Get an IP, but still can't communicate with network...

bthornton · 03-01-2005, 08:50 PM

This is on my Fedora Core 3 laptop.

Up until some recent and unknown change on my laptop last week, I was able to use my T-Mobile wireless account in Linux to connect to the Internet. Then, "out of nowhere", it stopped working (I could get an IP, but I couldn't even get to the T-mobile login page). I figured that this was a T-mobile problem until today when I tried using the hardwired ethernet connection in my public library with the intention of hooking up there (it's just a simple unsecured DHCP ethernet line)... I got the exact same results there.

In both cases, I was previously able to connect without any problems (they're both DHCP, so it's pretty much plug-and-play). I have checked my syslog and DHCP reports that I do indeed get an IP at both the library and for T-Mobile Hotspots. Also, my /etc/resolv.conf gets updated appropriately with the nameservers of the respective networks. So, whether it's the wireless T-mobile account or the plain-Jane ethernet connection, there is communication happening. I can even ping my own IP. However, I cannot ping even the nameservers.

I wish I could tell you more details, but I didn't intentionally change any network settings before it stopped working out of nowhere. My only guess is that, since I frequently do RPM system updates with Synaptic, a package must have been updated which is causing this (but I'm not sure which since I don't explicitly specify).

Here's some more weirdness to add to the problem: This same laptop works on the same networks when booted into Windows. Moreover, this laptop also has no problems hooking on to my wireless network at home (which is configured via DHCP).

I'm sensing/guessing that this *might* be a routing issue, but I'm not for sure. Can anyone please tell me what to look at given the conditions I've listed?

Thanks a lot!

fancypiper · 03-01-2005, 09:00 PM

Please post the result of the command:

traceroute yahoo.com

bthornton · 03-01-2005, 09:05 PM

I'll try that out tomorrow when I'm on one of the networks (I'm at home now).

However, my guess is that the command will drop out before it's even able to resolve 'yahoo.com' to an IP (remember that I can't even ping the nameservers listed in /etc/resolv.conf ).

fancypiper · 03-01-2005, 09:16 PM

Sometimes you can get a better connection by taking down and bringing up the ehternet card.

ifdown eth0
ifup eth0

traceroute should tell you where the communication stops in the routing.

In Windows, try in the command line (IIRC, I'm a little hazy in Windows):

tracert yahoo.com

Matir · 03-01-2005, 09:17 PM

Please also post the output of the "route" command (the kernel routing table).

bthornton · 03-01-2005, 09:18 PM

Ya, I've tried the "ifup/ifdown" dance many many times to no avail.

However, if you give me a few, I can paste up both my Windows routing table and my Linux routing table after getting hooked up to the T-Mobile network. I don't know if I'm comparing apples and oranges, but they look radically different.

bthornton · 03-01-2005, 09:31 PM

output of 'route' in Linux on a fresh boot (i.e. before any network interfaces are brought up):

Code:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
169.254.0.0     *               255.255.0.0     U     0      0        0 lo

output of 'route' in Linux after the ath0 (wireless) interface is brought up at a T-Mobile hotspot

Code:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.254.107.224  *               255.255.255.224 U     0      0        0 ath0
169.254.0.0     *               255.255.0.0     U     0      0        0 ath0
default         10.254.107.225  0.0.0.0         UG    0      0        0 ath0

...and... output of the 'route print' command in Windows after being successfully connected at a T-Mobile hotspot

Code:

===========================================================================

Interface List

0x1 ........................... MS TCP Loopback interface

0x30002 ...00 09 5b c1 fc 00 ...... NETGEAR 108 Mbps Wireless PC Card WG511T - P

acket Scheduler Miniport

===========================================================================

===========================================================================

Active Routes:

Network Destination        Netmask          Gateway       Interface  Metric

          0.0.0.0          0.0.0.0   10.254.107.225  10.254.107.245       30

   10.254.107.224  255.255.255.224   10.254.107.245  10.254.107.245       30

   10.254.107.245  255.255.255.255        127.0.0.1       127.0.0.1       30

   10.255.255.255  255.255.255.255   10.254.107.245  10.254.107.245       30

        127.0.0.0        255.0.0.0        127.0.0.1       127.0.0.1       1

        224.0.0.0        240.0.0.0   10.254.107.245  10.254.107.245       30

  255.255.255.255  255.255.255.255   10.254.107.245  10.254.107.245       1

Default Gateway:    10.254.107.225

===========================================================================

Persistent Routes:

  None

bthornton · 03-02-2005, 10:13 AM

What do you guys think?

