Microsoft Azure

Networking — Virtual Network & NSGs

Build an isolated private network with subnets and control traffic with Network Security Groups.

An Azure Virtual Network (VNet) is your private, isolated network, defined by an address space (e.g. 10.0.0.0/16) and divided into subnets. Resources placed in subnets communicate privately. Internet egress for private resources typically goes through a NAT Gateway or a firewall; inbound public traffic enters via a public IP on a Load Balancer or Application Gateway. The pattern mirrors a tiered architecture: public-facing gateway, private app tier, isolated data tier.

A secure office complex: the VNet is the campus, subnets are buildings, and NSGs are the badge readers at each door that allow or deny based on who you are and where you came from. Private Endpoints are like installing a partner company's service desk inside your own lobby instead of sending staff out to the street.

Key Concepts

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Traffic is controlled with Network Security Groups (NSGs) — stateful allow/deny rules by port, protocol, source, and destination, attachable to subnets or individual NICs. Application Security Groups let you group VMs logically and write rules against the group rather than IPs. Beyond a single VNet, connectivity uses VNet Peering (VNet-to-VNet), VPN/ExpressRoute (to on-prem), and Private Endpoints (reach Azure PaaS services over a private IP instead of the public internet).