From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Frederic Sowa Subject: Re: why are IPv6 addresses removed on link down Date: Tue, 13 Jan 2015 11:35:46 +0100 Message-ID: <1421145346.13626.12.camel@redhat.com> References: <54B4A7E4.7030301@gmail.com> <20150112231021.316648e3@urahara> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: David Ahern , "netdev@vger.kernel.org" To: Stephen Hemminger Return-path: Received: from mx1.redhat.com ([209.132.183.28]:55188 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751285AbbAMKf4 (ORCPT ); Tue, 13 Jan 2015 05:35:56 -0500 In-Reply-To: <20150112231021.316648e3@urahara> Sender: netdev-owner@vger.kernel.org List-ID: On Mo, 2015-01-12 at 23:10 -0800, Stephen Hemminger wrote: > On Mon, 12 Jan 2015 22:06:44 -0700 > David Ahern wrote: > > > We noticed that IPv6 addresses are removed on a link down. e.g., > > ip link set dev eth1 > > > > > > Looking at the code it appears to be this code path in addrconf.c: > > > > case NETDEV_DOWN: > > case NETDEV_UNREGISTER: > > /* > > * Remove all addresses from this interface. > > */ > > addrconf_ifdown(dev, event != NETDEV_DOWN); > > break; > > > > IPv4 addresses are NOT removed on a link down. Is there a particular > > reason IPv6 addresses are? > > > > Thanks, > > David > > See RFC's which describes how IPv6 does Duplicate Address Detection. > Address is not valid when link is down, since DAD is not possible. It should be no problem if the kernel would reacquire them on ifup and do proper DAD. We simply must not use them while the interface is dead (also making sure they don't get used for loopback routing). The problem the IPv6 addresses get removed is much more a historical artifact nowadays, I think. It is part of user space API and scripts deal with that already. Bye, Hannes