@jakobp 

 

Looks like your ISP might be insisting on the connection being from a 'fixed' MAC address. Try using the MAC address clone function on the ER605 ( manual page 33 ) to set the same MAC address as the PC that works.

  @MisterW 

 

Thanks for the reply. No my ISP is not enforcing a certain MAC as I have tried with different devices and got a connection. It only seems that getting a public facing IP is bound to the routers MAC address. 

 

And sorry I should have mentioned the things I already tried in my post.

 

Things I already tried and didn't work:

• Downgrading firmware
• Running on a controller
• Running in standalone
• Factory reset
• Cloning my Laptops MAC
• Using a random MAC
• Using unicast DHCP
• Restarting Modem and router
• Using a different cable

 

I also did packet inspection while trying it with different MACs and unicast DHCP with the same behavior as in my post.

 

I couldn't think of anything else to try. The only way I got it working in the meantime is getting an IP on my Laptop and using that as a static address. But that is not the ideal way to do it. Currently I'm running an older router running openWRT (using the ER605's WAN MAC) which works without issues.

It does look like something not quite right. Strange that everything else seems to work ok apart from the ER605 ? TBH I've not much experience of ISPs using DHCP , mine uses PPPoE. I've dropped you a PM

  @jakobp 

 

Is there a chance you could get a packet capture using the router that works, so we can see any difference in the DHCP/ARP conversations

  @MisterW 

 

I sadly couldn't get port mirroring working quickly in openWRT so I did a capture on my laptop hooked up to the fiber modem directly. Laptop is running Windows. It gets the IP normally by DHCP, then sends three ARP probes for the IP and finally an ARP annouce after it didn't get a reply to the probes (No duplicate IP ARP reply from the ISP). This seems to be in line with the ARP RFC from what I understand.

Heres the overview of the capture:

2    5.911216    0.0.0.0    255.255.255.255    DHCP    342    DHCP Discover - Transaction ID 0xe830ae03
3    5.914730    ISP_DHCP_Server    WAN_IP    DHCP    405    DHCP Offer    - Transaction ID 0xe830ae03
4    5.915349    0.0.0.0    255.255.255.255    DHCP    360    DHCP Request  - Transaction ID 0xe830ae03
5    5.931066    ISP_DHCP_Server    WAN_IP    DHCP    420    DHCP ACK      - Transaction ID 0xe830ae03
8    7.253867    Laptop_MAC    Broadcast    ARP    42    Who has WAN_IP? (ARP Probe)
9    8.255726    Laptop_MAC    Broadcast    ARP    42    Who has WAN_IP? (ARP Probe)
11    9.256186    Laptop_MAC    Broadcast    ARP    42    Who has WAN_IP? (ARP Probe)
12    10.253051    Laptop_MAC    Broadcast    ARP    42    ARP Announcement for WAN_IP

Hi  @Clive_A 

 

Thanks for the reply.

 

From what I understand it should ARP probe the IP a few times before it sends the ARP announce. At least form what I read in the RFC. I'm no expert though, just trying to understand what might be going wrong.

 

Yes I get an IP address in the same network segment. I can also see the non working router going through that DHCP offer/decline every few seconds trying with different adresses.

 

My ISP is also looking into the issue now, so maybe they can also resolve the issue on their end.

  @jakobp 

 

Interesting!

I'll have to have a good read through the RFC myself.

 

I wonder if, in the case of the ER605, the ARP announce is sent when the ISP systems are still finalising the IP allocation, and so its not sure who's been allocated it!.

Obviously in the Windows case the ARP probes will delay the sending of the announce.

 

As a matter of interest , is it a UK ISP ? and if so which ?

 

I have a colleague using Virgin media in the UK, they use DHCP and he's not having any problems with the ER605

 

I sadly couldn't get port mirroring working quickly in openWRT

 

When I've needed to capture on Openwrt I've used Wireshark. Provided you can ssh into Openwrt, then you can set it (wireshark) to run tcpdump remotely on the Openwrt device and capture straight into Wireshark

 

  @MisterW 

 

Yeah the RFC was kind of interesting. I've never dug that deep for an network issue before. At least I learnt something new.

 

Hmm you could be onto something, didn't think of that yet. Maybe it is a kind of race condition.

 

I'm located in Austria, it's a local fiber to the home provider.

  @jakobp 

 

I'm located in Austria, it's a local fiber to the home provider.

 

That might mean they will at least look into the problem. I was afraid that it was going to be a UK ISP using the BT/Openreach network. There'd be no chance of getting the monolith that is Openreach to investigate.