end-to-end break and NAT

[kobem]

hey i am sorry again but i have been thinking something for about 2 years. And it was end-to-end
thing.

for example i am using MSN Messenger, i want to transmit a file via MSN Messenger to my friend
at his house who uses MSN Messenger. However, there is NAT implemented on my modem.This
will change my IP address(source) by matching it with the public address as you know.

And NAT is told to break the end-to-end rule. How can this become?
since just source IP address changes not the ports at the transport layer.


2- About this end-to-end rule again. let's consider the MSN Messenger. Even NAT is applied
on my modem, packets reach the destination(my friend) somehow. So what is the disadvantage
about NAT?

[BosonMichael]

Here you go!

[kobem]

hey i just have 2 months to deliver my thesis. I know IP is connectionless and do not make
end-to-end, just send the packets.

see that from wikipedia

"End-to-end connectivity is a property of the Internet that allows all nodes of the network to send packets to all other nodes of the network, without requiring intermediate network elements to further interpret them."


but even if you think IP, the intermediate devices(routers) exist between end nodes. And
these will break end-to-end.
.............
I'm trying to say is that even if you do not implement NAT but you have routers between end nodes,
end -to-end rule gets broken , am i wrong?
....................

[BosonMichael]

No, not really.

[Bluerinse]

You are correct Kobem..

End-to-end connectivity has been a core principle of the Internet, supported for example by the Internet Architecture Board. Current Internet architectural documents observe that NAT is a violation of the End-to-End Principle, but that NAT does have a valid role in careful design

Drawbacks (Disadvantages)

Hosts behind NAT-enabled routers do not have true end-to-end connectivity and cannot participate in some Internet protocols. Services that require the initiation of TCP connections from the outside network, or stateless protocols such as those using UDP, can be disrupted. Unless the NAT router makes a specific effort to support such protocols, incoming packets cannot reach their destination. Some protocols can accommodate one instance of NAT between participating hosts ("passive mode" FTP, for example), sometimes with the assistance of an Application Layer Gateway (see below), but fail when both systems are separated from the Internet by NAT. Use of NAT also complicates tunneling protocols such as IPsec because NAT modifies values in the headers which interfere with the integrity checks done by IPsec and other tunneling protocols.

Source..

http://en.wikipedia.org/wiki/Network...ss_translation

[kobem]

Originally Posted by Bluerinse

You are correct Kobem..





Source..

http://en.wikipedia.org/wiki/Network...ss_translation

the thing i am trying to tell is that, TCP is not fully performed. If you make use of NAT or
not , you can't apply end-to-end.

so why do we blame for NAT ? what is the difference if everytime some intermediate
devices exist among end nodes?

[kobem]

he please reply

[hbroomhall]

I'm afraid I'm baffled as to quite what the question is.

The article that Bluerinse points to is a very good discussion of the pros and cons.

Harry.

[kobem]

Originally Posted by hbroomhall

I'm afraid I'm baffled as to quite what the question is.

The article that Bluerinse points to is a very good discussion of the pros and cons.

Harry.

i read that article.

i want to express this: even if you do not implement NAT,there are always routers among end nodes.
In Internet environment you never clinch one end to other end. (intermediary devices exist all time)
NAT is told to break down some mechanisms such as mobile IP,IPSec since NAT changes
source address of internal device(end node).

even if you do run NAT, do source and destination ports change ?

[hbroomhall]

Originally Posted by kobem

i read that article.

i want to express this: even if you do not implement NAT,there are always routers among end nodes.
In Internet environment you never clinch one end to other end. (intermediary devices exist all time)
NAT is told to break down some mechanisms such as mobile IP,IPSec since NAT changes
source address of internal device(end node).

even if you do run NAT, do source and destination ports change ?

NAT often implies PAT - as that article mentions.

Harry.

[kobem]

Originally Posted by hbroomhall

NAT often implies PAT - as that article mentions.

Harry.

PAT yes.. i forgot it. many-to-one mapping by using ports.