Have a customer plugged directly into Comcast router (LIPU and BIPU) everything works fine for weeks then all phones drop and connection is not restored until cards are reset. We have replaced both cards and cards are on latest and greatest firmware but problem still happens. Cards are in cabinet 2 slot 3 and 5 and slots 4 and 6 are vacant. SPI and firewall are off on the router and it appears to happen around the same time every month.

Have you tried just resetting the the comcast router ?

I always had troubles with BIPU cards. After a while they won't allow the phones to register, even in a local area network.

I haven't had the same issues with LIPU cards.

I have not tried to reset just the Comcast router as most of the times when it happens no one is onsite who is knowledgeable to do so. Comcast see's no errors and other IP's respond so it seems to just be the cards. I have gone to the highs Comcast tier in troubleshooting. I do not think it is a DDOS attack however I do not want to rule that out. Have also replaced the 5 port switch that goes from the Comcast router to the phone system. When the cards go down sometimes they will respond to pings and sometimes they will not which is even more frustrating.

We have similar setups in dozens of other locations without any issues.