MESSAGE
| DATE | 2016-04-11 |
| FROM | prmarino1@gmail.com
|
| SUBJECT | Re: [Hangout-NYLXS] networking and fragments
|
In most cases that is correct except In stateful inspection firewalls like iptables, you always defragment and reassemble the packets if possible. This is done for several reasons mostly for connection tracking and to prevent several well know type of attacks which utilize packet fragmentation.
Is also makes it easier for sniffers like snort to detect attacks.
Also load balancers tend to do this as well mostly because a large number of the are implementation of LVS (Linux Virtual Server which despite the name has nothing to do with VM's)
Original Message
From: Jose A. Rodriguez
Sent: Monday, April 11, 2016 21:07
To: Ruben Safir
Reply To: NYLXS Discussions List
Subject: Re: [Hangout-NYLXS] networking and fragments
The key here is "before they reach the transport later at the destination". Doesn't say "before they reach the network layer at the destination". Indeed datagram fragments are not reassembled at the intermediate routers. The destination network layer reassembles all the fragments. After reassembly the payload (tcp it udp segment) is extracted and passed to the transport layer.
> On Apr 11, 2016, at 8:33 PM, Ruben Safir wrote:
>
> Hi
>
> I'm reading this line in the Ross - Kause textbook "Computer Networking -
> Top-Down Aproach" and it says
>
>
> "The solution is to fragment the data in the IP datagram into two or
> more smaller IP datagrams, encapsulate each of these smaller IP
> datagrams in a separate link-layer frame; and send these frames over
> the outgoing link. Each of these smaller data-grams is referred to as a
> fragment.
>
> Fragments need to be reassembled before they reach the transport layer
> at the destination. Indeed, both TCP and UDP are expecting to receive
> complete, unfragmented segments from the network layer."
>
> I thought that was wrong. They have to be reassembled AT the
> destination, not before that.
>
> ?
>
> Where am I confused, or is this in fact incorrect?
>
> Reuvain
>
> --
> So many immigrant groups have swept through our town
> that Brooklyn, like Atlantis, reaches mythological
> proportions in the mind of the world - RI Safir 1998
> http://www.mrbrklyn.com
>
> DRM is THEFT - We are the STAKEHOLDERS - RI Safir 2002
> http://www.nylxs.com - Leadership Development in Free Software
> http://www2.mrbrklyn.com/resources - Unpublished Archive
> http://www.coinhangout.com - coins!
> http://www.brooklyn-living.com
>
> Being so tracked is for FARM ANIMALS and and extermination camps,
> but incompatible with living as a free human being. -RI Safir 2013
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