dhclient: lease renewal woes

Rudy Zijlstra rudy at grumpydevil.homelinux.org
Wed Aug 29 15:36:10 UTC 2012

On 29-08-12 17:31, Mr Dash Four wrote:
>>> How? I know all of the parameters you listed above as they've never 
>>> changed (and I am with this provider close to 10 years now), but I 
>>> also need my own (i.e. my firewall's) IP address when I get it from 
>>> my provider (and this IP address changes from time to time, so it is 
>>> not a constant), so how am I going to pull that one off?
>> You surprise me. If the modem is the DHCP server in your network, 
>> then the modem LAN IP address, usually or so, should be 
>> your firewall/gateway address.
> No, that is not the case. My firewall address is a public address and 
> not a private one. My firewall gateway address is also a public 
> address and has nothing whatsoever to do with the CM DHCP server 
> address. My firewall's IP address, along with the default gateway are 
> on the same (vast public) network of my provider, BUT this network is 
> not part of the CM's IP address. Does that make sense?
> Here by "firewall" I mean the machine which is directly connected to 
> the CM and uses it to obtain the DHCP lease (for that public IP 
> address). On that same machine I also have 6 other interfaces - all 
> internal - through which I route traffic.

ok, what you have is:

CMTS --- CM --- Linux Firewall --- Other PC

The CM is running in Bridge mode and is actually not the DHCP server. 
The DHCP server is behind the CMTS (that is the counter to the CM).
Yes, the address you get on the linux firewall will occasionally change. 
But, there is no big reason for the "Other PC" to change, as you can 
make that invisible to them.

Before we continue on this, please confirm the above setup

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