68 SunATM 3U CompactPCI Adapter Installation and User’s Guide • February 2001
standards for providing redundantATM ARP servers for a subnet. As specified, the
ATMARP 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-ATMaddress resolution step
altogether.
The RFC requires a router for passing data between subnets. SunATMsoftware
provides ATMutilities that allow configurations to specify IP-to-ATM addresses in
/etc/opt/SUNWconn/atm/aarconfig files. The aarsetup program uses the
informationin /etc/opt/SUNWconn/atm/aarconfig to create IP-to-ATM address
resolution tables. Dynamic entries into a server’s resolution table are also supported.
TABLE5-2 shows the format of the /etc/opt/SUNWconn/atm/aarconfig file for
specifying the IP-to-ATMaddress. It is important for the file to be consistent on all
systems in the subnet. See “Editing the aarconfig File” on page44.
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 fromits clients. An ATM server has to be configured for each subnet. The
ATMARP server code conforms to RFC 1577: clients send ATM ARP requests to the
server to resolvea destination IP address to an ATM address. The server then replies
to ATMARP requests by sending an ATM ARP response. If the server does not have
the IP-to-ATMaddress entry, then it replies with NAK.
All the IP-to-ATMaddress entries specified in the /etc/opt/SUNWconn/atm/
aarconfig file are enteredinto a kernel resident table by the ATMARP 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
responseis 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-ATMaddress
entry and responds to an ATMARP request with either an ATM ARP reply or ATM
ARP NAK (if there is no entry in the table). Note that an ATMARP 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 registerwith the ARP
server and thereforegain access to the subnet. Toresolve this issue, you can provide
a list of hosts or networks with aentries in the server’s
/etc/opt/SUNWconn/atm/aarconfig file. If no aentries appear,any host can
connect to the server.If any aentries exist, only those hosts whose addresses match
those specified will be allowed to connect.