On Sun, Oct 16, 2005 at 01:45:40AM -0700, Tony Li wrote: > > > > >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 ? > > > Mark, > > 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...
Maybe its time to pull out some of Noel's work on both topics. Reasonable introductions to both the e2e principle and locator/id split topics can be found on http://users.exis.net/~jnc/tech/end_end.html and http://users.exis.net/~jnc/tech/endpoints.txt respectively. Dave
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