• If you wish to have multiple subscriptions and/or use multiple regions you will have multiple virtual networks
• In the past we could connect virtual networks using S25 VPN or by connecting to the same ExpressRoute circuit but both approaches have problems
• VNet Peering enables VNets to be connected via the Microsoft backbone in the same or different regions (global peering)
• There is a small ingress and egress charge for traffic via network peering
• IP address spaces CANNOT overlap

VNet Peering

• Best option
• Can span subscriptions and tenants
• Not transitive i.e. VNET1 can not talk to VNET3 / Need to create peering relationship between them
  • Without peering, I could add Azure Firewall or Network virtual appliance in Hub network (VNET2) and tell:
    • VNET3 if you want to talk to VNET1, next hop is IP of that forwarder
    • VNET1 if you want to talke to VNET3, next hop is IP of that forwarder
  • This above thing is UDR
  • There is also border gateway protocol

flowchart LR
VNET1 --> |Peer| VNET2 --> |Peer| VNET3
VNET1 --- |NotTransitive|VNET3

Express Route

• Bad idea because of latency
• Traffic goes from VNET1 to express route MeetME and then from there to VNET2

flowchart LR
	VNET1 --> ExpressRoute --> VNET2	
	ExpressRoute --> MeetME --> ExpressRoute

S2S VPN

• VPN is basically encrypting traffic
• Bad idea because of bad throughput and bandwidth

flowchart LR
VNET1 <--> |S2SVPN| VNET2

Priority

• More specific subnet chosen
  • Between, 10.0.0.0/16 and 10.0.0.0/24, /24 route will be chosen

Between different route types for the same prefix:

1. User-defined routes
2. BGP routes
3. System routes

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references:

ExpressRoute Locations MS Learn