Device Groups Multicast Address

[pcdiem]

Have you looked for this feature in other issues and in the docs?
Yes

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When I wrote device groups support, I chose to make use of the existing SSDP UDP multicast code used by emulation support in the interest of code size. This can cause conflicts with overly sensitive UPnP devices and forces devices with emulation otherwise disabled to receive all UPnP packets received from the network. Device groups is not UPnP and really should not be using the SSDP multicast address.

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If I can get a 32-bit setting allocation, I'll submit a PR to make the device group multicast address configurable.

We could make the default device group multicast address be the SSDP multicast address (239.255.255.250). This would enable this to be a non-breaking change but would require that the emulation code continue to check for device group messages. It would be best if users migrated off the SSDP multicast address so we could eliminate the extra code. The migration is unlikely to happen though unless there is a breaking change that requires users to upgrade all devices using the device groups feature. Even new users would likely leave the multicast address at the default SSDP multicast address.

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I've made the modifications to device group support to use a dedicated multicast address defined at compile-time. The modifications add 175 bytes to the binary. I also have modifications to support using the dedicated multicast address while still supporting devices that use the SSDP multicast address which add 268 byes to the binary. This would allow users to continue to use 8.2.0 firmware. At some point in the future we could make the breaking change to remove SSDP multicast address support.

Overall, the device groups feature has only been available since the latest non-development release (8.2.0) and the number of users using it is relatively small. For this reason, I'd be in favor of making a breaking change that would require all devices using the device group feature to upgrade.

If we go with the breaking change, the device groups multicast address setting would be a nice feature but not necessary since the compile-time setting is not the SSDP multicast address.

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(Please, remember to close the issue when the problem has been addressed)

[Jason2866]

My 2 cents. Let´s do a clean fix (with breaking change) now.

[arendst]

Agree

[ascillato2]

👍