From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753742Ab2LEDYX (ORCPT ); Tue, 4 Dec 2012 22:24:23 -0500 Received: from plane.gmane.org ([80.91.229.3]:34507 "EHLO plane.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752810Ab2LEDYU (ORCPT ); Tue, 4 Dec 2012 22:24:20 -0500 X-Injected-Via-Gmane: http://gmane.org/ To: linux-kernel@vger.kernel.org From: Woody Wu Subject: Re: Why a host not ping-able? Date: Wed, 5 Dec 2012 03:24:00 +0000 (UTC) Message-ID: References: <1354620894.27682.5@driftwood> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: 59.37.26.98 User-Agent: slrn/0.9.9p1 (Linux) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2012-12-04, Rob Landley wrote: > On 12/04/2012 12:17:25 AM, Woody Wu wrote: >> Hi, list >> >> I am not sure this has something with kernel. > > It doesn't. > >> But the system I just >> generated cannot be reached from ping. It can ping outside, but if I >> ping it from outside, I just get "Destination Host Unreachable". > > Some distributions' default firewall rules respond to icmp packets with > a host unreachable packet. This is a system/network administration > thing (iptables) and nothing to do with kernel development. > >> I think there is not firewall in between, > > There's a firewall built into linux, read the man page for the > "iptables" command. The "iptables-save" command dumps your entire > current ruleset to stdout so you can see what's in there. (You might > have to run it as root, I forget.) > > https://help.ubuntu.com/community/IptablesHowTo > This 'distribution' I am running is a tailor linux 3.4.19 on an embedded system (Samsung S3C2410). Because this is a very small system, I believe I did not add any ip-table options in the kernel. And, I did not install any user space firware packet for it. So maybe this is really a firewall play in between. Now I run tcpdump on the target system with 'tcpdump -i eth0'. Then when I ping it from another Linux box, I see nothing from the tcpdump output. Does this confirm there is a firewall blocked the ping packets? Thanks in advance. -- woody I can't go back to yesterday - because I was a different person then.