HI all,
Just a heads up for those of you who are installing asterisk based systems in the field. We almost lost an account last week because we were randomly (apparently) dropping calls. Looking at the logs, it looked as though we were losing communication with the carrier (carrier was going UNREACHABLE). Fortunately, we were using a carrier who we know well and they kindly agreed to log the IP traffic in to them for us. We also had a trace put onto the DSL line by the provider. Unfortunately, everyone came up blank. Neither we, nor the carrier nor the DSL provider could see why we were going off-line. Major head-scratching time. In all the time we've worked with Asterisk, we have NEVER known it to drop a call. Eventually, we decided to look at the router (which had been supplied by a third party, who knew we were running VoIP operations and who had set the router up for us and the customer)...
Turns out that the Vigor router has a not-so-smart DoS detection and prevention mechanism. Every time the packet rate exceeds a preset DoSattack threshold (which was co-incidentally, or maybe accidentally, set by our "Voip expert" networking partner to happen at about 2 simultaneous calls), the router assumes it is under attack and shuts itself down for 10 seconds. Wonderful. We turned off the mechanism (might have been smarter to have simply upped the packet rate, but we were so pissed off with the Vigor that we didn't bother). Problem solved.
Kind Regards
S
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