From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [RFC] ipv4: add link_filter sysctl Date: Wed, 18 Mar 2009 18:21:15 -0700 (PDT) Message-ID: <20090318.182115.43965264.davem@davemloft.net> References: <20090313161253.0f02da26@nehalam> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org To: shemminger@vyatta.com Return-path: Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:50091 "EHLO sunset.davemloft.net" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751196AbZCSBV2 (ORCPT ); Wed, 18 Mar 2009 21:21:28 -0400 In-Reply-To: <20090313161253.0f02da26@nehalam> Sender: netdev-owner@vger.kernel.org List-ID: From: Stephen Hemminger Date: Fri, 13 Mar 2009 16:12:53 -0700 > Add a new parameter that controls how kernel responds to packets > when interface is down. This is done to solve the problem of: > > Assume topology of: > A <-----------> Router X--- down link > 10.1.1.2/24 10.1.1.1/24 10.2.1.1/24 > eth0 eth1 > > If A pings 10.2.1.1 then with normal Linux semantics Router would > respond even if eth1 link on 10.2.1.1 was down. This causes some network > management tools (that work with other router OS's) to falsely > report that link is okay. > > The problem is that a Linux router does not respond the way > other systems do. This is the router equivalent of "Strong ES" > model, it is not the same as "Strong ES" as defined in Host > Requirements. > > The new parameter adds an additional check on slow input packet > path, and causes route cache flush if enabled and carrier is > lost. > > Signed-off-by: Stephen Hemminger There is nothing "router" about this situation. When 10.2.1.1 is being pinged, it is in the role of an end-system in that transaction. The "router" is reachable by "A", and as a consequence so is that IP address 10.2.1.1, and therefore the ping should succeed.