for example, i send a order to buy 2100 stocks for 5 limit ARCA ecn - sell orders 100 - 4.96 2000 - 4.97 EDGX Ecn -sell orders 100 - 4.95 2000 - 4.98 Order will be filled just one ecn ?
You're asking how a smart routed order will work when all smart routes are built differently. If you have access to route your order without a smart route, and the above are the only offers in the world, REG-NMS would demand an order sent to ARCA to route out to EDGX for the 100 shares at 4.95, then route back to ARCA for the 100 shares at 4.96, then fill your order at 4.97 on ARCA. If you sent it to EDGX, you would get filled on the 100 at 4.95, then route out to ARCA to fill your order on ARCA at 100 at 4.96 then the balance at 4.97.