# DevEUI for non-hardware assigned values

**URL:** <https://www.thethingsnetwork.org/forum/t/deveui-for-non-hardware-assigned-values/2093>\
**Category:** End Devices (Nodes)\
**Created:** [May 11, 2016, 12:28pm UTC](https://www.thethingsnetwork.org/forum/t/deveui-for-non-hardware-assigned-values/2093 "2016-05-11T12:28:31Z")\
**Posts on this page:** 1\
**Showing post:** 30

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**Author:** ![arjanvanb](https://www.thethingsnetwork.org/forum/user_avatar/www.thethingsnetwork.org/arjanvanb/32/46626_2.png) [@arjanvanb](https://www.thethingsnetwork.org/forum/u/arjanvanb)\
**Post date:** [March 5, 2017, 11:23am UTC](https://www.thethingsnetwork.org/forum/t/deveui-for-non-hardware-assigned-values/2093/30 "2017-03-05T11:23:24Z")

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> [@htdvisser](#):
>
> These MAC addresses are 48 bits long, which means that you can fill the first 48 bits of the DevEUI with your MAC address, and choose the remaining 16 bits yourself.

A more common, though **deprecated** , approach seems to be to insert `0xFFFE` in the middle; see “Mapping an EUI-48 to an EUI-64” in [IEEE SA - Registration Authority](https://standards.ieee.org/develop/regauth/tut/eui.pdf#page=15), emphasis for the past tense mine:

> Some standards have described how an EUI-48 value could be mapped to an EUI-64, as follows: Let the six octets of the EUI-48 be labeled eui48[0] through eui48[5]. Let the eight octets of the mapped EUI-64 be labeled eui64[0] through eui64[7]. The following mapping **has been** described:
> 
> eui64[0] = eui48[0]  
> eui64[1] = eui48[1]  
> eui64[2] = eui48[2]  
> eui64[3] = FFhex  
> eui64[4] = FEhex or eui64[4] = FFhex  
> eui64[5] = eui48[3]  
> eui64[6] = eui48[4]  
> eui64[7] = eui48[5]
> 
> In other words, the EUI-64 value **was** generated by inserting either the value FFFEhex or the value FFFFhex in between eui48[2] and eui48[3].

But beware it also notes this **is deprecated** , emphasis mine:

> Mapping an EUI-48 assigned with an MA-S/OUI-36 or MA-M assignment to an EUI-64 **potentially creates a duplicate** of an EUI-64 assigned with a different MA-S/OUI-36 or MA-M. The IEEE RA has taken appropriate actions to mitigate creation of duplicates based on this mapping but, to protect the integrity of EUI-64 identifiers, **this mapping is deprecated**.

Earlier it stated, again emphasis mine:

> The mapping described here **is deprecated** and it should not be used in new applications as it includes **an unacceptable probability of duplicating** an EUI-64.

(It’s also [used in IPv6](http://superuser.com/questions/243669/how-to-avoid-exposing-my-mac-address-when-using-ipv6) but there it also sets a specific bit which in IPv6 defines universal/global scope, so would probably not suffer any chances of duplicating IPv6 addresses.)

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