multicast_to_unicast with hostapd on RPi

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I'm trying to use hostapd's multicast_to_unicast feature.
The AP is working fine, but I get this error: 



nl80211: multicast to unicast not supported on interface wlan0


I'm on Raspbian with next kernel (4.14.21-v7+ #1095) and with the latest hostapd (compiled from git).



As far I can see it means that the nl80211 I'm using does not support NL80211_CMD_SET_MULTICAST_TO_UNICAST command, but I don't understand why and what should I do.



Update: according to source the error is returned when set_multicast_to_unicast is NULL, and that field is populated by driver.
My card is based on rtl8812au and, for what I see in the driver, set_multicast_to_unicast is not defined.
The only way to get M2U working on this card is to write my own conversion routine and put it in the driver, right?




linux-kernel raspbian realtek hostapd multicast




share|improve this question


















  • 1




    Just out of curiosity: Could you describe your particular situation in which multicast-to-unicast conversion does something useful? Because I have a hard time imagining such situations, but that's probably just me.
    – dirkt
    Feb 25 at 14:42










  • With multicast the highest speed you can achieve is the speed of the slowest client. If you have a client with a weak signal it'll slow down all the other clients, regardless of their signal strenght. With multicast-to-unicast each packet is transmitted at the highest speed supported by the client.
    – Alex
    Feb 25 at 15:00










  • Maybe my understanding of hostapd is flawed, but I thought that with encrypted channels you'll have to send each multicast packet to each receiver individually anyway (because it's encrypted individually), and I'd assume that this happens at the highest speed between AP and STA, and what multicast-to-unicast does is just rewrite the broadcast address into a unicast address? Which is probably not what you want...
    – dirkt
    Feb 25 at 15:04










  • If I'm not wrong with multicast you have a per-group (not per-client) encryption key.
    – Alex
    Feb 25 at 15:24










  • How should a per-group key work? You can freely mix multicast packets with unicast packets. And that would also mean I should be able to sniff DHCP packets from other clients. Now I'm getting really curious ... you happen to know any docs?
    – dirkt
    Feb 25 at 15:32














up vote
1
down vote

favorite












I'm trying to use hostapd's multicast_to_unicast feature.
The AP is working fine, but I get this error: 



nl80211: multicast to unicast not supported on interface wlan0


I'm on Raspbian with next kernel (4.14.21-v7+ #1095) and with the latest hostapd (compiled from git).



As far I can see it means that the nl80211 I'm using does not support NL80211_CMD_SET_MULTICAST_TO_UNICAST command, but I don't understand why and what should I do.



Update: according to source the error is returned when set_multicast_to_unicast is NULL, and that field is populated by driver.
My card is based on rtl8812au and, for what I see in the driver, set_multicast_to_unicast is not defined.
The only way to get M2U working on this card is to write my own conversion routine and put it in the driver, right?




linux-kernel raspbian realtek hostapd multicast




share|improve this question


















  • 1




    Just out of curiosity: Could you describe your particular situation in which multicast-to-unicast conversion does something useful? Because I have a hard time imagining such situations, but that's probably just me.
    – dirkt
    Feb 25 at 14:42










  • With multicast the highest speed you can achieve is the speed of the slowest client. If you have a client with a weak signal it'll slow down all the other clients, regardless of their signal strenght. With multicast-to-unicast each packet is transmitted at the highest speed supported by the client.
    – Alex
    Feb 25 at 15:00










  • Maybe my understanding of hostapd is flawed, but I thought that with encrypted channels you'll have to send each multicast packet to each receiver individually anyway (because it's encrypted individually), and I'd assume that this happens at the highest speed between AP and STA, and what multicast-to-unicast does is just rewrite the broadcast address into a unicast address? Which is probably not what you want...
    – dirkt
    Feb 25 at 15:04










  • If I'm not wrong with multicast you have a per-group (not per-client) encryption key.
    – Alex
    Feb 25 at 15:24










  • How should a per-group key work? You can freely mix multicast packets with unicast packets. And that would also mean I should be able to sniff DHCP packets from other clients. Now I'm getting really curious ... you happen to know any docs?
    – dirkt
    Feb 25 at 15:32












up vote
1
down vote

favorite









up vote
1
down vote

favorite











I'm trying to use hostapd's multicast_to_unicast feature.
The AP is working fine, but I get this error: 



nl80211: multicast to unicast not supported on interface wlan0


I'm on Raspbian with next kernel (4.14.21-v7+ #1095) and with the latest hostapd (compiled from git).



As far I can see it means that the nl80211 I'm using does not support NL80211_CMD_SET_MULTICAST_TO_UNICAST command, but I don't understand why and what should I do.



Update: according to source the error is returned when set_multicast_to_unicast is NULL, and that field is populated by driver.
My card is based on rtl8812au and, for what I see in the driver, set_multicast_to_unicast is not defined.
The only way to get M2U working on this card is to write my own conversion routine and put it in the driver, right?




linux-kernel raspbian realtek hostapd multicast




share|improve this question














I'm trying to use hostapd's multicast_to_unicast feature.
The AP is working fine, but I get this error: 



nl80211: multicast to unicast not supported on interface wlan0


I'm on Raspbian with next kernel (4.14.21-v7+ #1095) and with the latest hostapd (compiled from git).



As far I can see it means that the nl80211 I'm using does not support NL80211_CMD_SET_MULTICAST_TO_UNICAST command, but I don't understand why and what should I do.



