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SubjectRe: NCSA telnet doesn't work any more, NCSA patch

On 27 Mar 1996 inr-linux-kernel@ms2.inr.ac.ru wrote:

> Jacek Zapala (jacek@deuter.im.pw.EDU.PL) wrote:

> : I have already posted this in linux-net, but got no single response. Now
> : I have some more data, so I'm posting this once more.

> NCSA telnet is broken, it cannot talk with Solaris2.x, OSF/1
> and with Linux > 1.3.3?. The cause is TCP Path MTU Discovery algorithm.
>
> These OSes send all the TCP segments with DF flag (Do not Fragment) set
> to automatically determine maximal MTU of the path.
>
> NCSA telnet incorrectly interpret the corresponding field
> in the IP packet and drops datagrams.
>
> I tried to report this bug to NCSA telnet maintainers, but
> I found that it seems to be not more supported.

here is the fix to NCSA telnet ENGINE/IP.C:

"diff -u" begins here ------------>
--- 2 Wed Mar 27 20:15:44 1996
+++ IP.C Wed Mar 27 20:20:42 1996
@@ -138,7 +138,7 @@
iplen-=hlen;

/* check for fragment and handle. note that the &0x20 above was WRONG */
- if(p->i.frags&0xffbf ) { /* NOW check for a fragmented packet - mtk add*/
+ if(p->i.frags&0xffdf ) { /* NOW check for a fragmented packet - mtk add*/
/* don't forget to ignore the "dont fragment" bit - RMG 931230 */
#ifdef AUX /* RMG */
fprintf(stdaux," Frags: %x ",p->i.frags);
<-------------- "diff -u" ended here
this is against 2.3.08.

OR if you worry about recompiling, just search the binary for 0xffbf and
change it to 0xffdf by hand. (statistically there are about 4 occurences
of 0xffbf, try and err :))

-- mingo

ps. this is the appropriate forum for posting this patch, since this will
cut down on Linus' incoming e-mail 8) [or is he already filtering out
"ncsa telnet" mails? :D ]



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