[95960] in North American Network Operators' Group
Re: Thoughts on increasing MTUs on the internet
daemon@ATHENA.MIT.EDU (Gian Constantine)
Thu Apr 12 10:05:01 2007
In-Reply-To: <20070412115026.GB31278@mx.ytti.net>
From: Gian Constantine <constantinegi@corp.earthlink.net>
Date: Thu, 12 Apr 2007 10:04:22 -0400
To: NANOG list <nanog@merit.edu>
Errors-To: owner-nanog@merit.edu
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I agree. The throughput gains are small. You're talking about a
difference between a 4% header overhead versus a 1% header overhead
(for TCP).
One could argue a decreased pps impact on intermediate systems, but
when factoring in the existing packet size distribution on the
Internet and the perceived adjustment seen by a migration to 4470 MTU
support, the gains remain small.
Development costs and the OpEx costs of implementation and support
will, likely, always outweigh the gains.
Gian Anthony Constantine
On Apr 12, 2007, at 7:50 AM, Saku Ytti wrote:
>
> On (2007-04-12 11:20 +0200), Iljitsch van Beijnum wrote:
>
>> What do you guys think about a mechanism that allows hosts and
>> routers on a subnet to automatically discover the MTU they can use
>> towards other systems on the same subnet, so that:
>> 1. It's no longer necessary to limit the subnet MTU to that of the
>> least capable system
>>
>> 2. It's no longer necessary to manage 1500 byte+ MTUs manually
>
> To me this sounds adding complexity for rather small pay-off. And
> then we'd have to ask IXP people, would the enable this feature
> if it was available? If so, why don't they offer high MTU VLAN
> today?
> And in the end, pay-off of larger MTU is quite small, perhaps
> some interrupts are saved but not sure how relevant that is
> in poll() based NIC drivers. Of course bigger pay-off
> would be that users could use tunneling and still offer 1500
> to LAN.
>
> IXP peeps, why are you not offering high MTU VLAN option?
> From my point of view, this is biggest reason why we today
> generally don't have higher end-to-end MTU.
> I know that some IXPs do, eg. NetNOD but generally it's
> not offered even though many users would opt to use it.
>
> Thanks,
> --
> ++ytti
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<HTML><BODY style=3D"word-wrap: break-word; -khtml-nbsp-mode: space; =
-khtml-line-break: after-white-space; ">I agree. The throughput gains =
are small. You're talking about a difference between a 4% header =
overhead versus a 1% header overhead (for TCP).<DIV><BR =
class=3D"khtml-block-placeholder"></DIV><DIV>One could argue a decreased =
pps impact on intermediate systems, but when factoring in the existing =
packet size distribution on the Internet and the perceived adjustment =
seen by a migration to 4470 MTU support, the gains remain =
small.</DIV><DIV><BR =
class=3D"khtml-block-placeholder"></DIV><DIV>Development costs and the =
OpEx costs of implementation and support will, likely, always outweigh =
the gains.</DIV><DIV><BR><DIV> <SPAN class=3D"Apple-style-span" =
style=3D"border-collapse: separate; border-spacing: 0px 0px; color: =
rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: =
normal; font-variant: normal; font-weight: normal; letter-spacing: =
normal; line-height: normal; text-align: auto; =
-khtml-text-decorations-in-effect: none; text-indent: 0px; =
-apple-text-size-adjust: auto; text-transform: none; orphans: 2; =
white-space: normal; widows: 2; word-spacing: 0px; "><SPAN =
class=3D"Apple-style-span" style=3D"border-collapse: separate; =
border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; =
font-size: 12px; font-style: normal; font-variant: normal; font-weight: =
normal; letter-spacing: normal; line-height: normal; text-align: auto; =
-khtml-text-decorations-in-effect: none; text-indent: 0px; =
-apple-text-size-adjust: auto; text-transform: none; orphans: 2; =
white-space: normal; widows: 2; word-spacing: 0px; "><DIV>Gian Anthony =
Constantine</DIV><BR class=3D"Apple-interchange-newline"></SPAN></SPAN> =
</DIV><BR><DIV><DIV>On Apr 12, 2007, at 7:50 AM, Saku Ytti =
wrote:</DIV><BR class=3D"Apple-interchange-newline"><BLOCKQUOTE =
type=3D"cite"><DIV style=3D"margin-top: 0px; margin-right: 0px; =
margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV =
style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: 0px; =
