How to refresh network card buffer?

[Cos]

Hi all

The background is I have around 100pcs router-like products. they all
have a fixed IP address 192.168.1.100 and of course different MAC
address.

I need to connect them one by one to configure.

The trouble is while I disconnect one unit and change to another unit,
the FreeBSD can not recognize the unit immediately. It need around
more than 10 minutes to ping 192.168.1.200 successfully.

I can refresh it by "ifconfig ue0 down" and "ifconfig ue0 up", it
works but I think the way is not smart.

I guess there is something like buffer to record IP and MAC pair has
to be cleaned. Could anybody advise?

-- 
with kind regards