This is called a gratuitous ARP. Used to update the ARP caches of other
nodes.
On 07/12/2010 10:48 PM, Rahul Nabar wrote:
On Mon, Jul 12, 2010 at 11:25 PM, Patrick Geoffray<patr...@myri.com> wrote:
Rahul,
On 7/13/2010 12:04 AM, Rahul Nabar wrote:
I am puzzled by a bunch of ARP requests on my network that I captured
using tcpdump. Shouldn't ARP discovery requests always be sent to a
broadcast address?
No, the kernel regularly refreshes the entries in the ARP cache with unicast
requests. If that fails, then it sends the expensive broadcasts.
Thanks Patrick. I wasn't aware of this. I guess it makes sense now
that I found the correct section of the RFP
(http://tools.ietf.org/html/rfc1122#page-22).
I see the converse situation too: Some ARP replies are being sent to a
broadcast domain instead of a single MAC. Is that normal too?
00:26:b9:58:e5:9f> ff:ff:ff:ff:ff:ff, ARP, length 60: arp reply
172.16.0.29 is-at 00:26:b9:58:e5:9f
00:26:b9:56:38:71> ff:ff:ff:ff:ff:ff, ARP, length 60: arp reply
172.16.0.14 is-at 00:26:b9:56:38:71
I'd have (naively) expected these replies to go to the specific MAC
which had issued an ARP request on 172.16.0.29 or 172.16.0.14.
--
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Tom Ammon
Network Engineer
Office: 801.587.0976
Mobile: 801.674.9273
Center for High Performance Computing
University of Utah
http://www.chpc.utah.edu
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