[Openswan Users] (p)mtu problem between winxp and openswan2.3.0

VRZ (VRZ Koblenz) VRZ at Lsv.rlp.de
Wed Mar 30 15:29:27 CEST 2005


i am using openswan 2.3.0 under suse9.3 (kernel 2.6.10).  If i start a
connection from my winxp pro workstation (sp2) via adsl a vpn-connection
every thing works fine until i start a vnc-session. Then the screen is
frozen and nothing works. This is a classical (p)mtu-prohlem as i read
but until now i haven'f found any solution for this problem.

Here is  what i did:

Under windows xp the largest packet i can ping without defragmentation
is 1395 bytes (ping -f -l 1395 xx.xx.xx.xx). The mtu of my linuxbox is
1492 bytes. I am tuning via iptables the mtu:

#iptables -A FORWARD -p tcp -m tcp --tcp-flags SYN,RST SYN -j TCPMSS
--set-mss 1452
iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS

none of them fixed the problem.

During the session setup my linux box writes the following message to
the systemlog:
kernel: pmtu discovery on SA ESP/54c693d0/54a99ca9

Do you have any suggestions?

Regards from germany

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