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Re: LAN configuration problem?

On Wed, 2 Jul 1997, Randy Edwards wrote:

(i've deleted lots of stuff which seemed fine and didn't seem to need a

> > can your linux machine ping the win95 machine?
>    Nope, when I ping the Win95 box I get a 100% loss.

> > what's in your arp table on the linux machine? try 'arp -an'. You want
> > to see arp entries for both machines.
>    Ahh, this is something.  After trying a ping from each machine, after
> running an arp -an the output is:
> Address                 HWtype  HWaddress           Flags Mask Iface
>             ether   00:C0:26:80:1E:73   C     *    eth0
>    If I could ask, what does this mean?  As you can tell my knowledge of
> Linux/TCP/IP networking is limited and I haven't gotten up to the chapter on
> arp yet reading the NAG. :-)

The arp table matches IP addresses against Hardware addresses in the
ethernet card (also known as MAC addresses).   Each ethernet card has a
hard-coded unique MAC address.

IP (Internet Protocol) is just one of many networking protocols which
can run "on top of" the lower-level ethernet protocols. e.g. IPX for
novell, IP, and appletalk protocols can all run simultaneously on the
same ethernet.

So, this table is saying that IP address (your win95 machine?)
is at the machine with ethernet card 00:C0:26:80:1E:73

(see man arp for details)

> > try running tcpdump on the linux machine - according to the RX & TX
> > lines above, it looks like there is definitely some activity. You can
> > monitor the network with tcpdump.
>    Okay, here's what tcpdump puts out when I ping the Linux box from the
> Win95 box:
> tcpdump: listening on eth0
> 10:03:55.265899 arp who-has spartacus.golgotha.net tell horeb

this is the win95 machine asking for the linux box's hardware address.

> 10:03:55.265899 arp reply spartacus.golgotha.net is-at 0:c0:26:80:1f:71

this is the linux box saying "here i am".

> 10:03:55.265899 horeb > spartacus.golgotha.net: icmp: echo request

win95 sends a ping.

> 10:03:55.265899 spartacus.golgotha.net > horeb: icmp: echo reply

linux replies.

> 10:03:56.705899 horeb > spartacus.golgotha.net: icmp: echo request
> 10:03:56.705899 spartacus.golgotha.net > horeb: icmp: echo reply

and again

> 10:03:58.185899 horeb > spartacus.golgotha.net: icmp: echo request
> 10:03:58.185899 spartacus.golgotha.net > horeb: icmp: echo reply

and again

> 10:03:59.225899 horeb > spartacus.golgotha.net: icmp: echo request
> 10:03:59.225899 spartacus.golgotha.net > horeb: icmp: echo reply 

and again

I can't see a problem on the linux end. It looks as if it should work
fine. Is there anything in /var/log/messages (or in the output of
'dmesg') which suggests a fault with either the network card or the

is the tcpdump output similar when you ping the win95 machine from
linux? From what you said above about 100% packet loss when pinging from
linux to win95, I'd guess that you'll see the "echo requests" in tcpdump
but not the "echo replies"....which indicates that the win95 machine
isn't able to receive packets.

are there any irq conflicts with the ethernet card on the win95 machine?
irq conflicts with network cards often manifest as being able to send but
not receive packets.

> Now, looking at the above, I see a difference in the tcpdump response
> and the hardware address response of arp -an: 1E:73 and 1F:71. Now,
> that doesn't seem quite right but I'm unsure of how to interpret that
> -- any ideas? If so, I'd greatly apprecite 'em.

It's ok. The Linux box's MAC address IS different to the win95 machines
MAC address.


craig sanders
networking consultant                  Available for casual or contract
temporary autonomous zone              system administration tasks.

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