8:37 a.m.
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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.
Le 8 ao=FBt 2017 =E0 13:34, Moacir Ferreira =
<moacirferreira(a)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(a)orange.fr =
<mailto:fabrice.bacchella@orange.fr>>
Sent: Tuesday, August 8, 2017 12:23 PM
To: Moacir Ferreira
Cc: users(a)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(a)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 =
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
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<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(a)hotmail.com</a>&gt; 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(a)orange.fr</a>&gt;<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(a)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(a)hotmail.com</a>&gt; 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--