Sun Microsystems 3U manual Common Problems, Are you trying to use the /usr/sbin/arp command?

Common Problems

This section describes some common problems that you may experience during or after the SunATM adapter installation. Please review this section before calling Sun Service for assistance.

Are you trying to use the /usr/sbin/arp command?

Since the Classical Internet Protocol (IP) network model resolves IP-to-ATM address pairs rather than IP to MAC address pairs, the /usr/sbin/arp command does not support Classical IP interfaces at this time. A version of the arp command, /etc/ opt/SUNWconn/atm/bin/atmarp, provides similar functionality for Classical IP interfaces. Refer to the atmarp (1M) man page for more information.

Are you using a router with Classical IP and LAN Emulation (LANE)?

Performance problems occur if a router uses ATM Classical IP (default 9180 byte MTU) and LAN Emulation (default 1500 byte MTU) links simultaneously when a TCP connection is set up using one interface in one direction and the other interface in the opposite direction, TCP is confused about the maximum packet size.

For example, suppose a TCP connection is set up between Host A and Host B, where packets from Host A travel to Host B over the LANE interface and packets from Host B travel to Host A travel over the Classical IP interface. Host A attempts to send a 9180 byte packet that cannot traverse the LANE network to Host B. TCP recovers from this error and retransmits the packet, but a significant performance loss will be noted.

Possible workarounds to improve performance are:

■Adjust the MTU size, if possible, of the Classical IP link to 1500 bytes.

■Depending upon the network topology, adjust the routing table on Host B to ensure that the route back to Host A points to the LANE interface.

This problem is not unique to ATM networks. It may affect any network configuration that has multiple routes with differing MTUs (such as FDDI and Ethernet or Token Ring). The problem is more pronounced with ATM subnets because of the different default MTUs of Classical IP and LANE.

Are you trying to use the /usr/sbin/snoop command?

The /usr/bin/snoop command, which can be used to detect network problems, does not support SunATM interfaces at this time. A version of the snoop command, /etc/opt/SUNWconn/atm/bin/atmsnoop, provides this support. Refer to the atmsnoop(1M) man page for more information.

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