WAN Interface not asking for an IPv4 address from LTE modem LM1200 on power cycle

ddbnj

This is a remote site.

I am being notified that the backup WAN is down.

If I release / renew the ip address on status --interfaces it comes back up.

I captured the port 67 and 68 messages but nothing unusual. No local address requests.

I tried using the advanced DHCP functions, changing the timings to either pfsense defaults or FreeBSD defaults but the behavior persists.

I suspect the carrier is changing the address for the modem occasionally but pfsense does not send a new dhclient request when the gateway is down.

I'm recreating the event when I power down the modem, wait for 5 minutes. Make sure the gateway is reported down on pfsense. When the modem is powered on, Pfsense does not request a new address.

This is a netgate 4100 and I don't have any extra ports.

Any ideas?

Thanks,

Devan

chpalmer

@ddbnj a few ideas.. #1. Who is the carrier just for future reference?

1a. The carrier may not be sending a short enough lease time..

Can you put the modem in NAT mode and just double NAT the circuit?
Is the modem firmware up to date?
My LB 1120 does just fine in bridge mode . Do you have another modem that you can try? ~~Even using something like a phone and a wireless bridge with an ethernet port?~~ Nevermind.. that will not give you bridge mode.
Can you swap WAN interfaces?
Check online for the proper MTU for your carrier. Verizon is 1400.

chpalmer

@ddbnj Also- show a screenshot of your System/Routing/Gateways/Edit for that modems gateway..

ddbnj

@chpalmer

First, thank you for helping me tackle this.

I use the modem at two locations. The one in question is connected via a moca bridge which may be the cause of the misbehavior. The other one is fine.

The modem is in bridge mode and frankly I have had a bear of a time having two routers in the system so I'm always hesitant to set the LTE modem in anything other than bridge mode.

The carrier is Tello which is just a front end for T-Mobile.

I don't have an MTU set so I will try 1400 now.

for reference here is the packet capture.

10:49:14.147247 IP 0.0.0.0.68 > 255.255.255.255.67: UDP, length 300
10:49:14.163990 IP 25.96.191.1.67 > 255.255.255.255.68: UDP, length 300
10:49:14.164471 IP 0.0.0.0.68 > 255.255.255.255.67: UDP, length 300
10:49:17.420068 IP 25.96.191.1.67 > 25.96.191.206.68: UDP, length 319
10:49:19.497189 IP 0.0.0.0.68 > 255.255.255.255.67: UDP, length 300
10:49:19.509984 IP 25.96.191.1.67 > 25.96.191.206.68: UDP, length 328
16:23:15.426204 IP 0.0.0.0.68 > 255.255.255.255.67: UDP, length 300
16:23:15.433025 IP 26.47.48.1.67 > 255.255.255.255.68: UDP, length 300
16:23:15.433367 IP 0.0.0.0.68 > 255.255.255.255.67: UDP, length 300
16:23:18.684137 IP 26.47.48.1.67 > 26.47.48.5.68: UDP, length 319
16:23:20.713552 IP 0.0.0.0.68 > 255.255.255.255.67: UDP, length 300
16:23:20.726165 IP 26.47.48.1.67 > 26.47.48.5.68: UDP, length 328

It was offline until I renewed the lease manually at 16:23.

Screenshot 2025-03-30 163005.png Screenshot 2025-03-30 162952.png Screenshot 2025-03-30 162918.png

Sorry the screenshots are out of order.

chpalmer

@ddbnj

Looking up t-mo MTU looks like some are using 1420..

Your MOCA setup probably does not drop the interface like the modem would (I believe) and therefore does not have a reason to "reset" itself. That is my SWAG anyways..

I have never been in the room when my modem gets a new address so can not attest to that personally but it would be a good test if you can move the modem within reach of the patch cord to directly connect the two devices..

My guess there is you have the modem in a spot for better cellular coverage. I use- https://www.amazon.com/dp/B07ZBVX8VL/ref=twister_B08NVPTG52?_encoding=UTF8&th=1 and two runs of LMR600 to get the coverage where I need it. Might be a better option for you if you find out the Moca is the cause.

With a weight of 1 is this your primary WAN?

ddbnj

@chpalmer

Thanks again.

Nice MIMO antenna.

This is my backup WAN which I'm using gateway groups and BGP to manage.

The system works very well except for needing to renew the lease.

As of now, I get a message via pushover when the gateway goes down. Then I renew the lease. Running new wire to the basement seems a harder solution.

It seems unreasonable that the modem would have to send a notice to the router that the IP address is changing. The router should initiate a DCHP request if the connection is down.

There may be a script somewhere on this forum which does a gateway check and client refresh. I have to dig it up.

chpalmer

@ddbnj Under your system logs / DHCP do you have a similar line?

Mar 30 13:48:19 dhclient 74865 bound to 100.91.192.244 -- renewal in 54000 seconds.

54000 seconds is 15 hours. So I can safely guess that just before 5am tomorrow I should see a different address on my LTE WAN.

Your should work the same way even if it was down for a time before.. That time is set by the server on the T-Mo end. Im curious what yours says..

While having a script do what you want could work it is truly a bandaid.. (relying on the modem to drop the interface momentarily as I mentioned earlier would be just a different colored bandaid.. ;) )

Another solution if this is a business account is to get a static IP from the provider.. Verizon used to let standard customers do that but now limit it to business customers.