# CAN MOb Filter Generation

**URL:** <https://forum.opencyphal.org/t/can-mob-filter-generation/1066>\
**Category:** Libcanard\
**Created:** [January 8, 2021, 5:01pm UTC](https://forum.opencyphal.org/t/can-mob-filter-generation/1066 "2021-01-08T17:01:36Z")\
**Posts on this page:** 1\
**Showing post:** 2

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**Author:** ![pavel.kirienko](https://forum.opencyphal.org/user_avatar/forum.opencyphal.org/pavel.kirienko/32/9_2.png) [@pavel.kirienko](https://forum.opencyphal.org/u/pavel.kirienko)\
**Post date:** [January 8, 2021, 5:27pm UTC](https://forum.opencyphal.org/t/can-mob-filter-generation/1066/2 "2021-01-08T17:27:10Z")

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Hi Samuel,

> [@schwghrt](#):
>
> Can I get the expected extended message ID from the Receive Subscription, or do I need to generate the expected 29-bit Extended ID myself?

You need to do it manually. There is no such automation in Libcanard at the moment (maybe we could discuss adding it?).

You will find this thread helpful as our comrade Abraham was recently solving the very same problem:

> [@CAN filter configuration to use along libcanard V1](https://forum.opencyphal.org/t/can-filter-configuration-to-use-along-libcanard-v1/1021):
>
> Hello, I’m trying to configure the CAN reception filters for receiving 7609.Heartbeat.V1 messages in a mask + id filtering scheme. For the simplest case of uniquely allowing this subject throughout the hardware filters, my first thought is to use (0x1FFF \<\< 8) for the mask and (0x1D55 \<\< 8) for the corresponding ID. This comes from the CAN bit layout of V1 spec. Is this approach accurate or which is the mask intented to use when using messages? The intrigue started when reviewing t…

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