TCP maximum segment size a Win NT

[Petr Lampa]

>
>
>
> On Wed, 14 Feb 1996, Borek Lupomesky wrote:
>
> > > Ano default je TCPIP nastaveno tak, aby behalo dobre na funcnich linkach,
> >
> >    Hmmm, jakou ma souvislost fragmentace IP datagramu s kvalitou linek. Moje
> > mineni je, ze zadnou. Proste strucne receno: Windows NT maji vadnou
> > implementaci IP protokolu. S tim zadny MS Knowledge Base nic neudela. (Nebo
> > ano?)
>
> Co se meho mineni tyce, tak na dobrych linkach s dobre nakonfigurovanym
> software by k fragmentaci dochazet nemelo.
>

To doufam nemyslite vazne? Doporucuji nahlednout do STD 3 (Requirements
for Internet Hosts -- Communication Layers, jinak take rfc1122) a
rfc1812 (Requirements for IP Version 4 Routers):

      3.2.1.4  Fragmentation and Reassembly: RFC-791 Section 3.2

            The Internet model requires that every host support
            reassembly.  See Sections 3.3.2 and 3.3.3 for the
            requirements on fragmentation and reassembly.

      3.3.2  Reassembly

         The IP layer MUST implement reassembly of IP datagrams.
	 ...


      3.3.3  Fragmentation

         Optionally, the IP layer MAY implement a mechanism to fragment
         outgoing datagrams intentionally.
          ...
          ...
         A host that does not implement local fragmentation MUST ensure
         that the transport layer (for TCP) or the application layer
         (for UDP) obtains MMS_S from the IP layer and does not send a
         datagram exceeding MMS_S in size.

----------------------------------------

Cili strucne hezky cesky (pro presnost napul anglicky):
- reassembly (skladani fragmentovanych IP paketu) musi umet kazdy host!
  Nikdo nezaruci, ze odnekud neprijde fragmentovany IP datagram (vstupni
  router cilove site je nesmi skladat, protoze neni zaruceno, ze nektere
  casti neprijdou jinym vstupnim routerem cilove site - viz rfc1812).
- fragmentaci (rozbiti dlouhych IP datagramu) nemusi host umet, ale v tom
  pripade musi posilat spravne dlouhe pakety podle MTU (MMS_S) lokalniho
  ciloveho hostu. Host, ktery neumi fragmentaci, ovsem nesmi byt routerem
  (rfc1812)!

Zaver: Pokud neumi Windows/NT reassembly, nesmi byt pripojen k Internetu.
       Pokud neumi Windows/NT fragmentaci, nesmi byt pouzit jako router.

							Petr Lampa

--
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