Distance for the Node to connect to the gateway MQTT-SN ?

Question

Hi all, 
 I have a question. 
 When I try send message coap, it can send as mesh network. 
 But when I send search gateway msg, connect msg from publish (subscribe) Node to NCP. Seem it can't send as mesh network. I have to put Node in the coverage area of ​​NCP then it can discovery and connect to Gateway. If I put NCP --> Node 1 --> Node 2 in a straight line. Node 1 can connect to mqtt gateway, but node 2 can't . But I can ping from Node 2 to Node 1 and NCP. 
 If I connect Node1 and Node 2 to MQTT gateway and put NCP --> Node 1 --> Node 2 in a straight line. I can send data from Node 1 and Node 2 to NCP as mesh network. 
 I check message type of discovery and connect message. I saw it same with coap message. They are all used otUdpSend. 
 So Why is there such a difference?

LucD · Answer

Adding some lines the paho MQTT-SN gateway code to set the multicast hop (in my case I picked 5) fixed the issue, as the default value is 1 if you do not set this option and thus the GWINFO message doesn't get broadcasted past the initial hop.

Distance for the Node to connect to the gateway MQTT-SN ?

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