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Full Mesh Topology Overview

date_range 12-Jun-18

Contrail Service Orchestration supports the full mesh topology on tenants in a software-defined WAN (SD-WAN) implementation. In a full mesh topology, all sites of a tenant are connected to one another. The topology is selected when the tenant is created and cannot be modified later. A tenant supports only one full mesh network because all sites of the tenant are connected to one another. Sites in a full mesh topology can be of hub or spoke type. The sites are connected to one another through GRE and GRE_IPsec overlay tunnels. The default overlay tunnel encapsulation is GRE_IPsec.

In the full mesh topology, a WAN interface of one type is connected to a WAN interface of the same type. For instance, WAN interfaces of type MPLS can connect to WAN interfaces of type MPLS only, and WAN interfaces of type Internet can connect to WAN interfaces of type Internet only. Consider that a tenant has two sites with one WAN interface each. If the interface type on one site is MPLS and the interface type on the other site is Internet, then the two sites cannot be connected to each other through the full mesh topology.

The following requirements must be satisfied for connections between WAN interfaces:

  • IP addresses of Internet WAN interfaces must be reachable on the Internet. Also, IP addresses must be preserved and change in IP addresses is not supported.

  • For connections between MPLS WAN interfaces, the MPLS subscription for all sites must be from the same service provider. Also, the MPLS WAN interfaces must have IP reachability.

The full mesh topology supports static SD-WAN policies and static advanced policy-based routing (APBR). Full mesh topology also supports LAN segmentation, departments, and multiple VPNs.

Contrail Service Orchestration supports only sparse mode connections in full mesh topology. In sparse mode, a WAN interface of a specific type in a site is connected to only one other interface of the same type (see Figure 1). This configuration reduces the number of overlay tunnels formed and is easy to maintain. However, sparse mode is susceptible to SD-WAN network performance deterioration due to connectivity disruptions because if connectivity on one tunnel is lost, then the respective connected WAN interfaces become unreachable.

Figure 1: Sparse Mode
Sparse Mode

Local Breakout in Full Mesh Topology

Local breakout is supported on all sites in the full mesh topology. Local breakout is the ability of a site to route Internet traffic directly from the site. A site can have multiple WAN interfaces, but by default, only two WAN interfaces that are not enabled exclusively for local breakout traffic are chosen for connecting to the full mesh network. For instance, consider a site has four WAN interfaces. If WAN_1 on the site is enabled exclusively for local breakout traffic, then only WAN_0 and WAN_2 are chosen for forming a full mesh. WAN interfaces that are enabled exclusively for local breakout traffic cannot be used for non-Internet traffic and this makes those WAN interfaces essentially unusable in the full mesh topology. For WAN interfaces that are chosen to connect to the full mesh network, you do not need to provide overlay tunnel information while configuring the site. The overlay tunnel information is computed automatically.

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