[6bone] Problems with big packets!?

[John Fraizer]

On Fri, 4 Oct 2002, Hugh LaMaster wrote:

> Several messages have suggested that packet sizes > 1500 bytes,
> or even 1000 bytes, are unreasonable.  I certainly wouldn't
> expect the existing 6bone to support packets > 1500 bytes,
> but, packets of length 9000 over WANs are quite reasonable.
> 
> Existing ATM and POS links usually default to 4470, but, 
> sometimes default to 9180 and certainly settable to 9180 
> or even larger (e.g. Cisco GSR Engine 0 OC-3/12 POS cards
> and Engine 2 OC-48 POS cards support MTU 17994,  
> some GigE switches/ports support 9180, and some NICs 
> support 9000.  People trying to do high-bandwidth applications
> over WANs with large RTT's would be well-advised to set up the
> path with 9180/9000 end-end.  
> 
> It would be unfortunate for high-bandwidth applications if only 
> 1500 byte packets end up being supported by IPv6.
> 
> --Hugh LaMaster

OK Hugh.  Just so the rest of the world doesn't get confused here:

END-TO-END is the key point when using MTUs >1500.

If you have a path that looks like this (MTUs):

[1500]-[4500]-[4500]-[17994]-[17994]-[4500]-[1500]

...It doesn't matter what is in the middle, the max packet size
(unfragmented) that is going to get through the chain is 1500.

With v6-in-v4 tunnels, 1500 won't even make it through.


---
John Fraizer              | High-Security Datacenter Services |
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