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piook
join:2015-01-17

piook

Member

[Connectivity] Occassional Loss of connectivity but modem shows all is fine

First let me say that I am a network Admin and have a fair amount of knowledge with these matters and have seen all manner of issues with internet connections of all sorts over the years. I have a netgear cg3000dcr business gateway (had an SMC before and experienced same issues) and about twice a week we lose the connection to the internet. When this happens I cannot ping the modems gateway address or anything beyond it. I get no reply about 99% of the time with an occasional response with 2.5 sec latency. From outside my network (a computer at another location) i can ping the modem's gateway address but not my modem's IP address. When all is well i can ping both fine from outside my network. Also, at all times the modem shows it is connected and all the signal levels are quite solid.

My wife called comcast since i was at work and they say everything is fine with the connection but reluctantly decide to send someone out (at my wife's insistence) but by the time the tech arrives (usually the next day) everything is fine again.

I am not sure what to do at this point because there is obviously something going on but comcast is not seeing anything wrong (either from the office when we are experiencing the issue or when the tech finally gets here and the issue is no longer occurring). They usually say my issue is a problem my router. Though it obviously is not since I can get to its config page and to the modem's config page on the other side of it. Plus using the ping utility on the modem shows the same thing happening as do the pings from my computer when connected directly to the modem. I can show comcast my ping data that shows that there is a problem but they don't seem to care about that.

To me based on what I can see it seems like i am a victim of a DOS attack. Not sure why i would be but it explains the behavior i am witnessing. But you would think comcast would be able to see this too then? It is not an issue that causes the modem to think it is down but it does completely break all traffic to the net. If this is the case then if I can force a public IP change to the modem then the problem should resolve itself. But when i suggested this to comcast they tried to sell me static IP addresses.

Any help is appreciated.
whiteblinder
join:2009-02-13

whiteblinder

Member

Conserning DDoS.
If you don't have static IP address, you can also use just regular DOCSIS3 modem, not a gateway. For that setup you need your own router, if you have multiple computers. By changing router's WAN MAC address, you will get new ip address after power-cycling modem. Business gateways will usually tend to keep the same ip address. I think, you can also request that gateway to bridge mode. This way you will have only one ethernet port on gateway with internet IP address, not local LAN IP (10.x.x.x)

Is it possible, that you have something causing flood of packets on your LAN side? Layer 2 Broadcast storm? That should not be intermittent.
Do you have ability to see any logs from Comcast gateway?

Johkal
Cool Cat
MVM
join:2002-11-13
Pennsyltucky

Johkal to piook

MVM

to piook
Please post your signal levels and log entries.

owlyn
MVM
join:2004-06-05
Newtown, PA

owlyn

MVM

Check your upstream power levels when the problem occurs.