We were experimenting with pings with a large datagram size (1500 bytes / 1600 bytes) and we were pinging from an ASA to a 7940 ephone. As soon as we executed the commands the phone rebooted. The pings did not arrive. The phone is running P00308000400.
ASA01> ping Interface: INSIDE Target IP address: 192.168.10.110 Repeat count:  300 Datagram size:  1600 Timeout in seconds:  Extended commands [n]: Sweep range of sizes [n]: Type escape sequence to abort. Sending 300, 1600-byte ICMP Echos to 192.168.10.110, timeout is 2 seconds: ???????? Success rate is 0 percent (0/8)
470762: May 3 21:16:38.856 CET: %IPPHONE-6-UNREGISTER_ABNORMAL: ephone-13:SEP00 112189D28C IP:192.168.10.110 Socket:3 DeviceType:Phone has unregistered abnormal ly.
Ofcourse this is not a major issue, but I guess someone could use this as a DoS attack on someones phone setup.
There are definitely documented DoS attacks on IP phones based on excessive or simply large ICMP packets being sent to the phone. Can you post what version of firmware you are currently on and what version of CUCM you are running as well? This will help determine what version of firmware you might upgrade to and test from there.
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