05/05/2026
In Cisco ACI, there are three ways to advertise a bridge domain subnet. Note that in all cases you need to mark the subnet as "Advertise Externally"
1. Associate a L3OUT in BD
In this way you can if a subnet is advertised to outside within each BD, however under the L3OUT you won't be able see what are the subnets you are advertising.
2. Add each subnet within the L3OUT External EPG and mark as "Export Route Control Subnet"
In this way L3OUT can decide which subnet it will advertise. The problem with this method is you won't be able to differenciate BD subnets and transit routes. Using a description may help there.
3. Use a route-map with the L3OUT
Gives better flexibility. But maintaing this configuration may be overwhelming depeding on you setup.
There is no recommendation to use which option. It is suggested that stick to only one of the given options.
