ER605 declines DHCP offers from LTE Modem

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ER605 declines DHCP offers from LTE Modem
ER605 declines DHCP offers from LTE Modem
2021-11-26 06:00:04 - last edited 2021-12-09 13:10:54
Model: ER605 (TL-R605)  
Hardware Version: V1
Firmware Version: 1.1.1 Build 20210723 Rel.64608

Wireshark was used to show that the ER605 declines DHCP offers from a Netgear MR1100 LTE Router configured as an IP Passthrough device.  My previous router (a TP-Link Archer C59 running OpenWrt) worked fine with same LTE modem.  The System Log of the ER605 shows the following error messages:

 

[osg:10-27-F5-17-63-81] failed to obtain the IP address for WAN because IP-Address/Gateway can't be a broadcast address or a network address (IP-Address=10.247.116.156, Mask=255.255.255.255, Gateway=10.247.116.1).

 

A partial Wireshark capture is shown below:

No.    Time    Source    Destination    Protocol    Length    Info
372    231.783495    0.0.0.0    255.255.255.255    DHCP    342    DHCP Discover - Transaction ID 0x9df8d423
373    231.786354    10.247.116.1    255.255.255.255    DHCP    344    DHCP Offer    - Transaction ID 0x9df8d423
374    232.179619    0.0.0.0    255.255.255.255    DHCP    342    DHCP Decline  - Transaction ID 0xc998102c

 

Could the ER605 be rejecting the offered IP address because it is in a private address range?  This is unavoidable in my situation because my internet service is AT&T LTE service using carrier-grade NAT - I will always be assigned a 10.x.x.x  address.

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Re:ER605 declines DHCP offers from LTE Modem-Solution
2021-12-09 13:10:40 - last edited 2021-12-09 13:10:54

The MR1100 DHCP offer's subnet mask (255.255.255.255) was causing the ER605 to decline the DHCP offer.  TP-Link Tech Support sent a beta version of firmware which fixed the problem.  If anyone else has this problem, contact TP-Link Tech Support and ask for the September beta release of the firmware.

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Re:ER605 declines DHCP offers from LTE Modem
2021-11-29 06:27:51 - last edited 2021-11-29 06:33:55

@Shubopady 

1. No. ER605 is like a regular router. It accepts a private or public IP.

From the subnet, 255.255.255.255, I can tell that this IP 10.247.116.156 is single usable IP in the ATT router. It means 10.247.116.156/32. Do you have another device using this IP? Subnet from the other router usually comes 255.255.255.0 10.247.116.X/24. meaning there are 253 IP addresses available. 

 

2. Try the unicast DHCP option? In the WAN settings, enable >> Get IP using Unicast DHCP

3. Change the subnet on your router to 255.255.255.0? 

4. Reboot the modem. I remember some modem will record the MAC of the first connected device. Make sure the router's the first plugged device to the modem. 

 

Those are my perception of your issue.

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Re:ER605 declines DHCP offers from LTE Modem
2021-11-29 21:24:43

@John1234 

 

Thanks for the response.

 

1. No, I don't have another device using 10.247.116.156.  The AT&T router is in "IP Passthrough" mode and seems to always assign an address to my router like 10.X.X.X.  Since the WAN connection of my router is the AT&T router's only connection, it seems that 255.255.255.255 is OK for the subnet.

 

2. Tried unicast.  Didn't help.

 

3. Subnet on WAN side of my router should be set by DHCP, right?

 

4. Rebooted until there were holes in my boots.

 

Really, thanks for the response and the suggestions.  At this point, I think that there may be some unfathomable (for me, anyway) incompatibility between the old AT&T modem and the ER605.  I may just have to stick with the old router running OpenWrt.

 

Thanks again for trying to help, John.  Kudos.

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Re:ER605 declines DHCP offers from LTE Modem
2021-11-30 06:12:23

@Shubopady 

:) You're welcome

Huh, strange. So, so it is passing through the IP from the ISP. What about contacting your ISP and checking if they have anything on their end? Did they record the MAC address and stop another router from connecting to their server? 

 

I think your ISP is using some kind of switch on their end and giving you a static IP(they configured on their switch). Since I deal with TP switch a lot. I know some kind of switch will learn the MAC address. 

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Re:ER605 declines DHCP offers from LTE Modem
2021-11-30 13:16:09

@John1234 

 

Good suggestion to contact the ISP, but I don't have the 7 or 8 hours that it would take to get through AT&T's customer/technical support to someone that might understand the problem, only to be told that AT&T didn't intend for me to use a wifi hotspot for my primary internet service.  I've been down that road before :)

 

If I connect my laptop instead of my router to the AT&T box, my laptop gets a good DHCP assignment.  I can switch back and forth between my laptop and my old router.  I do have to wait a while (for caches to clear?), but both of them work.  Doesn't that eliminate the MAC address as the source of the problem?

 

Again, thanks for your responses and suggestions, but at this point, I'm giving up on the ER605 unless TP-Link tech support provides a solution.  If I do get a solution from them, I'll come back and post it here.

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Re:ER605 declines DHCP offers from LTE Modem
2021-12-01 06:16:37

@Shubopady 

Like you said, you gotta wait for a while to get it working. I am still thinking it is recording the MAC address of the connected devices. What if you do MAC clone? Clone the MAC address of your PC or the router.

Which one is working now? Clone its MAC address to the ER605 and connect ER605 to the modem and test. 

User Guide instructions:

Choose the menu Network > MAC > MAC to load the following page.

 

So, if clone works, I believe that is your modem doing this headache to you. ISP will record the MAC address of the device and only allows the "remembered" MAC addresses to get Internet. To flush that, try to reboot, remove the power and battery of your modem, and call ISP to flush MAC on their end. 

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Re:ER605 declines DHCP offers from LTE Modem-Solution
2021-12-09 13:10:40 - last edited 2021-12-09 13:10:54

The MR1100 DHCP offer's subnet mask (255.255.255.255) was causing the ER605 to decline the DHCP offer.  TP-Link Tech Support sent a beta version of firmware which fixed the problem.  If anyone else has this problem, contact TP-Link Tech Support and ask for the September beta release of the firmware.

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