Fw: HTTP Stack, MTU And Fragmentation

Rehi list,

finally i found a workaround by reading iptables' manpage. There is a 
possibility as the excerpt of the manpage states below. The original 
problem are badly fragmented packages cause the domino http task to die. 
(at least 'my' dominos do so)

Hope that helps others to work around, too.


Mit freundlichem Gruß/ kind regards

Stefan Schreiner

S&W Communication und Software Development GesmbH
Rilkeplatz 1
1040 Wien

t: +43 1 505 39 26 - 28
f: +43 1 504 29 76
m: [email protected]

---
TCPMSS
       This  target  allows to alter the MSS value of TCP SYN packets, to 
con-
       trol the maximum size for that connection (usually limiting it to 
your
       outgoing  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 
con-
       figuration 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).

       These options are mutually exclusive.

---
iptables -A INPUT -t filter -p tcp --tcp-flags SYN,RST, SYN -j TCPMSS 
--set-mss 1252