Archer C7 problem with ARP cache or something...
Hi,
Ever since the last firmware update, the router seems to be behaving strangely. I have several address reservations configured in the DHCP section and they all stopped working one by one. The behavior is more or less like this:
- Addresse becomes unreachable.
- Check on the machine: it's not getting an IP
- Check on the router log: it supposedly offered the right address to the machine (send ack ip 192.168.x.x and dns 1.1.1.1 to xx:xx:xx:xx:xx:xx)
- Configure static IP on the machine: it works!
- If I try to reconfigure address reservation for that MAC in the TP-Link interface, I get: :-( The to-be-added address already exists.
This was nagging but with an easy workaround but today the router stopped getting internet connectivity. After some fiddling, I realized it was the same problem. The router is supposed to get address 192.168.12.5 via DHCP from the ISP's box, which is working fine. I changed the TP-Link's address to static and now it works.
Any ideas?
Thanks,
Nacho
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Hi Nacho, can you please show us some screenshots about the Address Reservation settings on the C7, and where did you set the Static IP address? We will try to investigate then.
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@Kevin_Z sure, here they are
And here's what happens when I try to re-enable the 192.168.22.2 reservation:
That's the DHCP part. The other half is the router's own IP. Here's the static config:
If I try to set it back to Dynamic IP, I lose internet connectivity. The 192.168.12.0/24 network is under my control and DHCP works fine in it. The only changes that I can recall between when it all worked fine and now are:
- I updated the firmware.
- I went from dynamic IP (192.168.0.0/24) to bypassing the outside router and getting an outside world IP on the Archer and then back to dynamic IP (192.168.12.0/24).
- The 192.168.12.0/24 subnet is my home DMZ. Devices in the 192.168.12.0/24 can be reached from devices in the 192.168.22.0/24 but the opposite is not true (this is normal, this is how I want it).
Here are some entries from the Archer log that I think might be relevant:
2021-03-02 11:35:03 imb[12838]: <6> 218011 ARP Binding enabled
2021-03-02 11:35:16 imb[3039]: <5> 218021 IP 192.168.22.2 and MAC 04:D3:B0:7E:A4:5F bound succeeded 2021-03-04 07:06:04 dhcps[31302]: <6> 212052 send offer ip 192.168.22.217 and dns 1.1.1.1 to fc:03:9f:07:a1:d9 2021-03-04 07:06:04 dhcps[31302]: <6> 212051 receive discover from fc:03:9f:07:a1:d9 2021-03-04 07:05:22 dhcps[31302]: <6> 212052 send offer ip 192.168.22.2 and dns 1.1.1.1 to 04:d3:b0:7e:a4:5f 2021-03-04 07:05:22 dhcps[31302]: <6> 212051 receive discover from 04:d3:b0:7e:a4:5f 2021-03-04 07:04:18 dhcps[31302]: <6> 212052 send offer ip 192.168.22.2 and dns 1.1.1.1 to 04:d3:b0:7e:a4:5f 2021-03-04 07:04:18 dhcps[31302]: <6> 212051 receive discover from 04:d3:b0:7e:a4:5f 2021-03-04 07:03:13 dhcps[31302]: <6> 212052 send offer ip 192.168.22.2 and dns 1.1.1.1 to 04:d3:b0:7e:a4:5f
All the while, IPv6 is still working fine.
Thanks,
Nacho
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After you upgraded the router firmware, did you reset it and reconfigure it? Or did you input the previous config file back into the router? As the issue is weird, as reported by the system log, the device is still getting the reservation IP address, that is correct, no issue. It is suggested to delete the Address Reservation rules, and add them back manually again, check if it will work properly.
As for the Static IP address concern, can you please provide the detailed network layout, how is the C7 connected to the network, will it get a WAN IP address if you change the WAN connection type to Dynamic? If not, we may need to investigate with the whole system log as well.
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Hi!
Thank you for following up, here are some answers:
> After you upgraded the router firmware, did you reset it and reconfigure it?
No
> Or did you input the previous config file back into the router?
No, I didn't need to do it. The configuration stayed there between updates.
> It is suggested to delete the Address Reservation rules, and add them back manually again, check if it will work properly
All of them? Some are still working properly.
> As for the Static IP address concern, can you please provide the detailed network layout,
The layout is like this:
Proprietary ISP box gets WAN address on its fiber connection side.
On the Ethernet side, it has a DHCP server handing out 192.168.12.0/24 IP addresses.
In the 192.168.12.0/24 network area there are 2 devices: a Linux Debian server and the C7.
C7 is connected via Ethernet cable to one of the Ethernet ports of the ISP box.
> how is the C7 connected to the network, will it get a WAN IP address if you change the WAN connection type to Dynamic?
If I set the WAN connection in the C7 config to dynamic, what should happen is that the C7 should get IP address 192.168.12.5 from the DHCP (address reserved at the DHCP of the ISP box). Instead, it silently loses connectivity to the internet. I say silently because there's no indication other than all the devices on the C7 wifi (192.168.22.0/24) losing internet access. Other devices on the 192.168.12.0/24 are not having any problem.
Should I try resetting the router and reconfiguring everything? How can I preserve the OpenVPN server cert and config if I do that?
I'm not in a big hurry to fix it because everything is working with static IPs right now but I'm curious about what's happening and would like to go back to dynamic IPs in the near future. My theory is that the C7 is being unable to rewrite entries in the ARP table for some reason... It explains why the problem is happening both on the LAN side and on the WAN side.
Best regards,
Nacho
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I see. It is suggested to reset the C7 to factory defaults when you have time to do this, and the VPN setting on it will be cleared after the firmware reset, you will need to reconfigure it from scratch as well. You can refer to the guide here:
https://www.tp-link.com/support/faq/2801/ (Case 3)
Just to confirm, who is your ISP, and what is the model number of the ISP box? When you configured Dynamic IP on the C7 WAN, does the internet LED on it become orange when you lose the connection on the devices, or it remains green?
Was all working fine before the firmware update? To locate this issue and try to fix it, we would like to follow up on your case via email. Please check your inbox and provide the information that we need.
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