It follows what the IRB described as "unfounded allegations" printed in the UK's Sunday Times newspaper.
A letter of protest from an English law firm purporting to act for the Asian Rugby Football (ARFU) Union was sent to the IRB.
But the ARFU has informed the IRB that the letter should not have been sent as, according to the IRB, "it does not represent the views of ARFU and that the person who it seems engaged the solicitors did not have the constitutional authority to do so".
In a statement the board added that it "takes exception to any suggestion that the vote was not carried out in a proper and professional manner".
The IRB said the process and procedure was approved by the directors of Rugby World Cup Limited and the IRB Council. It added that the vote itself was verified by independent auditors from Price Waterhouse Coopers, who informed them on the day that the vote took place "correctly and professionally".
The IRB statement adds that the secretary general of ARFU has written to the solicitors stating that they must cease and desist purporting to act for and on behalf of the Asian Rugby Football Union.
Meanwhile, the Japan Rugby Football Union (JRFU) has said it "firmly believes that RWC 2011 in New Zealand will be a great success and will do all it can to ensure the tournament is the best ever".
The JRFU said it too had no official involvement in the letter sent to the IRB.
The decision to award the Rugby World Cup 2011 to New Zealand sparked controversy, as many saw awarding the tournament to Japan as an ideal opportunity to help grow the sport globally.
