Re: [Xen-devel] RE: [patch, rfc] put IP addresses into xenstore (Gerd Knorr)

[Gerd Knorr <kraxel@xxxxxxx>]

Bonnell, David wrote:
> Arping sends ARP "who-has" requests, either broadcast or directed to a
> specific MAC address and displays the responses.
No.  It does that if you ping an IP address, but not if you ping a MAC 
address.  For pinging mac addresses it sends a ICMP ping, to the MAC 
address specified, with broadcast (IP-)address as destination in the 
header.  And thats exactly the problem, machines tend to not respond to 
broadcast pings for security reasons (allows certain kinds of DoS 
attacks), so this isn't going to work reliable.  Try "echo 1 > 
/proc/sys/net/ipv4/icmp_echo_ignore_broadcasts" in your domU and 
receiving the IP address with arping doesn't work any more ...
Another problem is that there are multiple arping versions out there, 
for example the iputils ship an arping utility to, and that one doesn't 
even support pinging hosts by MAC address.
cheers,

  Gerd


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