EXHIBIT 4.7


                                 March 22, 2006

Credit Suisse First Boston Mortgage Securities Corp.
11 Madison Avenue
New York, New York 10010-3629

      Re:   Issuance of Credit Suisse First Boston Mortgage Securities Corp.,
            Commercial Mortgage Pass-Through Certificates, Series 2006-C1
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Ladies and Gentlemen:

      We have acted as special counsel to Credit Suisse First Boston Mortgage
Securities Corp. (the "Depositor") in connection with the proposed sale by the
Depositor and purchase by Credit Suisse Securities (USA) LLC ("Credit Suisse"),
GMAC Commercial Holding Capital Markets Corp. ("GMACCHCM"), Banc of America
Securities LLC ("BofA"), and McDonald Investments, Inc. ("MDI" and, together
with Credit Suisse, GMACCHCM and BofA, the "Underwriters"), of the Depositor's
Commercial Mortgage Pass-Through Certificates, Series 2006-C1, Class A-1, Class
A-2, Class A-3, Class A-AB, Class A-4, Class A-1-A, Class A-M, Class A-J, Class
B, Class C, Class D, Class E and Class F Certificates (collectively, the "Public
Certificates" or "Certificates") pursuant to the terms of an Underwriting
Agreement, dated March 7, 2006 (the "Underwriting Agreement"), between the
Depositor and the Underwriters. The Public Certificates are being issued
pursuant to a Pooling and Servicing Agreement, dated as of March 1, 2006 (the
"Pooling and Servicing Agreement" and collectively with the Underwriting
Agreement, the "Agreements"), among the Depositor, GMAC Commercial Mortgage
Corporation, as master servicer ("Master Servicer No. 1"), KeyCorp Real Estate
Capital Markets, Inc., as master servicer ("Master Servicer No. 2"), NCB, FSB,
as master servicer ("Master Servicer No. 3" and collectively with Master
Servicer No. 1 and Master Servicer No. 2, the "Master Servicers"), GMAC
Commercial Mortgage Corporation, as special servicer ("Special Servicer No. 1"),
National Consumer Cooperative Bank, as special servicer "Special Servicer No. 2"
and collectively with Special Servicer No. 1, the "Special Servicers"), and
Wells Fargo Bank, N.A., as trustee (the "Trustee"). Capitalized terms used
herein but not defined herein have the respective meanings given to them in the
Underwriting Agreement or, if not defined therein, in the Pooling and Servicing
Agreement.

      In rendering the opinions set forth below, we have examined and relied
upon the originals, copies or specimens, certified or otherwise identified to
our satisfaction, of the Transaction Documents (as defined below) and such
certificates, corporate and public records, agreements and instruments and other
documents, including, among other things, the documents delivered on the date
hereof, as we have deemed appropriate as a basis for the opinions expressed
below. In such examination we have assumed the genuineness of all signatures,
the authenticity of all documents, agreements and instruments submitted to us as
originals, the conformity to original documents, agreements and instruments of
all documents, agreements and instruments submitted to us as copies or
specimens, the authenticity of the originals of such documents, agreements and
instruments submitted to us as copies or specimens, the conformity of the text
of each document filed with the Securities and Exchange Commission (the
"Commission") through the Commission's Electronic Data Gathering, Analysis and
Retrieval System to the printed document reviewed by us, and the accuracy of the
matters set forth in the documents, agreements and instruments we reviewed. As
to matters of fact relevant to the opinions expressed herein, we have relied
upon, and assumed the accuracy of, the representations and warranties contained
in the Underwriting Agreement and the Pooling and Servicing Agreement and we
have relied upon certificates and oral or written statements and other
information obtained from the Depositor, the other parties to the transaction
referenced herein, and public officials. Except as expressly set forth herein,
we have not undertaken any independent investigation (including, without
limitation, conducting any review, search or investigation of any public files,
records or dockets) to determine the existence or absence of the facts that are
material to our opinions, and no inference as to our knowledge concerning such
facts should be drawn from our reliance on the representations of the Depositor
and others in connection with the preparation and delivery of this letter.

      In particular, we have examined and relied upon:

      (i)   the Prospectus Supplement, dated March 7, 2006, and the Prospectus,
            dated March 7, 2006, each relating to the offering of the
            Certificates;

      (ii)  the Pooling and Servicing Agreement; and

      (iii) the Underwriting Agreement.

      Items (i) to (iii) above are referred to in this letter as the
"Transaction Documents".

      We have also assumed that all documents, agreements and instruments have
been duly authorized, executed and delivered by all parties thereto, that all
such parties are validly existing and in good standing under the laws of their
respective jurisdictions of organization, that all such parties had the power
and legal right to execute and deliver all such documents, agreements and
instruments, and (other than with respect to the Depositor) that such documents,
agreements and instruments are legal, valid and binding obligations of such
parties, enforceable against such parties in accordance with their respective
terms. As used herein, "to our knowledge", "known to us" or words of similar
import mean the actual knowledge, without independent investigation, of any
lawyer in our firm actively involved in the transactions contemplated by the
Underwriting Agreement.

      We express no opinion concerning the laws of any jurisdiction other than
the laws of the State of New York and, to the extent expressly referred to in
this letter, the federal laws of the United States of America.

      Based upon and subject to the foregoing, we are of the opinion that:

            1. The Certificates have been duly authorized by the Depositor and,
      when the Certificates have been duly executed, authenticated and delivered
      by the Trustee in the manner contemplated in the Pooling and Servicing
      Agreement and paid for by and sold to the Underwriters pursuant to the
      Underwriting Agreement, the Certificates will be binding obligations of
      the issuing trust, enforceable against the issuing trust in accordance
      with their terms, subject to applicable bankruptcy, insolvency, fraudulent
      conveyance, reorganization, moratorium, receivership or other laws
      relating to or affecting creditors' rights generally, and to general
      principles of equity (regardless of whether enforcement is sought in a
      proceeding at law or in equity), and will be validly issued and
      outstanding, fully paid and non-assessable and entitled to the benefits
      provided by the Pooling and Servicing Agreement.

            2. The descriptions of federal income tax consequences appearing
      under the heading "Federal Income Tax Consequences" in the Prospectus and
      under the heading "U.S. Federal Income Tax Consequences" in the Prospectus
      Supplement accurately describe the material federal income tax
      consequences to holders of the Certificates, under existing law and
      subject to the qualifications and assumptions stated therein. We also
      hereby confirm and adopt the opinions expressly set forth under such
      headings, under existing law and subject to the qualifications and
      assumptions stated therein.

      We hereby consent to the filing of this letter as an exhibit to the
Depositor's Registration Statement on Form S-3 (File No. 333-129918) (the
"Registration Statement"), as declared effective on February 14, 2006, as it
relates to the Certificates, and to the reference to this firm under the
headings "Legal Matters" and "Federal Income Tax Consequences" or "U.S. Federal
Income Tax Consequences", as applicable, in the Prospectus and in the Prospectus
Supplement. This consent is not to be construed as an admission that we are a
person whose consent is required to be filed with the Registration Statement
under the provisions of the Securities Act of 1933, as amended.

      In addition, we disclaim any obligation to update this letter for changes
in fact or law, or otherwise.

                                                          Very truly yours,