[c-nsp] Limiting number of ARP entries for 802.1q subinterfaces

[lists at Hojmark.ORG]

> Ok, so it's feasible to limit the amount of learned MAC
> addresses on L3 802.1q subinterface of a 7600 Series Router.

It may be configurable and *might* actually work, but it is not
*supported* for a L3 sub-interface. (See http://tinyurl.com/3nljv
which lists the supported features).

Instead, you could configure PortSec on L2 interfaces and then
do the routing on SVIs. That would be a supported configuration.

-A