[LUGOS] DHCP server in MTU

[b at aufbix.org]

Quoting Matija Grabnar <matija.grabnar at arnes.si>:

> On Sat, Apr 09, 2005 at 08:17:42PM +0200, Iztok Kham wrote:
>> Mi morda lahko kdo pove, ali se da nastaviti pri DHCP3 stre?miku kak?en
>> parameter, ki pove klientom, kak?en MTU morajo nastaviti?
> man dhcp-options:
>       option interface-mtu uint16;
>
>          This option specifies the MTU to use on this interface.   The  mini-
>          mum legal value for the MTU is 68.

Super, ampak a to dejansko deluje (na windows/linux/osx/pasekaj)? DHCP
parametrov je malo morje, je pa vprasanje, koliko jih DHCP clienti res
upostevajo...

Sicer pa je resitev verjetno lahko tudi tole (na routerju, ce je Linux):

   TCPMSS
       This target allows to alter the MSS value of TCP SYN packets, to control
the maximum size for that connection (usually limiting it to your  outgo-
       ing interface's MTU minus 40).  Of course, it can only be used in
conjunction with -p tcp.
       This  target is used to overcome criminally braindead ISPs or servers
which block ICMP Fragmentation Needed packets.  The symptoms of this problem
       are that everything works fine from your Linux firewall/router, but
machines behind it can never exchange large packets:
        1) Web browsers connect, then hang with no data received.
        2) Small mail works fine, but large emails hang.
        3) ssh works fine, but scp hangs after initial handshaking.
       Workaround: activate this option and add a rule to your firewall
configuration like:
        iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN \
                    -j TCPMSS --clamp-mss-to-pmtu

       --set-mss value
              Explicitly set MSS option to specified value.

       --clamp-mss-to-pmtu
              Automatically clamp MSS value to (path_MTU - 40).

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AUFBIX:  "bojni vzklik, poziv na boj" (battle cry...)
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