[nSLUG] Getting CPU cycles during an ARP storm

Bill Davidson bdavidso at supercity.ns.ca
Tue Sep 20 10:14:36 ADT 2005


On Sun, 2005-18-09 at 17:55 -0400, Stephen Gregory wrote:

> ...Arp should also be handled by the network card. And should not slow
> down the system. The only way an arp storm would impact the cpu is the
> network card was in promiscuous mode.

Aren't arp requests always broadcasts?  If a host says "who has w.x.y.z"
it needs to ask everybody.  So a card should not need to be in
promiscuous mode to receive arp requests.  And while I'm sure some newer
NIC's (especially I2O) may implement arp in firmware, for most
implementations I think it is in the kernel
(see /usr/src/linux/net/ipv4/arp.c).  It belongs there, because most NIC
drivers neither know nor care about TCP/IP.

Bill Davidson
bdavidso at supercity.ns.ca


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