Speed limited when using 5G Modem as WAN

[Unnamed0]

Hi everyone,

I’ve been struggling with a strange issue for over a week now. I’m moving from a place with 1Gbps fiber to a 5G mobile network. Recently, I moved my OPNSense router to the new location to test if everything was working well, and that’s where the issue began. The download speed when connected to the 5G modem seems to be capped at around 110-120Mbps—I can’t get more than that. My upload speed is only about 60Mbps, so it's hard to tell if that’s also being limited. This wasn’t the case with 1Gbps fiber, where I consistently got around 940Mbps.

Some key details:

- 5G modem: ZTE MC889, set to bridge mode
- When the 5G modem is connected directly to my PC, speed tests show around 500Mbps down and 60Mbps up.
- When the 5G modem is connected to OPNSense and then to my PC, the speed test only shows 120Mbps down and 60Mbps up.
- The same OPNSense router worked fine when connected to the ONT in my previous place.
- Physical setup: 5G Modem -> Patch Panel -> PoE Injector -> OPNSense
- The working direct connection: 5G Modem -> Patch Panel -> PoE Injector -> PC
- Interfaces in OPNSense are all negotiated on 2.5Gbps

I’m running out of ideas and this is getting really frustrating. If anyone has any suggestions, I’d really appreciate the help!

[dseven]

I suppose you could use `ifconfig` in a shell to verify that your WAN interface really is connected at 2500Base-T. Beyond that, I can't think of anything.....

[Unnamed0]

Yep, it is connected via 2500Base-T. It's a weird issue.. :/

[FraLem]

I suppose you could use `ifconfig` in a shell to verify that your WAN interface really is connected at 2500Base-T. Beyond that, I can't think of anything.....

How do you configure the IP of interface both on the PC & Router?

Rgds

[hoondi]

Hi FraLem,
I'm also on Cellular and I only wish I had your issue of attaining those speeds in the first place!
I'm surrounded by 4acres of forest right up to the house and it's illegal (not that I'd want to anyway) to cut down the trees.

Strength	17 / 31, dBm : -79
Selected Network	LTENR5G
Sub Network Type	FDD LTE / NR5G-NSA
Band:	5 / 1,450 + "LTE BAND 3",1275
RSRP:	-114 dBm
RSRQ:	-18 dB
SINR:	11 dB
5G RSRP:	-96 dBm
5G RSRQ:	-13 dB
5G SINR:	5 dB

As you can see, lousy at best.
My MTU is 1472 which is the default set by my carrier. That's all that comes to my mind to look at.


Otherwise, save your current config, erase your boot drive and do a quick clean and simple setup to test and see if speeds improve.


Cheers.

[Unnamed0]

I suppose you could use `ifconfig` in a shell to verify that your WAN interface really is connected at 2500Base-T. Beyond that, I can't think of anything.....

How do you configure the IP of interface both on the PC & Router?

Rgds

On both devices I'm using the same setup - static ip - 192.168.254.2, gateway 192.168.254.1, mask .0

[Unnamed0]

Hi FraLem,
I'm also on Cellular and I only wish I had your issue of attaining those speeds in the first place!
I'm surrounded by 4acres of forest right up to the house and it's illegal (not that I'd want to anyway) to cut down the trees.

Strength	17 / 31, dBm : -79
Selected Network	LTENR5G
Sub Network Type	FDD LTE / NR5G-NSA
Band:	5 / 1,450 + "LTE BAND 3",1275
RSRP:	-114 dBm
RSRQ:	-18 dB
SINR:	11 dB
5G RSRP:	-96 dBm
5G RSRQ:	-13 dB
5G SINR:	5 dB

As you can see, lousy at best.
My MTU is 1472 which is the default set by my carrier. That's all that comes to my mind to look at.


Otherwise, save your current config, erase your boot drive and do a quick clean and simple setup to test and see if speeds improve.


Cheers.

Thanks, I will test with the lower MTU.
Regarding location - yeah, I'm pretty lucky as I have about 4.5km to BTS and it's also hidden behind a forest, but getting pretty good signal (-100 RSRP, 22 SINR, -10 RSRQ), which gives me those stable speeds

[hoondi]

Have you considered StarLink?

Or is the cost v speed not there for you?
For me, StarLink is superior for both speed and latency, except that I have so many trees to contend with that the dish has to be on a pole of at least 40mt high before I cease experiencing any "obstruction".

The trees here are so dense and come so close to our house that I don't even need to own a lawn mover. Gives you and idea.

Hope the MTU is all it is for you.

[Unnamed0]

Have you considered StarLink?

Or is the cost v speed not there for you?
For me, StarLink is superior for both speed and latency, except that I have so many trees to contend with that the dish has to be on a pole of at least 40mt high before I cease experiencing any "obstruction".

The trees here are so dense and come so close to our house that I don't even need to own a lawn mover. Gives you and idea.

Hope the MTU is all it is for you.

StarLink is about 7x more expensive vs 5G - also according to maps, speed is only about 120-200mbps down compared to 500mbps on 5G.. So pretty uneconomic in Poland

[Greg_E]

If possible I recommend an external directional antenna array. I need to rotate mine because they moved my tower, it made a big difference in stability.

I'm thinking that you might possibly be dealing with dropped packets and resends, and this process may be different between Windows and BSD. Just a guess, but when we switched to LTE/5G my PFsense went nuts, so bad that I had to bypass it and go back to the consumer router. I haven't tried connecting an OPNsense to the modem and try again, haven't had time at home. I'm also stuck behind CGNAT with no way clear of it right now, so things are limited and I just can't be bothered right now.

If the MTU change works, please post back because it might help me too.

[Unnamed0]

I've just tested the MTU things and it's not the case... Tested various numbers between 1200 and 1500 and the speed is always same. The PC when connected directly to 5G Modem has 1500 MTU and it works good, so that's not the source of the issue here.

Does anyone have any else ideas?

[Unnamed0]

I've managed to fix the issue! It was caused by using the static IP on WAN interface (I was using the IP from subnet that 5G Modem provided and has the admin panel). Switching to DHCP WAN solved the issue.