From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sridhar Samudrala Subject: Re: [PATCH] macvlan: Introduce 'passthru' mode to takeover the underlying device Date: Sat, 30 Oct 2010 13:55:25 -0700 Message-ID: <4CCC863D.2070406@us.ibm.com> References: <1288307450.30131.82.camel@sridhar.beaverton.ibm.com> <201010291545.17910.arnd@arndb.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Cc: Patrick McHardy , Stephen Hemminger , "Michael S. Tsirkin" , netdev , "kvm@vger.kernel.org" To: Arnd Bergmann Return-path: In-Reply-To: <201010291545.17910.arnd@arndb.de> Sender: kvm-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 10/29/2010 6:45 AM, Arnd Bergmann wrote: > On Friday 29 October 2010, Sridhar Samudrala wrote: >> With the current default 'vepa' mode, a KVM guest using virtio with >> macvtap backend has the following limitations. >> - cannot change/add a mac address on the guest virtio-net > I believe this could be changed if there is a neeed, but I actually > consider it one of the design points of macvlan that the guest > is not able to change the mac address. With 802.1Qbg you rely on > the switch being able to identify the guest by its MAC address, > which the host kernel must ensure. > Currently the host cannot prevent a guest user from trying to change/add a mac address on the guest virtio-net. From guest point of view, the request succeeds, but the incoming packets are dropped siliently by the host interface. >> - cannot create a vlan device on the guest virtio-net > Why not? If this doesn't work, it's probably a bug! Because the host is not aware of the guest vlan tag and the host external interface will filter out incoming vlan tagged packets. > Why does the passthru mode enable it if it doesn't work > already? > passthru mode puts the host external interface in promiscuous mode which allows vlan tagged packets to be received. Even in tap/bridge mode, this works because adding an external interface to the bridge causes it to be put in promiscuous mode. Thanks Sridhar