Q. How many virtual networks can I connect to an ExpressRoute circuit?
A. A standard ExpressRoute circuit can be connecto to 10 vitual networks and those virtual networks would also then be connected to each other. If you wish to connect more than 10 virtual networks to a single ExpressRoute circuit then you can add the ExpressRoute premium add-on which increases the number of virtual networks that can be connected based on the tier/speed of the ExpressRoute circuit. These are detailed at https://azure.microsoft.com/en-us/documentation/articles/expressroute-faqs/ and at time of writing the number of virtual networks can be up to 50 for a Network Service Provider (NSP) and 100 for Exchange Provider (EXP) which with ExpressRoute premium can be outside of the continent of the ExpressRoute connection.
Note that the actual speed available to a virtual network depends on the type of gateway deployed. There are three types of gateway available as documented at https://azure.microsoft.com/en-us/documentation/articles/vpn-gateway-about-vpngateways/:
- Basic - 500 Mbps
- Standard - 1000 Mbps
- Premium - 2000 Mbps
Note this means if you have a 10 Gbps ExpressRoute circuit and connect to a virtual network using a premium gateway the maximum speed available via the link will be 2000 Mbps. The additional bandwidth would be used by additional virtual networks and other Azure services. You can connect a single virtual network to four separate ExpressRoute circuits however this would not increase the bandwidth and is instead used to provide