Hi,
On Mon, Jun 10, 2013 at 10:59:21PM +0200, Dick Visser wrote: > On 10 June 2013 22:48, Phil Pennock <[email protected]> wrote: > > On 2013-06-10 at 14:57 +0200, Dick Visser wrote: > >> This works for a while, but after a minute or so it changes back to the > >> default: > > > >> Any ideas what might be causing this? > > > > A thought, so only qualifies as "might", I don't know Windows to speak > > definitively, but ... IPv6 NDP Route Advertisement with the MTU option? > > > > Windows then updating the manually-configured value based upon learnt > > values on the wire? > > Yup, this was the case. I watched it continuously, and when an RA came > in, it overwrote the manually configured MTU. > Next question: how do I prevent that from happening? two things come to mind: a) as already stated by Christopher: by deactivating the processing of RAs on the Windows systems in question. It should be noted that this is a severe "deviation from default" (see https://www.troopers.de/wp-content/uploads/2013/01/TROOPERS13-Design+Configuration_of_IPv6_Segments_with_High_Security_Requirements-Enno_Rey.pdf for the term) and hence in general we don't like or recommend that approach. b) (much better): have the router advertise the lower MTU you want to use in the RAs by just setting a lower MTU on the (router) interfaces in question. See also: http://blog.ioshints.info/2013/01/mtu-issues-and-tcp-mss-clamping-in.html best Enno > > > -- > Dick Visser > System & Networking Engineer > TERENA Secretariat > Singel 468 D, 1017 AW Amsterdam > The Netherlands -- Enno Rey ERNW GmbH - Carl-Bosch-Str. 4 - 69115 Heidelberg - www.ernw.de Tel. +49 6221 480390 - Fax 6221 419008 - Cell +49 174 3082474 PGP FP 055F B3F3 FE9D 71DD C0D5 444E C611 033E 3296 1CC1 Handelsregister Mannheim: HRB 337135 Geschaeftsfuehrer: Enno Rey ======================================================= Blog: www.insinuator.net || Conference: www.troopers.de =======================================================
