i posted this on a linux forum i visit and the consensus was that this is a comcast issue, but figured i'd post here to get a second opinion... The modem is an SMCD3G if that helps at all. All IPv4.
so this one happens only after an extended, seemingly random period of time. i have 5 static IPs on comcast business with which i have 4 Arch linux machines connected, configured with 4 of these statics. If any one of them has had no traffic pass over their external interfaces for "some" time (usually half a day or more), these systems lose access completely from the internet. After this happens, the only way to restore connectivity is to ping (or initate any network transfer) from the machines out to the internet. When I do this on the machine, it IMMEDIATELY restores the connectivity.
Worringly, this appears like an issue with the cable modem, as, when the systems are knocked offline and I run a tcpdump on the external interface, I see absolutely NO traffic appear when I try to ping from the outside... it's like the cable modem forgets that there's a device even plugged in, and needs to be "reminded" that there's a machine there. A call to comcast support told me it was a problem with my equipment. Except that it happens with 4 different machines.... Additionally, when one goes down it disappears from the "Connected Devices" list on the gateway "Network" status page I can restore access by going into the modem config and clicking "Refresh" on the "Connected Devices" page, after which it immediately re-appears...
If i had to take a complete shot in the dark, i'd say that it's some sort of ARP caching that's not working properly, but i'd have no idea where to go from that. Because the packet capture shows absolutely nothing, I really don't have a lot to go by... but does anyone have any ideas? I've tried typical cable modem stuff (unplug/replug, have comcast re-push a config file down.)
Edited to add topic group category. uid://455626
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