Equipment (Modems,Gateways)
Modems, Gateways, and Networking Devices
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New Modem Cisco DPC3941B has 10ms higher ping just to the device

A tech came yesterday and upgraded our modem to Cisco DPC3941B. We have 5 static IP service on 50/10 plan. We have a tomato router behind the modem that handles all traffic/wireless, and don't use the Cisco for anything but pass through traffic. Bridge mode is disabled and apparently can't be enabled with multiple static IPs. Firewall is set to "low". We use VOIP so I try to ensure we have low latency/jitters.

 

The previous router we had was I believe an SMC. It would average around 13ms ping to google.com. The new modem averages arond 25ms and 10ms+ jitter.

 

When I connect my laptop directly to the modem and ping 10.1.10.1 (just pinging the modem), ping varies 5-10ms, and sometimes 30-90ms. That's in contrast to pinging our tomato router, which is consistently less than 1ms. Something does not seem right here. I would expect jitters around 1-2ms. That amount of jitter here, just to the modem, is enough to lower the quality of VOIP.

 

Below is graph of latency quality. Starting around week ago latency and jitters increased and pings were lost. Comcast replaced modem last Wed. 

 

mt-view-ping.png

 

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Re: New Modem Cisco DPC3941B has 10ms higher ping just to the device

Any update on this?

 

Noticed the exact same thing after the tech left after delivering the DPC3941B. Pings to the device's LAN interface are anywhere between 1-15ms, pings to comcast.com are as a result anywhere between 25-50ms on average, a rather large potential deviation.

 

https://www.dropbox.com/s/73cpn020ywmsxfp/dpc3941b-high-ping-jitter-on-lan-interface.png?dl=0

 

Attaching two devices to separate LAN ports on the DPC3941B, pinging between the two devices is ~1ms consistently, but pinging the DPC3941B directly yields the 1-15ms ping.

 

Device currently is not set to bridge mode, though I might try and see if that helps to resolve these high pings.

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Re: New Modem Cisco DPC3941B has 10ms higher ping just to the device

I'm having the same issue with my DPC3941B.  Pings to it are ~10ms whereas pinging anything else inside the network is <1ms.  It seems to be greatly slowing down the rest of my network and causing major headaches with the management software that I use.

 

Has anybody found a solution to this or is it a matter of replacing the hardware?

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Re: New Modem Cisco DPC3941B has 10ms higher ping just to the device

I've seen this issue as well, it appears as if routing traffic isn't being done properly. Pinging the gateway itself reveals this issue.

So I've replaced this device with one of the same model and the problem still was around.

 

Previous gateway worked just fine.

 

My theory on this is that they are using virtual interfaces and that they are being routed in such a way that causes excessive overhead. 

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Re: New Modem Cisco DPC3941B has 10ms higher ping just to the device

Hey just a word of advice from past experiences, get off the Comcast Cisco cable modem immediately if you are trying to run VoIP over it. Demand an SMC or a Netgear cable modem, but watch out, I can't seem to get more than 12Mbps upload speed on the SMCs. Check out my similar post that I just made here.

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