i want to connect two boards together on a tower by using their ether2 ports and a straight cable.
it is connected alright and i can see both in the neigbours and i can ping the mac adresses but can not reach them by the ip addresses

please help

Check the IP address configuration and ip route configuration.
There should not be nothing wrong on the RouterBOARDs.

should the ip be in the same block with the same subnet mask?

like if board a has 10.10.10.1 255.255.255.0 and board b 10.10.10.2 255.255.255.0 OR a have 10.10.10.1 255.255.255.0 and b 10.0.1.2 255.255.255.0?

then in the route i have problem making traffic pass through each other. it becomes very slow

When the boards are on the same Ethernet network, use the same subnet for them.