2.4 Azure Virtual WAN
📘Microsoft Azure Networking Solutions (AZ-700)
What is a Virtual Hub?
A Virtual Hub is the central networking point in Azure Virtual WAN. It acts like a regional network backbone that connects:
- Virtual networks (VNets) in Azure
- On-premises networks via VPN or ExpressRoute
- Branch offices using SD-WAN
Think of it as a central hub that manages traffic between multiple networks and ensures connectivity across Azure and on-premises.
What is Virtual Hub Routing?
Virtual Hub Routing controls how traffic flows inside the hub and between connected networks. Azure Virtual WAN provides automated and manual routing to make sure traffic goes the right way.
There are three main types of routing in a Virtual Hub:
- Static routing
- Dynamic routing (BGP)
- Custom routes using Route Tables
1. Static Routing
- Static routes are manually defined paths for network traffic.
- Each route specifies a destination IP range and a next hop (where to send the traffic).
Use case:
You have a VNet in Azure that needs to reach a specific on-premises subnet. You create a static route in the hub that points that subnet to the on-premises VPN connection.
Key points for exam:
- Must define address prefix and next hop.
- Does not automatically adapt if a new network is added.
- Useful for small, simple environments or specific routing requirements.
2. Dynamic Routing (BGP)
- Virtual Hub supports BGP (Border Gateway Protocol) for automatic route exchange between:
- The hub
- Connected VNets
- VPN/ExpressRoute connections
- BGP ensures that if a new subnet or VNet is added, routes are automatically propagated.
Use case:
You have multiple branch offices connected via VPN. When a new branch is added, it automatically receives routes to all other branches and Azure VNets without manual configuration.
Key exam points:
- Dynamic routing is enabled by default for hubs with VPN and ExpressRoute connections.
- Supports automatic route propagation.
- Routes can have preference values to influence path selection.
3. Custom Route Tables
Virtual WAN allows custom route tables for more advanced traffic control:
- You can associate route tables with hub connections, such as:
- VPN sites
- ExpressRoute circuits
- Virtual network connections
- Each route table contains routes that control traffic flow, including:
- Destination prefixes (subnet ranges)
- Next hop types:
- Internet (to route traffic to public endpoints)
- VNet (to route traffic to another virtual network)
- None (drop traffic)
Key points for exam:
- Route propagation allows connected VNets and sites to automatically receive hub routes.
- You can override default hub routing by creating custom routes.
- Supports hub-to-hub routing if multiple hubs exist.
Hub-to-Hub Routing
- In some cases, you have multiple hubs in different regions.
- Hub-to-hub routing allows traffic from one hub to go to another hub, enabling global connectivity.
- Must configure Hub Route Tables and enable propagation for cross-hub traffic.
Exam tip:
Hub-to-hub routing requires propagated routes from one hub to another, often used in multi-region enterprise environments.
Route Propagation in Azure Virtual WAN
- Virtual WAN automatically propagates routes between hubs and connected networks.
- Propagation types:
- From VNets to hub – VNet subnets are advertised to the hub.
- From hub to VNets – Hub routes are advertised to connected VNets.
- From VPN/ExpressRoute to hub – On-premises routes are advertised to the hub.
- You can disable propagation for specific connections if you want manual control.
Exam tip:
Understand which routes are propagated automatically vs. which require custom route configuration.
Next Hop Types in Virtual Hub
When configuring routing, the next hop determines where traffic goes:
| Next Hop | Description |
|---|---|
| VPN Site | Routes traffic to an on-premises VPN connection |
| ExpressRoute | Routes traffic to on-premises via ExpressRoute |
| Virtual Network | Routes traffic to another VNet connected to the hub |
| Internet | Routes traffic to public endpoints outside Azure |
| None | Drop traffic; block connectivity |
Key Exam Points – Configure Virtual Hub Routing
- Virtual Hub acts as a central routing point for VNets, VPNs, and ExpressRoute.
- Routing types: Static, Dynamic (BGP), Custom Route Tables.
- Automatic route propagation simplifies connectivity; custom tables allow fine-grained control.
- Hub-to-hub routing is supported for multi-region architectures.
- Next hop types control where traffic flows: VPN, ExpressRoute, VNet, Internet, or None.
- Propagation can be disabled or overridden when needed.
- Virtual Hub routing is crucial for enterprise-level network segmentation and traffic control.
Summary
- Virtual Hub routing is about controlling and optimizing traffic flow in a Virtual WAN.
- Understand static vs dynamic routing, custom route tables, hub-to-hub routing, and route propagation.
- For the exam, focus on how to configure routing, types of next hops, and propagation rules.
