That's what my bank said.
But how does ABA and ABN stand for "routing" in anyway
The ABA number you speak of is more accurately called the Routing Transit Number.
A routing transit number (RTN) is a nine digit bank code, used in the United States, which appears on the bottom of negotiable instruments such as checks identifying the financial institution on which it was drawn. This code was designed to facilitate the sorting, bundling, and shipment of paper checks back to the drawer's (check writer's) account.
The RTN is also used by Federal Reserve Banks to process Fedwire funds transfers, and by the Automated Clearing House to process direct deposits, bill payments, and other such automated transfers.
The RTN number is derived from the bank's transit number originated by the American Bankers Association, which designed it in 1910.
I am going to assume that the euphemistic ABA Number has been shortened by whoever told you about it and called it the ABN. Perhaps American Bank Number. Either way, the technical term is RTN. Perhaps a comment or editor can straighten me out about the ABN.
There is an international number known as the SWIFT number that serves the same purpose worldwide.
ISO 9362 (also known as SWIFT-BIC, BIC code, SWIFT ID or SWIFT code) defines a standard format of Business Identifier Codes approved by the International Organization for Standardization (ISO). It is a unique identification code for both financial and non-financial institutions. The acronym SWIFT stands for the Society for Worldwide Interbank Financial Telecommunication. When assigned to a non-financial institution, the code may also be known as a Business Entity Identifier or BEI. These codes are used when transferring money between banks, particularly for international wire transfers, and also for the exchange of other messages between banks. The codes can sometimes be found on account statements.
With number of Banks increasing every country at some point in time adopted an Identification code. In US these are called ABA number because they are allocated by American Bankers Association, in UK Sort Codes ... like wise for other countries. See list here http://en.wikipedia.org/wiki/Bank_code
In some countries the numbers are given by Central Bank.
To enable internationl payments, the SWIFT body apart from message formats, allocated a SWIFT BIC [Bank identification Code] so that Banks can be globally identified. Currently IBAN being adopted in Europe & Australia to identify an Account [at a Bank] Uniquely across globe.
In essence these number help uniquely identify a Location/Bank/Branch. The clearing house route the payments or collection instruments to the correct Bank on the basis of this number.