45.5. Ethernet Parameters

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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 parameters can be viewed using the modinfo command.


For information about using these tools, consult the man pages for ethtool, mii-tool, and modinfo.
Table 45.2. Ethernet Module Parameters
Hardware Module Parameters
3Com EtherLink PCI III/XL Vortex (3c590, 3c592, 3c595, 3c597) Boomerang (3c900, 3c905, 3c595) 3c59x.ko
debug — 3c59x debug level (0-6)
options — 3c59x: Bits 0-3: media type, bit 4: bus mastering, bit 9: full duplex
global_options — 3c59x: same as options, but applies to all NICs if options is unset
full_duplex — 3c59x full duplex setting(s) (1)
global_full_duplex — 3c59x: same as full_duplex, but applies to all NICs if full_duplex is unset
hw_checksums — 3c59x Hardware checksum checking by adapter(s) (0-1)
flow_ctrl — 3c59x 802.3x flow control usage (PAUSE only) (0-1)
enable_wol — 3c59x: Turn on Wake-on-LAN for adapter(s) (0-1)
global_enable_wol — 3c59x: same as enable_wol, but applies to all NICs if enable_wol is unset
rx_copybreak — 3c59x copy breakpoint for copy-only-tiny-frames
max_interrupt_work — 3c59x maximum events handled per interrupt
compaq_ioaddr — 3c59x PCI I/O base address (Compaq BIOS problem workaround)
compaq_irq — 3c59x PCI IRQ number (Compaq BIOS problem workaround)
compaq_device_id — 3c59x PCI device ID (Compaq BIOS problem workaround)
watchdog — 3c59x transmit timeout in milliseconds
global_use_mmio — 3c59x: same as use_mmio, but applies to all NICs if options is unset
use_mmio — 3c59x: use memory-mapped PCI I/O resource (0-1)
RTL8139, SMC EZ Card Fast Ethernet, RealTek cards using RTL8129, or RTL8139 Fast Ethernet chipsets 8139too.ko  
Broadcom 4400 10/100 PCI ethernet driver b44.ko
b44_debug — B44 bitmapped debugging message enable value
Broadcom NetXtreme II BCM5706/5708 Driver bnx2.ko
disable_msi — Disable Message Signaled Interrupt (MSI)
Intel Ether Express/100 driver e100.ko
debug — Debug level (0=none,...,16=all)
eeprom_bad_csum_allow — Allow bad eeprom checksums
Intel EtherExpress/1000 Gigabit e1000.ko
TxDescriptors — Number of transmit descriptors
RxDescriptors — Number of receive descriptors
Speed — Speed setting
Duplex — Duplex setting
AutoNeg — Advertised auto-negotiation setting
FlowControl — Flow Control setting
XsumRX — Disable or enable Receive Checksum offload
TxIntDelay — Transmit Interrupt Delay
TxAbsIntDelay — Transmit Absolute Interrupt Delay
RxIntDelay — Receive Interrupt Delay
RxAbsIntDelay — Receive Absolute Interrupt Delay
InterruptThrottleRate — Interrupt Throttling Rate
SmartPowerDownEnable — Enable PHY smart power down
KumeranLockLoss — Enable Kumeran lock loss workaround
Myricom 10G driver (10GbE) myri10ge.ko
myri10ge_fw_name — Firmware image name
myri10ge_ecrc_enable — Enable Extended CRC on PCI-E
myri10ge_max_intr_slots — Interrupt queue slots
myri10ge_small_bytes — Threshold of small packets
myri10ge_msi — Enable Message Signalled Interrupts
myri10ge_intr_coal_delay — Interrupt coalescing delay
