The provider did not help me.
But I was wondering why ssh command - ifdown wan; ifup wan
IP was not received, but ssh command - uhdcpc -i eth1 - was received IP.
And then tcpdump + google.com
And I saw that this is a big problem.
These 2 quotes helped -

DHCP Client Option 61 (dhcp-client-identifier)

The default, when the interface "Hostname" is not specified, sends the MAC address as the client ID. 
This can be troublesome when replacing a router.

Some ISP DHCP implementations require the same client ID unless the lease has been released or expired. 
But some routers don't send a client ID or send something other than the MAC. 
So simply spoofing the MAC doesn't work. 
Since OPNsense doesn't have a provision to release the lease this can force a long wait for the lease to expire or contacting the ISP, and probably escalating to technical support, for them to release the lease from their end.

Don't think it is a good practice, on a router that doesn't support DHCP release, to send a default client ID (a CID not explicitly configured). 
Such as is done by setting the "Hostname" for the interface.
A possibly related issue could be that the ISP is relying on a combination of MAC of the DHCP requestor AND the 'Client ID' (DHCP Option 61) for their lease management.

I note that when I WireShark the WAN handshake from a Netgear, it provides the MAC of the WAN port in the option 61 of the DHCP request.

By default, OpenWRT does NOT populate that field.

BTW- You must enter the 'Client ID' in HEX, and the first two characters (i.e first byte) must be '01' (zero one), usually followed by the hex values of the MAC, minus the colons or dashes.
So if the MAC is: AB:CD:EF:01:02:03 The correct Client ID is '01ABCDEF010203'

Client ID is under Network->Interfaces, click 'Edit' on the WAN, then click 'Advanced Settings' sub-tab.
1 Like