I have a modem which, as per topic, periodically stops NATing.
I have diagnosed this based on the fact I can still ping Internet addresses from the modem with no issues, and connect to the modem from any desktop, however my desktops are unable to ping those same Internet sites. I can resolve this by running:
clear ip nat translation *
This would lead you to believe there was some kind of memory exhaustion or similar basedon there being too many connections. I don't know what reasonable memory values are, but see here, taken during the problem:
Head Total(b) Used(b) Free(b) Lowest(b) Largest(b)
Processor 81920F50 21466288 10446512 11019776 10874400 10835784
I/O 2D99C00 2515968 783556 1732412 1623088 1731836
Also, my number of translations just doesn't look remotely high:
internetz#show ip nat statistics
Total active translations: 10 (0 static, 10 dynamic; 10 extended)
Hits: 12596816 Misses: 274138
CEF Translated packets: 12691877, CEF Punted packets: 36541
Expired translations: 296197
-- Inside Source
[Id: 1] access-list 100 interface Dialer0 refcount 4
Queued Packets: 0
Full config is below. You can see forwards for torrents, which were initially blamed for the issue, but I've had that service shutdown for days, and confirmed all the desktops were doing almost nothing with netstat, while still managing to stop the modem passing traffic.
And of course, IOS:
I pasted the config here but it was too long, so it's attached.
I was running the "plus" version but dropped down to see if the lower RAM requirement helped.