On Thu, 22 Jun 2000, Tony Nugent wrote:
> Strange. I can do:
>
> ping -b 255.255.255.255
>
> after which I do:
>
> cat /proc/net/arp
>
> and find a big bunch of new entries in the kernel's arp table.
Hmm on my system (Linux 2.2.12-9 (RedHat), netkit-base-0.10-37) I have to
ping the addresses individually to get them added. Perhaps this is kernel
version dependent?
# cat /proc/net/arp | grep 192.168.0.50
# ping -c 2 -b 255.255.255.255 &> /dev/null
# cat /proc/net/arp | grep 192.168.0.50
# ping -c 2 192.168.0.50 &> /dev/null
# cat /proc/net/arp | grep 192.168.0.50
192.168.0.50 0x1 0x2 00:30:F4:00:00:22 *
eth0
I guess the kernel [well, apparently my version at least :)] only adds ARP
cache entries in response to ARP requests since it's a waste to check
every incoming packet to see if its MAC is already in the ARP cache.
Obviously the broadcast pings don't initiate ARP requests since they don't
need to map an IP to a MAC address but use the "ethernet broadcast"
address (ff:ff:ff:ff:ff:ff) instead.
Jim
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