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Cisco 2920 drops connection with Comcast Metro Ethernet every 20 minutes

Posted on 2013-11-02
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Last Modified: 2013-11-04
I configured a Cisco 2920 router for a Comcast Metro Internet circuit. The link is up and I have access to Internet, however after about 20 minutes the connection will drop.

The network layout goes:
Comcast hardware (Comcast tech said it's a switch) -> gig0/0 port on Cisco
My laptop is connected to the gig0/1 port

I made up the IPs in the attached config file, but this is what they represent
Comcast switch: 192.168.0.49/30
Gig0/0 on Cisco: 192.168.0.50/30
Gig0/1 on Cisco: 192.168.0.145/28
Static IP on laptop: 192.168.0.146/28

I have running pings going to 4.2.2.1, the Comcast box, gig0/0 and gig0/1 ports.
After about 20 minutes, I lose ping to 4.2.2.1 and to the Comcast box from the laptop.
To restore Internet I found that pulling out the cable between the Comcast and the gig0/0 port then plugging it back in immediately restores the connection, seems like a link down and then link up in the Cisco restores it. When this happens I also cannot ping the Comcast directly from the Cisco.

If I connect a laptop directly to the link on the Comcast and set the laptop's IP to 192.168.0.50/30 and gateway to 192.168.0.49 I get an IP conflict error and I cannot ping 192.168.0.49 or the Internet.

I want to rule out any Cisco configuration flaws before I go back to Comcast and tell them it's their configuration that's the problem.

I've attached the running configure with made up IPs and took out any extra config that I don't think is needed for this issue.
cisco-2920.txt
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Question by:ctechsol
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dlethe earned 500 total points
ID: 39619563
Comcast metro is a premium service with 24x7 support and they can eliminate or at least diagnose most of the possibilities that can account for this from their keyboard.

So before you even look at the router config, call comcast support and have them tell you what the expected uptime you will have before they change IP numbers, drop your connection, whatever ….

In other words, you very well could have only 20 mins w/o a drop  because they set it up to do it that way because you didn't opt for static IP numbers, or maybe your cable needs to be replaced. Don't assume it has anything to do at all with your router.
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Author Comment

by:ctechsol
ID: 39621249
I have been troubleshooting with Comcast and do think the issues lies with them, but as they always love to say, "we checked our configuration and hardware and everything looks good".

I just want to be as thorough as possible and cover my ass. Today will be blame Comcast day.
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Expert Comment

by:dlethe
ID: 39621252
Like I wrote, Comcast is charging you for a premium connection and they advertise 24x7 support.  Raise a stink with them, and ask for a supervisor, and demand they place some hardware on your line if they must to diagnose and fix the problem.
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Expert Comment

by:agonza07
ID: 39621405
Had a problem like this with a T1 a couple weeks back. Turned out to be my router...

Try hooking up your laptop again, and restart the Comcast router. That may clear up the IP address conflict, and make sure nothing else is connected.

Another thing you can do is try the third port of the router to try and rule out your end.
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Author Closing Comment

by:ctechsol
ID: 39622738
After pushing them to check their config they "cleaned up" some settings from it and it's been going strong for almost 2 hours now. I was fairly confident the issue was with them but I wanted to cover my ass.

Thanks again
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Expert Comment

by:dlethe
ID: 39622751
That is often the case.  Amazing how vendors respond when you remind them you paid for 24x7 support.
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