Communication within same Bridge Domain

[Suprit Chinchodikar]

Hello,
Lets say I have two subnets 10.1.1.0/24 and 10.1.2.0/24 in the same bridge domain.
So, can these two subnets can communicate with each other directly? Also do we need any routing to be enabled for this communication?

Thanks,
Suprit

[RedNectar · Accepted solution]

Hi @Suprit Chinchodikar ,

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Lets say I have two subnets 10.1.1.0/24 and 10.1.2.0/24 in the same bridge domain.
So, can these two subnets can communicate with each other directly?

That depends on what EPG the endpoints are in.  Lets say you have endpoints 10.1.1.10 and 10.1.2.10 placed in EPG1.  In this case these two endpoints can communicate with each other "directly" - where "directly" means they each send traffic via their default gateway (which will be the IP address assigned to the BD in ACI) - there is no MAC-to-MAC "direct" communication.  In other words, no contract is needed for them to communicate.

If 10.1.1.10 and 10.1.2.10 placed in different EPGs, you'll need a contract to allow communication.

Also do we need any routing to be enabled for this communication?

Routing is enabled on every Bridge Domain by default. However, if you did NOT assign IP the default gateway IP addresses on the bridge domain routing will be disabled even if routing is left "enabled"

[Suprit Chinchodikar]

@RedNectar,
What is the use of the Custom Mac that gets generated while creating the BD?

[RedNectar]

Hi @Suprit Chinchodikar ,

I'm not sure why that option is ticked by default - possibly to make it easier to change if you want to. You'd get the same (default) MAC address even if you unticked the box.

BUT there are many use-cases for customising a MAC address.  In ACI, a common practice during migration is to set the MAC to be exactly the same as the previous device that was responding to the DB's IP Address. This can make migration easier because end devices don't have to go through an ARP timeout on the old MAC address.

[M02@rt37 · Accepted solution]

Hello @Suprit Chinchodikar 

Regarding routing, routing is enabled on every BD by default. However, if you did not assign IP addresses as the default gateway on the BD, the routing functionality may effectively be disabled even though routing is left "enabled" in the ACI configuration.

If endpoints are in the same EPG within the same Bridge Domain, they can communicate directly without the need for a contract. Communication occurs within the same Layer 2 domain.

Routing is typically enabled on every BD by default in ACI. If you want inter-subnet communication, you would assign IP addresses to the BD and configure the default gateway accordingly.

@RedNectar give the answer. That for that clarification.

 

[RedNectar]

M02@rt37 - Just love your graphic. Yours is definitely the better answer