Hi i have a rb pi3 with one lan on board and one lan card external and a 3G modem D-link for external connection over teamviewer.
So i try to bridge 2 lan card to be like middle router on some network, and a 3G Modem to can i connect to the router. But when i start rc.local :

sleep 10
sudo sh /home/pi/python/ifconfig.sh

sleep 30
sudo wvdial

where ifconfig.sh is
#!/bin/sh -e
sudo ifconfig eth0 0.0.0.0
sudo ifconfig eth1 0.0.0.0
sudo brctl addbr bridge0
sudo brctl addif bridge0 eth0
sudo brctl addif bridge0 eth1
sudo dhclient bridge0
sudo ifconfig bridge0 up

something was happened and 3g modem not connect or connection going trought lan cards.
Anybody can help me?

the script is run as root anyhow, you do not need sudo at all.

Yes , thats my fool mistake, but not correct the problem.