Hello all,
We have 2 routers-A and B, connected to each other. Router A is the main one, where we had 1 global IP address released by ISP.
Before long, we received 5 additional global IPs from the ISP and we want to group our customers behind router B to use them. We devided them in 3 groups but we are not sure what to do next. Please advise.

I am unclear as to what the goal is...

Are you wanting to NAT multi local address out of all of them and balance?

Are you wanting to NAT 1 to 1 some of them and multi out one?

***Assuming what you want is something like this... Assign all the Public IPs to Router A wan port. Then setup NAT rules to balance your customer groups http://wiki.mikrotik.com/wiki/Manual:IP/Firewall/NAT


*******Other Consideration I assume you are not doing***********
Are you wanting to assign the public IPs downstream?

Also are routers A and B in parallel using VRRP?

I will explain what I did:
Say, one group has ip address 10.0.20.0/24. for this group, configuration looks like this:

chain=prerouting action=mark-routing new-routing-mark=10.0.20.0/24
passthrough=no src-address=10.0.20.0/24

chain=srcnat action=src-nat to-addresses=146.255.243.XX
src-address=10.0.20.0/24

146.255.243.XX is new IP address provided by ISP. We had global IP address 92.241.71.xx untill this new one. Now, the problem: before this configuration, I was able to axxess local network 10.0.20.0/24 from outside, but now I am not. Also, when I disable interface with 92.241.71.XX IP address, connection to Internet fails. What is the mistake?

You are lacking the dst-nat rule

chain=dstnat action=dst-nat to-addresses=10.0.20.0/24
dst-address=146.255.243.XX