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alt(7) Miscellaneous Information Manual alt(7) NAME alt - DEGPA Gigabit Ethernet interface SYNOPSIS pseudo-driver alt DESCRIPTION The alt interface provides access to Gigabit Ethernet (1000Mbs) through the DIGITAL DEGPA device. The interface supports full-duplex operation in a switched or point-to-point configuration, and provides the follow- ing features: The interface has Link Autonegotiation enabled by default. Some switches do not support Link Autonegotiation. To turn Link Autonegoti- ation off, use the following command: # lan_config -ialt0 -a0 Note that you may add this command to the /etc/inet.local file to preserve the setting of Link Autonegotiation across system restarts. JUMBO packets are disabled by default. JUMBO packets provide a non-standard larger packet size. This enables the interface to carry more data with less CPU overhead. To enable JUMBO packets, use the following command: # ifconfig alt0 ipmtu 9000 Note that there are several interoperability issues with using JUMBO packets (for example, if your switch goes from 1000Mbps to a 100Mbps client, JUMBO packets will not work on a 100Mbps LAN). In order to use JUMBO frames, you will need a switch that sup- ports JUMBO frames or a point-to-point configuration with a partner that supports JUMBO frames. Receive flow control is enabled. There is currently no way to turn this off. Gigabit Ethernet performance with TCP/IP depends on several factors. Some of the influencing factors are as follows: The speed at which data can be delivered to the interface influences throughput. If your CPU(s) are busy doing several tasks, the task using Gigabit Ethernet may not get enough run time to deliver packets. In general, faster CPUs will deliver better throughput. Fast access to the PCI bus is critical for high throughput. Using a 64-bit PCI slot will give you better performance and use less PCI resources than a 32-bit PCI slot. Putting the interface on the same PCI bus as other peripherals will de- grade throughput. Each system type may also have different PCI-to-host speed considerations (the speed at which the PCI-to-host hardware al- lows the device to operate). The standard TCP/IP applications (for ex- ample, ftp and rcp) are not designed to run at Gigabit speeds. TCP ap- plications that expect performance should use a message size of 65000 bytes and a window size of 128000 bytes. Even when an application is modified to use these settings, high throughput may not be attainable. This is particularly true when an application is waiting for data to send (data from a disk, for example). ERRORS The following diagnostic and error messages contain relevant informa- tion provided by the alt interface, and are displayed to the console. Each message begins with the adapter identification, including the num- ber of the adapter. The alt interface could not find adequate I/O ad- dressing on this system to operate. This is a fatal error, and the DEGPA-SA will not operate on this system running DIGITAL UNIX. There was a memory allocation problem or the device initialization has failed. This is indicative of a hardware problem. Indicates that the Gigabit Ethernet link is up. The Autonegotiated keyword indicates that the link was autonegotiated. Note, this will only be on if autonegotia- tion is enabled). The ReceiveFlowControl keyword indicates that Re- ceive Flow control is enabled on the link. Indicates that the link is no longer established. No communication will occur over the link while it is down. RELATED INFORMATION Commands: ifconfig(8), lan_config(8) Network information: arp(7), inet(7), netintro(7), inet.local(8) delim off alt(7)