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On 09/02/2011 09:03 AM, Michael Rash wrote:
> On Sep 01, 2011, Ele Asurareo wrote:
> 
> Hello fwknop list,
> 
>> Hello Ele,

Thanks for the reply Michael,

> 
> I'm a new user of fwknop with GPG authentication on Debian. I first
> heard about it during Michael's presentation at The Last HOPE and kept
> the idea in the reptile brain for the right time.
> 
> I've put together a Xen virtual hosting environment based on the
> packages in Debian Stable (Squeeze). It works great! Except for one
> mysterious problem.
> 
> I'm connecting to the host OS, which is supported by an ethernet bridge
> (xenbr1) between the physical interface (eth1) and the domU virtual
> interfaces (vif1.n). xenbr1 is assigned an IP address. fwknopd listens
> on xenbr1 in pcap mode.
> 
> I configured fwknopd successfully and sent a successful SPA packet to
> the IP of xenbr1. The firewall rule was added to allow access and I
> could SSH properly as expected. I went home and tried to connect from
> there, which was successful. Two days have passed and I've verified the
> server hasn't been rebooted nor has anyone else used SPA to connect to
> the SSH port. Strangely, I can no longer get the SPA packet to open the
> SSH port. I've confirmed this with nmap. Despite authenticating as
> before, I cannot connect.
> 
> I have a few hypothesis I will test tomorrow when I'm in front of a
> local console but I would appreciate any special advice to operate
> fwknopd reliably on a Linux ethernet bridge.
> 
>> Are you running the perl version or the more updated C version?  In
>> virtual environments I've sometimes seen odd behavior with sniffers not
>> seeing the expected traffic, but I don't really have specifics.  I think
>> it would be a good idea to see if fwknopd is seeing the traffic at all.
>> You could run "tcpdump -i <intf> -l -nn udp port 62201 -w 62201.pcap" and
>> see if tcpdump is able to log the SPA packets too as an additional check
>> to ensure that sniffers can see the traffic.

I'm running the Perl version 1.9.12 packaged by the Debian maintainer
for the stable distribution. I'd like to hold off on a packet dump since
I get such wildly different results on my home network versus a LAN on
the same CIDR block as the server in question.

I swapped out some old network hardware that was known to be "sort of
broken" sitting on the subnet in question. I can connect to the server
from my home network as expected. I'll wait it out over the weekend and
check again in a couple days.

Regards.
Ele

> 
>> Another thing to check is whether the system clocks between the fwknopd
>> server system and your client system are relatively in-sync.  By default,
>> fwknopd requires the time stamp on any incoming SPA packet to not be
>> older than 120 seconds - this is required in order to prevent a certain
>> type of MITM attack (as discovered by Sebastien).  If you really want
>> to disable this (such as if you aren't using NTP and time sync is
>> otherwise difficult), then you can set ENABLE_SPA_PACKET_AGING to "N",
>> but I wouldn't recommend it.
> 
>> fwknopd does supply some log information via syslog that may be helpful
>> too - usually in /var/log/messages.
> 
>> Thanks,
> 
>> --Mike
> 
> 
> Thanks for your help,
> Ele
>>
-
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