netdev - Re: [PATCH RESEND] ip_gre: sendto/recvfrom NBMA address

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Date:	Wed, 24 Oct 2007 00:20:36 +0400
From:	Alexey Kuznetsov <kuznet@....inr.ac.ru>
To:	Timo Ter?s <timo.teras@....fi>
Cc:	Patrick McHardy <kaber@...sh.net>, davem@...emloft.net,
	netdev@...r.kernel.org
Subject: Re: [PATCH RESEND] ip_gre: sendto/recvfrom NBMA address

Hello!

Me wrote:

> Ack. This is good idea.
> 
> Frankly, I was sure ip_gre worked in this way all these years.
> I do not remember any reasons why it was crippled.
> 
> The only dubious case is when next hop is set using routing tables.
> But code in ipgre_tunnel_xmit() is ready to accept this situation,
> it checks for zero destination address and fixes it when it is able to.

Nevertheless, it does not work.

The reason is that NOARP arp entries on device with initialized
hard_header are initialized not to all zeros, but to dev->dev_addr.
So that, netxthop from routing tables is ignored and all gre packets
are lost in loopback. Not good.

The problem can be ignored. I am even not sure that someone uses
this feature. Actually, it was not recommended in documentation.

Alternatively, arp.c can be changed to generate 0 addresses instead
of dev->dev_addr. Normally it is equally good, but I am not sure
about possible side effects.

Another thoughts?

Alexey
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