--- name: transit-gateway-about title: About IBM Cloud Transit Gateway description: As the number of your Virtual Private Clouds (VPCs) grows, you need a way to manage the interconnection between these resources across multiple regions. IBM Cloud® Transit Gateway is designed specifically for this purpose. last-updated: 2026-09-08 --- > ## Documentation Index > The table of contents for this documentation set is at https://cloud.ibm.com/docs/transit-gateway?format=markdown > The index for all IBM Cloud docs is at: https://cloud.ibm.com/docs/llms.txt > Use these files to discover more information as needed. # About IBM Cloud Transit Gateway {: #about} As the number of your Virtual Private Clouds (VPCs) grows, you need a way to manage the interconnection between these resources across multiple regions. IBM Cloud® Transit Gateway is designed specifically for this purpose. {: shortdesc} With IBM Cloud Transit Gateway, you can create single or multiple transit gateways to connect VPCs together. You can also connect your IBM Cloud classic infrastructure to a transit gateway to provide seamless communication with classic infrastructure resources. Any new network that you connect to a transit gateway is then automatically made available to every other network connected to it so that you can scale your network as it grows. Transit gateways provide flexibility by allowing you to add networks to local gateways. Networks can be attached to multiple local gateways and a single global gateway, enabling you to keep local traffic on a local gateway. ## Overview of features {: #feature-overview} IBM Cloud Transit Gateway offers the following features: ### Privacy {: #privacy} * Connections to and from an IBM Cloud Transit Gateway on the IBM private network are not exposed to the public internet, thus reducing public egress and VPN costs and reducing security threats. * IBM Cloud Transit Gateway is a fully redundant, fault-tolerant service with no single point of failure within these [IBM Cloud Multi-Zone Regions (MZR)](https://cloud.ibm.com/docs/transit-gateway?topic=transit-gateway-tg-locations&format=markdown). ### Security and access management {: #security-iam} IBM Cloud Transit Gateway integrates with Identity and Access Management (IAM), letting you manage access to your transit gateway. Using IAM, you can create and manage [IBM Cloud users and groups](https://cloud.ibm.com/docs/transit-gateway?topic=transit-gateway-iam&format=markdown), as well as user permissions to allow or deny their access. ### Routing {: #routing} IBM Cloud Transit Gateway supports local and global routing between VPCs and the IBM Cloud classic infrastructure. All routing options remain within the private IBM Cloud infrastructure without operating on the public internet, and are optimized for performance. IBM Cloud Transit Gateway allows customers greater flexibility, redundancy, and speed in scaling their workloads, and in connecting isolated networks that run on IBM Cloud. ### Prefix filtering {: #prefix-filtering} IBM Cloud Transit Gateway supports prefix filtering on connections, allowing you to control which routes are advertised to and from each connected network. You can permit or deny specific prefixes to prevent unintended route propagation and reduce the risk of routing conflicts. For more information, see [Adding and deleting prefix filters](https://cloud.ibm.com/docs/transit-gateway?topic=transit-gateway-adding-prefix-filters&format=markdown). ### Route reports {: #route-reports} IBM Cloud Transit Gateway provides route reports that display all the routes known to a transit gateway across its connections. Route reports help you verify connectivity, identify overlapping prefixes, and troubleshoot routing issues before they affect traffic. For more information, see [Generating a route report](https://cloud.ibm.com/docs/transit-gateway?topic=transit-gateway-route-reports&interface=ui&format=markdown). ### Optimized traffic and fault tolerance {: #vpc-optimized-traffic-fault-tolerance} Transit Gateway is a regional service that employs routers located in each Availability Zone. In a typical setup, when virtual server instances are deployed across different VPCs, these instances attempt to communicate with each other. Traffic between VPCs remains within the same zone, ensuring efficient local routing and optimized data transfer. This standard behavior also applies when using a transit VPC and advertising static routes from one VPC to advertise the same prefix across all zones. Even if firewalls are deployed within the VPCs (resulting in duplicate firewalls in the other advertised zones), traffic still favors the transit gateway in its respective zone. This routing behavior ensures that traffic returns through the same zone's transit gateway, maintaining routing within the same zone. VPCs typically prioritize the transit gateway within their zone, minimizing cross-zone traffic. During a zonal failure, such as when a transit gateway experiences a failure in one zone (resulting from the failure of all zone's routers), communication could be disrupted. In such cases, traffic might be routed differently, with one direction of traffic sent through an alternate path, while the response might return from a different route. In general, though, VPC traffic typically remains within the same zone. {: note} ### Easily connect across boundaries {: #boundaries} IBM Cloud Transit Gateway interconnects your IBM Cloud VPCs with compute and classic resources across the globe. You can also interconnect VPCs and classic resources across IBM Cloud accounts. IBM Cloud Transit Gateway supports the use of Generic Routing Encapsulation (GRE) tunnels to connect endpoints. GRE tunnels enable the transit gateway to connect to overlay networks hosted on classic infrastructure resources for unique use cases. With GRE enhanced route propagation enabled, all GRE tunnels connected to the same transit gateway share routes and can communicate across zones. When this setting is disabled, network traffic cannot be exchanged between unbound GRE tunnels in different zones or between tunnels within redundant GREs. For more information, see [GRE tunnels](https://cloud.ibm.com/docs/transit-gateway?topic=transit-gateway-gre-connection&interface=ui&format=markdown). ### Direct Link connectivity {: #directlink} IBM Cloud Transit Gateway supports Direct Link connections. Connecting Direct Link to your IBM Cloud Transit Gateway on-premises network grants access to all networks connected on the transit gateway. Similarly, all other connections on the transit gateway have access to your network. As with other network connections to the IBM Cloud Transit Gateway, special consideration must be taken to avoid IP overlap issues. For more information, see [Dealing with overlapping VPC prefixes and classic infrastructure subnets](https://cloud.ibm.com/docs/transit-gateway?topic=transit-gateway-overlapping-vpc-prefixes-and-classic-subnets&format=markdown). ### VPN gateway connectivity {: #vpn-connectivity} IBM Cloud Transit Gateway supports VPN gateway connections, enabling on-premises or external networks to connect with other networks in IBM Cloud over secure IPsec tunnels. The VPN gateway acts as a spoke within the transit gateway architecture, using dynamic routing with eBGP over redundant GRE tunnels to provide scalable and resilient connectivity. For more information, see [VPN gateway connection considerations](https://cloud.ibm.com/docs/transit-gateway?topic=transit-gateway-helpful-tips&format=markdown#vpn-connection-considerations). ### Power Virtual Server connectivity {: #powervs} IBM Cloud Transit Gateway supports Power Virtual Server connections. Connecting a Power Virtual Server instance to your IBM Cloud Transit Gateway network grants access to all networks connected on the transit gateway. Similarly, all other connections on the transit gateway have access to your network. As with other network connections to the IBM Cloud Transit Gateway, special consideration must be taken to avoid IP overlap issues. For more information, see [Dealing with overlapping VPC prefixes and classic infrastructure subnets](https://cloud.ibm.com/docs/transit-gateway?topic=transit-gateway-overlapping-vpc-prefixes-and-classic-subnets&format=markdown). ## Interconnectivity patterns {: #patterns} For examples of how you can implement IBM Cloud Transit Gateway to interconnect VPCs, classic infrastructure, Direct Link, VPN gateways, and Power Virtual Server resources across accounts and regions, see [Interconnectivity patterns](https://cloud.ibm.com/docs/transit-gateway?topic=transit-gateway-patterns&format=markdown).