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Can't ping residential router

Posted on 2004-08-18
Medium Priority
Last Modified: 2010-03-18
I'm running a very limited (no GUI) install of RH 9 on an Intel box.  This is cabled to a hub and from there to a residential router with ADSL Internet.

From the Linux box I can ping other computers on the hub and on the router.  However, I cannot ping the router!

All other computers can ping each other and the router but not the Linux box.

During the Linux install I was prompted for network info and entered an assigned IP, the router ( as the gateway and external DNS server names.

Any suggestion on what could be wrong and how do I get back to the network set-up page.

Question by:John4343
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LVL 15

Expert Comment

ID: 11832998
Hi John4343,

Can I just clarify, the following?

Your Linux box can ping other PCs on the network - but not the router
Other PCs on the network can ping each other, AND the router
Other PCs on the network can't ping your Linux box?

There's a possibility that this is a subnet issue, or it could be a firewalling (ipchains) problem.

Can you please post the output from the "ipconfig" command?
Can you also please post the IP and subnet mask of another PC on the network?

This'll help eliminate the subnet problem from our enquiries.

Is this just a basic install of RH?  Did you choose to include any firewalling or routing elements?

If you can tell me the answers to the above, I'll be in a better position to point you in the right direction.

Author Comment

ID: 11834169
After doing a power-up today the linux box can no longer ping anything (..unreachable).  All other network computers (Windows) can ping each other and the router.  The network card led is on as is the hub for the linux cable.

The Linux box ifconfig replies:

inet addr:

The other network computers provide:

IP Address (or whatever in last number)

As part of the Linux setup I ran ntsysv and left activated; atd, crond, iptables, keytable, kudzu, network, random, rawdevices, sshd, syslog,and xinetd.  Then ran init 2 ; init 3

telnet irlp.net 1000 of course returns a lookup table error

I also turned on ports 2074 to 2093, 15425 to 15427 and 22 in the router to direct certain traffic to the linux box at

LVL 15

Expert Comment

ID: 11834322
The IP details look OK.
It's strange that you're not able to ping anything now.
Can the linux box ping itself?

If you do "netstat -rn" it will show your routing table, it would be interesting to see that - although I don't imagine there being anything unusual there.

Ah!  Just noticed that you've got iptables running.

iptables is a firewalling element of the kernel, and could easily explain the problems you're encountering.

You can find out more about iptables at http://www.siliconvalleyccie.com/linux-hn/iptables-intro.htm

I suggest that you run "/etc/init.d/iptables status" to see the status of this, and what filtering (if any) it's doing.
Can you please post the results of this here?
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Author Comment

ID: 11835667
Ok, some progress...

iptables status did nothing so went to the site you provided above and ran:

touch /etc/sysconfig/iptables
chmod 200 /etc/sysconfig/iptables
chkconfig iptables on

After restarting iptables status responds:

table: filter
chain INPUT (Policy ACCEPT)
target prot opt source
chain FORWARD (Policy ACCEPT)
target prot opt source
chain OUTPUT (Policy ACCEPT)
target prot opt source

netstat -rn responds:

Dest              Gateway    Genmask         Flags   Msg  Window  irtt   IFace  U        0       0           0     eth0      U        0       0           0     eth0          U        0       0           0     lo          UG      0       0           0     eth0

At that point the Linux box could ping all computers connected to its hub.  This is wired to the router and the router, and any computers connected to it, cannot be pinged. Others computers on the hub however can ping the router and its connected computers.

I then temporarily connected the Linux box to the router and it works.  I can even access sites on the internet!

So, having got iptables running it seems the issue is connecting to the router through the hub.  Not a problem with Windows but apparently so with Linux.  I can live with this but my wife says she does not like the cable running down stairs to the basement!  Seriously, I can configure another cable but it would be nice to go through the hub.

Thanks for all the help.

LVL 15

Expert Comment

ID: 11835971
Curiouser and curiouser!

The iptables status stuff that you've posted looks absolutely fine.  Essentially, it's not filtering anything.
The routing tables (netstat -rn) look OK, but I'm intrigued by the route.  Do you have multiple addresses on your ethernet card (eth0), or did you configure this route manually for some reason?

I got a little confused about what you were saying with regards to the pings and where everything was cabled.  Can I please clarify:

Linux, PCs, Router -  plugged into same hub
Linux box can ping PCs but not router
PCs can ping each other, router and Linux box

Linux box plugged into Router (presumably with crossover cable?)
Linux box can ping router

Does that summary sound right?  There's something distinctly odd happening if it is the case.

Can you please post the following?
The make & model of the hub and router
The number & OSs of the other PCs


Author Comment

ID: 11836304
Here is the setup:

Our infamous Linux box, two Windows 2000 servers (one is primary domain controller) and a win XP Home edition are all connected to a Linksys W5Hub 5 port hub.

Hub is attached to a D-Link DL-704P router which has an ADSL modem.  Win98, Win2000 and Win XP Pro machines are connected to this router.

Basically everything can see everything (the exception is the XP home pc on the hub that can browse the web but does not join the domain) but everything can ping everything including the router.

The Linux box can ping things on the hub but does not see the router or anything connected to it!

I was also surprised by the route and have no idea where this came from.  The RH install cd is a stripped down version someone created so maybe it came from there?
LVL 15

Expert Comment

ID: 11839181
I'm afraid I'm running out of ideas here, but I've just had some inspiration about the odd route.

MS machines will default to a "169" address if they're configured for DHCP and can't pick up an address.
Now why you'd have a route set up for that I don't understand, but it's worth a little further investigation.

Sorry, I know I keep sending you back to find out a little more information, but can you please supply the IP address(es) and MAC address(es) of each device on the network?
It would also be useful to see the routing tables from the Windows PCs

You can get the IPs and MACs from the Windows machines with "ipconfig /all" and the Linux box with "ifconfig eth0"
You can get the routing tables from the Windows machines with "route print"


Author Comment

ID: 11843904
I just powered down everything, including the hub and router, then powered up in this sequence:  router, hub then Linux box

With nothing else turned on the Linux box cannot ping the router.  However, cabling directly from the Linux box to the router works.

So, I found an old Surcom hub and tried it AND IT WORKS!!!!  Weirdest thing but who cares if it woks.

LVL 15

Accepted Solution

scampgb earned 1000 total points
ID: 11843997
You're right, that's the strangest thing!
Sounds like a dodgy hub.
LVL 15

Expert Comment

ID: 11844602
Hi John.  Thanks for the "A" :-)

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