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How does it work ?

Posted on 2010-09-03
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Last Modified: 2013-11-30
Hello Gurus,
I have a general question.
is it possible that when sending a file (or downloading a file) each packet comes from a different route  ? (different hops?) .Is it possible to receive a packet before the other ?

My main issue is If I have on my server 2 internet connections from 2 different ISPs
can those 2 connection be active at the same time ?
Is it possible ?
please help (i need some documentation on this..
Thanks)
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Question by:ammounpierre
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Expert Comment

by:Tomas Valenta
ID: 33594845
To be able to use both ISP connection you must have filled in TCP/IP on every computer two default gateway. Then computer
communicate randomly from both but if you download file this file allways you use one gateway. The better is to use router (or firewall)
which is able to use two connections and load ballance communication between them.
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Author Comment

by:ammounpierre
ID: 33594983
If I use a router , then I will be able to use both connections at the same time ?
is it possible that 1 packet comes from connection1 and another comes from connection2 ?

thanks
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Expert Comment

by:Tomas Valenta
ID: 33595166
The router (must have loadballance capability) is able to use second connection if first is at full capacity.
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Expert Comment

by:Fred Marshall
ID: 33597684
Just to be clear:

- a device which performs router functions (be it a router box or a computer) may be able to join internet sources if it's set up to perform that purpose.  If it serves a LAN as well then nothing on the LAN need be configured to deal with this - in general anyway.

- there are protocols and devices which deal with packets arriving out of order.  So, that should not be a concern on the LAN.  But, whether the router function you have deals with this or not would be a question.  There may be Packet Order Correction at the near end or Same Order Delivery and there may be packet retransmission.  Check the functions of the Transport Layer.

From Wikipedia:
Even though every packet has the same destination address, they can be routed on different paths through the network. When the client program on the destination computer receives them, the TCP layer (Transport Layer) reassembles the individual segments and ensures they are correctly ordered and error free as it streams them to an application.

.... this implies that a multi-homed box (i.e. multiple ports for internet service for example), must have a TCP/IP stack that deals with the composite results from the ports.  I'm not sure how Microsoft does this but I'd imagine it's buried in Bridging...

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Accepted Solution

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RobArdill earned 2000 total points
ID: 33633685
TCP handles out of order packets, among many other tasks. However....

The bit of information that is missing to get a true answer, is if the source computer is using a public globally route-able/unique address or a private address RFC1918 (192.168.x.x/172.16.x.x/10.x.x.x)

In the case where the computer is using a globally unique address, then it possible to have a single IP (UDP/TCP) session transmit and receive packets via multiple paths.

In the case where the computer is using a RFC1918 address, the actual outbound IP packets adopt  a globally unique address assigned by NAT. The assigned  address used is typically the WAN IP/outside address that the ISP allocates to you. When this happens all subsequent packets must and will route via that same connection.  There are various routers that will employ load balancing per IP session, however they often employ logic that understand the application protocol in use such as VoIP, BT, FTP and many others.
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