[c-nsp] ASA5510 with SIP dropping intermittent

[Jimmy Stewpot]

Hello,

I am currently running a Cisco ASA 5510 device running software version 8.0(3)6. The configuration is very simple, we have a group of voice servers behind the system talking to an upstream Voice service provider using SIP. Outbound calls work 100% of the time, however we have a policy in place with permits inbound connections. Most of the time it works however in an apparently random fashion it drops incoming calls. There have been no changes to the device in months and its only started to occur over the last week. I have been ripping my hair out trying to resolve this issue with little to no luck.

When I check what is going on I see the following messages in the log.

Feb 16 10:48:10 <IP> %ASA-6-106015: Deny TCP (no connection) from /57345 to /5060 flags PSH ACK on interface Outside 

The configuration is as follows.

Voice Server (192.168.1.20/24) -> ASA internal (192.168.1.254) || ASA External (Public Address) -> Internet.

We have an inbound policy permitting any inbound SIP udp and tcp to the Public Address. We then have a one to one mapping

static (inside,Outside)  192.168.1.20 netmask 255.255.255.255

Everything seems fine, and I don't understand why its dropping the connections on a very intermittent basis. It seems that its probably something to do with the inspect. If we disable inspect it breaks all phone connections. I found the following bug reference number in the release notes for 8.2. CSCtb23281 but I don't have Cisco Logins which provide me with the bugs db any more... 

Any advice or assistance would be greatly appreciated.

Regards,

Jimmy Stewpot.