Le 8 ao=FBt 2017 =E0 13:34, Moacir Ferreira = <moacirferreira@hotmail.com> a =E9crit : =20 True! But in some point of the network it may be necessary to make the = MTU 1500. For example, if your data need to cross the Internet. The = border router in between your LAN and the Internet will have to fragment = a large frame back to a normal one to send it over the Internet. This = router will just "die" if you have a heavy load.=20 =20 Moacir =20 From: Fabrice Bacchella <fabrice.bacchella@orange.fr = <mailto:fabrice.bacchella@orange.fr>> Sent: Tuesday, August 8, 2017 12:23 PM To: Moacir Ferreira Cc: users@ovirt.org <mailto:users@ovirt.org> Subject: Re: [ovirt-users] Users Digest, Vol 71, Issue 37 =20 =20
Le 8 ao=FBt 2017 =E0 11:49, Moacir Ferreira = <moacirferreira@hotmail.com <mailto:moacirferreira@hotmail.com>> a =E9crit= : =20 This is by far more complex. A good NIC will have an offload engine = (LSO - Large Segment Offload) and, if so, the NIC driver will report a = MTU of 64K to the IP stack. The IP stack will then send data to the NIC = as if the MTU were 64K and the NIC will fragment it to the size of the = "declared" MTU on the interface so PMTUD will not be efficient in such = scenario. If all this takes place in the server, then you get no =
--Apple-Mail=_F6670B9A-B615-4233-98F3-E288BA07A1A0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=iso-8859-1 The border router will do like any other router on the world. If the DF = bit is set (common case) or if it's IPv6, it will not fragment but send = an ICMP. problem. But if a standard router is configured to support 9K jumbo = frame in one interface (i.e.: LAN connection) and 1500 in another (i.e.: = WAN connection) then the router will be responsible for the = fragmentation.
=20 That's happen only if the bit don't fragment is not set, otherwise = router are not allowed to do that and send back a "packet to big" ICMP, = it's called path mtu discovery. To my knowledge, it's usually set, and = even mandatory on IPv6.
--Apple-Mail=_F6670B9A-B615-4233-98F3-E288BA07A1A0 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=iso-8859-1 <html><head><meta http-equiv=3D"Content-Type" content=3D"text/html = charset=3Diso-8859-1"></head><body style=3D"word-wrap: break-word; = -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" = class=3D"">The border router will do like any other router on the world. = If the DF bit is set (common case) or if it's IPv6, it will not fragment = but send an ICMP.<div class=3D""><br class=3D""><div><blockquote = type=3D"cite" class=3D""><div class=3D"">Le 8 ao=FBt 2017 =E0 13:34, = Moacir Ferreira <<a href=3D"mailto:moacirferreira@hotmail.com" = class=3D"">moacirferreira@hotmail.com</a>> a =E9crit :</div><br = class=3D"Apple-interchange-newline"><div class=3D""><div = id=3D"divtagdefaultwrapper" dir=3D"ltr" style=3D"font-style: normal; = font-variant-caps: normal; font-weight: normal; letter-spacing: normal; = orphans: auto; text-align: start; text-indent: 0px; text-transform: = none; white-space: normal; widows: auto; word-spacing: 0px; = -webkit-text-stroke-width: 0px; font-size: 12pt; font-family: Calibri, = Helvetica, sans-serif;" class=3D""><div style=3D"margin-top: 0px; = margin-bottom: 0px;" class=3D"">True! But in some point of the network = it may be necessary to make the MTU 1500. For example, if your data need = to cross the Internet. The border router in between your LAN and the = Internet will have to fragment a large frame back to a normal one to = send it over the Internet. This router will just "die" if you have a = heavy load.<span class=3D"Apple-converted-space"> </span><br = class=3D""></div><br class=3D"">Moacir<br class=3D""><br class=3D""><div = style=3D"color: rgb(49, 55, 57);" class=3D""><hr tabindex=3D"-1" = style=3D"display: inline-block; width: 919.234375px;" class=3D""><div = id=3D"divRplyFwdMsg" dir=3D"ltr" class=3D""><font face=3D"Calibri, = sans-serif" style=3D"font-size: 11pt;" class=3D""><b = class=3D"">From:</b><span = class=3D"Apple-converted-space"> </span>Fabrice Bacchella <<a = href=3D"mailto:fabrice.bacchella@orange.fr" = class=3D"">fabrice.bacchella@orange.fr</a>><br class=3D""><b = class=3D"">Sent:</b><span = class=3D"Apple-converted-space"> </span>Tuesday, August 8, 2017 = 12:23 PM<br class=3D""><b class=3D"">To:</b><span = class=3D"Apple-converted-space"> </span>Moacir Ferreira<br = class=3D""><b class=3D"">Cc:</b><span = class=3D"Apple-converted-space"> </span><a = href=3D"mailto:users@ovirt.org" class=3D"">users@ovirt.org</a><br = class=3D""><b class=3D"">Subject:</b><span = class=3D"Apple-converted-space"> </span>Re: [ovirt-users] Users = Digest, Vol 71, Issue 37</font><div class=3D""> </div></div><div = class=3D""><br class=3D""><div class=3D""><blockquote type=3D"cite" = class=3D""><div class=3D"">Le 8 ao=FBt 2017 =E0 11:49, Moacir Ferreira = <<a href=3D"mailto:moacirferreira@hotmail.com" = class=3D"">moacirferreira@hotmail.com</a>> a =E9crit :</div><br = class=3D"Apple-interchange-newline"><div class=3D""><div = id=3D"divtagdefaultwrapper" dir=3D"ltr" class=3D"" style=3D"font-style: = normal; font-weight: normal; letter-spacing: normal; orphans: auto; = text-align: start; text-indent: 0px; text-transform: none; white-space: = normal; widows: auto; word-spacing: 0px; font-size: 12pt; font-family: = Calibri, Helvetica, sans-serif;"><div class=3D"" style=3D"margin-top: = 0px; margin-bottom: 0px;">This is by far more complex. A good NIC will = have an offload engine (LSO - Large Segment Offload) and, if so, the NIC = driver will report a MTU of 64K to the IP stack. The IP stack will then = send data to the NIC as if the MTU were 64K and the NIC will fragment it = to the size of the "declared" MTU on the interface so PMTUD will not be = efficient in such scenario. If all this takes place in the server, then = you get no problem. But if a standard router is configured to support 9K = jumbo frame in one interface (i.e.: LAN connection) and 1500 in another = (i.e.: WAN connection) then the router will be responsible for the = fragmentation.</div></div></div></blockquote><br class=3D""></div><div = class=3D"">That's happen only if the bit don't fragment is not set, = otherwise router are not allowed to do that and send back a "packet to = big" ICMP, it's called path mtu discovery. To my knowledge, it's usually = set, and even mandatory on = IPv6.</div></div></div></div></div></blockquote></div><br = class=3D""></div></body></html>= --Apple-Mail=_F6670B9A-B615-4233-98F3-E288BA07A1A0--