Hello ,
I want to find a suitable protocol to connect directly the brown router with the red router because i use radiusmanager and each router must have it’s unique ip.
Hi,
IP Tunnel for general purposes
IPSec for a secure tunnel
EOIP Tunnel for bridging your network and carrying Layer 2 traffic
witch of these three methods is the correct to use? please be more specific
in what situation ?
Look ,
My RB2011 is my main router with local ip 192.168.88.1/22.
I want to connect the red router with the main brown router but the red router is connected via pppoe to the middle router!!! Please help me! 
If you can ping last router so you can use ip/ip tunnel,if not you should setup up router’s routing tables in order to get ping