Re: Can't ping local computers

From: Allen Kistler (ackistler_at_oohay.moc)
Date: 07/17/04 

Date: Sat, 17 Jul 2004 17:02:59 GMT

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?

Relevant Pages

  • Re: How do I stop my PC from returning a "Ping"?
    ... to send out packets and retrieve the incoming replies as well. ... I would bet that he is behind a router, the router is getting the IP ... The router probably can be set up to disable ICMP ... >> Hmmm, but "ping of death" attacks could be pretty major, should they ...
    (microsoft.public.windowsxp.security_admin)
  • Re: Solaris 10 IP Multipathing
    ... for obscure CPU spikes which drop ICMP echo packets and lead to ICMP failovers ... All ping targets must be in the same subnet as the primary interface. ... Since the default router is used as the first target, ...
    (comp.unix.solaris)
  • Re: Solaris 10 IP Multipathing
    ... disabled ICMP due to ping floods etc. ... Your point about setting up the ping list is a very good one. ... Since the default router is used as the first target, ...
    (comp.unix.solaris)
  • Re: What happens when I ping my own WAN IP from LAN side?
    ... respond to the ping directly without forwarding it to the ISP? ... That depends - if it's a firewall rule to ignore ICMP echo, ... If the router does not forward the request on to the ISP, ...
    (comp.dcom.lans.ethernet)
  • Re: Why Linux is blind to this ARP reply ?
    ... Make sure it's not a firewall issue with Linux. ... > I placed ethereal in windows and tcpdump in linux. ... > Ethereal sees the ARP reply when the router is ping from ... What are you trying to ping? ...
    (comp.os.linux.misc)