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Ask the Expert- SD-WAN

%Error reading: A TFTP copy operation times out when the Cisco IOS Software file size is over 16MB


Core Issue

This occurs while performing a Cisco IOS  Software upgrade through TFTP, due to an issue with one of these options: 

  • The currently running Cisco IOS Software
  • The TFTP server
  • Both the currently running Cisco IOS Software and the TFTP server


To use TFTP to copy images larger than 16MB to a Cisco router, perform these steps:

  1. Verify that the current Cisco IOS Software version does not have the 16MB limitation by issuing  the show version command.

The Cisco IOS Software, or boot mode version, must be a minimum of 12.0(14)S, 12.1(6), 12.0(14)ST, 12.0(14)SC, 12.1(6)E, 12.1(5)DB, 12.1(5)DC, 12.1(5)T4, 12.1(6)EC, 12.1(6)E01, later versions of these trains, or any 12.2 or 12.3 version.

  • If the installed Cisco IOS Software version has the 16MB limitation, upgrade to a version that has the fix.

    The image of the new version's file size should be less than 16MB. If the router has bootflash, upgrade the bootflash image and perform the TFTP copy from boot mode.

  • Obtain a TFTP server program that does not have the 16MB limitation.

    If you already have a TFTP server program, check for an available patch or upgrade.

For more information and instructions on upgrading through FTP or Remote Copy Protocol (RCP), refer to Field Notice: Cisco IOS TFTP Client Cannot Transfer Files Larger than 16MB in Size.

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