Application Centric Infrastructure

[tapansaha2021]

Hi,

I am having doubt in forwarding scope in bridge domain.

Why the BD SVI mac address are same,though they are part of different bridge domain with different subnet.

As in EPG4 part of BD2 having BD SVI mac 0022.bdf8.19ff and EPG3 part of BD1 having same BD SVI mac though they are different subnet and BD.

Please find the attachment for reference.

Regards,

Tapan Saha

[RedNectar]

Hi Tapan,

00:22:BD:F8:19:FF is indeed the MAC address used by ACI for all Bridge Domains by default. 

Many people feel uncomfortable that the same MAC address is used in multiple broadcast domains, so if you are one of those, Cisco has provided an option for you to be able to change the MAC address to whatever you want.

Technically, there is no reason why every bridge domain can't have the same MAC address - so long as the BDs are not joined - which of course they should NOT ever be.

Cisco COULD have taken another option. They could have figured out that there would be a maximum of 21000 Bridge Domains per ACI implementation and allocated every customer 21000 MAC addresses.  That would mean that the IEEE allocated prefix 00:22:BD would be good for about 800 customers (go figure it out 2^24/21000 ≈ 800). Then Cisco would have to apply for (and pay for) another MAC address allocation.

And they would have to manage all these different MAC prefixes in software - via the APIC. So the APIC software would need to be customised somehow for every 800 customers.

All that is way too hard. Much simpler to just use the same MAC address on all BDs and trust that customers have good L2 practices.

I hope this helps.

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[Sergiu.Daniluk]

Hi @tapansaha2021 

This might help: the BD, in the end, is just an SVI. On all Nexus platforms, by default, the SVIs have the same mac address:

N9K-2# show int vlan 222-225 | grep Hardware
  Hardware is EtherSVI, address is  a0b4.3943.4fc7
  Hardware is EtherSVI, address is  a0b4.3943.4fc7
  Hardware is EtherSVI, address is  a0b4.3943.4fc7
  Hardware is EtherSVI, address is  a0b4.3943.4fc7

Stay safe,

Sergiu

[tapansaha2021]

Thanks.