View source for IPXE 网络启动中关于tftp的解释

iPXE 网络启动中经常发现tftp error code 8<blockquote>Apr  3 17:14:29 localhost kernel: txgbe 0000:02:00.0 enp2s0f0: NIC Link is Down

Apr  3 17:14:29 localhost kernel: txgbe 0000:02:00.0 enp2s0f0: NIC Link is Up 10 Gbps, Flow Control: RX/TX

Apr  3 17:14:30 localhost dhcpd: Solicit message from fe80::b2d5:9dff:fe5a:1f47 port 546, transaction ID 0x47252A00

Apr  3 17:14:30 localhost dhcpd: Sending Advertise to fe80::b2d5:9dff:fe5a:1f47 port 546

Apr  3 17:14:30 localhost dhcpd: Request message from fe80::b2d5:9dff:fe5a:1f47 port 546, transaction ID 0x47252B00

Apr  3 17:14:30 localhost dhcpd: Sending Reply to fe80::b2d5:9dff:fe5a:1f47 port 546

Apr  3 17:14:30 localhost in.tftpd[2599]: Error code 8: User aborted the transfer

Apr  3 17:14:30 localhost in.tftpd[2600]: Client 3ffe:501:ffff:100::40 finished ipxe.efi

Apr  3 17:14:30 localhost dhcpd: Release message from fe80::b2d5:9dff:fe5a:1f47 port 546, transaction ID 0x47252C00

Apr  3 17:14:30 localhost dhcpd: Client 00:01:00:01:22:51:d0:d0:30:09:f9:20:2c:f0 releases address 3ffe:501:ffff:100::40

Apr  3 17:14:30 localhost dhcpd: Sending Reply to fe80::b2d5:9dff:fe5a:1f47 port 546</blockquote>[rfc:2347 RFC2347]中关于tftp过程有详细解释. 

客户端可以带多个tftp option对 [opt1,value1]...[optN,vauleN] 且option的顺序不重要. 

服务端收到并能正确识别option时, 回应OACK(Option Acknowledgment)包. 服务端OACK包只包含客户端请求的option字段, 不能包含未请求的option字段。

也就是说, 只能由客户端发起option初始化协商. 

如果option被服务端识别但是invalid, 服务端的OACK中会携带一个正确的值. 客户端必须使用服务端OACK中的值, 并且不能使用未被服务端识别的option字段.


下面的例子中

客户端发起read request(opc=1), 请求filename是ipxe.efi, mode是octet. 同时携带两个option: tsize=0, blksize=1228

transfer size 客户端只知道filename并不知file size

服务端OACK(opc=6)时携带option: tsize=966176,blksize=1228

客户端发起第二次read request, 只携带一个option: blksize=1228

[[File:Tftp-flow.jpg|alt=tftp-flow]]

tsize = 966176 bytes

blksize = 1228 bytes

需要 966176/1228 = 787 (向上取整).

[[File:Tftp-flow-2.jpg|alt=tftp-flow-2]]