I am using Debian GNU Linux 3.0 and I don't have any serial card at my PC....but it detects an serial card ( I think ) "sl0" and set an IP for it...after disabling it...when I restart it detects the serial card ( sl0 ) again..and set an IP for it ....which IP I have set to my eth0 also....How can I disable it permanently.....

Thanks in Advance....

Just a guess. Is Linux detecting a modem?
Modems can be on any of the serial ports-/dev/ttyS* (*=0 through 3)
Can you post the lines from the "ifconfig" command that refer to this device?

I do have a modem..and it is external...zyxel modem...

But I don't think it is for modem...cause at another PC where I don't have any modem...there also I saw the configuration for sl0....

Is serial Line IP ( sl0 ) automatically installs with debian...

cause I install redhat again...but it was not detecting any serial card...

anyway my ifconfig command shows me.....

debian:/# ifconfig
eth0 Link encap:Ethernet HWaddr 00:00:21:14:51:7B
inet addr:192.168.0.2 Bcast:192.168.0.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:276 errors:0 dropped:0 overruns:0 frame:0
TX packets:1492 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
RX bytes:40627 (39.6 KiB) TX bytes:96994 (94.7 KiB)
Interrupt:11 Base address:0xec00

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:3924 Metric:1
RX packets:749 errors:0 dropped:0 overruns:0 frame:0
TX packets:749 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:58535 (57.1 KiB) TX bytes:58535 (57.1 KiB)

sl0 Link encap:Serial Line IP
inet addr:192.168.0.2 P-t-P:192.168.0.3 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:10
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)

Is the "sl0" device listed by "ifconfig" if you boot up with the power off on the modem?

Yes..Modem is always off.....

but sl0 is listed by ifconfig command....

That rules out the easy answers.
I am assuming there is nothing else plugged into a serial/com port. No other cards or external devices that could be causing this?
What version of Debian? The little I have worked with my 3.0 I always find COM1 refered to as /dev/ttyS0. It was only in a Google search that I saw COM1 refered to as sl0.
Does "ifdown /dev/sl0(or ttyS0)" shut it down?

when I give ifdown /dev/sl0 command......it shows......
ifdown: interface /dev/sl0 not configured

when I give ifdown /dev/ttys0 command.....it shows.....
ifdown: interface /dev/ttys0 not configured

I am using Debian GNU Linux 3.0

I think my modem is not creating the problem.....I assume that debian "by default" detects an SL ( Serial Line ) IP and sets an IP for it...which is set to eth0 also....

How can I disable it permanently.....to detects any serial card..and get any IP against the serial card....

I can give "ifconfig sl0 down" command......then it is disabled.....but after reboot.....it comes again...

I just want to disable the sl0 permanently.....

A Google search shows you're not the only one with this problem.
Here is "sl0 problem" with a reply (towards the end of the page) and one post without a reply.
I am not familar with "diald". If it is running on your system "man diald" should give you some info on it.