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Message-ID: <E1829B60731D1740BB7A0626B4FAF0A649E05EABD5@XCH-NW-01V.nw.nos.boeing.com> Date: Tue, 30 Mar 2010 08:58:32 -0700 From: "Templin, Fred L" <Fred.L.Templin@...ing.com> To: Andi Kleen <andi@...stfloor.org>, "Edgar E. Iglesias" <edgar.iglesias@...il.com> CC: Eric Dumazet <eric.dumazet@...il.com>, Rick Jones <rick.jones2@...com>, Glen Turner <gdt@....id.au>, "netdev@...r.kernel.org" <netdev@...r.kernel.org> Subject: RE: UDP path MTU discovery > -----Original Message----- > From: Andi Kleen [mailto:andi@...stfloor.org] > Sent: Monday, March 29, 2010 11:20 PM > To: Edgar E. Iglesias > Cc: Andi Kleen; Templin, Fred L; Eric Dumazet; Rick Jones; Glen Turner; netdev@...r.kernel.org > Subject: Re: UDP path MTU discovery > > > If you don't want to hassle with all of that, the app can stick to > > 1280 (or I guess for the extreme/lazy cases turn on fragmentation).. > > See the early mails in this thread. This is about apps who can't > limit themselves to 1280, but still don't want full blown PMTU. > [They probably should, but it can be a lot of work] Right. Some apps may need to send isolated packets that are larger than the path MTU without invoking path MTU discovery. > The MTU would allow to force fragmentation on the sending host > as a workaround similar to IPv4. Right again. Unlike IPv4, however, IPv6 does not allow in-the-network fragmentation. So when in doubt, apps that need to send isolated packets that may violate the path MTU should really perform host-based fragmentation with a maximum fragment size of 1280. Isn't there a socket option "IPV6_USE_MIN_MTU" that apps can use to force fragmentation on large packets (RFC3542)? Caveat - the app may have no way of knowing whether the destination is capable of reassembling fragmented packets larger than 1500... Fred fred.l.templin@...ing.com > -Andi > -- > ak@...ux.intel.com -- Speaking for myself only. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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