IPPhone 7940 not responding to ping

Unanswered Question
Feb 8th, 2008

Hello,

I have encountered today a very strange situation: I connected a 7940 phone to my desk switch (it's a lousy Surecom switch, with no VLANs or other stuff) and that switch is connected to another switch - and from there, to the company's routing infrastructure (also to a CallManager). I mention that my laptop is connected to the same Surecom switch as the phone.

The weird thing is that after phone starts, it respons to ping from my laptop, and it responds to 3-4 ping packets sourced from a router (that lies somewhere in the company network, but has direct connection, through switches, with the phone). After those 3-4 replies, phone no longer replies to pings sourced from the router, but only replies to pings coming from my laptop. I put the phone in another ports on the switch - same happened. I connected the phone to the upstream switch - same happened.

I really don't understand why the phone stops replying to pings (this is also a sign that no other packets from phone to router or CM are passing through).

Has any of you encountered such a situation?

Thanks,

Dan

I have this problem too.
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royalblues Fri, 02/08/2008 - 05:36

Might be 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://cisco.com/en/US/tech/tk1077/technologies_tech_note09186a008010edb8.shtml

HTH

Narayan

danhirjau Fri, 02/08/2008 - 05:45

It is not the problem that the router sends faster ICMP requests and some of them are lost and some of them aren't, because the situation is that no ICMP replies get back to the router after the first 3-4. Pings from router towards my laptop are working fine.

I also attached another IP Phone (a 7905), having an IP similar to 7940's, and this one is working "by the book": replies to all ICMP pings with no loss.

P.S.: the router is not Cisco, it's Juniper :))

Paolo Bevilacqua Fri, 02/08/2008 - 06:01

Hi, what Narayan is telling you is 100% correct, certain IP phone models by design do not reply to all pings, while other models do.

Please read the link posted above for more information about that.

danhirjau Fri, 02/08/2008 - 13:56

I read Narayan's link, but those statements have nothing to do with my case. If you read it thoroughly, I said that the 7940 phone STOPS replying ICMPs after 3-4 replies, arrived in order. And it never replies to any ICMP ever, until I take out the ethernet cable from the switch and plug it back. After that, the situation repeats.

Hope I made myself pretty clear now :)

Regards,

Dan

CCIP :)

danhirjau Sun, 02/10/2008 - 01:35

The phone software looks ok, but, since it cannot connect to the CM, no registration is done and therefore no calls can be completed.

Paolo Bevilacqua Sun, 02/10/2008 - 03:40

Suggest you do a factory reset: power cyle while pressing #, release when phone says reset sequence, press in sequence 123456789*0#, press 2 to erase network setting.

Note you must have the firmware files on the CM for this to work.

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