Cable Modem Management IP

In the US most DOCSIS cable modems (non-router device) allows you to manage or view settings through a static IP: or For some reason ipfire often (not always) prevents me from accessing this site and I am not really sure why. Other software firewall solutions such as smoothwall and pfsense never seem to have problems accessing this site.

My internal LAN (green) is using, with DHCP on the red interface to my cable modem, so my expectations is there should not an IP conflict.

Is anyone else experiencing this issue and any thoughts on how to troubleshoot this? I am using: IPFire 2.25 (x86_64) - Core Update 152 Development Build.

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This issue pop up quite several times here.
What you want to do is access a device on the red interface. I’m wondering, why this was sporadic possible for you.
I’m using the following script to access my modem on the red interface:


ip addr add $VLAN_RED_IP/24 dev red0
iptables -t nat -A POSTROUTING -o red0 -d $MODEM_IP -j MASQUERADE
exit 0

Caveat here: Access only works, when red is up.

You need to adjust the modem IP to and the VLAN_RED to in your setup.

I never had problems to reach my DOCSIS modem at the standard management IP ( if red0 was up ).
If you don’t use the network locally, IPFire routes ( if not denied by FW rules ) this network to the red interface.
Maybe your DOCSIS modem switches the ethernet interface up and down when the Cable Internet side has problems.
Also the red IP is out of the net when the CMTS cannot be reached. This leases have very short lease time ( 20s ), so problems/bugs in the DHCP client can show up as interface down states.

I am on IPFire 2.25 (x86_64) - Core Update 152 (static build). My ISP is Comcast. And my modem is Arris. I connect to the Arris device via (not https) via any computer on my green network (

All works OK. I don’t remember ever having a problem in the past. I’ll check a few more times this week.

Not sure if it matters but my modem is setup in bridged mode (NAT turned off).

Jon, that can not be right. If your green network is ‘’ is sent over the green interface and not through red0, which is necessary to reach the modem.

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You are correct! My green is I updated my other post. Thank you!

I’ve never heard of this nor can I find an according forward rule in iptables. Is this somewhere documented?

My routing table gives

# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         gateway         UG    203    0        0 red0     *        U     203    0        0 red0    *        U     0      0        0 green0    *        U     0      0        0 blue0

What I see is two issues with mine, one is where cannot access modem when cable connection goes down and the other when connection comes back up does not automattically get the public IP via DHCP without restarting
Found if get the public IP via DHCP from upstream cable company works as long as connection works. When connection drops then no modem access have to assign the modem private IP range to red interface. If restart no cable connection and get the private via DHCP from modem will work but then no cable public IP when connection comes back up.
Problem notice is once get a DHCP from cable company and connection drops does not automatically get that IP again until recycled, something with the DHCP client on ipfire ?
So once cable connection stops working I run a script to assign IP to red interface and recycle red interface then can access the modem when cable connection not working
I may try Marco solution
but the two scripts I run are as follows (I am not a script writer so some of what I have came from elsewhere modified)

to access modem when not getting DHCP IP from cable company

set secondary IP on Red Interface for Modem access

/sbin/ifconfig red0:0 down
/sbin/ifconfig red0:0
/sbin/ifconfig red0:0

This one kills all exiting dhcpd processes and restarts the dhcpd process to get new IP from cable company once connection is restored for some reason this does not happen automatically on ipfire, I do this instead of rebooting everything

Restart DHCP on Red Interface

Display all running dhcpcd processes

echo “Running dhcpcd processes”
echo $(ps -ef | grep dhcpcd | grep -v grep | awk ‘{print $2}’)

Kill All of the running dhcpcd processes

echo “killing all dhcpcd processes”
kill -9 $(ps -ef | grep dhcpcd | grep -v grep | awk ‘{print $2}’)

restart the connection Scheduler for Red Internface

echo “restarting the dhcpcd process on the Red Interface”
/usr/local/bin/connscheduler reconnect

Like mentioned not all my work cannot remember where found to do these before
Is what I have been doing, if can find a better way or find a way for ipfire to automatically restart the dhcpd process ?

The fact to get an IP out of when the connection of the modem to the CMTS is down is normal. The lease time is very short, so you have problems to do anything useful during this time. :frowning:
The renewal of the public IP may have problems. I suppose there are some little issues in dhcpcd.
Thus it isn’t a fault to install a little watch/restart script. Maybe that a thing is running on my system also. I’ll have a look at and post my solution.