An interesting feature available for AWS direct connect is the AWS Direct sitelink. Before sitelink, if you needed to interconnect multiple branches, you needed public Internet links, private MPLS links, or equivalent connectivity. This results in purchasing expensive links to interconnect the sites or adding complexity to the AWS networking infrastructure.
A typical deployment setup is shown below:
Alternatively, you can have a setup with traffic passing via the AWS infrastructure and using multiple transit gateway (TGW) and direct connect gateways (DXGW).
With sitelink, this changes as traffic can be routed directly between the different branches using the AWS direct connect links using the DXGW available and without entering the AWS region instead of implementing something like the above. Sitelink allows the different direct connect customer premises to communicate directly without external communications using private or transit Vifs with a DXGW. Since direct connect support, high MTU 8500 or MTU 9001 once enabling sitelink, you can use the AWS direct connect links as underlay paths.
As shown by the table below, there are strict conditions where sitelink can be enabled.
| Virtual interface type | Supported |
|---|---|
| Transit VIF | Yes |
| Private VIF attached to a DXGW with a virtual private gateway | Yes |
| Private VIF attached to a DXGW and are NOT associated with a virtual private gateway or a TGW | Yes |
| Private VIF attached to a virtual private gateway | No |
| Public VIF | No |
Before and after enabling sitelink
The AWS direct connect sitelink can be enabled for existing and new virtual interfaces and applied to a hosted or regular virtual interface configured to a DirectConnect gateway. There is no requirement for having the AWS directconnect links with the same speeds.
Backup connectivity between branch offices using Sitelink
Enabling sitelink can provide an alternative route if the connectivity between branch offices is degraded by using the directconnect gateway link as a backup. A simple example is described below:
Note that the VPC networks are excluded from the table below on purpose not to complicate this
| Device | Neighbour | Advertised Networks | Received Networks | AS Path | Preferred Route | Remarks |
|---|---|---|---|---|---|---|
| CR1 | CR2 | 10.100.0.0/16 | AS65001 | Yes by CR2 | Shortest AS PATH | |
| CR1 | DX1 | 10.100.0.0/16 | AS65001 | Yes by DX1 | ||
| CR1 | DX1 | 10.101.0.0/16 | AS65002,AS64513 | No | Better route via CR2 | |
| CR2 | CR1 | 10.101.0.0/16 | AS65002 | Yes by CR1 | Shortest AS PATH | |
| CR2 | DX2 | 10.101.0.0/16 | AS65002 | Yes by DX2 | Shortest AS PATH | |
| CR2 | DX2 | 10.100.0.0/16 | AS65001,AS64513 | No | Better route via CR1 |
Enabling Sitelink
To enable sitelink, it is very simple; all you need to do
- Go to the virtual interface settings from the Direct Connect menu
- Click the Enabled tick box under the Enable Sitelink Option as shown in the figure below.
