UDP receive buffer size option

Ubuntu has limit on buffer

$ sysctl -a | grep rmem
net.core.rmem_default = 212992
net.core.rmem_max = 212992
net.ipv4.tcp_rmem = 4096 131072 6291456
net.ipv4.udp_rmem_min = 4096

you have to change the option like this:
$ sysctl -w net.core.rmem_max=8388608
$ sysctl -w net.core.rmem_default=8388608