setting up a 0.0.0.0 virtual server with irule

A couple of things about your actual rule:

1) You will want to use the IP::addr command to compare your addresses

2) You want to be careful with whitespace separating statements, otherwise Tcl may get confused about which arguments are which.

Try this:

 
 when CLIENT_ACCEPTED { 
    if {[IP::addr [IP::local_addr] equals 172.18.200.254]} { 
       pool default-gateway-1 
    } elseif {[IP::addr [IP::local_addr] equals 172.18.203.253]} { 
       pool default-gateway-2 
    } else { 
       pool default-gateway-SNAT 
    } 
 }