A.3. Ethernet Parameters


Most modern Ethernet-based network interface cards (NICs), do not require module parameters to alter settings. Instead, they can be configured using ethtool or mii-tool. Only after these tools fail to work should module parameters be adjusted. Module paramaters can be viewed using the modinfo command.


For information about using these tools, consult the man pages for ethtool, mii-tool, and modinfo.

3Com EtherLink PCI III/XL Vortex (3c590, 3c592, 3c595, 3c597) Boomerang (3c900, 3c905, 3c595)3c59x.o

0 is off
1 is on

RTL8139, SMC EZ Card Fast Ethernet, RealTek cards using RTL8129, or RTL8139 Fast Ethernet chipsets8139too.o 
Intel Ether Express/100 drivere100.o

If X =
0 = autodetect speed and duplex
1 = 10Mbps, half duplex
2 = 10Mbps, full duplex
3 = 100Mbps, half duplex
4 = 100Mbps, full duplex

Intel EtherExpress/1000 Gigabite1000.o 
Intel i82557/i82558 PCI EtherExpressPro drivereepro100.o 
NatSemi DP83815 Fast Ethernetnatsemi.o 
AMD PCnet32 and AMD PCnetPCIpcnet32.o 
SIS 900/701G PCI Fast Ethernetsis900.o 
Digital 21x4x Tulip PCI Ethernet cards SMC EtherPower 10 PCI(8432T/8432BT) SMC EtherPower 10/100 PCI(9332DST) DEC EtherWorks 100/10 PCI(DE500-XA) DEC EtherWorks 10 PCI(DE450) DEC QSILVER's, Znyx 312 etherarray Allied Telesis LA100PCI-T Danpex EN-9400, Cogent EM110tulip.oio=io_port
VIA Rhine PCI Fast Ethernet cards with either the VIA VT86c100A Rhine-II PCI or 3043 Rhine-I D-Link DFE-930-TX PCI 10/100via-rhine.o 

Table A-2. Ethernet Module Parameters

A.3.1. Using Multiple Ethernet Cards

It is possible to use multiple Ethernet cards on a single machine. For each card there must be an alias and, possibly, options lines for each card in /etc/modules.conf. Refer to the chapter titled Kernel Modules in the Red Hat Enterprise Linux System Administration Guide for more information.

For additional information about using multiple Ethernet cards, refer to the Linux Ethernet-HOWTO online at http://www.redhat.com/mirrors/LDP/HOWTO/Ethernet-HOWTO.html.

A.3.2. The Channel Bonding Module

Red Hat Enterprise Linux allows administrators to bind NICs together into a single channel using the bonding kernel module and a special network interface, called a channel bonding interface. Channel bonding enables two or more network interfaces to act as one, simultaneously increasing the bandwidth and providing redundancy.

To channel bond multiple network interfaces, the administrator must perform the following steps:

  1. Add the following line to /etc/modules.conf:

    alias bond<N> bonding

    Replace <N> with the interface number, such as 0. For each configured channel bonding interface, there must be a corresponding entry in /etc/modules.conf.

  2. Configure a channel bonding interface as outlined in Section 8.2.3 Channel Bonding Interfaces.

  3. To enhance performance, adjust available module options to ascertain what combination works best. Pay particular attention to the miimon or arp_interval and the arp_ip_target parameters. Refer to Section A.3.2.1 bonding Module Directives for a listing of available options.

  4. After testing, place preferred module options in /etc/modules.conf.

A.3.2.1. bonding Module Directives

Before finalizing the settings for the bonding module, it is a good idea to test which settings work best. To do this, open a shell prompt as root and type:

tail -f /var/log/messages

Open another shell prompt and use the /sbin/insmod command to load the bonding module with different parameters while observing the kernel messages for errors.

The /sbin/insmod command is issued in the following format:

/sbin/insmod bond<N> <parameter=value> 

Replace <N> with the number for the bonding interface. Replace <parameter=value> with a space separated list of desired parameters for the interface.

