Pinging IP phones

[tahequivoice]

I have one customer complaining of static, and in the process of tracking it down I noticed that I would get an 11% packet loss of 100 packets to the phone, yet the interface on the switch shows no issues. I then checked against other phones on the network and saw the same thing, then went to 2 other locations and found the same thing, roughly every sixth or seventh packet would drop. Is this normal for the 7940 phones?

[Chandramohan Nagarajah]

No it's not normal, you should check and see how the data devices are responding. If they are also missing the pinging, check the LAN infrastructure.

[maharris · Accepted solution]

Well, IP phones do not behave very consistently with pings, there is a tech note about this:

Replying to a Ping

When trying to ping an Cisco IP Phone 79xx from a router, the phone will only reply to one ping out of two.

This is because the IP phones have been designed to only reply to an echo every 10ms, in order to withstand Denial of Service (DoS) attacks. A Cisco IOS gateway sends echos more frequently so one out of two will timeout. This is not the case for a PC since the time between two echos is greater than 10ms.

http://www.cisco.com/en/US/tech/tk652/tk701/technologies_tech_note09186a008010edb8.shtml

If all the phones are behaving pretty much the same, I would focus on the PCs behind them to know for sure if there is a problem.

Mary Beth

[tahequivoice]

MAH I didnt see your reply until after I posted my last response. I checked from my PC and sure enough got 100% replies. The article showed one out of every two, but my responses were one ou of every 7, so it was close, but not right on target, but enough for me to look elsewhere. Thanks

[tahequivoice]

Well, checked PC's and switches and they all respond OK, I went into one of our other custoemrs on a totally different network and found the exact same thing, the PC's, switches and routers all respond OK 100%, but the phones get only 89%. This other customer has not had any QOS issues with their voice, and the other one only has one user with static.