Mikrotik Dhcp Domain Search Option

I recently decided to replace my Netgear Nighthawk R7800¹ running DD-WRT², after encountering some stability problems which I wasn’t able to resolve. I decided to move away from normal consumer/enthusiast options and went for a Mikrotik hEX PoE³ paired with a UniFi AP AC LITE⁴.

RouterOS⁵ is a very capable commercial grade operating system (OS). Coming from a consumer grade networking device/OS can involve a steep learning curve if you’re not reasonably familiar with networking already. That said, even if you are, there can be some edge cases where the feature or documentation doesn’t behave as expected/described.

My first encounter with this in RouterOS was configuring a DHCP Option to set the Domain Search list^6,7,8. Despite what the RouterOS documentation⁹ says, it turns out that you can’t just use a string value to set this option properly in RouterOS. As noted by pessoft¹⁰ and others on the Mikrotik Forums¹¹ this particular DHCP option (there may be others, I am only commenting on this one here), must be correctly formatted according to some rules.

Unlike in the pessoft¹⁰ example, I elected not to use compression and simply concatenated the elements with a series of 0x00XX entries finishing with 0x00, as shown below:

/ip dhcp-server option add name=domain-search-list code=119 value="0x0A'engineroom'0x0A'middlearth'0x03'lan'0x0006'bridge'0x0A'middlearth'0x03'lan'0x000A'middlearth'0x03'lan'0x00"