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Cisco IP Phones call drops thru PIX Firewall

Dear Friends,

I have a problem on my IP Phone communiations...We have Cisco Call Manager 4.1 which is connected to DMZ port of PIX 515E 6.3 ver with IP address .On the Internal Interface I have 40 Cisco 7912G Ip phones with static address of ,,all are allowed to access CCM from Internal to DMZ and i have opened all the ports.We also have some around 100 7912G across WAN which gets registered with CCM and the communication between the external phones to Internal phones were smooth all these days.Nowadays we are facing a peculiar problem, that all the Internal phones are getting the registration lost and it renews the registration with the CCM once we dial some number ... Once call is placed this time is exactly 40 seconds on all the internal phones to loose the registration and gets registered again. We are not facing any problem on the external phones and they are able to contact each other and calls are not getting dropped.

I dont find any problem on the Call manager as external phones are working fine with the same call manager.. I am not able to find why this is occuring nowadays.. Can any one hint me..

Community Member

Re: Cisco IP Phones call drops thru PIX Firewall

Check the access list if DHCP is not permitted in the configuration


Re: Cisco IP Phones call drops thru PIX Firewall

It sounds like something is going to sleep between the inside and dmz interfaces on the pix - there should be sccp keepalives going between the CM and the phones, but if those sessions hang or go to sleep, once you pick the phone up and dial a number, that initiates traffic towards the CM and things wake back up.

Mary Beth

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