文章目錄

• • 文件大小問題
  • PXE 啟動使用

文件大小問題

有些老版本的tftp server程序，會有文件大小的限制，比如超過93M，文件傳輸就會出現(xiàn)問題。和協(xié)議格式，以及PXE 客戶端的實現(xiàn)決定了文件的大小，對于老版本
The original protocol has a transfer file size limit of 512 bytes/block x 65535 blocks = 32 MB. In 1998 this limit was extended to 65535 bytes/block x 65535 blocks = 4 GB by TFTP Blocksize Option RFC 2348. If the defined blocksize produces an IP packet size that exceeds the minimum MTU at any point of the network path, IP fragmentation and reassembly will occur not only adding more overhead[8] but also leading to total transfer failure when the minimalist IP stack implementation in a host’s BOOTP or PXE ROM does not (or fails to properly) implement IP fragmentation and reassembly.[9] If TFTP packets should be kept within the standard Ethernet MTU (1500), the blocksize value is calculated as 1500 minus headers of TFTP (4 bytes), UDP (8 bytes) and IP (20 bytes) = 1468 bytes/block, this gives a limit of 1468 bytes/block x 65535 blocks = 92 MB. Today most servers and clients support block number roll-over (block counter going back to 0 or 1[10] after 65535) which gives an essentially unlimited transfer file size.

PXE 啟動使用

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