Summary: Buffer space, TCP/IP window size

Date: Tue Nov 15 1994 - 09:38:33 CST


last week I asked about the limits for TCP window size on Sun systems:

_______________________________original request________________________________
I tried to enlarge my TCP buffers on SunOS4.1.x systems.
(see /usr/kvm/sys/netinet/in_proto.c:)
 * Default TCP buffer sizes (in bytes)
int tcp_sendspace = 1024*64;
int tcp_recvspace = 1024*64;

to a 64KB window. The modified kernel failed during startup of the portmapper
portmap cannot create socket: No buffer space available

My question are the following once: What are the limits for TCP Window size
on Suns (4.1.x and 5.x) and is it possible to enlarge buffers to 64KB.
________________________ end of original question_______________________________

I got a mail from Jim.Fiori@East.Sun.Com who answered all the questions I had:
( thanks to Jim.Fiori@East.Sun.Com ):

For SunOS 4.X, the actual limit is ~52K (a value enforced by the kernel in an
attempt to limit mbuf usage).

For SunOS 5.X, the limit is 64K.

My comments:

I tried 52K on a 4.1.3 system and it still failed, 48K were working fine.
I didn't check (yet) for SunOS 5.X

What was more important (at least for me) is the following addon:
An implementation of RFC 1323 (long,fat networks (LFN) is available
(at least for 4.1.3) as a consulting special (CONSULT-TCPLFN).
I can mail to anybody who is interested in a short description of this
consulting special (thanks again to Jim.Fiori@East.Sun.Com). It is a postscript
file, so I will not include it in this summary to avoid wasting bandwidth.

For your information (you might not have only suns, or connect exclusively to
a) DEC OSF/1 supports the Window Scale option of RFC 1323.
b) SGI running IRIX 5.0 or later has the RFC 1323 extensions.
c) Stock HP-UX 9.X TCP does not support RFC 1323.
   ( The RFC 1323 extensions are shipped with the 9.X EISA Fibre Channel
   software or you wait till the next major release is out :-)
d) Berkeley 4.4 should implement it too

Hope that helps,

Michael Fendt


Michael Fendt
ESO (European Southern Observatory)
Tel: +49 89 32006 441

This archive was generated by hypermail 2.1.2 : Fri Sep 28 2001 - 23:09:15 CDT