Linux - Networking This forum is for any issue related to networks or networking.
Routing, network cards, OSI, etc. Anything is fair game. |
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06-18-2003, 11:53 AM
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#1
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Member
Registered: Feb 2002
Posts: 51
Rep:
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networking connection loss
I am running RH9 and set httpd and vsftpd on it. Network connection is T1, DHCP on campus network. All of a sudden it lost connection to the network, cannot ping it from outside, and it cannot ping outside either, even the gateway.
Local login is ok, nothing looks different, only lost network connection.
After restart, eth0 back to work. But just a little while, it lost again. I had this problem a couple of months ago (using RH8), and it's just gone by itself, didn't figure out the reason. Now it happens again.
How can I diagnose it? Thx!
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06-18-2003, 06:16 PM
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#2
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Moderator
Registered: Feb 2002
Location: Grenoble
Distribution: Debian
Posts: 9,696
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Maybe run tcpdump in background (with results to file) - you will be able to see if there's something starange.
Plus, when the connection is down, shut the interface down. Then configure it again. Look if it helps.
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06-20-2003, 08:57 AM
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#3
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Member
Registered: Feb 2002
Posts: 51
Original Poster
Rep:
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Thx, Mara, can you give me a little bit more details how i can do it?
I'm a linux newbie, Thx again
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06-20-2003, 09:26 AM
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#4
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Member
Registered: Jun 2003
Location: Europe / Germany / Saarland / Neunkirchen
Distribution: Debian (SID), Gentoo
Posts: 131
Rep:
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Hi,
sounds like a dhcp problem ?
- What about the leasetime of the IP-Adress ?
- checked /var/log/syslog | /var/log/messages for errors ?
- which network card are you using (perhaps this problem is already known by ppl that are using this card too ?)
- is the interface also unavailable if you use a static ip configuration ?
- try to goole  (helps most of the time)
have a nice day
cu
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06-20-2003, 04:32 PM
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#5
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Moderator
Registered: Feb 2002
Location: Grenoble
Distribution: Debian
Posts: 9,696
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dragon, follow stony's advice.
How to use tcpdump? As root run
tcpdump -i eth0 >filename
Note that the file will grow very fast... Tcpdump is a program that shows you all the packets, so you can see which packet was last (before the interface went down).
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06-22-2003, 05:01 PM
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#6
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Member
Registered: Feb 2002
Posts: 51
Original Poster
Rep:
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thx, guys
in my dmesg output, there are lots of messages like the following:
IN=eth0 OUT= MAC=ff:ff:ff:ff:ff:ff:xx:xx:xx:xx:xx:xx:xx:xx SRC=xxx.xxx.xxx.16 DST=xxx.xxx.xxx.255 LEN=78 TOS=0x00 PREC=0x00 TTL=128 ID=20038 PROTO=UDP SPT=137 DPT=137 LEN=58
they are from the same subnet as my computer. is it normal? are these just DHCP requests?
I couldn't find any error message cause the loss of connection. is it possible I set something wrong that mess up with the DHCP server?
Thx
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06-23-2003, 07:31 AM
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#7
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Senior Member
Registered: Apr 2003
Location: Eire
Distribution: Slackware 12.0, OpenSuse 10.3
Posts: 1,120
Rep:
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No expert in it but at a guess (wild even) that looks like it could be broadcast attempts windows machines trying to find/register with the master browser or something along those lines. Just my guess.
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06-23-2003, 03:21 PM
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#8
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Member
Registered: Feb 2002
Posts: 51
Original Poster
Rep:
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is it DHCP request or something like that? i am using DHCP on a campus lan.
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06-23-2003, 04:24 PM
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#9
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Senior Member
Registered: Apr 2003
Location: Eire
Distribution: Slackware 12.0, OpenSuse 10.3
Posts: 1,120
Rep:
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Going by the port numbers - no.
137 (( 139) used by samba/MS file sharing/netbios stuff usually. I'd be lieing though if I said I knew exactly what it is but I don't think it's related to your conneciton loss.
If you're sure you haven't changed anything at all like hosts.allow/deny firewall or whatever, could it be an actual problem with your campus network that your tech people their might know about/sort out?
The fact you had it before and it sorted itself out sort of points in that direction.
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06-25-2003, 09:48 AM
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#10
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Member
Registered: Feb 2002
Posts: 51
Original Poster
Rep:
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thx
still don't know what caused the problem. Maybe just DHCP problem.
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