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Help Date: 21 June 2004

 

 

TCP/IP Over Radio - Windows Configuration

ARP Table Entries
IP ROUTE Table Entries

HOSTS File Entries
Ping Test

Diagnosing Routing Problems

Windows has three internal tables which it uses to direct TCP/IP data to the correct network adapter and to the correct remote computer. The IP Routing Table directs TCP/IP packets to a particular gateway/network interface card. The ARP (Address Resolution Protocol) table associates an IP address with the physical address -- in this case the callsign -- of a remote computer. And the HOSTS Table can be used to associate an IP address to a domain name and vice versa. ARP Table entries are likely to be most critical for TCP/IP over radio (TOR) clients and gateways, but entries in the other two tables can be useful in some situations.

Routing and ARP are somewhat complex subjects and complete explanations are beyond the scope of this Help section. If you want more information, do a web search for information about "IP Routing Table" and "understanding ARP table".

ARP Table

PE Pro's TOR feature uses Windows' ARP entries to associate a particular IP destination address, such as your gateway's, with a ham callsign. 

With an ARP entry, PE Pro knows immediately which callsign to use in addressing a packet destined for a particular IP address. But when Windows first boots up, the ARP table is empty and Windows must rebuild the IP address=callsign entries from network exchanges. So the first time a packet to a specific IP address needs to be sent, PE Pro must first send out an ARP request packet to "QST" asking for the station using the destination IP address to respond with its ham callsign. If a response comes back (it might not!), the IP address=callsign entry is put in the ARP table.

To simplify things, you can pre-enter the IP address=callsign information in the ARP table for any stations you are likely to be contacting with TOR. You can do that with a DOS batch file that runs automatically after PE Pro initializes.

The ARP entry can also be used to tell PE Pro to use particular radioport to contact this callsign. Normally PE Pro uses the default port that you specified on the TOR configuration page. The ability to specify a different port can be useful if some of your contacts are made on alternative radioports.

Determine the Correct ARP Entry Format for the Batch File

Each ARP entry includes an internet address and a hex physical address (call sign and radioport). To calculate the correct hex address for a station, use the free AGWsoft utility AGWARP.EXE   You can download this in zip format from:  http://www.raag.org/sv2agw/arpagw.zip  or http://www.elcom.gr/sv2agw/arpagw.zip

Unzip the utility and run it. It will ask you to:

  1. Enter a callsign (for example SV2AGW-8)
  2. Enter the PE Pro radioport to use to connect to that station (e.g. 2)
  3. Enter the IP address used by that callsign (e.g. 44.1.1.8)

The utility will then return a hex physical address. For the example above it would be ab:ac:0d:2c:44:86 . Finally it returns a closing  message, such as  "Type now <ARP -s 41.1.1.8 ab:ac:0d:2c:44:86>". Rather than type it, write down everything in between the brackets < >.  Press the Return key to close the utility. If you need physical addresses for any other stations, you will need to re-run the utility .

Create an ARP Entry Batch File

Open a DOS-prompt box (Start: Run: CMD) and type EDIT ARPROUTE.BAT (or another .bat name of your choice). If there is no existing file with that name, the edit program will create a new file named ARPROUTE.BAT with no data in it.

On a blank line, enter an ARP entry, i.e. the information you wrote down from the AGWARP utility, except replace any colons (:) in the physical address with dashes (-). For example:   ARP -s 41.1.1.8 ab-ac-0d-2c-44-86

If you have other ARP entries, add each on a separate line. When done, save the file to a folder of your choice, making note of the path. Test the file by double clicking on its icon and make sure no error messages occur. You can also see the ARP table and your new entry by opening a DOS-prompt box (Start: Run: CMD) and at the DOS prompt enter:  ARP -a    [You can also manually enter ARP entries from the DOS prompt instead of a batch file.]

Add the Batch File to PE Pro's Auto Start Feature.

From the PE Pro's Setup menu, select Auto Start Other Programs. Use the ADD button to navigate to and select the ARPROUTE.BAT file you created. Once entered into the auto start application list, the file will run each time PE Pro starts up and it will put your ARP entries into the Windows ARP table.
 

IP ROUTE Table

The IP Routing table helps Windows decide which network adapter to use to send a TCP/IP packet. It's choices might be the SV2AGW TOR virtual adapter, the hardware network interface card (if one exists), or back to your own computer (via a loop back port). For many users, no additions to the IP Routing table will be necessary, however, in some cases, Routing table additions will help your TOR communications.

By default, Windows will build the Routing table anew at each reboot. It's primary source of information is the Internet Protocol (TCP/IP) property settings of your network adapters, including the SV2AGW TOR adapter. The key information is the IP addressed assigned to the adapter. If you have a hardware network card installed, Windows will make that IP address the default gateway adapter, but the settings of your SV2AGW TOR adapter will create a special route for your ham radio network (those would be addresses that begin with 44, assuming you are using an IP address yourself that begins with 44),

For example, say your settings for the SV2AGW TOR adapter looked like this example ...

An entry would be placed in the IP Routing table indicating that any IP packet with a destination IP addresses beginning with 44 should be routed to your SV2AGW TOR adapter at IP address 44.128.34.2 (and then onto your gateway station at 44.128.6.1).

Why 44? That's determined by the subnet mask values under the four octets (44, 128, 34, and 2) in the IP Address.  A subnet mask value of 255 means "match all the binary digits of this octet"; a value of 0 means "no need to match any of these digits". In our example, only the first octet, 44, has a subnet mask value of 255. The other octets have a mask value of 0. So the Routing table will contain an entry that says, in essence, send all destination IP addresses beginning with 44 to the 44.128.34.2 adapter.

