LAPD and Host Communication

Establish a connection

To establish a connection link from the host to the switch, refer to the Hardware Installation and Maintenance Guide. Once you have connected to a communications link, obtain an Internet Protocol (IP) address. For more information see the API Developer’s Guide: Overview.

IP Address and Subnet Mask

The IP address is a 32-bit address used in IP routing. IP addresses and subnet masks can be assigned either through Reverse Address Resolution Protocol (RARP), Bootstrap Protocol (BOOTP), or through the IP Configure message.

When the ISDN card starts up and finds an invalid IP address or subnet mask stored in the Electrically Erasable Programmable Read-Only Memory (EEPROM), it will issue five RARP requests followed by five BOOTP requests. If the card does not contact either a RARP or BOOTP server, then the card will start up before Transmission Control Protocol/Internet Protocol (TCP/IP) has started. If the card is successful in contacting a RARP or BOOTP server, then the server’s values will be used for an IP address and subnet mask and TCP/IP is started. To store an invalid IP address and subnet mask in the EEPROM, use an IP Configure message with the IP address set to 255.255.255.255 and any value for the subnet mask.

When the ISDN Series 3 card starts up and it finds a valid IP address and subnet mask are stored in the EEPROM, both RARP and BOOTP attempts are skipped and TCP/IP is started with the IP address and subnet mask found in the EEPROM. The IP Configure message is the only method to set the IP address and subnet mask values in the EEPROM.

If the host sends a IP Configure message and the IP address and subnet mask in the message are different than the values stored in the EEPROM, the EEPROM will be overwritten with the new values. The card will need to be rebooted for the new IP address and subnet mask to take effect.

If the host assigns the same IP address and subnet mask, the message is acknowledged and the card does not have to be reset. This allows the host to send the IP Configure message whenever it considers it necessary.

The subnet mask defaults to the values shown in the following table for BOOTP and RARP. Make sure that cards are in the same subnet.

Incorrectly assigning a class to the switch may result in superfluous messaging that can adversely affect system performance. If a switch receives a broadcast message from another switch using a different class, it interprets the message as being addressed specifically to the switch using an incorrect IP address.

The switch responds by sending an Address Resolution Protocol (ARP) request to determine which node originated the message. The switch then sends an Internet Control Management Protocol (ICMP) message to indicate that the node ARP cache has an incorrect IP address stored for the switch. The other node clears the switch IP address from its ARP cache. The next time that node attempts to send a message to the switch, it sends out an ARP request to get the switch IP address.