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.t 

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