From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mahesh Bandewar Subject: Re: [PATCH 2/2] ipvlan: always allow the broadcast MAC address Date: Mon, 30 Mar 2015 10:56:34 -0700 Message-ID: References: <1427409698.18540.11.camel@redhat.com> <1427409822.18540.13.camel@redhat.com> <20150328193254.6c79784d@griffin> <1427726230.1913.9.camel@redhat.com> <1427737479.1913.20.camel@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: Jiri Benc , linux-netdev To: Dan Williams Return-path: Received: from mail-ob0-f180.google.com ([209.85.214.180]:35052 "EHLO mail-ob0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753544AbbC3R4z (ORCPT ); Mon, 30 Mar 2015 13:56:55 -0400 Received: by obcjt1 with SMTP id jt1so131398541obc.2 for ; Mon, 30 Mar 2015 10:56:54 -0700 (PDT) In-Reply-To: <1427737479.1913.20.camel@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: On Mon, Mar 30, 2015 at 10:44 AM, Dan Williams wrote: > On Mon, 2015-03-30 at 09:54 -0700, Mahesh Bandewar wrote: >> On Mon, Mar 30, 2015 at 7:37 AM, Dan Williams wrote: >> > On Sat, 2015-03-28 at 19:32 +0100, Jiri Benc wrote: >> >> On Fri, 27 Mar 2015 22:56:15 -0700, Mahesh Bandewar wrote: >> >> > The current logic disables broadcast by default and enables only when >> >> > an IPv4 address is added. If this is inverted and - >> >> > enables broadcast by default but disables it when only IPv6 >> >> > address(es) is / are added. These links can have multiple addresses >> >> > and hence have to be careful if any one of those is IPv4 then >> >> > broadcast bit has to be set. >> >> >> >> You'd have to be careful and ignore IPv6 link local addresses. >> >> Those are added automatically whenever IPv6 is enabled and their >> >> presence does not mean the network is not IPv4 only. >> >> >> >> But I don't like such magic behavior. It would lead to DHCP sometimes >> >> working and sometimes not in mixed v4/v6 environment depending on >> >> whether DHCPv4 or SLAAC was faster. >> >> >> >> Could we perhaps add a flag when creating ipvlan interface stating >> >> whether IPv4 broadcast should be always enabled? Or, rather, the other >> >> way round - whether it should be disabled by default. Call it "nodhcp" >> >> or so. >> >> >> >> Btw, speaking about IPv6 link local addresses, these actually do not >> >> work with ipvlan correctly. I'm getting DAD failures if I have more >> >> than one ipvlan interface, which is no wonder. This means that ipvlan >> >> cannot work with IPv6 reliably by default (unless you take care of ll >> >> address assignment and ensure all ipvlan interfaces get a different >> >> one). >> > >> > ipvlan doesn't set dev_id. Once dev_id is set the kernel's IPv6LL >> > address generation code will assign a different LL address to each >> > ipvlan interface created from the same physical interface, despite that >> > they have the same MAC address. >> > >> Yes, that was what my plan was but never got around fixing that >> >> > But of course you'd have to be careful to assign a *different* dev_id >> > than any of that physical interface's non-ipvlan children too, and I >> > have no idea how that would work since dev_id is currently done >> > per-driver. eg, if you have a physical interface with dev_id=1 which >> > you then create an ipvlan from, that ipvlan must not use dev_id=1 or it >> > will be assigned the same IPv6LL address as the parent. >> > >> The description is very clear for dev_id (in netdevice.h). So the idea >> of using the subsequent numbers after master's id should be possible. >> After all these logical devices are going to share the same link. Most >> physical drivers don't assign dev-id so the beginning is 0x0 (for the >> physical driver) and from 0x1 can be assigned to the logical links. >> The definition is not clear in terms of what is the beginning (0x0 or >> 0x1) but from the code that generates the IPv6LL it's common that it's >> 0x0 hence logical links on top of these links can use 0x1 onward. >> However a check to see if the master-link has dev-id and staying clear >> of that should be sufficient. > > My point was that if you have a parent with a non-zero dev_id, there can > be other siblings of the parent that have a different dev_id and share > the same MAC address. So creating an ipvlan with parent->dev_id + 1 > doesn't work, because the parent may have a sibling with parent->dev_id > + 1 and the same MAC address already. > May be I'm missing something but is there a scenario where sibling (physical / port) will be sharing the same LL-address? The definition / description in netdevice.h is - * @dev_id: Used to differentiate devices that share * the same link layer address So I's assuming the layered / stacked devices (children) rather than ports etc (siblings). What am I missing? > Dan >