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

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

[Bonnell, David]

I have been using arping to do a reverse ARP on the MAC address(es) to
obtain the IP address(es) used by each domain but this will be easier.


David Bonnell
Corporate Architect
BMC Software

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

[Gerd Knorr]

Bonnell, David wrote:
> I have been using arping to do a reverse ARP on the MAC address(es) to
> obtain the IP address(es) used by each domain but this will be easier.

How does that work?  What I've found depends on either the host replying 
to broadcast pings or on brute-force, i.e. try every IP address in the 
network (which isn't exactly nice, especially in a /16 ...).

cheers,
   Gerd

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

[Bonnell, David]

Arping sends ARP "who-has" requests, either broadcast or directed to a
specific MAC address and displays the responses.  I retrieve the MAC
address of each VIF of each domain from XenStore and use arping to
obtain the associated IP address.

http://freshmeat.net/projects/arping/


Regards,


David Bonnell
Corporate Architect
BMC Software

-----Original Message-----
From: Gerd Knorr [mailto:kraxel@suse.de] 
Sent: Thursday, 22 December 2005 10:48 AM
To: Bonnell, David
Cc: xen-devel@lists.xensource.com
Subject: Re: [Xen-devel] RE: [patch, rfc] put IP addresses into xenstore
(Gerd Knorr)

Bonnell, David wrote:
> I have been using arping to do a reverse ARP on the MAC address(es) to
> obtain the IP address(es) used by each domain but this will be easier.

How does that work?  What I've found depends on either the host replying

to broadcast pings or on brute-force, i.e. try every IP address in the 
network (which isn't exactly nice, especially in a /16 ...).

cheers,
   Gerd

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

[Gerd Knorr]

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