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TFTP Block size in ASA

I was just trying to see what the commands were to change the block size of TFTP in cisco ASA. 

3 Replies 3

Seb Rupik
VIP Advisor VIP Advisor
VIP Advisor

Hi there,

The command is not present on the ASA platform.


Any reason why you cannot use FTP or SCP? Both are significantly faster.





To change the TFTP block size on an ASA use "tftp blocksize 1000" or any value from 513-8192. I've seen the default of blocksize at 1468 give you that symptom of a file size of 0 when trying to copy a running config to a tftp server.

Matt G.


Cisco Employee
Cisco Employee

The command to change the block size of TFTP on a Cisco ASA is tftp-block-size. This command is used to specify the size of the blocks of data that are transferred during a TFTP session. By default, the block size is 512 bytes, but you can use the tftp-block-size command to specify a different block size if necessary.

To change the block size of TFTP on a Cisco ASA, use the following command:

tftp-block-size <bytes>

Where <bytes> is the desired block size in bytes. For example, to set the block size to 1024 bytes, you would use the following command:

tftp-block-size 1024

Note that this command must be entered in global configuration mode on the Cisco ASA. To enter global configuration mode, use the configure terminal command.

After changing the block size of TFTP on the Cisco ASA, you may need to restart the TFTP service in order for the changes to take effect. To restart the TFTP service, use the tftp restart command.

Additionally, the block size of the TFTP server on the remote device must be set to the same value as the block size on the Cisco ASA in order for the TFTP transfer to be successful.

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