7960's dropping pings

tboynton · ‎09-10-2001

I have 50+ 7960 in use at the moment. We just noticed that when you ping them from a Cisco device on the same LAN ping packets are being dropped by the phone. This does not happen from a UNIT host. Seems to be the difference in implementation of ping between the Cisco IOS and UNIX. It looks like the phone is receiving the packets too fast from the Cisco box and won't respond to them all. If you ping the same 7960 from a Cisco device across the WAN there is no ICMP packet loss due to greater delay. See below. Seems to be be related to around 7ms. The 7960 is connected to nocback

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 130.111.39.174, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 12/12/16 ms

GW-Thom#

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 130.111.39.174, timeout is 2 seconds:

!!.!.

Success rate is 60 percent (3/5), round-trip min/avg/max = 1/2/3 ms

cat-o-nocback#

Anyone seen this before? It is happening to all 7960's across our network.

Todd Boynton

UNET Technology Services

tboynton · ‎09-10-2001

I am running support patch A images for 3.1(1) on all phones. I did try to drop done to an earlier image but saw the same problem.

blcase · ‎09-10-2001

I have seen the same issue. The only difference was the packet loss was every other packet. Since the phones are working correctly, I haven't had time to look for fix (if there is one). We are also running 3.1(1) with the support patches for the phones.

Does anyone know if this is by design??

mtashiro · ‎09-10-2001

Don't know if it is by design or not but I havce noticed this since the beginning of the 7960 phones.

dgoodwin · ‎09-14-2001

Folks, this is by design. The behavior is that the phones should only send one ICMP Echo Reply every 10ms. This is a very basic built-in DoS attack prevention.

Notice in the first example from across the WAN that the minimum round-trip time was 12ms, so it's not surprising that you got all 5 pings back. But with less latency (less than 10ms) you will not get all of them back.