AWS Transit Gateway

As AWS infrastructure grows is can become distributed and complex. Common challenges include:

  1. Inability to create transitive relationships
  2. A lack of edge-to-edge routing meaning any VPN will have to be connected directly to each VPC that it needs connectivity with
  3. A complex management structure with no centralized management point

Transit Gateway Overview

TG takes complex and distributed infrastructures and simplifies them into a hub-spoke model.

Transit Gateway Benefits

  • Only a single connection is required from each VPC, VPN and Direct Connect connection. This simplifies scalability.
  • Transit Gateway is used as a hub that controls how traffic is routed between all connected networks.
  • Management connectivity is simplified.
  • Routes from connected VPCs/networks can be automatically propagated to Transit Gateway. Transit Gateway maintains a routing table with routes for all connected networks. Static and Dynamic routing are supported.
  • Equal Cost Multipath (ECMP) is supposed between on-premises gateway connections, enabling load balancing over multiple paths. ECMP can be used to aggregate bandwidth.
  • Currently, 5 Transit Gateways per account are supported, and a single VPC can have a maximum of 5 Transit Gateway attachments. Other TG limits include 5000 attachments, 1.25 Gbps per VPN, 50 Gbps maximum bandwidth per VPC, and up to 10000 routes.
  • Transit gateway routes do not propagate to VPC route tables. Entries must be made manually.
  • Overlapping CIDRs are not support.
Transit Gateway overview

Transit Gateway overview