Network integration planning is an important prerequisite for successful Azure Stack Hub integrated systems deployment, operation, and management. Border connectivity planning begins by choosing if you want use dynamic routing with border gateway protocol (BGP). This requires assigning a 16-bit autonomous system number (ASN), public or private, or using static routing.
The top of rack (TOR) switches require Layer 3 uplinks with Point-to-Point IPs (/30 networks) configured on the physical interfaces. Layer 2 uplinks with TOR switches supporting Azure Stack Hub operations isn't supported. The Border device can support 32-bit BGP autonomous system number (ASN).
Using a dynamic routing protocol like BGP guarantees that your system is always aware of network changes and facilitates administration. For enhanced security, a password may be set on the BGP peering between the TOR and the Border.
As shown in the following diagram, advertising of the private IP space on the TOR switch is blocked using a prefix-list. The prefix list denies the advertisement of the Private Network and it's applied as a route-map on the connection between the TOR and the border.
The Software Load Balancer (SLB) running inside the Azure Stack Hub solution peers to the TOR devices so it can dynamically advertise the VIP addresses.
To ensure that user traffic immediately and transparently recovers from failure, the VPC or MLAG configured between the TOR devices allows the use of multi-chassis link aggregation to the hosts and HSRP or VRRP that provides network redundancy for the IP networks.
Static routing requires additional configuration to the border devices. It requires more manual intervention and management as well as thorough analysis before any change. Issues caused by a configuration error may take more time to rollback depending on the changes made. This routing method isn't recommended, but it's supported.
To integrate Azure Stack Hub into your networking environment using static routing, all four physical links between the border and the TOR device must be connected. High availability can't be guaranteed because of how static routing works.
The border device must be configured with static routes pointing to each one of the four P2P IP's set between the TOR and the Border for traffic destined to any network inside Azure Stack Hub, but only the External or Public VIP network is required for operation. Static routes to the BMC and the External networks are required for initial deployment. Operators can choose to leave static routes in the border to access management resources that reside on the BMC and the Infrastructure network. Adding static routes to switch infrastructure and switch management networks is optional.
The TOR devices are configured with a static default route sending all traffic to the border devices. The one traffic exception to the default rule is for the private space, which is blocked using an Access Control List applied on the TOR to border connection.
Static routing applies only to the uplinks between the TOR and border switches. BGP dynamic routing is used inside the rack because it's an essential tool for the SLB and other components and can't be disabled or removed.
* The BMC network is optional after deployment.
** The Switch Infrastructure network is optional, as the whole network can be included in the Switch Management network.
*** The Switch Management network is required and can be added separately from the Switch Infrastructure network.