ARP Flooding While Creating BD

[Suprit Chinchodikar]

Hello,
What is the meaning of ARP flooding while creating a BD, is it for L2 Unknow Unicast traffic to flood or L3.
Also, when we create a BD and check the details we see option enabled for hardware proxy enabled by default.
I know that when we enable hardware proxy it limits the flooding and sends the ARP request to Spine Proxy.
So, whats the purpose of ARP flooding option being enabled by default while creating a BD

[RedNectar]

Hi @Suprit Chinchodikar ,

Re: 

whats the purpose of ARP flooding option being enabled by default while creating a BD

Great question. Reading this thread may help.

https://community.cisco.com/t5/application-centric-infrastructure/discussion-cisco-aci-ui-inconsistencies-please-contribute/m-p/4460787/highlight/true#M11070

As for the question 

What is the meaning of ARP flooding while creating a BD, is it for L2 Unknow Unicast traffic to flood or L3.

ARP flooding has nothing to do with L2 Unknown unicasts or L3 flooding.  It is simply a way to make ARP behave like it does in a legacy L2 network.  See the thread I mentioned above for some reasons WHY this might be a good idea.

Personally, I like to see ARP flooding turned off so ACI can do its best magic.  But alas, during migration, it is most likely to cause problems if left turned off, so (my theory) Cisco has tried to mimimise support calls by making the default for ARP flooding to be ENABLED.

[Suprit Chinchodikar]

@RedNectar,
Thanks for your brief explanation.
So, should we enable ARP flooding enabled by default or should we disable it while creating a BD.
Or it totally depends what you are going to achieve? Lets say for example we are migrating off from traditional network to ACI the arp flooding should be enabled or lets say we have a silent host in our fabric the arp flooding option should be enabled by default.
If, that's the case ACI takes which option in consideration? ARP flooding enabled while creating a BD or the Hardware Proxy mechanism which limits the arp flooding.

[RedNectar]

Hi @Suprit Chinchodikar ,

Thanks for your brief explanation.

Thank you

So, should we enable ARP flooding enabled by default or should we disable it while creating a BD.
Or it totally depends what you are going to achieve? Lets say for example we are migrating off from traditional network to ACI the arp flooding should be enabled or lets say we have a silent host in our fabric the arp flooding option should be enabled by default.

Correct. If migrating from a legacy network, leave ARP flooding turned on. Far less likely to have grief during this period.

If, that's the case ACI takes which option in consideration? ARP flooding enabled while creating a BD or the Hardware Proxy mechanism which limits the arp flooding.

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The hardware proxy function will still work for unknown destinations, but not for ARPs if ARP flooding is turned off.  I guess the ideal is that you leave ARP flooding on during migration, and turn it off after.  But who in their right mind would bother going back to turn off ARP flooding on a working system?  At the end of the day, it's going to save a few ARP broadcasts interrupting the CPU of your servers a few dozen times a day.  Long gone are the days when ARP broadcasts could get so bad that they'd slow down the servers noticeably.  BUT - if you are in the kind of environment where every nanosecond counts, it might be worthwhile.  Or maybe you are just a geek and think that having ARP broadcasts handled by the proxy is really cool. I certainly do. But I'd find it hard to advise a customer to do it unless it was a green fields site.