[c-nsp] DAI Scale

[Lukas Tribus]

> I have some 2960+ running WAPs. Each 2960 will probably have 100-200
> clients at peak (low bandwidth use) and I am thinking of turning on
> DAI on each 2960. I don't know how DAI functions on the hardware, so
> how well does it scale up on this platform? Will I run into issues
> doing this on 2960 switches since they are a low end platform?

With DAI, ARP is punted to the CPU and handled there. It depends on
the amount of ARP request per second it has to handle.

If all your hosts talk to the default gateway mostly and the subnet is
small, then don't worry. If you have huge subnets with a lot of intra
subnet traffic, then you may want to monitor the CPU load. The ARP
traffic is rate-limited though (hopefully on your platform as well).

Be advised, probably on most platforms, DAI will punt ARP traffic of all
Vlans to the CPU, even if you enable DAI only on a few Vlans.


Also, make sure you test this well in your lab. Enabling DAI even
on mature platforms is risky. I reported bugs with STP leading to layer 2
loops (CSCus14471), issues with mac learning (CSCuq54085), and even
DoS vulnerabilities (CSCuq4335) after enabling DAI on the ME3400 series.



Lukas