margin-left: 0px; ">On (2007-04-12 11:20 +0200), Iljitsch van Beijnum =
wrote:</DIV><DIV style=3D"margin-top: 0px; margin-right: 0px; =
margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV> =
<BLOCKQUOTE type=3D"cite"><DIV style=3D"margin-top: 0px; margin-right: =
0px; margin-bottom: 0px; margin-left: 0px; ">What do you guys think =
about a mechanism that allows hosts and <SPAN =
class=3D"Apple-converted-space">=A0</SPAN></DIV><DIV style=3D"margin-top: =
0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">routers =
on a subnet to automatically discover the MTU they can use <SPAN =
class=3D"Apple-converted-space">=A0</SPAN></DIV><DIV style=3D"margin-top: =
0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">towards =
other systems on the same subnet, so that:</DIV><DIV style=3D"margin-top: =
0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">1. It's =
no longer necessary to limit the subnet MTU to that of the <SPAN =
class=3D"Apple-converted-space">=A0</SPAN></DIV><DIV style=3D"margin-top: =
0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">least =
capable system</DIV><DIV style=3D"margin-top: 0px; margin-right: 0px; =
margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV =
style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: 0px; =
margin-left: 0px; ">2. It's no longer necessary to manage 1500 byte+ =
MTUs manually</DIV> </BLOCKQUOTE><DIV style=3D"margin-top: 0px; =
margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: =
14px; "><BR></DIV><DIV style=3D"margin-top: 0px; margin-right: 0px; =
margin-bottom: 0px; margin-left: 0px; ">To me this sounds adding =
complexity for rather small pay-off. And</DIV><DIV style=3D"margin-top: =
0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">then =
we'd have to ask IXP people, would the enable this feature</DIV><DIV =
style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: 0px; =
margin-left: 0px; ">if it was available? If so, why don't they offer =
high MTU VLAN</DIV><DIV style=3D"margin-top: 0px; margin-right: 0px; =
margin-bottom: 0px; margin-left: 0px; ">today?</DIV><DIV =
style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: 0px; =
margin-left: 0px; ">And in the end, pay-off of larger MTU is quite =
small, perhaps</DIV><DIV style=3D"margin-top: 0px; margin-right: 0px; =
margin-bottom: 0px; margin-left: 0px; ">some interrupts are saved but =
not sure how relevant that is</DIV><DIV style=3D"margin-top: 0px; =
margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">in poll() =
based NIC drivers. Of course bigger pay-off</DIV><DIV style=3D"margin-top:=
0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">would =
be that users could use tunneling and still offer 1500</DIV><DIV =
style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: 0px; =
margin-left: 0px; ">to LAN.</DIV><DIV style=3D"margin-top: 0px; =
margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: =
14px; "><BR></DIV><DIV style=3D"margin-top: 0px; margin-right: 0px; =
margin-bottom: 0px; margin-left: 0px; ">IXP peeps, why are you not =
offering high MTU VLAN option?</DIV><DIV style=3D"margin-top: 0px; =
margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">=46rom my =
point of view, this is biggest reason why we today</DIV><DIV =
style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: 0px; =
margin-left: 0px; ">generally don't have higher end-to-end =
MTU.</DIV><DIV style=3D"margin-top: 0px; margin-right: 0px; =
margin-bottom: 0px; margin-left: 0px; ">I know that some IXPs do, eg. =
NetNOD but generally it's</DIV><DIV style=3D"margin-top: 0px; =
margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">not offered =
even though many users would opt to use it.</DIV><DIV style=3D"margin-top:=
0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; =
min-height: 14px; "><BR></DIV><DIV style=3D"margin-top: 0px; =
margin-right: 0px; margin-bottom: 0px; margin-left: 0px; =
">Thanks,</DIV><DIV style=3D"margin-top: 0px; margin-right: 0px; =
margin-bottom: 0px; margin-left: 0px; ">--<SPAN =
class=3D"Apple-converted-space">=A0</SPAN></DIV><DIV style=3D"margin-top: =
0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><SPAN =
class=3D"Apple-converted-space">=A0 </SPAN>++ytti</DIV> =
</BLOCKQUOTE></DIV><BR></DIV></BODY></HTML>=
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