myri10ge_flow_control — Pause parameter
myri10ge_deassert_wait — Wait when deasserting legacy interrupts
myri10ge_force_firmware — Force firmware to assume aligned completions
myri10ge_skb_cross_4k — Can a small skb cross a 4KB boundary?
myri10ge_initial_mtu — Initial MTU
myri10ge_napi_weight — Set NAPI weight
myri10ge_watchdog_timeout — Set watchdog timeout
myri10ge_max_irq_loops — Set stuck legacy IRQ detection threshold
NatSemi DP83815 Fast Ethernet natsemi.ko
mtu — DP8381x MTU (all boards)
debug — DP8381x default debug level
rx_copybreak — DP8381x copy breakpoint for copy-only-tiny-frames
options — DP8381x: Bits 0-3: media type, bit 17: full duplex
full_duplex — DP8381x full duplex setting(s) (1)
AMD PCnet32 and AMD PCnetPCI pcnet32.ko  
PCnet32 and PCnetPCI pcnet32.ko
debug — pcnet32 debug level
max_interrupt_work — pcnet32 maximum events handled per interrupt
rx_copybreak — pcnet32 copy breakpoint for copy-only-tiny-frames
tx_start_pt — pcnet32 transmit start point (0-3)
pcnet32vlb — pcnet32 Vesa local bus (VLB) support (0/1)
options — pcnet32 initial option setting(s) (0-15)
full_duplex — pcnet32 full duplex setting(s) (1)
homepna — pcnet32 mode for 79C978 cards (1 for HomePNA, 0 for Ethernet, default Ethernet
RealTek RTL-8169 Gigabit Ethernet driver r8169.ko
media — force phy operation. Deprecated by ethtool (8).
rx_copybreak — Copy breakpoint for copy-only-tiny-frames
use_dac — Enable PCI DAC. Unsafe on 32 bit PCI slot.
debug — Debug verbosity level (0=none, ..., 16=all)
Neterion Xframe 10GbE Server Adapter s2io.ko  
SIS 900/701G PCI Fast Ethernet sis900.ko
multicast_filter_limit — SiS 900/7016 maximum number of filtered multicast addresses
max_interrupt_work — SiS 900/7016 maximum events handled per interrupt
sis900_debug — SiS 900/7016 bitmapped debugging message level
Adaptec Starfire Ethernet driver starfire.ko
max_interrupt_work — Maximum events handled per interrupt
mtu — MTU (all boards)
debug — Debug level (0-6)
rx_copybreak — Copy breakpoint for copy-only-tiny-frames
intr_latency — Maximum interrupt latency, in microseconds
small_frames — Maximum size of receive frames that bypass interrupt latency (0,64,128,256,512)
options — Deprecated: Bits 0-3: media type, bit 17: full duplex
full_duplex — Deprecated: Forced full-duplex setting (0/1)
enable_hw_cksum — Enable/disable hardware cksum support (0/1)
Broadcom Tigon3 tg3.ko
tg3_debug — Tigon3 bitmapped debugging message enable value
ThunderLAN PCI tlan.ko
aui — ThunderLAN use AUI port(s) (0-1)
duplex — ThunderLAN duplex setting(s) (0-default, 1-half, 2-full)
speed — ThunderLAN port speen setting(s) (0,10,100)
debug — ThunderLAN debug mask
bbuf — ThunderLAN use big buffer (0-1)
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 EM110 tulip.ko io 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 10/100 via-rhine.ko
max_interrupt_work — VIA Rhine maximum events handled per interrupt
debug — VIA Rhine debug level (0-7)
rx_copybreak — VIA Rhine copy breakpoint for copy-only-tiny-frames
avoid_D3 — Avoid power state D3 (work-around for broken BIOSes)

