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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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 3sVBFfVU9/UQBtfxhUz1dw==

<SEC-DOCUMENT>0001179110-08-017474.txt : 20080930
<SEC-HEADER>0001179110-08-017474.hdr.sgml : 20080930
<ACCEPTANCE-DATETIME>20080930183412
ACCESSION NUMBER:		0001179110-08-017474
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20080926
FILED AS OF DATE:		20080930
DATE AS OF CHANGE:		20080930

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			FOUNDRY NETWORKS INC
		CENTRAL INDEX KEY:			0001090071
		STANDARD INDUSTRIAL CLASSIFICATION:	COMPUTER COMMUNICATIONS EQUIPMENT [3576]
		IRS NUMBER:				770431154
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		4980 GREAT AMERICA PARKWAY
		CITY:			SANTA CLARA
		STATE:			CA
		ZIP:			95054
		BUSINESS PHONE:		408 207 1700

	MAIL ADDRESS:	
		STREET 1:		4980 GREAT AMERICA PARKWAY
		CITY:			SANTA CLARA
		STATE:			CA
		ZIP:			95054

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			BROCADE COMMUNICATIONS SYSTEMS INC
		CENTRAL INDEX KEY:			0001009626
		STANDARD INDUSTRIAL CLASSIFICATION:	COMPUTER PERIPHERAL EQUIPMENT, NEC [3577]
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1027

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-26689
		FILM NUMBER:		081098225

	BUSINESS ADDRESS:	
		STREET 1:		1745 TECHNOLOGY DRIVE
		CITY:			SAN JOSE
		STATE:			CA
		ZIP:			95110
		BUSINESS PHONE:		(408) 333-8000

	MAIL ADDRESS:	
		STREET 1:		1745 TECHNOLOGY DRIVE
		CITY:			SAN JOSE
		STATE:			CA
		ZIP:			95110
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 4 -
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2008-09-26</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001090071</issuerCik>
        <issuerName>FOUNDRY NETWORKS INC</issuerName>
        <issuerTradingSymbol>FDRY</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001009626</rptOwnerCik>
            <rptOwnerName>BROCADE COMMUNICATIONS SYSTEMS INC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1745 TECHNOLOGY DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SAN JOSE</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>95110</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2008-09-26</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1151788</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>18.1422</value>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>12688878</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2008-09-29</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1311122</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>18.0224</value>
                    <footnoteId id="F4"/>
                    <footnoteId id="F5"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>14000000</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">The purchases reported were effected pursuant to Rule 10b5-1 trading plan adopted by the reporting person.</footnote>
        <footnote id="F2">Excludes certain shares as set forth in Footnote 2 to Form 3 filed on September 24, 2008.</footnote>
        <footnote id="F3">The reported price represents a weighted average purchase price.  The range of prices was $17.9589 to $18.3100.</footnote>
        <footnote id="F4">The reporting person undertakes to provide to the staff, the issuer or a security holder full information regarding the number of shares purchased at each separate price.</footnote>
        <footnote id="F5">The reported price represents a weighted average purchase price.  The range of prices was $17.5000 to $18.2600.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Richard Deranleau, Chief Financial Officer and Vice President, Finance</signatureName>
        <signatureDate>2008-09-30</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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