RM551E-GL IP Passthrough (IPPT) aka bridge mode

This is actually the same as this issue, but for the RM551E-GL.

The documentation mentions the at+qmap=“mpdn_rule” comment set for this module as well, but at least in conjunction with ethernet usage, it doesn’t work and returns “ERROR”.

@Quectel: I want to use that modem with a M2 to Ethernet adapter and have the IPv4- and IPv6-addresses on that interface as assigned by the ISP.

IPv6 is relayed, but for the IPv4, Quectel or rather the embedded OpenWRT provides it’s own /22 network and performs NAT/PAT.

How can I change that?

I don’t think PCIe RC mode is officially supported yet. Nonetheless it does seem to work anyways. A feel like there are some things that need worked on for the QMAP set of commands on Quectel’s end but I’m still researching that.

The mpdn rule now requires an actual Mac address specified not the FF:FF:FF:… Wildcard.

Thanks, when specifying a concrete MAC address using the command e.g. AT+QMAP=“mpdn_rule”,0,1,0,1,1,“AB:CD:EF:AB:CD:EF”, it is accepted and when acts as follows:

If AT+QMAP=“ippt_nat” is set to “1”, then the ISP’s IP address is forwarded to the ethernet interface, however, the DNS-server still is provided by the modem with its IP address 192.168.224.1

If AT+QMAP=“ippt_nat” is set to “0”, then not only the ISP’s IP address is forwared to the ethernet interface, but also the DNS servers.

I have to investigate this further, but at least in the AT+QMAP=“mpdn_rule”,0,1,0,1,1,“AB:CD:EF:AB:CD:EF” & AT+QMAP=“ippt_nat”,0 - scenario, I’ve already lost routing towards the WAN twice. The connection stays up, the ISP’s IP address remains assigned, but no traffic is forwarded anymore randomly until the RM551E-GL is rebooted, which obviously sucks.

@Quectel: besides this possible bug, could you please elaborate on what that “ippt_nat” - option is actually supposed to be doing? Naming-wise, it is somehow counter-intuitive that a ippt_nat (namingly “IP PassThrough”) set to zero for “disabled” actually leads to passthrough in terms of the DNS servers, while a ippt_nat option set to “1” (for ethernet) actually leads to DNS servers referring to the modem (thus not being passthrough DNS-wise).

When in doubt, I would expect it it to be the other way around.

Dear @little-endian
RM551E is ES, it is not recommanded to use it and it is not stable now.

Could you tell me where you get it?

Hello silvia, thank you for your concern.

Well, good for Quectel that they have (end) customers willing to play their unpaid alpha testers out of technical interest.

By “Not recommended to use”, you probably mean in addition “… by end customers”, as someone obviously has to use them in order to iron out the bugs and I were you, I would welcome any source for feedback, being it a private person or not.

At your service, so what is your recommendation in terms of the next steps or tests to take? Are there any differences to be expected in the module’s behavior depending on the used ippt nat mode? Currently, I have only the AT+QMAP=“mpdn_rule”,0,1,0,1,1,“AB:CD:EF:AB:CD:EF" option applied but without AT+QMAP=“ippt_nat”,0 to see if that makes any difference.

Furthermore, how about picking up my remark about the counterintuitive ippt_nat behavior reagrding the DNS server forwarding?

Only stating that the RM551E-GL is some beta or even alpha product, although factual correct as you would know best, isn’t exactly helpful to improve the product, is it?

As about where I got it from: the usual suspect Alibaba, virtually the only source when it comes to any Quectel module as they aren’t directly sold anyway, at least not in good old Germany which used to have nice technical innovations on its own (good old days which are long gone now I guess).

1 Like

After several more days: the modem connect is stable as long as it’s used in routing mode. So I guess the bridge mode is indeed buggy yet.

@awesome Quectel support: what else can I test for you in order for you to improve the product?

Further update. Unfortunately, the connection issue not only occurs when using the bridge mode, although more often so far, but also in routing mode after all:

The modem is run with this adapter, hooked up to a bridged wireless access point.

The modem itself remains pingable, but the routing towards the WAN randomly stops working.

Since this doesn’t occur with a MC888A with O2 Germany, I assume it’s a bug of the RM551E-GL.

Dear @little-endian
For this issue, please capture log for analyze which inculde your problem.

I had same issues. PM sent. I seen the exact same issue and like you said worse on IPPT, but still happening in router mode.

Further update and clarification in order to prevent any confusion:

The observed issue when using the “routing mode” where the Quectel RM551 itself act as a NAT/PAT-router and controls the connection, seems to have been a singular/provider-related one as in general, at least in the past weeks, this is stable so far.

So in further test, I would concentrate on the original bridge mode issues.

If you could tell me how to do that with the RM551, I’m happy to do that.

What provider did you see it happen or not happen on? We have been noticing it on tmobile.

Iamroman above has a ticket open for same issue. Ticket 187579.