Cable Forum - View Single Post - Intermittent L3 Connection Loss

qasdfdsaq · 21-02-2011, 20:32

I have a funny feeling this is the same as what I get after a disconnect (which used to happen quite often on my modem, but it's now once a week or so).

Without really knowing why, it seems the modem waits for an explicit DHCP renew after a short loss of connectivity or reinitialization even if the old lease is still valid. As you say, you can't access the modem status pages or the internet until the router's WAN interface gets reset.

It feels a bit like the "DHCP required" option on Cisco wireless controllers which, after certain kinds of reconnect, will not allow any data to be passed until the client does a DHCP renew even if the old lease is still valid. The client doesn't realise, thinks it's old lease is still valid, and simply sees 100% packet loss.

Anyway, it looks like you might have the same problems as me - short, quick disconnect/reconnects without the modem rebooting, after which the modem/CMTS expects a DHCP request from the router but the router not realizing it needs to do one. I have a script as a workaround that monitors the WAN connection and issues DHCP renew requests if the modem drops, but doesn't actually stop the disconnections. VM have so far failed to address the actual cause of the disconnections, but at least now the connection comes back up without me having to reboot the router myself.

21-02-2011, 20:32	#3
qasdfdsaq cf.mega poster Join Date: Aug 2004 Posts: 11,207	Re: Intermittent L3 Connection Loss - Bad DHCP? I have a funny feeling this is the same as what I get after a disconnect (which used to happen quite often on my modem, but it's now once a week or so). Without really knowing why, it seems the modem waits for an explicit DHCP renew after a short loss of connectivity or reinitialization even if the old lease is still valid. As you say, you can't access the modem status pages or the internet until the router's WAN interface gets reset. It feels a bit like the "DHCP required" option on Cisco wireless controllers which, after certain kinds of reconnect, will not allow any data to be passed until the client does a DHCP renew even if the old lease is still valid. The client doesn't realise, thinks it's old lease is still valid, and simply sees 100% packet loss. Anyway, it looks like you might have the same problems as me - short, quick disconnect/reconnects without the modem rebooting, after which the modem/CMTS expects a DHCP request from the router but the router not realizing it needs to do one. I have a script as a workaround that monitors the WAN connection and issues DHCP renew requests if the modem drops, but doesn't actually stop the disconnections. VM have so far failed to address the actual cause of the disconnections, but at least now the connection comes back up without me having to reboot the router myself.