# unknown dhcp option 0x7d



## badbrain (Aug 4, 2019)

VirtualBox bridged interface. The adapter is my usb dongle wlan0. Host is MX Linux. Previous time I didn't notice it on dmesg since the system boot up very fast. This time due to the error "Unqualified hostname" FreeBSD refused to boot so I could see it. What is it? Does it have any effect on the system?


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## badbrain (Aug 6, 2019)

Does anyone know what "unknown dhcp option 0x7d" means? I believed `dhclient` generate this warning.


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## moridin (Aug 6, 2019)

According to https://www.iana.org/assignments/bootp-dhcp-parameters/bootp-dhcp-parameters.xhtml, 125 (0x7d) is "V-I Vendor-Specific Information", so it should be anything your router's manufacturer intended to be there.  Looking at RFC3925 linked against it, you *could* try using `tcpdump` to get and decipher the packet contents (though I really don't think it's worth spending your time on that).


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## Phishfry (Aug 6, 2019)

Your upstream DHCP server is sending a DHCP option that your DHCP client does not understand or support.
If you use net/dhcpdump you can see all the options that the DHCP server is trying to negotiate with the client.
Here is an example of dnsmasq dhcp options. They use a number for the option.
Your error message is using hex code.
Converted this is dhcp option 125. I used this >> https://www.rapidtables.com/convert/number/hex-to-decimal.html?x=0x7d
So you DHCP server is trying to negotiate option 125 with the FreeBSD client and the client does not understand option 125.
If everything is working fine you can probably ignore this.
Windows DHCP servers use options not present on Unix system clients. Same with some other DHCP servers.
They have added custom options not defined in RFC2132.


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## Phishfry (Aug 6, 2019)

Checking my dnsmasq server produced this for your option:


> 125 vendor-id-encap


So they are trying to encapsulate the VendorID of the dhcp server into the dhcp packet header and FreeBSD says bad option.


			RFC 3925:  Vendor-Identifying Vendor Options for Dynamic Host Configuration Protocol version 4 (DHCPv4)
		


My guess is that your host MXLinux DHCP server is using option 125, as it provides networking services to Virtualbox correct?.


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## badbrain (Aug 7, 2019)

Phishfry said:


> My guess is that your host MXLinux DHCP server is using option 125, as it provides networking services to Virtualbox correct?.


I don't think so. This unknown option error only appears when I use bridged interface of VirtualBox. With NAT it didn't show up. The weired thing is only FreeBSD dhclient throws this warning, DFBSD doesn't.


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