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Cisco Bug: CSCvt58150 - Expressway not closing aged tcp connection

Last Modified

Aug 28, 2020

Products (1)

  • Cisco TelePresence Video Communication Server (VCS)

Known Affected Releases

X12.5.4

Description (partial)

Symptom:
In a situation where Expressway is making a traversal call (eg. B2B or on-prem to WebEx), there are circumstances wherein it may re-use an old connection.  If the connection to be re-used is older than the firewall's TCP max idle time, the firewall will have closed the connection.  The result is that you will see a SIP message leave the Expressway as if all is well, but it will not arrive at the intended destination.

Conditions:
1) call must pass through Expressway C/E, as a B2B or WebEx call.  Firewall traversal is definitely involved.
2) two different calls, different source and destination URI is common.  From the expressway standpoint, the external-facing interface of the Expressway-E will be acting as UAC, and re-use the source port from a previous SIP session.
3) both of these calls must be made to the same destination IP.
4) the second transaction must be initiated after the edge firewall has dropped the connection due to idle timeout.  I believe the ASA default is 60 minutes.
5) the nature of this sort of usage pattern indicates it is more likely to happen with calls to conferencing platforms such as WebEx.
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