EXHIBIT 10.25.1

FIRST LOAN MODIFICATION TO THE ACCOUNTS RECEIVABLE FINANCING AGREEMENT

This First Loan Modification Agreement to the Accounts Receivable
Financing Agreement (this Loan Modification Agreement) is entered into as of
May 24, 2001, by and between SILICON VALLEY BANK, a California-chartered bank,
with its principal place of business at 3003 Tasman Drive, Santa Clara,
California 95054 and with a loan production office located at One Newton
Executive Park, Suite 200, 2221 Washington Street, Newton, Massachusetts 02462,
doing business under the name Silicon Valley East (Bank) (i) VISUAL
NETWORKS, INC., a Delaware corporation, (ii) VISUAL NETWORKS OPERATIONS, INC.,
a Delaware corporation, (iii) VISUAL NETWORKS INVESTMENTS, INC., a California
corporation, (iv) VISUAL NETWORKS TECHNOLOGIES, INC., a California corporation,
(v) VISUAL NETWORKS OF TEXAS, L.P., a Texas limited partnership, (vi) VISUAL
NETWORKS INSURANCE, INC., a Vermont corporation, (vii) INVERSE NETWORK
TECHNOLOGY, a California corporation, and (viii) AVESTA TECHNOLOGIES, INC., a
Delaware corporation (jointly, severally and collectively, the Borrower or
Borrowers).

1. DESCRIPTION OF EXISTING INDEBTEDNESS AND OBLIGATIONS. Among other
indebtedness and obligations which may be owing by Borrower to Bank, Borrower
is indebted to Bank pursuant to a loan arrangement dated as of February 28,
2001, evidenced by, among other documents, (i) a certain Accounts Receivable
Financing Agreement dated as of February 28, 2001, between Borrower and Bank
(as may be amended from time to time, the Financing Agreement) and, (ii) a
certain Loan and Security Agreement dated as of February 28, 2001, between
Borrower and Bank, (as may be amended from time to time, the Loan Agreement).
The Financing Agreement established: (i) a accounts receivable line of credit
in favor of Borrower in the maximum principal amount of Ten Million Dollars
($10,000,000.00) (the Accounts Receivable Line). Capitalized terms used but
not otherwise defined herein shall have the same meaning as in the Loan
Agreement.

Hereinafter, all indebtedness and obligations owing by Borrower to Bank shall
be referred to as the Obligations.

2. DESCRIPTION OF COLLATERAL. Repayment of the Obligations is secured by the
Collateral as described in the Financing Agreement (together with any other
collateral security granted to Bank, the Security Documents).

Hereinafter, the Security Documents, together with all other documents
evidencing or securing the Obligations shall be referred to as the Existing
Loan Documents.

3. DESCRIPTION OF CHANGE IN TERMS.



|A. |  | Modifications to Financing Agreement.
|-- |  | -------------------------------------



| | 1. |  | The Financing Agreement shall be amended by
deleting the following definitions appearing in Section 1
thereof:                                                                                                                                                                                                                                                             
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| |    |  | Net Lossis a reconciled amount that is calculated as the
net loss of the Borrower (on a consolidated basis) as
determined by GAAP, and adjusted by (i) non-cash charges
including, without limitation, intangible amortization and
depreciation, and (ii) non-recurring costs including, without
limitation, restructuring charges and intangible asset
write-downs.    
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| |    |  | Net Profitis a reconciled amount that is calculated as
the net income of the Borrower (on a consolidated basis) as
determined by GAAP, and adjusted by (i) non-cash charges
including, without limitation, intangible amortization and
depreciation, and (ii) non-recurring costs including, without
limitation, restructuring charges and intangible asset
write-downs.





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| |    | and inserting in lieu thereof the following:                                        
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| |    | and inserting in lieu thereof the following:                                        
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| |    | (M) Borrower shall maintain as of the last day of
each month unless otherwise noted:
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| |    |  | One Million Two Hundred Fifty Thousand Dollars
($1,250,000.00) for the quarter ending September 30, 2001;
(ii) quarterly Net Profit of at least One Million Dollars
($1,000,000.00) for the quarter ending December 31, 2001; and
(iii) a quarterly Net Profit of One Dollar ($1.00), for each
quarter thereafter.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
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| |    |  | (3) Debt Service Coverage Ratio. The Borrower shall
maintain, as of the last day of each month, a Debt Service
Coverage Ratio of not less than 2.50 to 1.0. For purposes
hereof Debt Service Coverage Ratio shall be defined as: (i)
during any month in which no Obligations were outstanding or
requested under the Financing Agreement, Eighty Percent (80%)
of the amount calculated by dividing the outstanding
Obligations under the Committed Equipment Line into the
following: accounts receivable, less accounts over ninety
(90) days past invoice date, less deferred revenue offsets
and customer deposit offsets, or (ii) during any month in
which Obligations were outstanding under the Financing
Agreement, the remaining amount of borrowing ability
available determined pursuant to the terms of the Financing
Agreement, divided by all outstanding Obligations under the
Committed Equipment Line.
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| | 3. |  | The Compliance Certificate appearing as Exhibit C
to the Financing Agreement is hereby replaced with the
Compliance Certificate attached as Exhibit Ahereto.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                

