Can't ping local computers

I have a small network consisting of two computers.

One computer runs Mac OS X. The other computer dual boots between
Windows XP Professional and Fedora Core 2.

When I'm running Windows both computers are able to ping each other.
When I'm running Linux, neither computer can ping the other.

What could be the cause for this?

Tron Thomas wrote:
> I have a small network consisting of two computers.
>
> One computer runs Mac OS X. The other computer dual boots between
> Windows XP Professional and Fedora Core 2.
>
> When I'm running Windows both computers are able to ping each other.
> When I'm running Linux, neither computer can ping the other.
>
> What could be the cause for this?

Are you sure networking works at all on your Linux box?
Does ifconfig show an interface with an IP address?
Start there.

Allen Kistler <(E-Mail Removed)> wrote in message news:<Lk3Kc.43$(E-Mail Removed)>. ..
> Are you sure networking works at all on your Linux box?
> Does ifconfig show an interface with an IP address?
> Start there.

Yes the network works in general. Both computers can access the
Internet without any problems via a router connected to a DSL modem.
Also both computers can ping the router. They cannot ping each other.

Tron Thomas wrote:

> Allen Kistler <(E-Mail Removed)> wrote in message
> news:<Lk3Kc.43$(E-Mail Removed)>. ..
>> Are you sure networking works at all on your Linux box?
>> Does ifconfig show an interface with an IP address?
>> Start there.
>
> Yes the network works in general. Both computers can access the
> Internet without any problems via a router connected to a DSL modem.
> Also both computers can ping the router. They cannot ping each other.
Check to make that each Linux box does not have a firewall setup that blocks
the icmp ping..

Jerry Smiley wrote:
> Tron Thomas wrote:
>
>>Yes the network works in general. Both computers can access the
>>Internet without any problems via a router connected to a DSL modem.
>>Also both computers can ping the router. They cannot ping each other.
>
> Check to make that each Linux box does not have a firewall setup that blocks
> the icmp ping..

It _is_ possible that you allow outgoing echo requests and incoming
replies on both boxes (ping works to the router), but block incoming
requests or outgoing replies (ping fails to each other).

That's not likely for Windows unless you purchased a firewall or are
testing SP2, since Windows only filters by tcp/udp port and ip protocol.
The fact that both can talk to the router rules out wiring or netmask
problems.

If you have arping (only works on local networks), you can try that from
the Linux box. arping uses arp packets instead of icmp packets.

tcpdump comes with most Linux distributions. If you run it on the Linux
box when you try to ping one way or the other, it will provide you with
a little more info.

tcpdump -ni eth0 [... or something similar. It's really flexible.]

1. Do you get a successful arp (who-has and is-at packets)?
2. Does the icmp echo request go out? Is there an icmp reply?

what I suspect that fedora has a default firewall policy which is
causing this trouble. you might try turning that firewall off or reset
to default values.

# /usr/sbin/iptables -F


# /usr/sbin/iptables -P INPUT ACCEPT
# /usr/sbin/iptables -P FORWARD ACCEPT
# /usr/sbin/iptables -P OUTPUT ACCEPT

hth

raqueeb hassan
kinshasa, drc

> Check to make that each Linux box does not have a firewall setup that blocks
> the icmp ping..

I forgot to add that you might need that firewall for security reason.
So, you can allow *only* icmp packets to traverse freely.

# /usr/sbin/iptables -A OUTPUT -p icmp --icmp-type echo-request -j
ACCEPT
# /usr/sbin/iptables -A INPUT -p icmp --icmp-type echo-reply -j
ACCEPT


--
raqueeb hassan
kinshasa, drc

Raqueeb Hassan wrote:
> what I suspect that fedora has a default firewall policy which is
> causing this trouble. you might try turning that firewall off or reset
> to default values.
>
> # /usr/sbin/iptables -F
>
>
> # /usr/sbin/iptables -P INPUT ACCEPT
> # /usr/sbin/iptables -P FORWARD ACCEPT
> # /usr/sbin/iptables -P OUTPUT ACCEPT
>
> hth
>
> raqueeb hassan
> kinshasa, drc

Just to get the thread back on track:

The OP's problem is *not* that he can't ping anything, because he can
ping his router.

The OP's problem is that he can't ping his Windows box.

Given the above, iptables is (at most, but not necessarily) responsible
for not being able to ping Linux from Windows.

(E-Mail Removed) (Raqueeb Hassan) wrote in message news:<(E-Mail Removed). com>...
> what I suspect that fedora has a default firewall policy which is
> causing this trouble. you might try turning that firewall off or reset
> to default values.
>
> # /usr/sbin/iptables -F
>
>
> # /usr/sbin/iptables -P INPUT ACCEPT
> # /usr/sbin/iptables -P FORWARD ACCEPT
> # /usr/sbin/iptables -P OUTPUT ACCEPT
>
> hth
>
> raqueeb hassan
> kinshasa, drc

None of the commands you suggested above produce any output when I try
them. Does that mean that things are blocked?

Allen Kistler <(E-Mail Removed)> wrote in message news:<7ZcKc.37765$(E-Mail Removed) igy.com>...
> Jerry Smiley wrote:
> > Check to make that each Linux box does not have a firewall setup that blocks
> > the icmp ping..
>
> It _is_ possible that you allow outgoing echo requests and incoming
> replies on both boxes (ping works to the router), but block incoming
> requests or outgoing replies (ping fails to each other).
>
> That's not likely for Windows unless you purchased a firewall or are
> testing SP2, since Windows only filters by tcp/udp port and ip protocol.
> The fact that both can talk to the router rules out wiring or netmask
> problems.
>
> If you have arping (only works on local networks), you can try that from
> the Linux box. arping uses arp packets instead of icmp packets.
>
> tcpdump comes with most Linux distributions. If you run it on the Linux
> box when you try to ping one way or the other, it will provide you with
> a little more info.
>
> tcpdump -ni eth0 [... or something similar. It's really flexible.]
>
> 1. Do you get a successful arp (who-has and is-at packets)?
> 2. Does the icmp echo request go out? Is there an icmp reply?

I have arping. I tried /usr/sbin/arping [Macintosh Computer Name].
The result I got was:

arping: socket: Operation not permitted

I do not have tcpdump on my Linux system.

What do I need to do to see if I get a successful arp?
How do I test the icmp echo request and icmp reply?