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kekraiser
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Starlink router with Ethernet connection LAN IP conflict

Fri Nov 04, 2022 1:32 am

Hello.

I have a Starlink terminal gen. 2 and want to configure it as second WAN\Internet connection. No automatic fail-over for now, just manual switching port on interface "combo1" with "Combo Mode" selector in WinBox. Starlink Ethernet adapter is used for connecting Starlink router to one of combo ports in Mikrotik router.

It is a two ways to setup ethernet connection for Starlink router:

1. Enable "Bypass Mode" in Starlink router, enable DHCP Client in Mikrotik router. CGNAT IP address from "100.64.0.0/10" subnet (or other) will be received. Starlink router Wi-Fi network and some other usefull stuff and settings are completely disabled and cannot be used from mobile app.

2. Do not enable "Bypass Mode", enable DHCP Client in Mikrotik router. LAN address from "192.168.1.0/24" subnet will be received. Starlink router Wi-Fi and other stuff are available.

For some reasons, I need Starlink router Wi-Fi available, so usage of "Bypass Mode" is not possible. Main issue here is that "192.168.1.0/24" subnet is already used in my router in DHCP Server config. So when I enable DHCP Client on "combo1" interface, and switch the port in "Combo Mode" selector to the one in which the Starlink router is connected, WinBox connection failed and network is going to unusable state. I guess this is due to a subnet or IP address conflict, when a second DHCP server appears on the same subnet and everything goes to hell.

Starlink router does not provide any option to change own DHCP Server IP range, "192.168.1.0/24" is hardcoded.

Obviously, I can move from "192.168.1.0/24" to some other subnet in Mikrotik router, leave this subnet for Starlink router. But I have a lot of other subnets and other configs based on subnets in my router, especially for "192.168.1.0/24", so this migration is going to be very hard.

Is there is some (magic) way to "isolate" Starlink router "192.168.1.0/24" subnet from same Mikrotik router subnet?

Thanks.
 
sindy
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Re: Starlink router with Ethernet connection LAN IP conflict

Fri Nov 04, 2022 8:13 pm

There might be, an ugly one. It depends on whether the Starlink accepts packets from devices that have their 192.168.1.x addresses assigned statically rather than obtained from the DHCP server in the Starlink terminal. Can you check that, please? I.e. configure an address from that subnet statically on your PC, connect it to the Starlink, and try to download or ping something in the internet.

If it works, the following would be the next steps:
  • assign some unrelated address&subnet to the WAN interface of the router (the one that will be connected to Starlink) - let's say 192.168.33.2/24, and set a default route with a gateway address within that subnet - 192.168.33.1
  • create a static ARP record, stating that the MAC address of 192.168.33.1 is the one of the Starlink interface (you have to find it it in advance if it is not on the label on the Starlink terminal)
  • set the arp parameter of the WAN interface of the router to proxy-arp, so that when the Starlink interface sends an ARP request for an address from 192.168.1.0/24, your router responds with the MAC address of its WAN interface because it has 192.168.1.0/24 on another interface
  • add an action=src-nat rule with to-addresses=192.168.1.N that differs from any address assigned by the Starlink's DHCP server (no idea whether there is a range within 192.168.1.2-192.168.1.254 from which it doesn't assign addresses to DHCP clients).
It will not be compatible with another IP configuration on the combo port (because whenever the combo port is up, the default route will become active), but it should allow you to use the 192.168.1.0/24 internally and still use the Starlink as an uplink.
 
kekraiser
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Re: Starlink router with Ethernet connection LAN IP conflict

Sun Nov 06, 2022 1:27 am

@sindy thank you for advise, but it looks like too ugly, and seems not working (maybe I fail something during its setup).

Anyway, solved by temporaty enabled bypass mode, have no time for experiments now.

Main goal - usage without bypass mode and active Starlink router - will be reachable soon with "MikroTik hAP ac" as wi-fi bridge and custom DHCP server range.
 
sindy
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Re: Starlink router with Ethernet connection LAN IP conflict

Sun Nov 06, 2022 11:37 am

If you can add an additional device with a WiFi interface into the scheme, all possibilities are open - you can use bypass mode to get the 100.64.x.y on the main router's WAN and use the hAP ac as a wireless access point instead of the one on the Starlink router, or you can let the hAP ac get its WAN address from the Starlink router, and give a 192.168.88.x address to the main router, so the two 192.168.1.0/24 networks will not meet on the same router.

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