Very Computer

by **Vincent Woudstr** » Sat, 26 Jan 2002 16:59:32

I hope somebody here can help me since I have tried several sollutions and
none worked so far.

At home I have a PIII 500 Mhz connected to an External modem (E-Tech Bullet
56K).

When I dialin to my ISP under Win98 and ping to my remote address I get
response like 99ms.
When I do the same under linux (Suse 7.1, kernel 2.4.1 but also others) I
get responses that vary a lot. Some pings return after 120ms but quite
regularly (about 40 %) of the pings are much slower. I've even seen pings
that took >15000ms to return. When I quit pinging after about 15 pings I get
an average of 400 - 500 ms which is way to slow.

There must be some configuration error because in my opinion I'm only
testing the ppp connection (pinging to remote address). There should not be
such a big difference between win98 and linux.

I also have an old PC installed with freeBSD 4.3 and I see the same slow
connection there. However I only investigated it further under linux.

Naturally I looked on the web for hints to help me solve this problem.
Here's what I've tried so far:

1) IRQ: Several web pages suggested I have a problem with conflicting
IRQ's. I checked the IRQ settings in Win98. There I'm using COM1, IRQ 4
which is normal. Under linux I use /dev/ttyS0 and IRQ 4 (checked with
setserial -a /dev/ttyS0). I also looked in /proc/interrupts and it did not
show any conflicting IRQ's.
I tried to set the IRQ to 5 but my modem would not respond to that. Is there
maybe a way to use /dev/ttyS1? I only have one external serial port.

2) AT initialisation string.: Next some web page suggested I should check
the initialisation string. I adjusted that so I have the same initialisation
string as under Win98. This didn't solve the problem.

3) Lowering the modem speed: Someone suggested I should lower the modem
speed. Somehow he had experienced a slow connection at 115200 and a faster
connection at 57600. So I adjusted the modem speed and the ttyS0 speed to
57600. This actually slowed things down further. I got 140ms returns and
still a lot of slower ping results.

4) mru/mtu: Another person suggested I should use an mru/mtu of 296. I tried
it but the pppd debug log showed that ppp negotiation adjusted it
automatically to 1524.

I'm not sure what to do next. Does anybody have any idea's?

I do hope so.

Cheers,
Vincent

by **R Smit** » Sat, 26 Jan 2002 18:49:32

> I hope somebody here can help me since I have tried several sollutions
> and none worked so far.

> At home I have a PIII 500 Mhz connected to an External modem (E-Tech
> Bullet 56K).

> When I dialin to my ISP under Win98 and ping to my remote address I get
> response like 99ms.
> When I do the same under linux (Suse 7.1, kernel 2.4.1 but also others)
> I get responses that vary a lot. Some pings return after 120ms but quite
> regularly (about 40 %) of the pings are much slower. I've even seen
> pings that took >15000ms to return. When I quit pinging after about 15
> pings I get an average of 400 - 500 ms which is way to slow.

Just a wild guess, but you can try...
# cat /proc/sys/net/ipv4/tcp_ecn
If it's 1 change to 0
# echo 0 > /proc/sys/net/ipv4/tcp_ecn
See /usr/src/linux/Documentation/filesystems/proc.txt

by **Vincent Woudstr** » Tue, 29 Jan 2002 16:36:31

Although I did get some useful suggestions (Thanks for that everyone) I
haven't solved the problem yet.

Here's an update about my exploration

- Someone suggested I might unmask harddisk IRQ's using "hdparm -u1 -k1
/dev/hda". It didn't help so I undid that change to the system again.

- Someone at work suggested I should look at ttysnoop to see what is going
on at the serial port. Unfortunatly, like so many things in linux, this
didn't work right away, and I didn't have time to look into it more. I will
look on the web for some tutorial.

- ifconfig after the pings doesn't show any errors. (see logs further)

- tcpdump doesn't show anything specific as far as I can see (although I
haven't used it before and might be missing something.

- It was suggested to change /proc/sys/net/ipv4/tcp_ecn to 0. However I
don't have this file. How can I create it?

Here are some log results:

First the output from a typical ping:

