North American Network Operators Group

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Re: IPv6 news

  • From: Tony Li
  • Date: Sun Oct 16 04:49:11 2005

Doesn't NAT, or more specifically the most commonly used, NAPT, create
hard state within the network, which then makes it violate the
end-to-end argument ? Also, because it has to understand transport and
application layer protocols, to be able to translate embedded addresses,
doesn't this also make it violate end-to-end ? I've understood the
fundamental benefit of following the end-to-end argument is that you end
up with a application agnostic network, which therefore doesn't create
future constraints on which applications can then be used over that
network. In an end-to-end "compliant" network, any new transport layer
protocols, such as SCTP or DCCP, and new user applications, only require
an upgrade of the end or edge node software, which can be performed in
an incremental, per edge node as needed basis. In other words, there
isn't any whole of network upgrade cost or functionality deployment
delay to support new applications, which was the drawback of application
specific networks, such as the traditional POTS network.

Have I somehow misunderstood the intent or benefits of the end-to-end
argument ?


This is probably the most common misunderstanding of the end-to-end principle out there. Someone else can dig up the quote, but basically, the principle says that the network should not replicate functionality that the hosts already have to perform. You have to look at X.25's hop-by-hop data windows to truly grok this point.

Many people pick this up and twist it into ~the network has to be application agnostic~ and then use this against NATs or firewalls, which is simply a misuse of the principle. Really, this is a separate principle in and of its own right. It's not one that I subscribe to, but that's a different conversation...