About virtual hub routing

The routing capabilities in a virtual hub are provided by a router that manages all routing between gateways using Border Gateway Protocol (BGP). A virtual hub can contain multiple gateways such as a Site-to-site VPN gateway, ExpressRoute gateway, Point-to-site gateway, Azure Firewall. This router also provides transit connectivity between virtual networks that connect to a virtual hub and can support up to an aggregate throughput of 50 Gbps. These routing capabilities apply to Standard Virtual WAN customers.

To configure routing, see How to configure virtual hub routing.

Routing concepts

The following sections describe the key concepts in virtual hub routing.

Hub route table

A virtual hub route table can contain one or more routes. A route includes its name, a label, a destination type, a list of destination prefixes, and next hop information for a packet to be routed. A Connection typically will have a routing configuration that associated or propagates to a route table

Connection

Connections are Resource Manager resources that have a routing configuration. The four types of connections are:

  • VPN connection: Connects a VPN site to a virtual hub VPN gateway.
  • ExpressRoute connection: Connects an ExpressRoute circuit to a virtual hub ExpressRoute gateway.
  • P2S configuration connection: Connects a User VPN (Point-to-site) configuration to a virtual hub User VPN (Point-to-site) gateway.
  • Hub virtual network connection: Connects virtual networks to a virtual hub.

You can set up the routing configuration for a virtual network connection during setup. By default, all connections associate and propagate to the Default route table.

Association

Each connection is associated to one route table. Associating a connection to a route table allows the traffic to be sent to the destination indicated as routes in the route table. The routing configuration of the connection will show the associated route table. Multiple connections can be associated to the same route table. All VPN, ExpressRoute, and User VPN connections are associated to the same (default) route table.

By default, all connections are associated to a Default route table in a virtual hub. Each virtual hub has its own Default route table, which can be edited to add a static route(s). Routes added statically take precedence over dynamically learned routes for the same prefixes.

Association

Propagation

Connections dynamically propagate routes to a route table. With a VPN connection, ExpressRoute connection, or P2S configuration connection, routes are propagated from the virtual hub to the on-premises router using BGP. Routes can be propagated to one or multiple route tables.

A None route table is also available for each virtual hub. Propagating to the None route table implies that no routes are required to be propagated from the connection. VPN, ExpressRoute, and User VPN connections propagate routes to the same set of route tables.

Propagation

Labels

Labels provide a mechanism to logically group route tables. This is especially helpful during propagation of routes from connections to multiple route tables. For example, the Default Route Table has a built in label called 'Default' . When users propagate connection routes to 'Default' label, it automatically applies to all the Default Route Tables across every hub in the Virtual WAN.

Configuring static routes in a virtual network connection

Configuring static routes provides a mechanism to steer traffic through a next hop IP, which could be of a Network Virtual Appliance (NVA) provisioned in a Spoke VNet attached to a virtual hub. The static route is composed of a route name, list of destination prefixes, and a next hop IP.

Reset Hub

Available only in the Azure portal , this option provides the user a means to bring any failed resources such as route tables, hub router or the virtual hub resource itself back to its rightful provisioning state. This is an additional option for user to consider prior to contacting Microsoft for support. This operation does not reset any of the gateways in a virtual hub.

Route tables in Basic and Standard virtual WANs prior to the feature set of Association and Propagation

Route tables now have features for association and propagation. A pre-existing route table is a route table that does not have these features. If you have pre-existing routes in Hub Routing and would like to use the new capabilities, consider the following:

  • Standard Virtual WAN Customers with pre-existing routes in virtual hub:

If you have pre-existing routes in Routing section for the hub in Azure portal, you will need to first delete them and then attempt creating new route tables (available in the Route Tables section for the hub in Azure portal)

  • Basic Virtual WAN Customers with pre-existing routes in virtual hub: If you have pre-existing routes in Routing section for the hub in Azure portal, you will need to first delete them, then upgrade your Basic Virtual WAN to Standard Virtual WAN. See Upgrade a virtual WAN from Basic to Standard.

Virtual WAN Routing Considerations

Please consider the following when configuring Virtual WAN routing:

  • All branch connections (Point-to-site, Site-to-site, and ExpressRoute) need to be associated to the Default route table. That way, all branches will learn the same prefixes.
  • All branch connections need to propagate their routes to the same set of route tables. For example, if you decide that branches should propagate to the Default route table, this configuration should be consistent across all branches. As a result, all connections associated to the Default route table will be able to reach all of the branches.
  • Branch-to-branch via Azure Firewall is currently not supported.
  • When using Azure Firewall in multiple regions, all spoke virtual networks must be associated to the same route table. For example, having a subset of the VNets going through the Azure Firewall while other VNets bypass the Azure Firewall in the same virtual hub is not possible.
  • A single next hop IP can be configured per VNet connection.
  • Virtual Hub does not support static route for 0.0.0.0/0 and next hop Virtual Network Connection (or an IP of an appliance in the VNet connection)
  • All information pertaining to 0.0.0.0/0 route is confined to a local hub's route table. This route does not propagate across hubs.

Next steps

To configure routing, see How to configure virtual hub routing.

For more information about Virtual WAN, see the FAQ.