Sun Microsystems 3U manual ATM ARP Address Resolution Tables

standards for providing redundant ATM ARP servers for a subnet. As specified, the ATM ARP server would constitute a single point of failure in the system. From a practical standpoint, however, early configurations can use an IP-to-ATM address database in every system, thus avoiding the IP-to-ATM address resolution step altogether.

The RFC requires a router for passing data between subnets. SunATM software provides ATM utilities that allow configurations to specify IP-to-ATM addresses in /etc/opt/SUNWconn/atm/aarconfig files. The aarsetup program uses the information in /etc/opt/SUNWconn/atm/aarconfig to create IP-to-ATM address resolution tables. Dynamic entries into a server’s resolution table are also supported.

TABLE 5-2shows the format of the /etc/opt/SUNWconn/atm/aarconfig file for specifying the IP-to-ATM address. It is important for the file to be consistent on all systems in the subnet. See “Editing the aarconfig File” on page 44.

ATM ARP Address Resolution Tables

Depending on the aarconfig file, the Classical IP software runs as either a server or a client. As a server, the Classical IP software handles ATM ARP requests originating from its clients. An ATM server has to be configured for each subnet. The ATM ARP server code conforms to RFC 1577: clients send ATM ARP requests to the server to resolve a destination IP address to an ATM address. The server then replies to ATM ARP requests by sending an ATM ARP response. If the server does not have the IP-to-ATM address entry, then it replies with NAK.

All the IP-to-ATM address entries specified in the /etc/opt/SUNWconn/atm/ aarconfig file are entered into a kernel resident table by the ATM ARP setup program, aarsetup. Additional entries in the kernel table are added dynamically using the inverse ARP process. When a client connects to the server, the server sends an inverse ARP request back to the client to obtain the client’s IP address. When a response is received, an entry is created for that client. The Classical IP software also responds to client ARP requests. The software looks up a kernel IP-to-ATM address entry and responds to an ATM ARP request with either an ATM ARP reply or ATM ARP NAK (if there is no entry in the table). Note that an ATM ARP client uses the virtual channel (VC) specified in the /etc/opt/SUNWconn/atm/aarconfig file to communicate with the server; or, if an ATM address is specified, it establishes a switched virtual circuit (SVC) connection to communicate with the server.

While dynamic entries in the ARP server’s table make network administration less complex, they also create a security problem. Any host can register with the ARP server and therefore gain access to the subnet. To resolve this issue, you can provide a list of hosts or networks with a entries in the server’s /etc/opt/SUNWconn/atm/aarconfig file. If no a entries appear, any host can connect to the server. If any a entries exist, only those hosts whose addresses match those specified will be allowed to connect.

68 SunATM 3U CompactPCI Adapter Installation and User’s Guide • February 2001