North American Network Operators Group

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Re: IPv6 news

  • From: Michael.Dillon
  • Date: Mon Oct 17 09:19:55 2005

> Is VJ compression considered a violation of the "end-to-end" principle?

VJ compression happens in the middle of the network, between
two routers/gateways. End-to-end refers to the hosts, i.e. 
the computers which "host" the end users' applications. Of
course, in the old days, many of these "hosts" also carried
out the function of a gateway using a dialup modem, but that
is still not violating the end-to-end model because the end
user application never knows about the VJ compression.

NAT is different because it causes some end-user applications
to fail entirely. For instance an application which sends
its IP address to another host with the instructions "call
me back when something interesting happens". The NAT box
in the middle causes the callback to fail in most cases.

And end-to-end multihoming solution that is consistent
with the end-to-end model will allow any application to
communicate with another host even when one of the hosts
moves to a different network location. BGP multihoming
achieves this by announcing the small number of possible
locations where a particular netblock can be found. The 
telephone system solves this by providing a central directory
service where the network looks up an 800 number (or any
portable number) to find the current location of the destination.
Some people have used DNS techniques to do a similar sort
of IPv4 multihoming, notably Paul Vixie and an Israeli
box vendor whose name escapes me at the moment.

Theoretically, in a network, a router/gateway could
have some intelligence/state so that it does not simply
forward packets based on destination addresses in the routing
table. Instead it does some kind of query/lookup to identify
the real destination location. If you stick this functionality
directly in the end hosts themselves, then you have SHIM6. 
If you stick the functionality in the provider edge router
then you have MPLS.

--Michael Dillon