Dear List,
I'm trying to connect a GnuGk to a Cisco VCS Expressway as traversal
client using a sligthly adopted version of the example configuration
in the manual (http://www.gnugk.org/gnugk-manual-10.html).
Unfortunately, the GnuGk is unable to register at the Cisco VCS.
I have done a detailed analysis of that behaviour:
As expected, the GnuGk sends a H.225 SCI to the VCS Expresway. A
packet decoding with Wireshark looks as follows:
Frame 12: 101 bytes on wire (808 bits), 101 bytes captured (808 bits)
Ethernet II, Src: CadmusCo_xx:22:xx (08:22:27:xx:22:xx), Dst: Cisco_xx:78:xx
(c4:7d:4f:xx:78:xx)
Internet Protocol Version 4, Src: 192.168.77.72 (192.168.77.72), Dst:
xx.15.130.112 (xx.15.130.112)
User Datagram Protocol, Src Port: h323gatestat (1719), Dst Port: backup-express
(6123)
H.225.0 RAS
RasMessage: serviceControlIndication (30)
serviceControlIndication
requestSeqNum: 1
serviceControl: 1 item
Item 0
ServiceControlSession
sessionId: 0
reason: open (0)
open: NULL
cryptoTokens: 1 item
Item 0
CryptoH323Token: cryptoGKPwdHash (1)
cryptoGKPwdHash
gatekeeperId: test
timeStamp: Jan 7, 2013 21:06:34.000000000 CET
token
algorithmOID: 1.2.840.113549.2.5 (md5)
paramS
hash: 3101089b79e22f2609507fbcb2174772 [bit
length 128]
featureSet
.... 0... replacementFeatureSet: False
supportedFeatures: 1 item
Item 0: Signalling Traversal
FeatureDescriptor
id: standard (0)
standard: 18 - Signalling Traversal
The VCS Answers (Ethernet/IP/UDP headers ommitted)
H.225.0 RAS
RasMessage: serviceControlResponse (31)
serviceControlResponse
requestSeqNum: 1
result: failed (1)
failed: NULL
To compare that with a working configuration, I registered another Cisco VCS
as traversal client and have again decoded a packet dump of the registration
with wireshark:
H.225.0 RAS
RasMessage: serviceControlIndication (30)
serviceControlIndication
requestSeqNum: 57923
serviceControl: 1 item
Item 0
ServiceControlSession
sessionId: 0
reason: open (0)
open: NULL
cryptoTokens: 1 item
Item 0
CryptoH323Token: cryptoGKPwdHash (1)
cryptoGKPwdHash
gatekeeperId: test
timeStamp: Jan 8, 2013 12:24:40.000000000 CET
token
algorithmOID: 1.2.840.113549.2.5 (md5)
paramS
hash: 54a3c3fe4fa909743b38bd940b882ed4 [bit
length 128]
featureSet
.... 0... replacementFeatureSet: False
supportedFeatures: 1 item
Item 0: Signalling Traversal
FeatureDescriptor
id: standard (0)
standard: 18 - Signalling Traversal
which leads to a successful registration:
H.225.0 RAS
RasMessage: serviceControlResponse (31)
serviceControlResponse
requestSeqNum: 57923
result: started (0)
started: NULL
featureSet
0... .... replacementFeatureSet: False
supportedFeatures: 1 item
Item 0: Signalling Traversal
FeatureDescriptor
id: standard (0)
standard: 18 - Signalling Traversal
genericData: 2 items
Item 0: Signalling Traversal
GenericData
id: standard (0)
standard: 18 - Signalling Traversal
parameters: 1 item
Item 1
GenericData
id: nonStandard (2)
nonStandard: c2f2d2a2-1527-11dd-a123-0fc456d89593
parameters: 1 item
Time is synchronized by ntp on the VCS and the GnuGk. The time is the
same on the Expressway and the GnuGk-Host
In the packet dump, I see only three differences from which I only see
two of them as a
1) requestSeqNum is appearantly random on the VCS and 1 on the GnuGk.
A randomly chosen requestSeqNum makes IP spoofing much more difficult, so
that may be a security measurement of the VCS to reject messages using
1 as sequence number. It should be fairly easy to exchange the 1 with
some unpredictable random number though (maybe using openssls RAND_*
funktions?). Unfortunately, GnuGk is real C++ code which is not one
of the languages i'm able to write.
2) The timestamp differs
Which is not surprising as the snapshots where taken at different
time.
That one is obvious and should not be a source of the problem
3) The hash differs.
That is as well obvious, as the timestamp is part of the hash. However, I
was not able to figure out how that hash is created exactly so i could
not verify wether the hash is created equally on both systems.
(In particular, my C++ is not good enough to identify the correct part
of the code in GnuGk and I have either not found or not understood how
to create that hash correctly in the standard. Any pointer to a
reasonably simple to understand description would be appreciated.)
Have I missed something? Any Ideas?
Thanks in advance,
Immo
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