# Gateway ID : x-FFFF-y or x-FFFE-y?

**URL:** <https://www.thethingsnetwork.org/forum/t/gateway-id-x-ffff-y-or-x-fffe-y/16331>\
**Category:** Gateways\
**Created:** [July 28, 2018, 1:41pm UTC](https://www.thethingsnetwork.org/forum/t/gateway-id-x-ffff-y-or-x-fffe-y/16331 "2018-07-28T13:41:52Z")\
**Posts on this page:** 1\
**Showing post:** 3

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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:** [August 17, 2018, 10:06am UTC](https://www.thethingsnetwork.org/forum/t/gateway-id-x-ffff-y-or-x-fffe-y/16331/3 "2018-08-17T10:06:59Z")

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> [@ivo\_noorhoff](#):
>
> This [post](https://www.thethingsnetwork.org/forum/t/deveui-for-non-hardware-assigned-values/2093/27) mentions “_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]._”

For future reference, that quote is written in the past tense, and that very same post also mentions (emphasis mine):

> [@DevEUI for non-hardware assigned values](https://www.thethingsnetwork.org/forum/t/deveui-for-non-hardware-assigned-values/2093/30):
>
> But beware it also notes:
> 
> > 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**.

(That said, chances for collisions with officially assigned EUIs within the very same TTN network are low.)

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