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Re: [RRG] Re: [RAM] Tunneling overheads and fragmentation

On 11-sep-2007, at 23:41, Dino Farinacci wrote:

Granted, this is a fairly old box in a small network, but I don't see anyone seriously claiming that ALL ISP networks support packets larger than 1500 bytes on ALL their internal links (and also on inter-ISP links).

I did a survey about a month ago and it is true. I will yield to those folks who responded to me to protect their privacy. ;-)

But the main gist was: 

o We are going to 9K MTUs on all our internal links.
o Where we don't have 9K MTUs, we use 4470.
o Virtually no one runs ISP links at 1500.

That's good news, because then we can apparently treat anyone using 1500 as an exception that can be dealt with operationally rather than something that must be addressed in the protocol.

But what about inter-ISP links? I'm assuming this isn't a big issue for high capacity private peering, but here in Europe a lot of peering happens over exchanges, which obviously use equipment that can easily handle larger packets, but so many people are on a big fat shared subnet that it's a given at someone will bring down the lowest common denominator to 1500.

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