45.5.1. 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/modprobe.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/modprobe.conf.
  2. Configure a channel bonding interface as outlined in Section 16.2.3, “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, “bonding Module Directives” for a list of available options and how to quickly determine the best ones for your bonded interface. bonding Module Directives

It is a good idea to test which channel bonding module parameters work best for your bonded interfaces before adding them to the BONDING_OPTS="<bonding parameters>" directive in your bonding interface configuration file (ifcfg-bond0 for example). Parameters to bonded interfaces can be configured without unloading (and reloading) the bonding module by manipulating files in the sysfs file system.
sysfs is a virtual file system that represents kernel objects as directories, files and symbolic links. sysfs can be used to query for information about kernel objects, and can also manipulate those objects through the use of normal file system commands. The sysfs virtual file system has a line in /etc/fstab, and is mounted under /sys. All bonded interfaces can be configured dynamically by interacting with and manipulating files under the /sys/class/net/ directory.
After you have created a channel bonding interface file such as ifcfg-bond0 and inserted SLAVE=yes and MASTER=bond0 directives in the bonded interfaces following the instructions in Section 16.2.3, “Channel Bonding Interfaces”, you can proceed to testing and determining the best parameters for your bonded interface.
First, bring up the bond you created by running ifconfig bond<N>  up as root:
ifconfig bond0 up
If you have correctly created the ifcfg-bond0 bonding interface file, you will be able to see bond0 listed in the output of running ifconfig (without any options):
~]# ifconfig
bond0     Link encap:Ethernet  HWaddr 00:00:00:00:00:00
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)
eth0      Link encap:Ethernet  HWaddr 52:54:00:26:9E:F1
          inet addr:  Bcast:  Mask:
          inet6 addr: fe80::5054:ff:fe26:9ef1/64 Scope:Link
          RX packets:207 errors:0 dropped:0 overruns:0 frame:0
          TX packets:205 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:70374 (68.7 KiB)  TX bytes:25298 (24.7 KiB)
[output truncated]
To view all existing bonds, even if they are not up, run:
~]# cat /sys/class/net/bonding_masters
You can configure each bond individually by manipulating the files located in the /sys/class/net/bond<N>/bonding/ directory. First, the bond you are configuring must be taken down:
ifconfig bond0 down
As an example, to enable MII monitoring on bond0 with a 1 second interval, you could run (as root):
echo 1000 > /sys/class/net/bond0/bonding/miimon
To configure bond0 for balance-alb mode, you could run either:
echo 6 > /sys/class/net/bond0/bonding/mode
...or, using the name of the mode:
echo balance-alb > /sys/class/net/bond0/bonding/mode
After configuring some options for the bond in question, you can bring it up and test it by running ifconfig bond<N> up . If you decide to change the options, take the interface down, modify its parameters using sysfs, bring it back up, and re-test.
Once you have determined the best set of parameters for your bond, add those parameters as a space-separated list to the BONDING_OPTS= directive of the /etc/sysconfig/network-scripts/ifcfg-bond<N> file for the bonded interface you are configuring. Whenever that bond is brought up (for example, by the system during the boot sequence if the ONBOOT=yes directive is set), the bonding options specified in the BONDING_OPTS will take effect for that bond. For more information on configuring bonded interfaces (and BONDING_OPTS), refer to Section 16.2.3, “Channel Bonding Interfaces”.
The following is a list of available channel bonding module parameters for the bonding module. For more in-depth information on configuring channel bonding and the exhaustive list of bonding module parameters, install the kernel-doc package and then locating and opening the included bonding.txt file:
yum -y install kernel-doc
nano -w $(rpm -ql kernel-doc | grep bonding.txt)

Bonding Interface Parameters

Specifies (in milliseconds) how often ARP monitoring occurs.


It is essential that both arp_interval and arp_ip_target parameters are specified, or, alternatively, the miimon parameter is specified. Failure to do so can cause degradation of network performance in the event that a link fails.
If using this setting while in mode=0 or mode=1 (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 /usr/share/doc/kernel-doc-<kernel_version>/Documentation/networking/bonding.txt
The value is set to 0 by default, which disables it.
arp_ip_target=<ip_address> [,<ip_address_2>,...<ip_address_16> ]
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.
Validate source/distribution of ARP probes; default is none. Other valid values are active, backup, and all.
Enables debug messages. Possible values are:
  • 0 — Debug messages are disabled. This is the default.
  • 1 — Debug messages are enabled.
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.
Specifies the rate at which link partners should transmit LACPDU packets in 802.3ad mode. Possible values are:
  • slow or 0 — Default setting. This specifies that partners should transmit LACPDUs every 30 seconds.
  • fast or 1 — Specifies that partners should transmit LACPDUs every 1 second.
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.