For addresses that don't begin with 44, Windows will use the Routing table to determine the correct routing. For example, if you also have a network card in your computer, then the routing table will probably suggest that packets for all non-44 addresses should be routed to the network card (the default gateway adapter) instead of the SV2AGW TOR adapter. If you don't have a network card, then the routing table will suggest that most packets go to the SV2AGW TOR adapter.

If you have a network card and will regularly contact stations using TOR that don't have an IP address beginning with 44, then you should add them to the Route table so that packets are sent to them via the SV2AGW TOR adapter and not the network card. The easiest way to do this is to add those routes into the batch file created for ARP entries (see above, Create an ARP Entry Batch File) or create a batch file as above if one doesn't exit.

To add a route to the IP Routing table, enter ROUTE ADD followed by the full IP address of the remote station followed by the IP address chosen for your SV2AGW TOR adapter (your IP address), for example:      

ROUTE ADD 133.275.12.6 44.128.34.2

 This tells windows to route any IP packets addressed to 133.275.12.6 to the SV2aGW TOR adapter at 44.128.34.2. Of course you would replace the number in green with the address of your distant station and replace the number in red with your SV2AGW TOR adapter's address (your ham radio IP address).

To add a route without using a batch file, open a DOS-prompt box (Start: Run: CMD) and enter your ROUTE ADD sentence as above.

To see your complete Route table, enter ROUTE PRINT at a DOS prompt 

HOSTS Table

The HOSTS file can be used to help translate an IP address to a name and vice versa. For example, if you had a HOSTS table entry that said 44.0.0.2 is the same as "My Web Page", you could enter "My Web Page" as a URL address in your browser and Windows would know to go to 44.0.0.2 to find it.

This same IP Address-Name translation can be performed by a domain name server, but the HOSTS files is especially useful when a domain name service (DNS) server is not available (common on many amateur radio networks) or when you want to use an easily remembered name in place of a hard to remember IP address or lengthy domain name.

Location of the HOSTS file on your computer:

Windows 98/Me c:\windows\hosts
Windows 2000/XP Pro c:\winnt\system32\drivers\etc\hosts
Windows XP Home c:\windows\system32\drivers\etc\host

Note: the HOSTS file has no extension to its name.

You can open the existing HOSTS file with a text editor. Instructions for adding entries to file are included in the file. [In some cases you may find a HOSTS.SAM file and not a HOSTS file. If you do, make a copy of the HOSTS.SAM file calling it HOSTS (no extension).]

Usually the HOSTS file already has one entry in it:  127.0.0.1   localhost

Any new entries would follow the same simple format: IP address, a space, name. For examples:  41.1.1.8   SV2AGW-8    or   41.1.1.8   mail.sv2agw.net

Ping Test

After you make your HOST, ROUTE and ARP entries, you can test them by using the Windows PING command. PING simply sends four packets to the destination station asking it to respond. PING then reports how long each response takes or, if no response is heard within a given length of time, PING reports the "request timed out".  

To send the PING command, open a DOS-prompt window (Start: Run: CMD) and enter the command in this format: PING <destination IP>,

You can use the -w option on the ping command to increase the time PING waits for a response (default is 1 second). For example, to wait for each response for 5 seconds (5000 milliseconds), use  -w 5000. e.g. PING 44.0.0.1 -w 5000

If all four requests time out, then Windows is not hearing a response from the destination IP and it is useless to try any other application. If you do get a reply, then all Windows applications using TCP/IP, i.e. Internet Explorer, Outlook Express, etc., will also be able to communicate with this destination.

Diagnosing Routing Problems

Open the PE Pro Monitor and watch the packets that PE Pro is sending when you execute the PING command. They should look like this:

2:Fm SV2AGW To SV2BBO <UI pid=CC Len=60 >[21:59:26]
IP:len:60 44.0.0.2->44.0.0.1 ihl:20 ttl:128 prot ICMP
ICMP:type Echo Request id:768 seq:7680 abcdefghijklmnopqrstuvwabcdefghi

  • If you don't see anything, then the ROUTE table is not configured to route packets to the SV2AGW TOR adapter for this destination IP address.
     
  • If the packet is addressed to QST instead of the expected callsign, then the ARP table entry associating the destination IP address with the destination callsign is missing or incorrect.
     
  • If the number that begins the packet (e.g. 2:) is not the correct radioport for TOR, then the ARP table has a hex address with the wrong radioport. Rerun the AGWARP.EXE program to get the correct hex address.

If the PING command reports the the request timed out:

  • The response time may have been too short. Increase it by using PING's " -w "  parameter described above.
     
  • The radioport number may be incorrect so you are transmitting on the wrong frequency. Either the default radioport in PE Pro's TOR settings is incorrect; or the ARP table entry for this callsign has a hex address with the wrong radioport (rerun the AGWARP.EXE program and re-enter the correct hex address in the ARP table).
     
  • You are using the wrong callsign and/or SSID number for the destination station.
     
  • There may be a transmission problem at your station (no power, cables not connected to TNC or radio, etc); or the other station simply can not hear your packets (poor signal); or the other station is not working properly or it is off the air. [In that case, try to successfully exchange a standard packet before trying a TOR packet exchange or PING test.]
     
  • The other station can not respond to PING requests because its PE Pro configuration and/or its SV2AGW TOR adapter configuration is incorrect.

Go to:
   TOR Introduction
   TOR Drivers
   TOR PE Pro Settings
   TOR Windows Settings
   TOR Application Setup
   TOR Gateway Setup

 

Copyright 2004 SV2AGW George Rossopoulos . All rights reserved.