On Tue, Jun 16, 2009 at 9:11 AM, Charlie Reitsma<reitsma AT denison DOT edu> 
wrote:
> So, perhaps, the ISP is mistaking the backup traffic as a broadcast storm.
> It would appear as a sudden spike of traffic leaving the server. If so, a
> conversation with the ISP should clear up the issue.

Other possibilities:

The Amanda server or a client is accidentally configured with a
broadcast address (this can happen easily in the tiny subnets hosting
providers will often make for customers)

An ARP cache is broken somewhere, so every packet requires an ARP probe.

(Charlie, your suggestion is the simplest, but broadcast traffic is
usually counted and reported separately, so I suspect this may,
indeed, be broadcast)

Dustin

-- 
Open Source Storage Engineer
http://www.zmanda.com