[AG-TECH] NZ AG3.1 Bridge - error

Nathan Gardiner nathan.gardiner at canterbury.ac.nz
Tue Aug 7 21:05:48 CDT 2007

Hi there,

We still seem to be having problems registering with the Bridge Server
in Argonne. It seems to work okay on our normal campus network (which
isn't multicast enabled) but doesn't seem to work on our KAREN network
(multicast enabled). 

See below from our network engineer on campus who has been doing some
packet sniffing on both networks. I have also attached some screenshots.


Nathan Gardiner
Human Interface Technology Lab NZ (HIT Lab NZ)
Room 110, Old Maths Building, University of Canterbury
DDI: +64 3 364 3072, Cell: +64 21 163 2956

-----Original Message-----
From: Craig Miller [mailto:craig.miller at canterbury.ac.nz] 
Sent: Wednesday, 8 August 2007 1:34 p.m.
To: Nathan Gardiner
Subject: Re: FW: New Zealand AG3.1 Bridge - error

Hi Nathan,

For some reason Ethereal will not let me export to a .txt file so I've
attached a couple of screen dumps that show the problem plus the actual
capture file in libpcap format (Ethereal).

Basically the connections are going along happily until after the HTTP
POST done by ag3bridge in packet #16.  The remote server
(vv3.mcs.anl.gov) in the successful transaction responds with an HTTP OK
in packets 18 and 20 but in the failed transaction there is no response
from the remote server other than an ACK that it had received the POST
request, ag3bridge then appears to time-out waiting for a response
(packet 18) and close the connection.

There is nothing I can see that would indicate why the remote server
fails to respond to the POST request - both POST requests are
essentially identical other than the source IP address.  These packets
from both captures were captured from the interface connected to the
KAREN switch so this is before any possible firewall rules implemented
by us (of which there are none onto the network anyway).

  Besides, I do not believe that this could be a result of any filtering
in the path between the two servers as the TCP connection to the remote
server has been successfully working up to that point and there is no
reason for those specific packets to be dropped.  This therefore all
points to an application level problem on the remote server - my guess
is that for some reason the remote server does not accept the IP address  Perhaps the application is filtering IP addresses it
accepts and doesn't recognise as a valid network (a
non-research range perhaps?) for connecting?

All it bit of a mystery...

Cheers, Craig

Nathan Gardiner wrote:
> Hi Craig,
> Here is the correspondence I've had with the Access Grid team over in 
> Australia.
> -----Original Message-----
> From: Christoph Willing [mailto:willing at vislab.uq.edu.au]
> Sent: Thursday, 2 August 2007 1:03 a.m.
> To: Nathan Gardiner
> Subject: Re: New Zealand AG3.1 Bridge - error
> The way the client registry code works is to ask the bridge registry 
> (at vv3.mcs.anl.gov:8030 in this case) to return a list of bridge 
> peers. Each bridge is contacted in turn to determine its "distance"
> from the client. Since your error says that self.serverProxy is None 
> type (its initialised state before trying to contact any peers) it 
> means that the registry returned an empty list (or no reply was 
> received.
> Try adding the line
> 	print 'XXXXXXXXXXXXXXXXXXXXXXX ', self.registryPeers just before
> line:
> 	for r in self.registryPeers:
> (about line 53 in the file /usr/lib/python2.5/site-packages/
> AccessGrid3/AccessGrid/Registry/RegistryClient.py)
> Now try running the bridge again from a shell and look for the line 
> with lots of X's - it should contain a list of bridge peers after the 
> X's. If there's nothing there, it again implicates your machine's 
> ability to contact the bridge registry and receive a list of bridge 
> peers.
> chris
>> -----Original Message-----
>> From: Christoph Willing [mailto:willing at vislab.uq.edu.au]
>> Sent: Tuesday, 31 July 2007 6:16 p.m.
>> To: Nathan Gardiner
>> Subject: Re: New Zealand AG3.1 Bridge - error
>> On 31/07/2007, at 12:37 PM, Nathan Gardiner wrote:
>>> Hi Chris,
>>> I was hoping you might be able to shed a little light on the problem

>>> that I'm facing setting up a AG3.1 Bridge Server for New Zealand. 
>>> I've attached a txt document detailing the error I get when I 
>>> attempt to start bridging.
>>> We have two networks here on campus. First the normal network that 
>>> is only unicast and firewalled, second the KAREN network which is 
>>> VLANed across the campus network and links us into the research 
>>> network nationally and internationally which is multicast enabled 
>>> and doesn't have a firewall and can only reach research network ip 
>>> addresses (can reach www.accessgrid.org etc.
>>> When I have the computer on the normal campus network the Bridge 
>>> works fine, but when I change it over to the KAREN network is comes 
>>> up with this error message (see attached). I suspect that it may be 
>>> trying to reach an address that isn't located on our research 
>>> network and
>> Nathan,
>> It looks like your bridge process can't register itself. The bridge 
>> registry service is returned by http://www.accessgrid.org/registry/
>> peers.txt (from your -u option); at the moment, that returns 
>> "vv3.mcs.anl.gov:8030". If that service is unavailable (either its 
>> down, or your process can't access it due to firewall, routing, etc.)

>> then you can't register so the bridge can't continue.
>> chris
>> Christoph Willing                       +61 7 3365 8350
>> QCIF Access Grid Manager
>> University of Queensland
> Christoph Willing                       +61 7 3365 8350
> QCIF Access Grid Manager
> University of Queensland

Craig Miller
Network Engineer
Information & Communication Technology Services University of Canterbury
Phone: (03)364-2987 x8342   Cell: 027 201 7798
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