In the default configuration, your SDDC network has a single edge (T0) router through which all North-South traffic flows. If you need additional bandwidth for the subset of this traffic that doesn't travel over a VPN or take any other route to or from the Internet, you can reconfigure your SDDC to be Multi-Edge by creating traffic groups, each of which creates an additional T0 router.
A traffic group uses an association map to map a prefix list of CIDR blocks to a T1 gateway, such as the Compute Gateway, in your SDDC. Prefix lists are independent of gateways. You can create and update them at any time, but you cannot remove a prefix list if it is included in an association map. Associating a prefix list with a gateway object routes all traffic from any CIDR block on the list through that gateway.
Because NAT rules always run on the default T0 router, additional T0 routers cannot handle traffic that has a source or destination that requires a NAT rule. This includes traffic to and from the Internet as well as traffic to and from an AWS S3 service. Keep this limitation in mind when you create prefix lists.
Prerequisites
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Before you can create traffic groups, you must use VMware Transit Connect™ to connect your SDDC to a VMware Managed Transit Gateway (VTGW). See Creating and Managing SDDC Deployment Groups in the VMware Cloud on AWS Operations Guide.
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Traffic groups can be created only in SDDCs that have large-size management appliances and at least four hosts. See Upsize SDDC Management Appliances for information about changing an SDDC's management appliance size from medium to large. See Add Hosts for information about adding hosts to an SDDC.
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The number of traffic groups that a multi-AZ (stretched cluster) SDDC can support depends on the number of hosts that the SDDC provides in each region, and can be represented with a formula like this:
TG=(hosts-per-region - 2)/2
where TG represents the maximum number of traffic groups that the SDDC can support and hosts-per-region is the number of hosts the SDDC deploys in each of the regions it occupies.
Procedure
Example: Route Table Changes After Adding a T0 Router
This simplified example shows the effect of creating traffic group and associating it with a prefix list of just two host routes (/32).
- Initial configuration
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Assume these values for route table entries in the default T0 router and the Compute Gateway (CGW) before adding the first traffic group and creating the new T0 router.
Table 1. Default T0 Routes Subnet Next Hop 0.0.0.0/0 Internet Gateway 192.168.150.51/24 CGW 192.168.151.0/24 CGW VTGW, DXGW subnets VTGW, DXGW connections Management CIDR MGW Table 2. CGW Routes With the Default T0 Subnet Next Hop 0.0.0.0/0 Default T0 192.168.150.0/24 Default T0 192.168.151.0/24 Default T0 - Multi-Edge configuration
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After the traffic group is created, new routes are added on the default T0. Assuming that the prefix list associated with the traffic group has these entries:
192.168.150.100/32 192.168.151.51/32
then the route tables for the default T0, new T0, and CGW end up like this.Table 3. Default T0 Routes After Adding a Traffic Group Subnet Next Hop 0.0.0.0/0 Internet Gateway 192.168.150.0/24 CGW 192.168.150.100/32 New T0 192.168.151.0/24 CGW 192.168.151.51/32 New T0 VTGW, DXGW subnets VTGW, DXGW connections Management CIDR MGW Table 4. Routes on the New T0 Subnet Next Hop 0.0.0.0/0 Default T0 192.168.150.100/32 CGW 192.168.151.51/32 CGW VTGW, DXGW subnets VTGW, DXGW connections Management CIDR MGW Table 5. CGW Routes With an Additional T0 Subnet Next Hop 0.0.0.0/0 Default T0 192.168.150.0/24 Default T0 192.168.150.100/32 New T0 192.168.151.0/24 Default T0 192.168.151.51/32 New T0