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Clear cable modem offline delete

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jobin007007
Clear cable modem offline delete

I am using CISCO ubr7246vxr with updated software.

Does running this command everyday 'Clear cable modem offline delete' help the CMTS? Somebody is telling me it would be beneficial to do this every hour and it allows more modems to lease. My argument is that lease time only depends on the 15 minute lease I have set up in the policy. this person is contenting that the offline modems still use up the IP address in case they get plugged in before 24 hours is up ( offline modems get removed every 24 hours automatically).

I am using this in a production plant. So in this case over 4000 modems get plugged into 1 D.S and U.S of the CMTS. They only remain on the CMTS for 1/2 hour in batches of 30 only and get unplugged right after. So after having 100 then 200, then 1000, then 3000 modems offline on the CMTS, does this cause issues? Does the clear cable modem offline delete improve this?

Please let me know and if you have any information and links. Here is a link I have.
http://www.cisco.com/c/en/us/support/docs/broadband-cable/cable-modems/4...

Thanks
Jobin Thomas

cmcaldas
modem age timer

Sorry, not a Cisco cmts guy, but thinking there would be a modem age timer option in the config.
Modems should be getting a private address, so if they use an address longer than week or month isn't a big deal unless the the scope for that network is too small and you need to keep a close eye on it. thinking it's a /20 (total of 4094 hosts, including gateway) private network. Option one, check on modem age timer option if it's available or just make it a /19 network.
Do you get warnings or alarms from your dhcp server?

Carl

pajaja
I beleive you're right

CMTS does not lease IP addresses (of course if you don't have a DHCP server configured on it) so deleting the modem wouldn't force the IP into an available state. You control the lease time on DHCP server with, well, the lease time :)

clear cable modem delete command clears the modem from internal CMTS databases (address tables, routing tables, station maintenance list, etc.). If your modem is already offline the only benefit I would see is the cleaner output of the show cable modem command. The cable modem age time cmcaldas suggested is unfortunately not configurable on Cisco CMTS and it is fixed to 24 hours. I believe that ARP entries are held for 4 hours as on other Cisco routers.

So I wouldn't worry much about it. If you know that the modem will be online only for 30mins, I would set the lease period to a short value (as you did) and maybe tweak the ARP timeout to a lower value. On the other hand, I also don't see any drawbacks to clearing the offline modems if you want to.

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