Ping is the lowest layer protocal, if you can transfer files from PC2 to PC1 then you can also ping from PC2 to PC1, File transfer is FTP, and the same layer as ping. A machine being able to ping itself is irrelevant as it uses a built in self test IP 127.0.0.1 (local loop back) to do this.

If indeed you cannot transfer files from PC2 to PC1 then you have a bad crosscable. Try this.....

at a command prompt "DOS prompt" type "route print", this will give you all active routes, IP's, and subnets, including the local loop back you use when a machine pings itself. I doubt there will be any problems, but it will give you a wealth of information to work with.

Thanks for your reply.

As I mentioned before, in NetBEUI (MS Windows protocol) I can file transfer on both side PC's.

In TCP/IP I can not ping only from one PC to other. A > B OK B > A not OK.

I can ping from A (100.10.10.10) to B (100.10.10.20)
I can not ping from B (100.10.10.20) to A (100.10.10.10)

I checked the cross cable again. IT is OK.

Here is the route prints sum of both PC. As you see at last line there is a difference.
Can you give me any other idea? Thank you.

100.10.10.20 (B)
------------

Network Address Netmask Gateway Address Interface Metric
100.10.10.0 255.255.255.0 100.10.10.20 100.10.10.20 1
100.10.10.20 255.255.255.255 127.0.0.1 127.0.0.1 1
100.255.255.255 255.255.255.255 100.10.10.20 100.10.10.20 1
127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
224.0.0.0 224.0.0.0 100.10.10.20 100.10.10.20 1
255.255.255.255 255.255.255.255 100.10.10.20 100.10.10.20 1

-----------------------------------------------------------------------------

100.10.10.10 (A)
------------

Network Address Netmask Gateway Address Interface Metric
100.10.10.0 255.255.255.0 100.10.10.10 100.10.10.10 1
100.10.10.10 255.255.255.255 127.0.0.1 127.0.0.1 1
100.255.255.255 255.255.255.255 100.10.10.10 100.10.10.10 1
127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
224.0.0.0 224.0.0.0 100.10.10.10 100.10.10.10 1
255.255.255.255 255.255.255.255 100.10.10.10 0.0.0.0 1

:shock:

2 things wrong with your statement.
1. Ping is not a protocol but a network application utilizing IP at OSI layer 3.
2. There is no such thing as a "lowest layer protocol" What about layer 2 protocols? Frame Relay, ATM, PPP none of which ranks higher than the other
2.1. Is Sprint Hiring? I want your job.

Greetings,
One thing that was not mentioned was is there a Gateway in the TCP/IP properties for PC1 and PC2. If this setting is incorrect on one of the PC's the ping reply will not "know" how to get back to PC2. They should be the same on both PC's.

do your ip's actually start with 100. or is that a typo? does PC1 have a firewall that disallow ICMP?

Your trolling sure did help solve this guys problems, good show.

gateway is not necessary if both PCs are on the same subnet.
Gateway AKA router.

I have almost exactly the same problem. Two machines, A and B, connected via crossover cable between two 100 mbps ethernet cards.

Machine A: Windows XP with internet connection sharing running on a cable modem. XP standard firewall is on. No problems accessing internet at all. Provides IP address to machine B via DHCP. Also has IPX installed, and Microsoft file sharing runs over that and that only (not TCP/IP).

Machine B: Windows 98, takes IP address from A via DHCP. Uses IPX for file sharing. No problems accessing internet at all.

The file sharing works perfectly, so two-way communication is fine with IPX. Internet connection is fine from both A and B (via A), so two-way communication is also fine in that respect.

BUT this this the problem: machine B (98) can ping machine A (XP) but not vice-versa. Any attempt, in fact, to initiate a connection over TCP/IP to B from A will fail, which is why I set file sharing over IPX.

Tried static IP addresses, turning off QoS, turning off firewalls, etc. but to no avail. Also tried uninstalling and reinstalling network hardware and software but no differences observed.

I am almost certain that the problem lies with B (98) because this problem also occurs on other networks where NAT is in use. Internet OK, but specific TCP/IP connections to the machine fail.

The weird thing is that two-way intra-network TCP/IP connections the other way (to the XP machine) are also fine!!!

1) get a real firewall, even if it's a www freebie & disable the XP firewall cause its truly useless
2) are you using IPX on the Win98 (sys B) because you cant ICS or because you simply cant ping?