7:34 a.m.
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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 rout=
er 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.
Moacir
________________________________
From: Fabrice Bacchella <fabrice.bacchella(a)orange.fr>
Sent: Tuesday, August 8, 2017 12:23 PM
To: Moacir Ferreira
Cc: users(a)ovirt.org
Subject: Re: [ovirt-users] Users Digest, Vol 71, Issue 37
Le 8 ao=FBt 2017 =E0 11:49, Moacir Ferreira <moacirferreira(a)hotmail.com<mai=
lto:moacirferreira@hotmail.com>> a =E9crit :
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 route=
r is configured to support 9K jumbo frame in one interface (i.e.: LAN conne=
ction) and 1500 in another (i.e.: WAN connection) then the router will be r=
esponsible for the fragmentation.
That's happen only if the bit don't fragment is not set, otherwise router a=
re 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.
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charset=3Diso-8859-=
1">
<style type=3D"text/css" style=3D"display:none;"><!-- P
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n-bottom:0;} --></style>
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<div id=3D"divtagdefaultwrapper"
style=3D"font-size:12pt;color:#000000;font=
-family:Calibri,Helvetica,sans-serif;" dir=3D"ltr">
<p>True! But in some point of the network it may be necessary to make the M=
TU 1500. For example, if your data need to cross the Internet. The border r=
outer in between your LAN and the Internet will have to fragment a large fr=
ame back to a normal one to send
it over the Internet. This router will just "die" if you have a =
heavy load. <br>
</p>
<br>
Moacir<br>
<br>
<div style=3D"color: rgb(49, 55, 57);">
<hr tabindex=3D"-1" style=3D"display:inline-block; width:98%">
<div id=3D"divRplyFwdMsg" dir=3D"ltr"><font
style=3D"font-size:11pt" face=
=3D"Calibri, sans-serif" color=3D"#000000"><b>From:</b>
Fabrice Bacchella &=
lt;fabrice.bacchella(a)orange.fr&gt;<br>
<b>Sent:</b> Tuesday, August 8, 2017 12:23 PM<br>
<b>To:</b> Moacir Ferreira<br>
<b>Cc:</b> users(a)ovirt.org<br>
<b>Subject:</b> Re: [ovirt-users] Users Digest, Vol 71, Issue 37</font>
<div> </div>
</div>
<div><br class=3D"">
<div>
<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=
> 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-alig=
n:start; text-indent:0px; text-transform:none; white-space:normal; widows:a=
uto; word-spacing:0px; font-size:12pt; font-family:Calibri,Helvetica,sans-s=
erif">
<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 O=
ffload) 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 efficie=
nt 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>That's happen only if the bit don't fragment is not set, otherwise
rou=
ter are not allowed to do that and send back a "packet to big" IC=
MP, it's called path mtu discovery. To my knowledge, it's usually set, and =
even mandatory on IPv6.</div>
<br class=3D"">
</div>
</div>
</div>
</body>
</html>
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