Update: according to source the error is returned when set_multicast_to_unicast is NULL, and that field is populated by driver.
My card is based on rtl8812au and, for what I see in the driver, set_multicast_to_unicast is not defined.
The only way to get M2U working on this card is to write my own conversion routine and put it in the driver, right?





linux-kernel raspbian realtek hostapd multicast





share|improve this question













share|improve this question




share|improve this question








edited Feb 26 at 0:06

























asked Feb 25 at 14:23









Alex

63




63







  • 1




    Just out of curiosity: Could you describe your particular situation in which multicast-to-unicast conversion does something useful? Because I have a hard time imagining such situations, but that's probably just me.
    – dirkt
    Feb 25 at 14:42










  • With multicast the highest speed you can achieve is the speed of the slowest client. If you have a client with a weak signal it'll slow down all the other clients, regardless of their signal strenght. With multicast-to-unicast each packet is transmitted at the highest speed supported by the client.
    – Alex
    Feb 25 at 15:00










  • Maybe my understanding of hostapd is flawed, but I thought that with encrypted channels you'll have to send each multicast packet to each receiver individually anyway (because it's encrypted individually), and I'd assume that this happens at the highest speed between AP and STA, and what multicast-to-unicast does is just rewrite the broadcast address into a unicast address? Which is probably not what you want...
    – dirkt
    Feb 25 at 15:04










  • If I'm not wrong with multicast you have a per-group (not per-client) encryption key.
    – Alex
    Feb 25 at 15:24










  • How should a per-group key work? You can freely mix multicast packets with unicast packets. And that would also mean I should be able to sniff DHCP packets from other clients. Now I'm getting really curious ... you happen to know any docs?
    – dirkt
    Feb 25 at 15:32












  • 1




    Just out of curiosity: Could you describe your particular situation in which multicast-to-unicast conversion does something useful? Because I have a hard time imagining such situations, but that's probably just me.
    – dirkt
    Feb 25 at 14:42










  • With multicast the highest speed you can achieve is the speed of the slowest client. If you have a client with a weak signal it'll slow down all the other clients, regardless of their signal strenght. With multicast-to-unicast each packet is transmitted at the highest speed supported by the client.
    – Alex
    Feb 25 at 15:00










  • Maybe my understanding of hostapd is flawed, but I thought that with encrypted channels you'll have to send each multicast packet to each receiver individually anyway (because it's encrypted individually), and I'd assume that this happens at the highest speed between AP and STA, and what multicast-to-unicast does is just rewrite the broadcast address into a unicast address? Which is probably not what you want...
    – dirkt
    Feb 25 at 15:04










  • If I'm not wrong with multicast you have a per-group (not per-client) encryption key.
    – Alex
    Feb 25 at 15:24










  • How should a per-group key work? You can freely mix multicast packets with unicast packets. And that would also mean I should be able to sniff DHCP packets from other clients. Now I'm getting really curious ... you happen to know any docs?
    – dirkt
    Feb 25 at 15:32







1




1




Just out of curiosity: Could you describe your particular situation in which multicast-to-unicast conversion does something useful? Because I have a hard time imagining such situations, but that's probably just me.
– dirkt
Feb 25 at 14:42




Just out of curiosity: Could you describe your particular situation in which multicast-to-unicast conversion does something useful? Because I have a hard time imagining such situations, but that's probably just me.
– dirkt
Feb 25 at 14:42












With multicast the highest speed you can achieve is the speed of the slowest client. If you have a client with a weak signal it'll slow down all the other clients, regardless of their signal strenght. With multicast-to-unicast each packet is transmitted at the highest speed supported by the client.
– Alex
Feb 25 at 15:00




With multicast the highest speed you can achieve is the speed of the slowest client. If you have a client with a weak signal it'll slow down all the other clients, regardless of their signal strenght. With multicast-to-unicast each packet is transmitted at the highest speed supported by the client.
– Alex
Feb 25 at 15:00












Maybe my understanding of hostapd is flawed, but I thought that with encrypted channels you'll have to send each multicast packet to each receiver individually anyway (because it's encrypted individually), and I'd assume that this happens at the highest speed between AP and STA, and what multicast-to-unicast does is just rewrite the broadcast address into a unicast address? Which is probably not what you want...
– dirkt
Feb 25 at 15:04




Maybe my understanding of hostapd is flawed, but I thought that with encrypted channels you'll have to send each multicast packet to each receiver individually anyway (because it's encrypted individually), and I'd assume that this happens at the highest speed between AP and STA, and what multicast-to-unicast does is just rewrite the broadcast address into a unicast address? Which is probably not what you want...
– dirkt
Feb 25 at 15:04












If I'm not wrong with multicast you have a per-group (not per-client) encryption key.
– Alex
Feb 25 at 15:24




If I'm not wrong with multicast you have a per-group (not per-client) encryption key.
– Alex
Feb 25 at 15:24












How should a per-group key work? You can freely mix multicast packets with unicast packets. And that would also mean I should be able to sniff DHCP packets from other clients. Now I'm getting really curious ... you happen to know any docs?
– dirkt
Feb 25 at 15:32




How should a per-group key work? You can freely mix multicast packets with unicast packets. And that would also mean I should be able to sniff DHCP packets from other clients. Now I'm getting really curious ... you happen to know any docs?
– dirkt
Feb 25 at 15:32















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