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New Member

packet loss between R2811 and ip phones


This is my topology:

R2811----Cat3750----CE500----(IP Phone+PC).

Call between IP Phone and IP Phone is very well but from IP Phone and PSTN through R2811 is intermittent.

When i ping from router 2811 to ip phones, i get 5 success and 1 fail.

All port on CE500 are configured as IP Phone+Deskop 100/full. giga ports connected to Cat3750 are switch ports 1000/full with native vlan data vlan.

I don't what is the reason of this issue.


Re: packet loss between R2811 and ip phones

i have actually seen the same issues and was wondering the reason. This is a design issue and not a configuration issue.

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.

From this link:

New Member

Re: packet loss between R2811 and ip phones

well, but this is not happening exactly, when Pin from the R2811 to IP Phone the result as below:

Promo7_CoreRouter#ping source repeat 100

Type escape sequence to abort.

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

Packet sent with a source address of



Success rate is 84 percent (84/100), round-trip min/avg/max = 1/1/4 ms