[HPADM] Excessive ARP activity

From: David R Antoch (dantoch@csc.com)
Date: Fri Dec 02 2005 - 13:24:33 EST


Admins,

I've been seeing excessive activity with the arp cache/table on
11.0 (K series, Gig E) and 11.11 (RP5470, 100BT) servers (all patched to
the latest ARPA and LAN cumulative patches). These machines sit on a
switched and subnetted network, including our PC community numbering in
the thousands. Now, I'm seeing arp table entries cyclically increasing
to over 2400+ entries , then getting cleared at the normal ndd arp
"arp_cleanup_interval" interval, which is set to 5 minutes on the
11.0's and 1 minute on the 11.11 machine. (must be defaults because I
never changed that interval in rc.config.d/nddconf. After getting
cleared, they climb back up at a rate of ~ 20 -30 per second. Now, I
know these servers are NOT talking to that many machines. The busiest
production box (11.0 K580) usually has ~ 150 - 180 concurrent
user/connections. And this condition exists on the development 11.0 K
box, with only one or two admins logged in. I dont think any other server
platforms are exhibiting this, either. I'm not running any kind of
routing daemon (routed, gated, etc..) or rarpd either. From what I
understood about ARP, it is my machine that would issue an arp request
for arp activity to be initiated, thus populating my local arp cache table.
But there's NO WAY that I know of, that these servers are trying to talk to
that number of machines. How can these servers be putting out a
broadcast arp request, if that's whats happening, that is being
responded to by all these PC's? Has anyone seen anything similar?

Thx,
Dave

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