Oddly enough, I just now realized that the strange and abritrary "169.254.0.0" network (I assume this has to do with IPv6) used to be associated with the loopback interface (lo); then, when I plug into the network, this changes over to the network interface (ath0, in this case).

Duudson · 03-02-2005, 02:48 PM

Quote:

Originally posted by bthornton
What do you guys think?

Oddly enough, I just now realized that the strange and abritrary "169.254.0.0" network (I assume this has to do with IPv6) used to be associated with the loopback interface (lo); then, when I plug into the network, this changes over to the network interface (ath0, in this case).

That's "zeroconf" route, and it's not the problem here. You can disable it by adding a line to /etc/sysconfig/network:
NOZEROCONF=yes

Can you ping the default gateway?

bthornton · 03-02-2005, 09:54 PM

I haven't tried pinging the gateway, but my guess is that I won't have too much luck. Even if I could, I don't know what it would tell me.

I did try the traceroute command and it just timed out.

For the record, I went over to my library and hooked into the network again but this time booted up with a Knoppix CD. Not too surprisingly, it hooked right up (got an IP via DHCP); I didn't even have to do anything and I was on the 'net.

Darin · 03-03-2005, 05:12 AM

How far out can you get? These pings verify connectivity in various stages from your computer out to The Internet. If you can't get one to work, you likely will not be able to go any farther down the list. Where does it stop working?:

ping 127.0.0.1
#use ifconfig to see if you have an IP address and what it is
ping {your IP address}
# you either assigned this or it shows up when you type /sbin/route -e
ping {default gateway}
# you either assigned this as the DNS server or it shows up when you type cat /etc/resolv.conf
ping {nameserver}
ping 64.179.4.149
ping www.linuxquestions.org

fancypiper · 03-03-2005, 08:15 AM

What does your /etc/hosts file look like?

Here is mine for an example:

Code:

# Duron tinwhistle /etc/hosts file
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1       tinwhistle      localhost       localhost.localdomain
192.168.0.2     bones
192.168.0.3     tinwhistle
192.168.0.4     uilleann

bthornton · 03-03-2005, 12:23 PM

1. I can ping localhost/127.0.0.1
2. I can ping my own assigned DHCP address
3. I get no response when pinging the default gateway (as listed in the route command)
4. I get no response when pinging the DHCP-assigned nameservers (as listed in /etc/resolv.conf)
5. My /etc/hosts file is in good shape (looks like the one posted)

I'm still thinking this is a routing issue. When I issue the route command, there is about a 15-second delay when trying to put up the last line (the one beginning with "default"). My guess is that there should not be a delay there, and that is indicative of a routing problem.

I've even tried disabling iptables, just to get that out of the mix (it was never a problem before, but just to reduce potential variables); it had no effect.

Here is a list of the files which I have checked and believe to be relevent:
1. /etc/sysconfig/networking-scripts/ifcfg-ath0
2. /etc/resolv.conf
3. /etc/hosts
4. /etc/modules.conf (to make sure that the correct interface is being referenced--which it is)

All of the above "look good". Are there any other relevent configuration files which I left out?

Thanks again for the help guys; this one really has me stumped. I'm even thinking about (*gasp*) reinstalling Linux... (I've been using Linux since RedHat 5.1 and never had to do that before

).

Duudson · 03-03-2005, 02:56 PM

Quote:

Originally posted by bthornton

I'm still thinking this is a routing issue. When I issue the route command, there is about a 15-second delay when trying to put up the last line (the one beginning with "default"). My guess is that there should not be a delay there, and that is indicative of a routing problem.

That's because route is trying to solve name for your default gateway. route -n should be fast.

Unfortunately I don't have any ideas of the actual problem.

bthornton · 03-03-2005, 08:33 PM

Okay, I've got half of this problem isolated now... I'm actually writing this on my laptop (booted in FC3) from my school library--this is the hardwired connection. I checked out my 'ifcfg-eth0' file and, while it was set to be DHCP, there were still reminants of hard-coded/static gateways in the file (remnants of what I was using at home before I switched over to DHCP completely).

So, now we're just at the issue of the wireless connection. On that note, I did just notice the following message output to the console whenever I run "system-config-network"

Code:

Warning : Device ath0 has been compiled with version 17
of Wireless Extension, while we are using version 16.
Some things may be broken...

Suppose this might have something to do with the wireless driver itself? I'm using the Atheros driver as provided by MadWIFI (I think that's how those things are related).