Is it possible to write a simple TFTP server as an iRule to return static content? I see some examples for load balancing TFTP requests, but not for actually acting as a TFTP server. I have a very small and static TFTP file that I need to distribute, and rather than running a dedicated TFTP server it would be far better if it could be deployed as an iRule. Is this possible? Any resources I should be looking at?

Interesting question. I'm looking at a simple TFTP server written in Tcl (http://wiki.tcl.tk/12711) and trying to discern whether or not this is doable. There is also an iRule posted to the codeshare repository that helps do LB for tftp servers (http://devcentral.f5.com/wiki/default.aspx/iRules/TFTP_Load_Balancing.html). It's probably possible to do this, though I'm wondering how the encoding of the file in chunks can be done most efficiently. There's an example of a simple UDP server implemented in an iRule here: http://devcentral.f5.com/wiki/default.aspx/iRules/fast_DNS.html ...that returns an immediate answer from the LTM to certain DNS queries.

I don't think the protocol handling would be that difficult, the problem is how to handle serving up the file, that command is disabled in iRules. Here's a start, maybe someone else has some ideas? when CLIENT_ACCEPTED { log local0. "Client connected from [IP::client_addr]" binary scan [UDP::payload] xc opcode log local0. "Opcode is $opcode" if { $opcode == 1 } { binary scan [UDP::payload] xxa* string log local0. "String is $string" set stringlist [split $string \000] set file [lindex $stringlist 0] set mode [lindex $stringlist 1] log local0. "File is $file, Mode is $mode" if { $mode != "octet" && $mode != "netascii" } { reject } else { log local0. "Send the file!" write goes here } } else { reject } }

BTW, the code above is hacked from the example jquinby mentioned on the TCL wiki. Obviously don't need a few of those variables, just there for development.

The logic is working from a pumpkin tftp client in netascii mode: Mar 12 06:30:25 tmm tmm[1893]: Rule tftp_server : Client connected from 10.10.10.10 Mar 12 06:30:25 tmm tmm[1893]: Rule tftp_server : Opcode is 1 Mar 12 06:30:25 tmm tmm[1893]: Rule tftp_server : String is test.txtÀnetasciiÀtsizeÀ0ÀblksizeÀ2048ÀtimeoutÀ30À Mar 12 06:30:25 tmm tmm[1893]: Rule tftp_server : File is test.txt, Mode is netascii Mar 12 06:30:25 tmm tmm[1893]: Rule tftp_server : Send the file!

I think dropping the file into some sort of class (along the lines of the http-server-in-an-irule) is a possibility, but the TFTP protocol specifies 512 byte chunks sent to the client after each previous one is ACK'ed. 1. client sends RRQ (opcode 1) with filename 2. Server sends block 1, client rx's and ACKs block 1. 3. Server sends block 2, client acks block 2, and so on. 4. As soon as the client gets a block thats <512 bytes, it knows that this is the final block. We can also do away with the necessity of handling write-requests (WRQ, opcode 2), since this is read-only. Respond to them with opcode 5 ("error", along with an error number and some useful ascii text).

TFTP Server? | DevCentral

25 Replies

JRahm
Admin
Mar 19, 2009
Yeah, I read the RFC the same way, the server really should ack each segment before sending the next block. I'll work on completing the implementation for future use cases, but it will be a little while.
James_Quinby_46
Historic F5 Account
Mar 19, 2009
Now if you guys can just figure out a way to serve the LTM ISO from a datagroup, you could build an "Enterprise Manager in an iRule" rule! :D

Hmmm....
Matthew_Gamble_
Nimbostratus
Mar 23, 2009
What format are you putting the file on disk in? I've tried text, binary, and hex, but I keep getting this error:

Mar 23 15:24:54 tmm tmm[13663]: Rule Test-TFTP_Server : Opcode is 1

Mar 23 15:24:54 tmm tmm[13663]: Rule Test-TFTP_Server : String is test.txtÀnetasciiÀ

Mar 23 15:24:54 tmm tmm[13663]: Rule Test-TFTP_Server : File is test.txt, Mode is netascii

Mar 23 15:24:54 tmm tmm[13663]: Rule Test-TFTP_Server : Block is integer, no increment necessary

Mar 23 15:24:54 tmm tmm[13663]: 01220001:3: TCL error: Rule Test-TFTP_Server - expected hexadecimal string but got "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

I followed the directions in http://devcentral.f5.com/wiki/default.aspx/iRules/LTMMaintenancePage.html and it's all on a single line. I'm sure I'm doing something pretty stupid, but if anyone could point me in the right direction it would be greatly appreciated.

Thanks!
James_Quinby_46
Historic F5 Account
Mar 23, 2009
mgamble -

See here:

http://devcentral.f5.com/Default.aspx?tabid=63&articleType=ArticleView&articleId=343

...for a more complete writeup on the iRule, including a link that will do the hex encoding of the file.
HR_38560
Nimbostratus
Sep 04, 2014
Hi there, nice solution.

I'm trying to change this irule to make use of ifiles instead of hex/string converted files/arrays. Anyone manage to do this already, i'm kind of stuck on the part where i divide the binary (ifile) into 512 byte chunks....