[strongSwan] IP reassembly bug with strongSwan?

Daniel.Merget at rohde-schwarz.com Daniel.Merget at rohde-schwarz.com
Tue May 31 10:48:49 CEST 2011

First of all thanks for your time and help!

> What virtualization platform are you using? KVM, ESXi, etc.

I am using VMware Workstation 6.5.5 on a Windows XP host system.

> With what version of the Linux kernel are you experiencing this issue? 
> Did you try different versions?

The virtual machines run on Ubuntu 10.0 with kernel 2.6.35-22-generic. I 
have not yet tried to compile a newer kernel version, but I noticed there 
have been some changes commited to the working tree concerning IPv4 
fragmentation and reassembly. Thus in the next step, I want to test my 
setup using net-next kernel (2.6.39) which provides a lot of network 

> What do you mean by "the machine froze"?
> Do you have console access to the machine?
> Is it not responding at all or do you only lose network access?

The whole Linux GUI freezes, I can move the mouse around, but cannot 
trigger any actions. Network loses connection to the machine. VMware 
Workstation rests completely stable. After rebooting the machine 
(power-off), I also inspected the kernel logs: there are no hints or any 
suspicious notifications at all. In /var/log/messages the logger actually 
stopped in the middle of the line (some event long before the triggered 

> Do you think it's possible that the virtualization infrastructure or 
some firewall is doing some kindof processing on the packet and that it's 
the virtualization platform that crashes.

I think I can definitely eliminate the firewall as a cause because I 
configured iptables to simply accept all packets and no further filtering 
is done (it's all virtual, so there is no malicious packets from outside).
For the virtualization platform, I am actually not 100% sure but there is 
no fail-proof way I can test it. Regardless, I set up a third virtual 
machine to forward all incoming packets to the corresponding target 
without modifying the contents (except for TTL). The fact that this 
machine keeps on running perfectly, however, seems to condradict the 
conjecture that VMware Workstation is the cause.

As noted above, I will test the setup with a new kernel version. I am 
convinced now that it is very likely a kernel issue (and maybe it is 
already fixed).

As soon as I have finished testing I will share my results and keep you up 
to date.

Best regards,

Daniel Merget
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