4. RATIFICATION OF INTELLECTUAL PROPERTY SECURITY AGREEMENT. Borrower hereby
ratifies, confirms and reaffirms, all and singular, the terms and conditions of
a certain Intellectual Property Security Agreement dated as of February 28,
2001, between Borrower and Bank, and acknowledges, confirms and agrees that
said Intellectual Property Security Agreement (including all Exhibits attached
thereto) shall remain in full force and effect and contain an accurate and
complete listing of all Intellectual Property Collateral as defined in said
Intellectual Property Security Agreement.

5. ADDITIONAL COVENANTS: RATIFICATION OF PERFECTION CERTIFICATE. Borrower
shall not, without providing the Bank with thirty (30) days prior written
notice: (i) relocate its principal executive office or add any new offices or
business locations or keep any Collateral in any additional locations, or (ii)
change its state of formation, or (iii) change its organizational structure,
(iv) change its legal name, or (v) change any organizational number (if any)
assigned by its state of formation. Borrower hereby ratifies, confirms and
reaffirms, all and singular, the terms and disclosures contained in certain
Perfection Certificates dated as of February 28, 2001, between Borrower and
Bank, and acknowledges, confirms and agrees the disclosures and information
above Borrower provided to Bank in the Perfection Certificates have not
changed, as of the date hereof.

6. AUTHORIZATION TO FILE. Borrower hereby authorizes Bank to file financing
statements without notice to Borrower, with all appropriate jurisdictions, as
Bank deems appropriate, in order to further perfect or protect Banks interest
in the Collateral.

7. CONCERNING REVISED ARTICLE 9 OF THE UNIFORM COMMERCIAL CODE. The Borrower
affirms and reaffirms that notwithstanding the terms of the Security Documents
to the contrary, (i) that the definition of Code, UCC or Uniform
Commercial Code as set forth in the Security Documents shall be deemed to mean
and refer to the Uniform Commercial Code as adopted by The Commonwealth of
Massachusetts (presently, Mass. Gen. Laws. Ch. 106), may be amended and in
effect from time to time and (ii) the Collateral is all assets of the Borrower.
In connection therewith, the Collateral shall include, without limitation, the
following categories of assets as defined in the Code: goods (including
inventory, equipment and any accessions thereto), instruments (including
promissory notes), documents, accounts (including health-care-insurance
receivables, and license fees), chattel paper (whether tangible or electronic),
deposit accounts, letter-of-credit rights (whether or not the letter of credit
is evidenced by a writing), commercial tort claims, securities and all other
investment property, general intangibles (including payment intangibles and
software), supporting obligations and any and all proceeds of any thereof,
wherever located, whether now owned or hereafter acquired.

8. CONSISTENT CHANGES. The Existing Loan Documents are hereby amended wherever
necessary to





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reflect the changes described above.

9. RATIFICATION OF LOAN DOCUMENTS. Borrower hereby ratifies, confirms, and
reaffirms all terms and conditions of all security or other collateral granted
to the Bank, and confirms that the indebtedness secured thereby includes,
without limitation, the Obligations.

10. NO DEFENSES OF BORROWER. Borrower agrees that, as of this date, it has no
defenses against the obligations to pay any amounts under the Obligations.

11. CONTINUING VALIDITY. Borrower understands and agrees that in modifying the
existing Obligations, Bank is relying upon Borrowers representations,
warranties, and agreements, as set forth in the Existing Loan Documents.
Except as expressly modified pursuant to this Loan Modification Agreement, the
terms of the Existing Loan Documents remain unchanged and in full force and
effect. Banks agreement to modifications to the existing Obligations pursuant
to this Loan Modification Agreement in no way shall obligate Bank to make any
future modifications to the Obligations. Nothing in this Loan Modification
Agreement shall constitute a satisfaction of the Obligations. It is the
intention of Bank and Borrower to retain as liable parties all makers of
Existing Loan Documents, unless the party is expressly released by Bank in
writing. No maker will be released by virtue of this Loan Modification
Agreement.

