[e2e] Layering vs. modularization

George Michaelson ggm at apnic.net
Thu May 15 19:10:25 PDT 2008

On 16/05/2008, at 11:27 AM, David P. Reed wrote:

> Encasulation means that the "totally ordered stack of layers"  
> suddenly can grow to infinite depth, as the sequence of layers is  
> laid on top of a subsequence selected from the same layers.

to riff on the encapsulation word, there are some real-world views on  
it emerging, for instance the V6 routing community in Europe very  
strongly deprecate and police world-wide emerging V6 tunnels. They  
don't like 'em, because of the end to end RTT and wierd routing  
consequences for the 'system as a whole' -OTOH many people who want to  
'promote' V6 love them, because they magically increase the footprint.

Likewise considering MPLS (which is almost always an IP sublayer  
providing magic flow routing to an IP payload encapsulation) you get  
some very odd real-world outcomes when you eg forget the MPLS cloud is  
worldwide, link in Asia, and see a low-AS path preference emerge in  
France for a device in .. Tokyo.

We (the wider we) all expect our VPN to work. Demand it even. I've  
even been shown that in some circumstances the net benefit to me of  
using far-off-faroffia's routing view when I am on VPN is magically  
'better' even allowing for the double-packet transits. Which is odd,  
but then, so is the likely double or triple compress/encode  
consequences of SSH over VPN over ...


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