Trouble with ppp and serial_cs under kernel 2.6.13.5

Hi all,

the following problem exists with kernel 2.6.13.5, serial_cs and
my Merlin U630 UMTS modem. It is a PCMCIA serial device (supported by
serial_cs). The modem worked flawlessly under 2.6.8.
Connections using pppd (version 2.4.2) had no problems.

Now I upgraded to kernel 2.6.13.5. The card is recognized and pppd
connections come up. ping, traceroute, DNS lookups work but web sites
do not. This is a ifconfig output:

ppp0 Link encap:Point-to-Point Protocol
inet addr:10.227.145.228 P-t-P:10.64.64.64 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:500 Metric:1
RX packets:2508 errors:59 dropped:0 overruns:0 frame:0
TX packets:3606 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:3
RX bytes:557154 (544.0 KiB) TX bytes:301977 (294.8 KiB)

Note the high number of RX errors! The TCP connections now do only work
with kernel 2.6.13.5 if I decrease the MRU from 1500 to 500. This of course
triples the overhead and reduces speed. What could be the problem?

Thanks for your tips,
kind regards,
Jens.

P.S: pppd options:
noauth
defaultroute
/dev/ttyS1
460800
mru 500
persist
novj
usepeerdns
active-filter 'port 110 or port 80 or port 25 or port 53 or port 443 or
port 20 or port 21 or port 22 or port 113 or port 119 or port 123 or
port 220'

On Fri, 21 Apr 2006, in the Usenet newsgroup comp.os.linux.networking, in
article <(E-Mail Removed)>, Jens
Glaser wrote:

>the following problem exists with kernel 2.6.13.5, serial_cs and
>my Merlin U630 UMTS modem. It is a PCMCIA serial device (supported by
>serial_cs). The modem worked flawlessly under 2.6.8.
>Connections using pppd (version 2.4.2) had no problems.

I'll assume you have some reason to be using 2.6.13.5 rather than 2.6.14.4
that was released the same day.

>Now I upgraded to kernel 2.6.13.5. The card is recognized and pppd
>connections come up. ping, traceroute, DNS lookups work but web sites
>do not.

What does a tcpdump show?

>This is a ifconfig output:

OK

>Note the high number of RX errors!

59 out of 2508 is a concern. ppp-2.4.2? I think 'kdebug' is still a valid
option. Add 'kdebug 7' as an option, and then look at the system logs (which
will get huge with that option) and see what the error is. DO NOT POST THE
ENTIRE LOG!!! ONE LINE SHOULD TELL ENOUGH! pppd should specify what it
thinks is wrong with the frame.

>The TCP connections now do only work with kernel 2.6.13.5 if I decrease the
>MRU from 1500 to 500. This of course triples the overhead and reduces speed.
>What could be the problem?

Are you sure you have to go all the way down to 500?

>P.S: pppd options:

>460800

That is a valid speed, but what happens if you drop it down to 115200 (or
even 230400)?

>active-filter [snip]

Wow - don't see than many people using that option. Are you using the
idle timer (idle xxx) or demand mode?

Old guy

Hi,

> I'll assume you have some reason to be using 2.6.13.5 rather than 2.6.14.4
> that was released the same day.
>[..]

Thank you for the response and excuse me for not answering all the
questions but I now found the solution in an older post:

http://groups.google.com/group/linux...3574eb8b8b9ad6

For kernel 2.6.10-2.6.15 one has to set the 'low_latency' option for
the card's serial port (with setserial). Then everything works. 2.6.16
should not need this option.

Kind regards,
Jens.

Hi,

try the Sierra Wireless AirCard 775 (GPRS/EDGE) or 850 (GPRS/EDGE +
UMTS/HSDPA). They have a how-to to itegrate within Linux. We veryfied
kernel 2.4+2.6 and it works without any problems.

Cheers,
Markus