US Cable Support → OptimumOnline > Filtering bogons within CV network

Filtering bogons within CV network

If you use a Cisco IOS router behind your CV modem and you are leery of bogon addresses hitting your Internet-facing interface, be careful when you filter them out.

My service went out earlier today but only TV came back shortly afterwards.

It wasn't CV's fault; the modem started blinking all the usual lights shortly after TV came back, but I wasn't getting back online.

Turns out CV hands you a DHCP lease from somewhere internally using an address in the IANA 10.0.0.0 block; probably head-end or whatnot. From my end, that address is 10.240.176.25.



Just an FYI..... Carry on..

The CMTS acts as a relay DHCP server in broadcast DHCP. It also acts as the Default Gateway for the Modem Subnet. It's primary address which you will see in a tracert is the private IP that is the used for the Modem Default Gateway. Your Modem also had a private IP on the WAN side in the same subnet. The broadcast DHCP replies will as you indicate come from the private IP of the CMTS.
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The Modem will only act as a DHCP server when it is not connected to the CMTS. So on boot, it handed you the 192 address before it had synced. Once it synced the CMTS gave you the public address. When synced the modem acts as a transparent bridge. Since you still had a private IP when prompted for privileged access it probably would not have been the CMTS requesting access credentials.
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Warning, If you post nonsense and use misinformation and are here to argue based on those methods, you will be put on ignore.

Yes, you're right. It was my router asking. And it should be the router asking since its external interface was assigned the address.

Had a mental bleep when I posted that.