netdev - Re: Kernel sends ICMP unreachable for GRE packets even if there is a listening socket

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Date:	Tue, 10 Feb 2015 08:09:56 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Steinar H. Gunderson" <sgunderson@...foot.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Kernel sends ICMP unreachable for GRE packets even if there is
 a listening socket

On Tue, 2015-02-10 at 16:24 +0100, Steinar H. Gunderson wrote:
> [Resent from Bugzilla]
> 
> Hi,
> 
> I have a userspace GRE listener, which opens a raw socket (error handling removed):
> 
>         int gresock = socket(AF_INET6, SOCK_RAW, IPPROTO_GRE);
>         bind(gresock, (sockaddr *)&my_addr, sizeof(my_addr));
> 
> and then select()s and recvfrom()s on it, as well as sendto().
> 
> This works great. I can send and receive GRE packets. However, Linux _also_
> sends ICMPv6 unreachables when the other end sends to me. I assume this is
> because I don't have a corresponding kernel GRE tunnel interface. (I don't use
> the kernel GRE because I want, among others, stronger reordering functionality
> and possibly error correction, which is not in any standard.)
> 
> Can this be suppressed when I have such a socket giong? ip6tables -A OUTPUT can
> stop them, but it seems very hacky and kludgy.

Thats because you loaded ip6_gre maybe ?


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