Normally yes. But the unsual situation you originally described, would
require that the applications use the session layer to establish who gets
what data. This would have to be carried in the same TCP connnection.
Following the OSI model
Applicaiton
Pressentation
Session (session multiplexing would occur here)
Transport (NAT or PAT occur here)
Network
DataLink
Physical
-----Original Message-----
From: Fred Danson [mailto:[EMAIL PROTECTED]]
Sent: Thursday, January 25, 2001 10:12 AM
To: [EMAIL PROTECTED]
Subject: RE: Question about Napt
If the host is using the same port for 2 different applications, wouldn't
the applications get confused? Dont the applications need 2 different
streams of traffic going with 2 different ports?
>From: [EMAIL PROTECTED]
>To: [EMAIL PROTECTED], [EMAIL PROTECTED]
>Subject: RE: Question about Napt
>Date: Thu, 25 Jan 2001 10:07:30 -0500
>
>Here's my 2cents
>
>All TCP/UDP sessions can be uniquely identified using four pieces of
>information
>source tuple
>1) source ip address
>2) source socket
>destination tuple
>3) destination ip address
>4) destination socket
>
>The router would keep a table of inside connections and map those to a
>table
>of outside connections that it originates.
>On the outside connections it has to be able to pick the source socket to
>originate from. This allows the router to create unique connections
>without
>duplication. As to the multiplexing part, the router really wouldn't be
>involed. The host would be doing the multiplexing. If I understand what
>you have written the host would be using the same unique information to
>create the second session: same source ip address, same source socket, same
>destination ip address, and the same destination socket. So the router
>really wouldn't care that there were two sessions, it only keys on the
>source and destination tuples.
>
>
>-----Original Message-----
>From: Fred Danson [mailto:[EMAIL PROTECTED]]
>Sent: Thursday, January 25, 2001 9:07 AM
>To: [EMAIL PROTECTED]
>Subject: Question about Napt
>
>
> Hi, I was reading RFC3022 about Napt last night, and I still dont
>understand one thing about it. From what I understand is that Napt allows
>you to use one single globally unique IP address on the WAN interface of
>your router, and then a large number of local addresses inside your network
>which aren't globally unique.
> Now the router will be able to translate the different traffic
>streams
>coming from the WAN according to the port on the packet. So if host A
>inside
>
>the network wanted to communicate with Host B which is on a different
>outside network, it would directly address the outside site, and the router
>would catch the packet enroute and change the source IP address to the
>router WAN interface IP address and also change the source port to a port
>of
>
>the router's discretion.
> Normally, from what I understand, ports are used to multiplex streams
>of traffic across a link. If Host A was using two applications and wanted
>to
>
>start a second session with Host B. Would the router allow this? The RFC
>states "While not a common practice, it is possible to have an application
>on a private host establish multiple simutaneous sessions originating from
>the same tuple of (private address, private TU port). In such a case, a
>single binding for the tuple of (private address, private TU port) may be
>used for translation of packets pertaining to all sessions originating from
>the same tuple on a host. How exactly would the applications know which
>traffic stream was for itself?
> Also, how many local hosts can the router assign to a single IP
>address
>before it has to use a second IP address? Could a company of 100000 use a
>single IP address for NAPT? or would it need to use more than one?
>
>
>Thanks in advance,
>
>Freddy
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