traffic. This ACL can be different than the Interface ACL---> class-map FTP-CLASS-MAP match ac

Microsoft Windows NLB Feature for Stateful Applications

NLB is a software-based load balancer (Windows Feature) that resides on each member in the cluster. Load Balancing is based on number of client connection requests and the NLB algorithm does not dynamically respond to changes in the load on each cluster host (such as the CPU load or memory usage or Network Usage). Thus, If client population is less and/or the connections produce varying loads on the server, the load balancing algorithm of Microsoft NLB is less effective. Udacity has special offers worldwide to help anyone learn important, higher-paying job skills during this challenging time. Click here to get your offer and start learning now! To understand how NLB preserve the session state, first let me take you through the difference between a stateful and stateless connections: Stateless The application connection is said to be stateless if the server does not store any state about the client session instead the session data is saved at th client side. The server does n

Cisco ASA Firewall: Packet Flow/Mode of Operation

Scenario : So here is a packet initiated from Inside to the Outside [ingress to egress]. 1) A user who is sitting inside of the network is trying to access a website located at the Internet (outside) 2) The packet hits the inside interface (Ingress) of ASA. 3) Once the packet reached ASA, it will verify whether this is an existing connection by checking its internal connection table. If it is an existing connection, the ACL check (step 4) will be bypassed and move to step 5. ASA will check for the TCP flag if its a TCP packet. If the packet contains a SYN flag, then the new connection entry will be created in the connection table(connection counter gets incremented). Other than SYN flag, the packet will be discarded and a log entry will be created. "Remember the 3-way handshake process. SYN/SYN-ACK/ACK. If the TCP connection flags are not in the order as it is intended to be, ASA will simply drop the packet. Most of the scanning/attacks are done by these flag manipula

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