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Stale ARP table at Comcast?

New Poster

Stale ARP table at Comcast?

My internet is currently down. I checked the Xfinity app to see if there was an outage. It showed there wasn't, and my internet showed as connected, but my cable modem showed as not connected (MB8600). When I called Comcast, they walked me through the ususal steps rebooting equipment, bypassing my router, etc. They even had me call the manufacturer of the cable modem (Motorola). Motorola said everything looks good, no issues with the equipment. When I pull up the cable modem status, all channels are bonded, and the ranges look correct. I can get an IP address connected directly to the modem, and it shows Comcasts DNS servers. However, I cannot resolve any host names when I ping, nor can I get a reply when I try to ping the IP addresses directly. 

Here's my issue. When I first called, they showed a different cable modem active on my account (an old one that I had returned to the store). The tech said it was plugged in and active somewhere, but I verified it wasn't at my house. I had them remove it from the account altogether (on my second call), to see if that was causing some sort of conflict. I've seen issues when an arp table doesn't refresh, and the traffic is being sent to the wrong IP/MAC address. I have a feeling that's what's happening here, and the traffic is getting misrouted to the old modem. They can't even send a reset command to it, since it is showing offline to them (even though I'm getting an IP address, and the lights are good on the modem), but they can see it is active. I couldn't get them to verify the route or the traffic (apparently they can't do that?), and the best they could do was schedule a tech to come check the lines. They also gave me a choice to go pick up a Comcast modem from the local store, but that bypasses the issue since I want it to work with my equipment. Does anyone know if they refresh their arp and/or routing tables, and if so what is the frequency?

New Poster

Re: Stale ARP table at Comcast?

Just a quick update. I tried calling back to see if they could assign me a new IP address to bypass any routing or IP conflicts, but they said they can't do that (not sure why). I was hoping that might force a refresh on their end. So I have to wait until tomorrow for my scheduled appointment. Not great since I work from home. Hopefully the tech they send can figure something out. I'm still not convinced it's an equipment issue at my house.

New Poster

Re: Stale ARP table at Comcast?

Final update. My internet just automagically came back online. Not sure if someone did something on Comcasts side (they said no), or if their cache finally cleared/updated. Either way I don't care as long as my internet is back.