On my L2-screen (Realtick) I see some bids/aks twice - for example: ISLAND 17.49 2 ISLD 17.49 2 (exactly in this form: once "ISLAND", once "ISLD") - but this isn't the case for all ECN or even all ISLAND bids/offers. Thank you for your help, Harry
You are displaying the Island book within your Level 2 box Harry. In other words, all the bids and offers currently live in the ISLD server are being interdispersed within your L2 box at the appropriate price level. In regareds to your question, the Nasdaq will take the best bid and offer from Island and display it as part of the Nasdaq quote in the L2 as ISLD. THus, the best bid and offer from ISLD will actually show up twice, once as ISLD (nasdaq quote) and once as ISLAND coming right from the ISLD servers into your L2 box. If this is confusing you on your screen, simply right click on the L2 box, go to "quote sources" and choose the "show selected exchange only" option. Make sure you have only Nasdaq selected and this will remove all the "island" orders. PS you can do the same for Arca and Redi, which show up as archip and redibook if you elect to show all orders in the L2.