Zyxel DHCP client does not honour NO DNS

PeterUK

Zywall 110 V4.72(AAAA.0)ITS-22WK28-r104687

USG60 V4.72(AAKY.0)ITS-22WK35-r105124

Come across this bug where a Zywall 110 running the DHCP server has no DNS IP set for clients and a USG60 as DHCP client receives the offer and ACK with no DNS IP yet the USG60 puts in a DNS IP for Domain Zone Forwarder in config > system > DNS of the gateway IP of the DHCP server when I do not want it too.

Is thier a way to stop this? Thanks

Zyxel_Cooldia

Hi @PeterUK,

The issue can be reproduced in lab test.
We are checking internally, please wait for my update.

PeterUK

It be nice to disable any added DNS to Zywall so that the Zywall has to do lookups by recursion root servers.

Zyxel_Cooldia

As confirmed, if DHCP server does not provide DNS server option to gateway, gateway will take server identifier as default DNS server. This network scenario is relatively rare in practice. We would suggest to set up static IP on WAN interface and manually add DNS zone forwarder for your network.

PeterUK

But the Zywall can do DNS without adding a DNS in Domain Zone Forwarder which is what I want you can test this yourself with static IP which is what I'm doing as a backup DNS but was looking to do DHCP for some interfaces.

jasailafan

Do you want zywall to do DNS lookup by recursion root servers assuming the DHCP server does not provide DNS options?

PeterUK

Yes without any added Domain Zone Forwarder

Zyxel_Cooldia

Hi @PeterUK,
Could you share more information about this scenario in practice.
Just wondering about why you need gateway to do the DNS query by recursion root servers?

PeterUK

Because why not? I have a bind setup doing this but should that system go down I fail over to the USG60 to do the DNS

Zyxel_Cooldia

Hi @PeterUK,

Thanks for your feedback, i will post this to ideas section. 
https://community.zyxel.com/en/discussion/14615/zyxel-dhcp-client-does-not-honour-no-dns/p1?new=1