[NR7302] DHCP renewal fails on IP pass-through

mbo77

I'm operating a NR7302 on a Telekom 5G network in pass-through mode. The router is an OpenWRT device.

The interface is set to renew the lease from time to time, but when this happens, the renewal fails and a new lease is requested. This leads to an interruption of appr. 10 seconds.

Here is the tcpdump when a renewal is happening.

NR7302 IP passthrough DHCP renewal.txt

As you can see, the renewal request is denied ("NACK" / "lease not found"), so the router starts a new discovery.

Is this a known issue, or maybe some kind of misconfiguration on my side?

mbo77

OK, got it solved, with only a minimum of mystery left. I had to enable the ARP Proxy, now the renewals are transferred correctly between the router and the APN.

The only mystery left is the default lease time value with 0. Is it always 24h or derived from the ISP's DHCP server? Given the request above, the latter doesn't seem to be the case.

PeterUK

This might be your ISP doing when they change the 10. IP if they change it every so many hours

IP pass-through is not a true interaction with the ISP gateway instead the NR7302 acks as a proxy 1:1 not NAT so you get the IP you would of got by true interaction with the gateway.

One of the problems thats posted here is Zyxel lease can be longer then the real lease and so you may lose connection
https://community.zyxel.com/en/discussion/25880/feature-request-immediate-dhcp-renewal-for-ip-passthrough-mode#latest

It would be best if Zyxel can relay the lease time the ISP is doing.

mbo77

OK, got it solved, with only a minimum of mystery left. I had to enable the ARP Proxy, now the renewals are transferred correctly between the router and the APN.

The only mystery left is the default lease time value with 0. Is it always 24h or derived from the ISP's DHCP server? Given the request above, the latter doesn't seem to be the case.