Once satisfied that there are no errors and after verifying the performance of the bonding interface, add the appropriate bonding module parameters to /etc/modules.conf.

The following is a list of available parameters for the bonding module:

  • mode= — Specifies one of four policies allowed for the bonding module. Acceptable values for this parameter are:

    • 0 — Sets a round-robin policy for fault tolerance and load balancing. Transmissions are received and sent out sequentially on each bonded slave interface beginning with the first one available.

    • 1 — Sets an active-backup policy for fault tolerance. Transmissions are received and sent out via the first available bonded slave interface. Another bonded slave interface is only used if the active bonded slave interface fails.

    • 2 — Sets an XOR (exclusive-or) policy for fault tolerance and load balancing. Using this method, the interface matches up the incoming request's MAC address with the MAC address for one of the slave NICs. Once this link is established, transmissions are sent out sequentially beginning with the first available interface.

    • 3 — Sets a broadcast policy for fault tolerance. All transmissions are sent on all slave interfaces.

    • 4 — Sets an IEEE 802.3ad dynamic link aggregation policy. Creates aggregation groups that share the same speed and duplex settings. Transmits and receives on all slaves in the active aggregator. Requires a switch that is 802.3ad compliant.

    • 5 — Sets a Transmit Load Balancing (TLB) policy for fault tolerance and load balancing. The outgoing traffic is distributed according to the current load on each slave interface. Incoming traffic is received by the current slave. If the receiving slave fails, another slave takes over the MAC address of the failed slave.

    • 6 — Sets an Active Load Balancing (ALB) policy for fault tolerance and load balancing. Includes transmit and receive load balancing for IPV4 traffic. Receive load balancing is achieved through ARP negotiation.

  • miimon= — Specifies (in milliseconds) how often MII link monitoring occurs. This is useful if high availability is required because MII is used to verify that the NIC is active. To verify that the driver for a particular NIC supports the MII tool, type the following command as root:

    ethtool <interface-name> | grep "Link detected:"

    In this command, replace <interface-name> with the name of the device interface, such as eth0, not the bond interface. If MII is supported, the command returns:

    Link detected: yes

    If using a bonded interface for high availability, the module for each NIC must support MII.

    Setting the value to 0 (the default), turns this feature off. When configuring this setting, a good starting point for this parameter is 100.

  • downdelay= — Specifies (in milliseconds) how long to wait after link failure before disabling the link. The value must be a multiple of the value specified in the miimon parameter. The value is set to 0 by default, which disables it.

  • updelay= — Specifies (in milliseconds) how long to wait before enabling a link. The value must be a multiple of the value specified in the miimon parameter. The value is set to 0 by default, which disables it.

  • arp_interval= — Specifies (in milliseconds) how often ARP monitoring occurs.

    If using this setting while in mode 0 or 2 (the two load-balancing modes), the network switch must be configured to distribute packets evenly across the NICs. For more information on how to accomplish this, refer to


    The value is set to 0 by default, which disables it.

  • arp_ip_target= — Specifies the target IP address of ARP requests when the arp_interval parameter is enabled. Up to 16 IP addresses can be specified in a comma separated list.

  • primary= — Specifies the interface name, such as eth0, of the primary device. The primary device is the first of the bonding interfaces to be used and is not abandoned unless it fails. This setting is particularly useful when one NIC in the bonding interface is faster and, therefore, able to handle a bigger load.

    This setting is only valid when the bonding interface is in active-backup mode. Refer to


    for more information.

  • multicast= — Specifies an integer value for the type of multicast support desired.

    Acceptable values for this parameter are:

    • 0 — Disables multicast support.

    • 1 — Enables multicast support, but only on the active slave.

    • 2 — Enables multicast support on all slaves (the default).


It is essential that either the arp_interval and arp_ip_target or miimon parameters are specified. Failure to due so can cause degradation of network performance in the event a link fails.

Refer to:


for detailed instructions regarding bonding interfaces.