Messages in this thread | | | Date | Mon, 13 Dec 1999 19:14:15 +0000 | From | "Steinar H. Gunderson" <> | Subject | Finding the optimal packet size |
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Hi,
(If you send answers, please Cc me, as I'm nowhere near being able to handle the load of this list.)
I'm writing an FTP server program. Earlier versions have just sent out 1460-byte chunks (using send()) at a time, which worked perfectly well on my machine (Ethernet, 2.2.0 through 2.2.13, MTU: 1500). But then, I test it on another machine (Ethernet, 2.2.5, MTU: 1500), and that machine _fragments_ the packet into 1448 and 12 byte chunks!
Now, I'm setting IP_TOS to MAX_THROUGHPUT (or whatever that constant is called...), so I guessed the kernel would fix this for me. Not so...
Is there any portable way (both across Linux kernels, and possibly also to other Unices, such as Solaris) I could find the `right' MTU, and have the kernel send packets of _only_ that size? (I'd like to send only one packet at once, if that's possible.) If not, why does one machine differ from the other? (They're using the same glibc2 compilation, even.)
If anybody needs anything to test on, the FTP server (0.0.8pre5) can be downloaded from http://members.xoom.com/sneeze/betaftpd.html (but I doubt it will be useful, given the nature of the problem).
Thanks in advance for any help :-)
/* Steinar */ -- Homepage: http://members.xoom.com/sneeze/
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