Cisco ACI: What Is A Bridge Domain

Bridge domains are a bit confusing in Cisco ACI, as they don't seem to have a direct analog to traditional networking. But it actually does: Primary VLAN. EPGs are secondary VLANs. Why not call it a VLAN? Because we also have other encapsulations now (VXLAN).

[@thenbali]

great stuff! ACI is a mind boggler and this is an awesome breakdown of one of the most confusing pieces

[@rajpjunior]

I could not resist. I had to subscribe! Great Job explaining this to me as if I was a toddler!!! :-D

[@praveensreedhar7210]

thanks for your video,

[@mandaarbendale777]

very good explanation

[@khansheheyar]

very good explanation with example keep it up

[@thomasxeon1912]

So in short....
There is 2 type of VLAN
Primary VLAN
Secondary VLAN
Primary VLAN is quite similar to the normal VLAN we are using
Secondary VLAN is split version VLAN of Primary.
In order for Primary and Secondary VLAN need to talk to each other, we need BD.
BD is similar to the gateway for communication
Correct me if I am wrong

[@shadeland]

Not quite.
Yes, there are two types of VLANs. Secondary and Primary. Hosts do not go in the primary. Hosts only go into the secondary VLANs. Secondary VLANs are tied to a primary VLAN. Hosts in a secondary VLAN can talk, hosts in different secondary VLANs cannot talk.
In ACI, the same is true. Hosts only go in the secondary VLANs (EPGs). Secondary VLANs are tied to a primary VLAN (bridge domain). Hosts in a secondary VLAN can talk unrestricted, hosts in different secondary VLANs (EPGS) (attached to the same primary VLAN) cannot talk, unless there's a contract.

[@Wr3nch-850]

to the point :-)

[@cciedclab3754]

v good

[@avinashshankarpalli2130]

Can we have multiple subnets/vlans in BD?

[@shadeland]

Yes, you can. The VLANs would be the EPGs, as they almost always translate to VLANs on the outside. They would be like secondary private VLANs. As for mulitple subnets, super easy to add several to a Bridge Domain.

[@avinashshankarpalli2130]

@@shadelandok so can the epg's be created with multiple subnets combined in the same BD or we can only have EPG with same subnet?

[@shadeland]

@@avinashshankarpalli2130 The EPGs are created under the BD, so yes, you can have multiple EPGs/VLANs sharing a single subnet (or group of subnets).