Strange issue with Arris TM1602AP2 and R7800

[Voxel]

Just an interesting post about another modem problem, giving some insight to Arris modem startup.
I think it's good to keep all info in this thread!
https://community.netgear.com/t5/Ni...-connection-in-bridge-mode/m-p/1641596#M41611

Yes I've pointed it in othre thread (for 72SF).

Voxel.

 

[Voxel]

In the 62SF version of some of the init scripts WAN_IF is set to eth0 if it's not set,
but in 72SF this is not done.

eth0: There were my changes needed for LTE modem only. (/etc/init.d/modem). I've changed it in 66SF if I am not mistaken. You already tried to disable /etc/init.d/modem ...

Use brwan.

Voxel.

 

[NetBytes]

It's now half a year later and I'm still spending time here and there to try to fix this issue.
The main issue is that the router seems to start in bridge mode (not router) for the first 30 seconds or so as it's booting-up.
This appears to allow all the connected devices on the lan to directly attempt access to the internet and perform a dhcp
request. The flood of dhcp requests from multiple devices reach the cable modem and it shuts off the internet.
The cable modem re-sets it's security when I perform a wire disconnect from the R7800, count to 10, and re-connect.

I have two ideas but not enough knowledge how to implement them correctly. I hope some of the other smart folks here can help.

1) The router's clients seem to have direct access out to the internet as if the router's dhcp server is not running yet.
Can I move this sub-system's startup earlier in the boot process?

2) Is there a way on startup to block all access out of the wan port until the startup has completed?
I am thinking something like initial firewall rules which can block the port from use and
then be opened once the R7800 is fully 'booted'.

I am open to other ideas.
Please know I have already tried everything suggested in this thread, short of buying new hardware.

 

[R. Gerrits]

I am open to other ideas.
Please know I have already tried everything suggested in this thread, short of buying new hardware.

didn't read the whole thread, but here's my take:

It seems that temporary all switch-ports are tagged to the same vlan or that both ethwan and ethlan are temporary joined to the same bridge.

afaics (by quickly browsing / searching the firmware), the switch and bridge are configured in /etc/init.d/opmode.
this already sits faily early in the boot proces:

root@R7800:/rom$ ls  /etc/rc.d/S*   
/etc/rc.d/S10boot
/etc/rc.d/S10ca-certificates
/etc/rc.d/S11ubus
/etc/rc.d/S13haveged
/etc/rc.d/S19enet
/etc/rc.d/S20detcable
/etc/rc.d/S20opmode

But before /etc/init.d/opmode is started, all the switch ports are indeed all in the same vlan.
(checked by adding swconfig dev switch0 show >> /tmp/bootlogsw.txt to the start of /etc/init.d/opmode and looking at that log after boot)

Also tested it by adding the same command to the beginning and end of /etc/init.d/boot.
At the beginning of that boot script, it returns nothing. but at the end of the script it also shows all ports in the same vlan.

So one solution would be to try to find where exactly in /etc/init.d/boot the switch is brought online. and then immediatelly after that, already add some lines to call swconfig to apply the correct VLAN config. (And hope this is fast enough)

Or you could try at the end of /etc/init.d/opmode to add something like:

ifconfig ethwan down
sleep 10
ifconfig ethwan up

(i.e. bring down the wan interface, wait 10 seconds and bring up the wan interface, and hope that this also triggers the cable modem to reassign an IP-address)

 

[NetBytes]

@R. Gerrits thank you - this is a new thing to try.
I will attempt this as time and family permit and will again report back.