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Re: Jumbo Frames (was Re: MAE-EAST Moving? from Tysons corner to reston VA. )
From: michael.dillon () gtsip net
Date: 19 Jun 2000 10:18:09 +0100


On Mon, 19 June 2000, "Bora Akyol" wrote:

As long as most end users are running Ethernet, Fast Ethernet, DSL or Cable
Modems, what is the point of jumbo frames/packets other than transferring
BGP tables really fast. Did any one look into how many packets are moved
through an OC-48 in 1 seconds. (approx. 6 million 40 byte packets). I think
even without jumbo frames, this bandwidth will saturate most CPUs.

Jumbo frames are pointless until most of the Internet end users switch to a
jumbo frame based media.

Yes, they look cool on the feature list (we support it as well). Yes they
are marginally more efficient than 1500 byte MTUs ( 40/1500 vs 40/9000). But
in reality, 99% or more of the traffic out there is less than 1500 bytes. In
terms of packet counts, last time I looked at one, 50% of the packets were
around 40 byte packets (ACKs) with another 40% or so at approx 576 bytes or
so.

What is the big, clear advantage of supporting jumbo frames?

When 1500 byte frames from the customer's LAN enter the customer's router and enter some form of IP tunnel, then a core 
fabric which supports larger than 1500 byte frames will not cause fragmentation. It's not necessary to do the full 
jumbo size frames. I suspect that supporting two levels of encapsulation will be enough in 99.9% of the cases. For the 
sake of argument, what would be the downside of using a 2000 byte MTU as the minimum MTU in your core?

---
Michael Dillon   Phone: +44 (20) 7769 8489   
                 Mobile: +44 (79) 7099 2658
Director of Product Engineering, GTS IP Services
151 Shaftesbury Ave.
London WC2H 8AL
UK



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