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From: Martin Volf <mv@inv.cz>
To: lartc@vger.kernel.org
Subject: Re: [LARTC] Is 'publish' proxy arp still broken ?
Date: Wed, 22 Dec 2004 18:01:16 +0000	[thread overview]
Message-ID: <41C9B66C.5090201@inv.cz> (raw)
In-Reply-To: <09c301c4e79c$4b721a60$da529145@mtbrook.bozemanpass.com>

David Boreham wrote:
...
> There seem to be a number of preconditions that
> must be met before the arp...pub form of proxy arp
> will work. If these conditions are not met the kernel
> silently fails to answer the arp request (as oposed to
> for example the user seeing an error message when
> they run the user-space program).
> 
> First, the /proc/sys/net/ipv4/conf/<dev>/proxy_arp
> must be enabled on the interface where you desire
> arp responses to be sent.
...

I don't have this enabled and the syntax "arp -i eth0 -Ds 1.2.3.4 eth0 pub" is 
working as expected.

With /proc/.../proxy_arp enabled it seems that linux answers arp request for 
all ip addresses, which are routed to other interfaces, e.g. with this routing 
table:

192.168.1.0     0.0.0.0         255.255.255.0   U     0      0        0 eth1
10.0.0.0        0.0.0.0         255.255.255.0   U     0      0        0 eth0
0.0.0.0         10.0.0.1        0.0.0.0         UG    0      0        0 eth0

it answers arp request on eth1 for _all_ foreign ip addresses except 
192.168.1.0/24.

I saw it once, when a machine with ms windows was trying to find out its ip 
address from dhcp server, which I didn't have. It didn't get any and was 
trying to find unused one from the subnet 169.254.0.0/16 (link local 
addresses, RFC 3330) - it didn't succeed, because my linux router, which had 
/proc/.../proxy_arp enabled, answered all arp requests for this subnet...

-- 
Martin

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LARTC mailing list / LARTC@mailman.ds9a.nl
http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO: http://lartc.org/

  parent reply	other threads:[~2004-12-22 18:01 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2004-12-21 20:33 [LARTC] Is 'publish' proxy arp still broken ? David Boreham
2004-12-22  4:02 ` gypsy
2004-12-22 16:09 ` David Boreham
2004-12-22 17:27 ` Martin Volf
2004-12-22 18:01 ` Martin Volf [this message]
2004-12-22 18:04 ` David Boreham

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