PING 213.116.1.15 (213.116.1.15): 56 data bytes
64 bytes from 213.116.1.15: icmp_seq=0 ttl=255 time=315.466 ms
64 bytes from 213.116.1.15: icmp_seq=1 ttl=255 time=1010.011 ms
64 bytes from 213.116.1.15: icmp_seq=2 ttl=255 time=139.483 ms
64 bytes from 213.116.1.15: icmp_seq=3 ttl=255 time=720.005 ms
64 bytes from 213.116.1.15: icmp_seq=4 ttl=255 time=139.962 ms
64 bytes from 213.116.1.15: icmp_seq=5 ttl=255 time=149.986 ms
64 bytes from 213.116.1.15: icmp_seq=6 ttl=255 time=649.999 ms
64 bytes from 213.116.1.15: icmp_seq=7 ttl=255 time=119.975 ms
64 bytes from 213.116.1.15: icmp_seq=8 ttl=255 time=119.993 ms
64 bytes from 213.116.1.15: icmp_seq=9 ttl=255 time=169.987 ms
64 bytes from 213.116.1.15: icmp_seq=10 ttl=255 time=129.985 ms
64 bytes from 213.116.1.15: icmp_seq=11 ttl=255 time=129.984 ms
64 bytes from 213.116.1.15: icmp_seq=12 ttl=255 time=749.992 ms
64 bytes from 213.116.1.15: icmp_seq=13 ttl=255 time=129.973 ms
64 bytes from 213.116.1.15: icmp_seq=14 ttl=255 time=2540.010 ms
64 bytes from 213.116.1.15: icmp_seq=15 ttl=255 time=2259.981 ms
64 bytes from 213.116.1.15: icmp_seq=16 ttl=255 time=1270.007 ms
64 bytes from 213.116.1.15: icmp_seq=17 ttl=255 time=279.967 ms
64 bytes from 213.116.1.15: icmp_seq=18 ttl=255 time=129.986 ms
64 bytes from 213.116.1.15: icmp_seq=19 ttl=255 time=129.961 ms
64 bytes from 213.116.1.15: icmp_seq=20 ttl=255 time=1880.016 ms
64 bytes from 213.116.1.15: icmp_seq=21 ttl=255 time=889.993 ms
64 bytes from 213.116.1.15: icmp_seq=22 ttl=255 time=129.985 ms
64 bytes from 213.116.1.15: icmp_seq=23 ttl=255 time=119.992 ms
64 bytes from 213.116.1.15: icmp_seq=24 ttl=255 time=119.971 ms
64 bytes from 213.116.1.15: icmp_seq=25 ttl=255 time=119.988 ms
64 bytes from 213.116.1.15: icmp_seq=26 ttl=255 time=1840.021 ms
64 bytes from 213.116.1.15: icmp_seq=27 ttl=255 time=840.106 ms
64 bytes from 213.116.1.15: icmp_seq=28 ttl=255 time=760.000 ms
64 bytes from 213.116.1.15: icmp_seq=29 ttl=255 time=119.967 ms
64 bytes from 213.116.1.15: icmp_seq=30 ttl=255 time=679.994 ms
64 bytes from 213.116.1.15: icmp_seq=31 ttl=255 time=119.990 ms
64 bytes from 213.116.1.15: icmp_seq=32 ttl=255 time=119.962 ms
64 bytes from 213.116.1.15: icmp_seq=33 ttl=255 time=129.984 ms
--- 213.116.1.15 ping statistics ---
34 packets transmitted, 34 packets received, 0% packet loss
round-trip min/avg/max = 119.962/563.373/2540.010 ms

This same ping I logged with tcpdump -i ppp0:

11:44:33.053493 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:33.055098 1Cust16.tnt15.rtm1.nl.uu.net.1029 >
CACHE12.NS.NL.uu.net.domain: 3136+ PTR? 15.1.116.213.in-addr.arpa. (43) (DF)
11:44:33.368777 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:33.408767 CACHE12.NS.NL.uu.net.domain >
1Cust16.tnt15.rtm1.nl.uu.net.1029: 3136 1/4/4 PTR tnt15.rtm1.nl.uu.net.
(240) (DF)
11:44:33.409264 1Cust16.tnt15.rtm1.nl.uu.net.1029 >
CACHE12.NS.NL.uu.net.domain: 3137+ PTR? 16.124.116.213.in-addr.arpa. (45)
(DF)
11:44:33.578771 CACHE12.NS.NL.uu.net.domain >
1Cust16.tnt15.rtm1.nl.uu.net.1029: 3137* 1/4/4 PTR
1Cust16.tnt15.rtm1.nl.uu.net. (250) (DF)
11:44:33.579173 1Cust16.tnt15.rtm1.nl.uu.net.1029 >
CACHE12.NS.NL.uu.net.domain: 3138+ PTR? 39.251.79.193.in-addr.arpa. (44)
(DF)
11:44:34.048832 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:35.048774 CACHE12.NS.NL.uu.net.domain >
1Cust16.tnt15.rtm1.nl.uu.net.1029: 3138 1/2/2 PTR CACHE12.NS.NL.uu.net.
(151) (DF)
11:44:35.049345 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:35.058765 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:35.188771 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:36.048843 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:36.768775 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:37.048865 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:37.188766 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:38.048845 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:38.198772 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:39.048846 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:39.698775 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:40.048854 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:40.168772 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:41.048842 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:41.168772 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:42.048858 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:42.218765 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:43.048831 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:43.178763 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:44.048831 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:44.178762 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:45.048831 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:45.798763 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:46.048851 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:46.178762 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:47.048930 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:48.048850 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:49.048838 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:49.588776 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:50.048846 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:50.308765 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:50.318764 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:50.328764 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:51.048850 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:51.178774 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:52.048868 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:52.178764 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:53.048841 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:54.048849 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:54.928780 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:54.938766 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:55.048829 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:55.178762 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:56.048842 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:56.168772 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:57.048853 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:57.168763 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:58.048836 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:44:58.168765 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:44:59.048837 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:45:00.048833 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:45:00.888769 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:45:00.888778 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:45:01.048837 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:45:01.808767 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:45:02.048846 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:45:02.168762 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:45:03.048838 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:45:03.728766 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:45:04.048828 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:45:04.168769 tnt15.rtm1.nl.uu.net > 1Cust16.tnt15.rtm1.nl.uu.net: icmp:
echo reply
11:45:05.048876 1Cust16.tnt15.rtm1.nl.uu.net > tnt15.rtm1.nl.uu.net: icmp:
echo request (DF)
11:45:05.168766 tnt15.rtm1.nl.uu.net > ...

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Very Computer

Slow ppp connection over 56K external modem

Slow ppp connection over 56K external modem

Slow ppp connection over 56K external modem

Slow ppp connection over 56K external modem