Understanding why PING doesn't work.

[G0AOZ]

This is the scenario...

Small local area network, three computers attached. Two machines are running Windows XP, the third machine is running a specialist DOS based application called XROUTER. All machines have static IP addresses in the 192.168.2.x range.

When the machines are hooked up to a Linksys router (WAG54G), all machines can PING each other. When they're connected to seemingly any other router, only the Windows machines can PING each, not the XROUTER PC.

Apart from setting the router's own IP Address to 192.168.2.1 it doesn't seem to matter how the routers are configured, or indeed not at all, the results are always the same.

Any ideas why only the Linksys will allow the DOS (XROUTER) machine to PING and be PING'd? I'm obviously missing something here...


ROGER - G0AOZ.

 

[goombawaho]

Question 1 - Why do you care if you have a functioning system with the WAG54G??

Comment 1 - Other router is bad somehow??? Ping in Windows and DOS should all be equivalent given functioning hardware and software.

Comment 2 - There no chance that your IP addresses are conflicting on the second router.

 

[G0AOZ]

Why do you care if you have a functioning system..."?

Ultimately, the XROUTER (DOS) system will be remote from the rest of the network. It will be linked by two RF systems - no phone line is available. If the remote system fails for some reason, power, TNC, or transceiver failure, etc., being able to PING that DOS system will help to establish where the fault lies.

I have tried four other routers, which are new and have been tested in a conventional network/ADSL setup. I deem it very unlikely they'd ALL be bad. Possible, but very unlikely...

There were never two routers connected at the same time. Also tried switching off all three machines when router was changed over. Whilst DHCP was left enabled (by default) on each router, no IP Address conflicts were apparent.

Yes, we will be using the Linksys WAG54G. I was just trying to understand WHY all other routers we tried didn't give the same results when machines were PING'd.

ROGER - G0AOZ.

 

[goombawaho]

I was just thinking that you've got one that worked, why were you worrying about the other, but now I see what you are trying to implement.

That IS weird if you have tried multiple routers and only one will work for you. I'm out of ideas at the moment.

 

[edfair]

I did some Lantastic networking for customers. One added a couple of workstations for new employees and added a printer on one of the workstations. In attempting to copy files or print to the new machines the transfer would hang up. Everything would indicate that it was trying to transfer, just nothing was getting there. Then, maybe up to 45 minutes later, something connected and the jobs would complete.
Turns out there are some subtle differences in the timings of different devices depending on what chipsets are used and they can be critical in sending and receiving. My solution was to order and install network cards of the same manufacturer.
I would probably try several different NICs in the DOS machine to see if it would make a difference.
There is also the Lantastic solution. Obsolete but still available with DOS/XP interconnect if the applications are not network specific.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[tlcscousin]

Ultimately, the XROUTER (DOS) system will be remote from the rest of the network. It will be linked by two RF systems
I assume this means it gets a public IP?
The rest are behind a router so if you change the router it gets a different public IP then it had.
If this is in fact the case it can be an ARP cache entry the ARP table expects the IP address associated with the MAC address to be the same as it has in cache.
I am not really savvy on ARP i just know when we move an IP from one router to another we have to have the ARP cache for that IP address deleted from the edge router.
What you could try before changing routers is copy the MAC address of the router you currently have and clone it to the new one.
This should clear up the issue and is an easy test, if it doesnt work remove the cloned MAC address.

 

[BadBigBen]

just some thoughts on the subject:

have you tried a switch between the router and the PC's, where each PC is attached to the switch?

are any of the PC's connected via WiFi or wireless? I know that some routers do not allow a ping between wired and wireless, but will allow, for instance, a shared network drive to work if you specify the IP and share name (\\IP\share)... (my home router acts this way)...

also, some wireless routers, you need to disable the DHCP altogether, when you have static IP's, for them to communicate correctly...




Ben
"If it works don't fix it! If it doesn't use a sledgehammer..."
How to ask a question, when posting them to a professional forum.
Only ask questions with yes/no answers if you want "yes" or "no"

 

[Noway2]

Ping uses ICMP messaging. Is there a configuration switch to turn it off?

 

[stduc]

XP can be configure to respond/not respond to ICMP messages.

Go to Network Connection, right click the connection, then properties, then advanced, then windows firewall settings, then advanced, then ICMP settings. Tick "Allow incoming echo request" to let XP respond to pings.

Alternatively disable all firewalls including XPs own.

 

[EmuDan]

Do all the routers have Auto-MDIX support? If not, maybe you will need a crossover connection to the XROUTER PC.

Dan

 

[G0AOZ]

Thanks for all your thoughts on this one. I am away from site at the moment, but here's a few answers to points raised.

1. Might be difficult to find network cards which match the laptops AND which offer Packet drivers running at DOS for XROUTER.

2. "It will be linked by two RF systems I assume this means it gets a public IP?" The cable modem which will provide an Internet connection will indeed get a WAN IP. However, I don't think this has any bearing on the problem, which is there even within a closed system not connected to the outside world.

3. Not sure if the routers I've looked at offer facilities for copying/cloning MAC addresses.

4. Yes, already tried a switch in between router and PCs - made no difference. Pinged XROUTER with Linksys, no ping with others routers.

5. All machines are wired - deliberately kept wireless out of the equation. I have yet to try switching off DHCP.

6. Configuration switch to turn off ICMP - do you mean within the router? I will look at this next.

7. Since I can make all machines ping each other successfully by only using the Linksys router, I am not sure that altering XP's firewall or ICMP settings is relevant.

8. Auto-MDIX support must be ok with all routers, otherwise pinging between the XP machines wouldn't happen on the ones other than the Linksys.

It's been suggested I look for a switch to turn off/on 'Filter Anonymous Internet Request, so that's something else to check when I'm next on site. And although it's circumventing the problem, someone has suggested adding an IP ROUTE entry to the XROUTER system configuration file.


ROGER - G0AOZ.

 

[BadBigBen]

4. Yes, already tried a switch in between router and PCs - made no difference. Pinged XROUTER with Linksys, no ping with others routers.

Hmmm... with a switch, I would think that pinging between the PC's would work, as there is no router in the equation...

someone has suggested adding an IP ROUTE entry to the XROUTER

I think you mean port forwarding... it would be worth a try... it would allow a direct route to the XROUTER PC from the internet at a given port or port range...

I am more or less out of ideas, seeing that a switch did not work between the PC's, except when PC's are not in the same subnet... double check the subnet setting and IP setting...

though you could try to clear the ARP cache (arp -d *), the DNS table (ipconfig /flushdns) on all PC's...




Ben
"If it works don't fix it! If it doesn't use a sledgehammer..."
How to ask a question, when posting them to a professional forum.
Only ask questions with yes/no answers if you want "yes" or "no"

 

[stduc]

Not all routers are equal obviously.

Have you tried using trace route (tracert)? Though I doubt it will help - it's worth a try I guess.

I wonder if using a packet tracer and examining the packets will help? There might be something odd about the XROUTER packets that for some reason only the linksys can forward?

 

[edfair]

If you added a switch between and there was no direct connect of machines to router you have removed the router as a current part of the network except for whatever stuff is stored localy about it.

What happens if you physically remove the connection between router and switch, changing your XP machines to no gateway? You may have to do a cold boot.

Ed Fair
Give the wrong symptoms, get the wrong solutions.