12. RIGHT OF SET-OFF. In consideration of Banks agreement to enter into this
Loan Modification Agreement, Borrower and any guarantor hereby reaffirm and
hereby grant to Bank, a lien, security interest and right of setoff as security
for all Obligations to Bank, whether now existing or hereafter arising upon and
against all deposits, credits, collateral and property, now or hereafter in the
possession, custody, safekeeping or control of Bank or any entity under the
control of Silicon Valley Bank or in transit to any of them. At any time after
the occurrence and during the continuance of an Event of Default, without
demand or notice, Bank may set off the same or any part thereof and apply the
same to any liability or obligation of Borrower and any guarantor even though
unmatured and regardless of the adequacy of any other collateral securing the
loan. ANY AND ALL RIGHTS TO REQUIRE BANK TO EXERCISE ITS RIGHTS OR REMEDIES
WITH RESPECT TO ANY OTHER COLLATERAL WHICH SECURES THE OBLIGATIONS, PRIOR TO
EXERCISING ITS RIGHT OF SETOFF WITH RESPECT TO SUCH DEPOSITS, CREDITS OR OTHER
PROPERTY OF THE BORROWER OR ANY GUARANTOR, ARE HEREBY KNOWINGLY, VOLUNTARILY
AND IRREVOCABLY WAIVED.

13. JURISDICTION/VENUE. Borrower accepts for itself and in connection with its
properties, unconditionally, the non-exclusive jurisdiction of any state or
federal court of competent jurisdiction in the Commonwealth of Massachusetts in
any action, suit, or proceeding of any kind against it which arises out of or
by reason of this Loan Modification Agreement; provided, however, that if for
any reason Bank cannot avail itself of the courts of the Commonwealth of
Massachusetts, then venue shall lie in Santa Clara County, California.

14. COUNTERSIGNATURE. This Loan Modification Agreement shall become effective
only when it shall have been executed by Borrower and Bank (provided, however,
in no event shall this Loan Modification Agreement become effective until
signed by an officer of Bank in California).

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This Loan Modification Agreement is executed as a sealed instrument under
the laws of the Commonwealth of Massachusetts as of the date first written
above.

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|BORROWERS:                                                                                     |  | BANK:                                                     
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|VISUAL NETWORKS, INC                                                                           |  | SILICON VALLEY BANK, doing business as
SILICON VALLEY EAST
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|By: /s/ Peter J. Minihane                                                                      |  | By: /s/ Justin J. Peterson                                
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|Name: Peter J. Minihane                                                                        |  | Name: Justin J. Peterson                                  
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|Title: Chief Financial Officer                                                                 |  | Title: Vice President                                     
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|VISUAL NETWORKS OPERATIONS, INC                                                                |  | SILICON VALLEY BANK                                       
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|By: /s/ Peter J. Minihane                                                                      |  | By: /s/ Lee A. Shodiss                                    
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|Name: Peter J. Minihane                                                                        |  | Name: Lee A. Shodiss                                      
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|Title: Treasurer                                                                               |  | Title: Sr. Vice President                                 
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|VISUAL NETWORKS INVESTMENTS, INC                                                              
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|By: /s/ Peter J. Minihane                                                                     
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|Name: Peter J. Minihane                                                                       
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|Title: Treasurer                                                                              
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|VISUAL NETWORKS TECHNOLOGIES, INC                                                             
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|By: /s/ Peter J. Minihane                                                                     
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|Name: Peter J. Minihane                                                                       
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|Title: Treasurer                                                                              
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|VISUAL NETWORKS OF TEXAS, L.P.,
by Visual Networks Texas Operations, Inc., its
General Partner
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|By: /s/ Peter J. Minihane                                                                     
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|Name: Peter J. Minihane                                                                       
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|Title: Treasurer                                                                              





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|BORROWERS:(Contd)            
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|VISUAL NETWORKS INSURANCE, INC
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|By: /s/ Peter J. Minihane     
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|Name: Peter J. Minihane       
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|Title: Treasurer              
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|INVERSE NETWORK TECHNOLOGY    
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|By: /s/ Peter J. Minihane     
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|Name: Peter J. Minihane       
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|Title: President              
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|AVESTA TECHNOLOGIES, INC      
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|By: /s/ Peter J. Minihane     
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|Name: Peter J. Minihane       
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|Title: President