bcm - DEGXA Gigabit Ethernet interface
The bcm interface provides access to Gigabit Ethernet
(1000Mbs) through the DEGXA device. The interface supports
full-duplex operation in a switched or point-topoint
configuration, and provides the following features:
The interface has Link Autonegotiation enabled by default.
Some switches do not support Link Autonegotiation. To
turn Link Autonegotiation off, use the following command:
# lan_config -ibcm0 -a0
Note that you may add this command to the
/etc/inet.local file to preserve the setting of
Link Autonegotiation across system restarts.
If you manually set the speed by using the ifconfig
or lan_config commands, autonegotiation is automatically
disabled. If you then want to enable autonegotiation
(for example on interface bcm0), use the
# lan_config -ibcm0 -a1 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 bcm0 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 supports 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.
For the DEGXA-SX, we recommend that you use the auto-negotiation
protocol. This protocol has been thoroughly
tested, and works reliably with many different switch vendors
over Gigabit Ethernet. If you disable auto-negotiation,
the switch port setting and the DEGXA-SX setting
must match perfectly, otherwise you might encounter interoperability
problems. The DEGXA-SX (fiber optic version)
runs at 1000Mbps only.
For the DEGXA-TX (the copper version of the Gigabit Ethernet
NIC), you must enable auto-negotiation. This is a
mandatory requirement of the IEEE 802.3ab auto-negotiation
protocol. The DEGXA-TX can run at 1000, 100, or 10 Mbps.
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
degrade throughput. Each system type may also have different
PCI-to-host speed considerations (the speed at
which the PCI-to-host hardware allows the device to operate).
The standard TCP/IP applications (for example, ftp
and rcp) are not designed to run at Gigabit speeds. TCP
applications 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).
The following diagnostic and error messages contain relevant
information provided by the bcm interface, and are
displayed to the console. Each message begins with the
adapter identification, including the number of the
adapter. The bcm interface could not find adequate I/O
addressing on this system to operate. This is a fatal
error, and the DEGXA-SA will not operate on this system.
Indicates that the Gigabit Ethernet link is up, and the
autonegotiation protocol was used to set the speed and
duplex mode. Note, this will only appear if autonegotiation
is enabled. Indicates that the Gigabit Ethernet link
is up, and was manually configured. Indicates that the
link is no longer established. No communication will
occur over the link while it is down.
Commands: ifconfig(8), lan_config(8)
Network information: arp(7), inet(7), netintro(7)
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