Direct Connect (DX)

• DX is region specific offering
  • It allows On-Prem physical locations to connect to a specific AWS region/location
• DX supports max of 50 VIFs (including Private and Public) per physical connection
• DX does not support Transit VIF for AWS-TGW connectivity

Direct Connect Gateway (DXGW)

• Only supports Private and Transit VIFs
  • DXGW mainly used to access private resources in VPCs
• Does not support public VIF
  • DXGW does not provide any benefit of Public Internet Connectivity
• VGW associated with a DXGW must be “attached” to a VPC
• Does not support transitive routing or transit connectivity
  • VPC in Region-1 cannot directly communicate with VPC in Region-2
  • DX Location-1 cannot directly communicate with DX Location-2
• Up to 30 DX physical connections can connect to one single DXGW for physical link redundancy purposes
  • In another words 30 DX locations/regions
• DX supports max of 50 VIFs (for DXGW only Private and Transit VIFs are applicable)
  • It means one can have Max of 50 DXGW per physical DX link
  • But one DXGW can connect to max of 10 VPCs
  • It means Max of 500 VPCs (50 x 10 VPC) per physical DX link across accounts and regions

DXGW with AWS-TGW Limitations

• Transit VIF can only be attached to a DXGW
• Only one Transit VIF for any AWS Direct Connect 1/2/5/10 Gbps connection
  • Less than 1G connections does not support Transit VIF
  • Max of 3 AWS-TGW can connect to one DXGW behind one Transit VIF
• A single DXGW cannot attach with both Private and Transit VIF
  • This could be a serious limitation for some customers
  • I think the underline assumption is that if a customer is alreadt using AWS-TGW then why would he want to use a private VIF attached to the same DXGW?

DXGW without and with AWS-TGW Comparision

DXGW without AWS-TGW| DXGW with AWS-TGW
—|—
10 VPCs per DXGW| 3 TGWs per DXGW
50 DXGW max (b/c of 50 Private VIF)| With Transit VIF only one DXGW is possible
500 VPCs total| 5,000 VPCs per TGW
15,000 VPC per DX physical link
Private VIF supported on all Direct Connect connection types| Transit VIF supported only on dedicated or hosted connections of speed 1Gbps and above
No additional charges| Additional charge for TGW data processing

References

https://docs.aws.amazon.com/vpc/latest/tgw/transit-gateway-limits.html
https://docs.aws.amazon.com/directconnect/latest/UserGuide/limits.html

Credits

Abdul Rahim
Kamran Habib
Saad Mirza
Hammad Alam