packet loss between R2811 and ip phones

Unanswered Question
Jul 26th, 2008
User Badges:


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.

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
mattcalderon Sun, 07/27/2008 - 17:05
User Badges:
  • Silver, 250 points or more

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:

helawamry Mon, 07/28/2008 - 12:59
User Badges:

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



This Discussion