From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Sylvain Coutant" Subject: RE: Ethernet MTU Date: Wed, 16 Aug 2006 13:05:25 +0200 Message-ID: <00cd01c6c123$e0aa2160$2f00a8c0@ELTON> References: <62b0912f0608160336s34f6cc9cu739ede8c45a4ab9f@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <62b0912f0608160336s34f6cc9cu739ede8c45a4ab9f@mail.gmail.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: 'Molle Bestefich' , 'James Harper' Cc: 'xen-devel' , xen-users@lists.xensource.com List-Id: xen-devel@lists.xenproject.org > James Harper wrote: > > 802.1q lives under IP. >=20 > That's right. >=20 > But the VLAN exposes a virtual interface. > That virtual interface should automatically have an MTU size of the > underlying interface minus 4 bytes (for the VLAN tag). It should. It does not. It's usually not a problem as networking = equipment handle frames up to 1520-1540 bytes without much trouble, at = least equipments able to manage tagged frames. > And then IP fragmentation, working on top of that virtual Ethernet > interface, should perform fragmentation correctly. IP fragmentation handling is for routers when they connect two networks = with different mtu sizes. This is not the case here, the IP stack = generates frames that are as large as the mtu makes it possible. Spamming xen-devel with non-Xen related network education and RFCs was = not my intent, I was just wondering about jumbo frames support into Xen = networking layer ... BR, -- Sylvain