![]() ![]() the transfer would typically end after a few hundred data packets because of the timeouts. Without the "anticipation window" option enabled, the behavior was the same as with any other regular TFTP server, i.e. Larger "anticipation window" typically caused speed to decrease and the number of timeouts to increase. I have tried experimenting with different values of the "anticipation window" option but I was unable to find a value which would significantly improve the speed, i.e. However, the speed was rather low, only around 10 kB/s. I can confirm that the TP-Link Archer C2 device that has TFTP flashing issues when used with a regular TFTP server (serial number 2161374002651) was able to use Tftpd64 configured as described above to successfully download the firmware. I have tried using Tftpd64 with "anticipation window" of 1000 that was running in a Windows virtual machine. That being said, such a behavior is able to work-around the apparent issues with some TP-Link Archer C2 devices where their U-Boot bootloader is unable to successfully download the firmware update over TFTP. the support for clients specifying the desired TFTP window size. It resembles the newer RFC 7440 specification with the windowsize option but it only implements a part of it while omitting e.g. So, the behavior of Tftpd32/Tftpd64 with the "anticipation window" of at least 512 bytes does not follow the original TFTP specification. > 192.168.0.100.69: TFTP, length 27, RRQ "test.bin" octet timeout 1Īccording to the RFC 1350: THE TFTP PROTOCOL (REVISION 2), the data packets must be acknowledged by the client before the server can send more data packets:Įach data packet contains one block of data, and must be acknowledged by an acknowledgment packet before the next packet can be sent. It only specifies the timeout option, as captured by tcpdump:ġ92.168. The TFTP download procedure implemented within the U-Boot bootloader of the TP-Link Archer C2 devices does not specify the windowsize option when performing the TFTP Read Request. However, if I understand correctly, RFC 7440 specifies that a larger window size needs to be asked for by the client. Such a behavior of the TFTP server resembles the behavior introduced in RFC 7440: TFTP Windowsize Option. ![]() The code of Tftpd64 seems to confirm that the anticipation window's size is used to determine the number of extra data packets to send before waiting for their acknowledgement. So, in effect, instead of a typical operation where only one data packet is sent to a client and then the server waits for its acknowledgement, Tftpd32/Tftpd64 would send two data packets and then wait for the client's acknowledgements. Since the default size of the TFTP data packet is 512 bytes, when setting the anticipation window to 1000 bytes, it instructs Tftpd32/Tftpd64 to extend the number of 512 byte data packets that are sent to clients without waiting for their acknowledgement by 1 (1000 / 512 is ~1.95). Tftpd32 is able to send packets before receiving acknowledgements. I assume that it refers to the data packets within the anticipation window.Īlso, on the Tftpd64's Wiki, there is a Settings section which contains the following note next to the description of the "anticipation window" option: Tftpd32 will send data packets without waiting for acknowledgements On the Tftpd32's website, there is a FAQ section which contains the question "How do i tune the anticipation window ?". I have tried to look into why the TFTP servers that are typically available on Linux (namely tftp-hpa and atftp) would behave differently than Tftpd32 or Tftpd64 which is configured to use the "anticipation window" option. The device kept failing when TFTP'ing from a Linux box. # Transferring control to Linux (at address 80000000). Loading: Got ARP REPLY, set server/gtwy eth addr (74:d4:35:e7:5d:9e) ![]() *** Warning: no boot file name using 'test.bin' I have tried booting the initramfs OpenWrt image from memory address 0x81000000 on an Archer C2 device which does not experience the TFTP transfer issues (serial number 2161373008976) and I can confirm that it works: MT7620 # tftpboot 0x81000000
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