FAST5366LTE-A incorrect gateway and DNS server in DHCP

[Guy611]

A few days ago, my FAST5366LTE-A WiFi started showing intermittent errors. Devices would connect OK, but have no Internet.

This happened on both wired and wireless connections.

The Fetch Box went first, then others. Optus support were of no help, but eventually I noticed that the default gateway in the DHCP did not match the actual IP address of the modem. I factory reset the modem, and everything worked for a little while, the DHCP gateway went back to the router IP, but then it changed again (always to xxx.xxx.xxx.50). There is no other DHCP server on my network, and no device on the .50 address.

I reset the modem again, the same thing happened.

I have now changed the modem IP address to match the address it insists on publishing in DHCP. We'll see how that goes.

Have Optus pushed any firmware updates or other changes that would account for this behaviour? Until now, this modem has been well-behaved and there have been no local network changes I can think of.

[YetAnotherAcc]

What firmware version is your on?

If it happens again go to the router's device info and see what it says for gateway there. How does the gateway IP address compare to the public IPv4 Address? Is the .50 the only difference between those two addresses, i.e:

Public IPv4 Address: xxx.xxx.xxx.xxx

Gateway:  xxx.xxx.xxx.50

or is the gateway address similar to the routers IP address, i.e.:

Router IP Address: 192.168.0.1

Gateway: 192.168.0.50

or is it something else?

[Jack_YC]

Hi @Guy611, thanks for letting us know about this issue you're experiencing with your connection. 

It's good to see you've been able to try some troubleshooting steps and come up with some work arounds whilst this has been occurring. 

If that error does occur again, please let us know what firmware version you're using as @YetAnotherAcc suggested. That may provide us with some more insight into this issue. 

I also recommend checking our Modem User Guides for some more helpful info. 

[Guy611]

Hi guys, the firmware version is SG4Y1L002039. After a factory reset, the internal IP defaults to 192.168.0.1, but the DHCP pushes 192.168.0.50 as both the default gw and the DNS server address. I have now set the internal IP to .50 as there seems to be no way to override/correct what the DHCP publishes.

[Guy611]

There is no obvious relationship between the public IP and the DHCP or internal. It is a 114.74.xxx.xxx address. And the last octet is not the same or anything like that.

[YetAnotherAcc]

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@Guy611 wrote:
Hi guys, the firmware version is SG4Y1L002039.  

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@Jack_YC I asked @Tina_YC for info about that firmware version just over a week ago but she still has not got back to me. Can you shed any light on it?

After a factory reset, the internal IP defaults to 192.168.0.1, but the DHCP pushes 192.168.0.50 as both the default gw and the DNS server address. 

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That is definitely unusual but if you get any internet at all then it shouldn't be a gateway issue because a wrong/invalid gateway should block internet totally.

I have now set the internal IP to .50.

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I doubt it will make a difference as per my reason above.

as there seems to be no way to override/correct what the DHCP publishes.

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And there won't be. 

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There is no obvious relationship between the public IP and the DHCP or internal. It is a 114.74.xxx.xxx address. And the last octet is not the same or anything like that.

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I was trying to ascertain if the fetch box was getting the same gateway as the router itself, and if the routers gateway was a local LAN IP or an Optus supplied one. When you originally stated that its always  xxx.xxx.xxx.50 I thought that might have been an Optus supplied one that the router forwarded to the fetch box.

[Jono_YC]

Thanks for clarifying that, @Guy611

If you’re still needing a hand, we recommend messaging us via the My Optus App. Our team is available 24/7 and are ready to assist customers as quickly as possible.

We're also available to assist via Social Media. Please send us a private message to Optus on Facebook or a DM on Twitter with the details for further assistance.

[Sarah_YC]

Thanks for following up about the firmware version: SG4Y1L002039, @YetAnotherAcc! We haven't received any information as off yet, we'll keep you posted as soon as we receive an update on this. 

[Guy611]

The Fetch would get a correct IP address and mask etc. from the router's DHCP. The only things wrong were the default gw and DNS server, which were both .50. As a result the Fetch said "No Internet". Changing the fetch from DHCP/auto to manual and changing those 2 settings restored Internet to the Fetch.
Now I'm back on auto, but set the router internal IP to .50. So it's working, but it's an odd behaviour.

[Guy611]

Oh, I see what you're asking. No, the default gw the router receives is also not related to the one being published internally.