Del dhcp request domain-name-servers does not always work

PeterUK

DHCP.txt

USG FLEX 200H V1.39(ABWV.0)

So I get the idea you don't want to change the DHCP client Discover/Request and for good reason but do like: turns out it does remove domain-name-servers from Discover/Request

del vrf main interface ethernet Backup_4G ipv4 dhcp request domain-name-servers

thereby removing it in config to show
/ vrf "main" interface ethernet "Backup_4G" ipv4 dhcp "request" "subnet-mask"
/ vrf "main" interface ethernet "Backup_4G" ipv4 dhcp "request" "broadcast-address"
/ vrf "main" interface ethernet "Backup_4G" ipv4 dhcp "request" "time-offset"
/ vrf "main" interface ethernet "Backup_4G" ipv4 dhcp "request" "routers"
/ vrf "main" interface ethernet "Backup_4G" ipv4 dhcp "request" "domain-name"
/ vrf "main" interface ethernet "Backup_4G" ipv4 dhcp "request" "domain-search"
/ vrf "main" interface ethernet "Backup_4G" ipv4 dhcp "request" "host-name"
/ vrf "main" interface ethernet "Backup_4G" ipv4 dhcp "request" "nis-domain"
/ vrf "main" interface ethernet "Backup_4G" ipv4 dhcp "request" "nis-servers"
/ vrf "main" interface ethernet "Backup_4G" ipv4 dhcp "request" "ntp-servers"
/ vrf "main" interface ethernet "Backup_4G" ipv4 dhcp "request" "interface-mtu"
without
/ vrf "main" interface vlan "Backup_4G" ipv4 dhcp "request" "domain-name-servers"

and when the offer/ack come back to not add it to the Global Zone Forwarder but this does not happen in all cases likely due to the way offer/ack is done that the ignore domain-name-servers is added when it should not. the reason is Netgear add the domain-name-servers for offer/ack even if you did not ask for it

So here is attached is that case

Zyxel_Melen

Hi @PeterUK

Seems like without / vrf "main" interface vlan "Backup_4G" ipv4 dhcp "request" "domain-name-servers", the firewall won't add this option in the DHCP discovery/request packet. Is there any issue or concern?

PeterUK

hi Melen

The issue is I don't want to add any Global Zone Forwarder by any DHCP interface just want the Default which is why I do

del vrf main interface ethernet Backup_4G ipv4 dhcp request domain-name-servers

which does remove the request domain-name-servers from the Discover/Request but some servers give the DNS in there offer/ack when not asked for in Discover/Request

I'm hoping the option can be made better to really not add DNS to the Global Zone Forwarder

Zyxel_Melen

Hi @PeterUK

We have received your request, and the product team will evaluate it.

I also create the idea post to record it:

https://community.zyxel.com/en/discussion/33980/usg-flex-h-not-add-dns-to-the-global-zone-forwarder-when-no-dhcp-dns-option-in-dhcp-request

PeterUK

I think you missed the problem so to stop going round in circles the current way to make DHCP not ask for DNS works! but the DHCP server can ignore this and given you the DNS ANYWAY! causing it to be added to Global Zone Forwarder.