It is essential that both arp_interval and arp_ip_target parameters are specified, or, alternatively, the miimon parameter is specified. Failure to do so can cause degradation of network performance in the event that a link fails.
...where <value> is one of:
  • balance-rr or 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.
  • active-backup or 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.
  • balance-xor or 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.
  • broadcast or 3 — Sets a broadcast policy for fault tolerance. All transmissions are sent on all slave interfaces.
  • 802.3ad or 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.
  • balance-tlb or 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.
  • balance-alb or 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.
Specifies the number of unsolicited IPv6 Neighbor Advertisements to be issued after a failover event. One unsolicited NA is issued immediately after the failover.
The valid range is 0 - 255; the default value is 1. This option affects only the active-backup mode.
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 /usr/share/doc/kernel-doc-<kernel-version>/Documentation/networking/bonding.txt for more information.
Specifies the reselection policy for the primary slave. This affects how the primary slave is chosen to become the active slave when failure of the active slave or recovery of the primary slave occurs. This option is designed to prevent flip-flopping between the primary slave and other slaves. Possible values are:
  • always or 0 (default) — The primary slave becomes the active slave whenever it comes back up.
  • better or 1 — The primary slave becomes the active slave when it comes back up, if the speed and duplex of the primary slave is better than the speed and duplex of the current active slave.
  • failure or 2 — The primary slave becomes the active slave only if the current active slave fails and the primary slave is up.
The primary_reselect setting is ignored in two cases:
  • If no slaves are active, the first slave to recover is made the active slave.
  • When initially enslaved, the primary slave is always made the active slave.
Changing the primary_reselect policy via sysfs will cause an immediate selection of the best active slave according to the new policy. This may or may not result in a change of the active slave, depending upon the circumstances
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.
Specifies whether or not miimon should use MII/ETHTOOL ioctls or netif_carrier_ok() to determine the link state. The netif_carrier_ok() function relies on the device driver to maintains its state with netif_carrier_on/off ; most device drivers support this function.
The MII/ETHROOL ioctls tools utilize a deprecated calling sequence within the kernel. However, this is still configurable in case your device driver does not support netif_carrier_on/off .
Valid values are:
  • 1 — Default setting. Enables the use of netif_carrier_ok().
  • 0 — Enables the use of MII/ETHTOOL ioctls.


If the bonding interface insists that the link is up when it should not be, it is possible that your network device driver does not support netif_carrier_on/off .
Selects the transmit hash policy used for slave selection in balance-xor and 802.3ad modes. Possible values are:
  • 0 or layer2 — Default setting. This option uses the XOR of hardware MAC addresses to generate the hash. The formula used is:
    (<source_MAC_address> XOR <destination_MAC>) MODULO <slave_count>
    This algorithm will place all traffic to a particular network peer on the same slave, and is 802.3ad compliant.
  • 1 or layer3+4 — Uses upper layer protocol information (when available) to generate the hash. This allows for traffic to a particular network peer to span multiple slaves, although a single connection will not span multiple slaves.
    The formula for unfragmented TCP and UDP packets used is:
    ((<source_port> XOR <dest_port>) XOR
      ((<source_IP> XOR <dest_IP>) AND 0xffff)
        MODULO <slave_count>
    For fragmented TCP or UDP packets and all other IP protocol traffic, the source and destination port information is omitted. For non-IP traffic, the formula is the same as the layer2 transmit hash policy.
    This policy intends to mimic the behavior of certain switches; particularly, Cisco switches with PFC2 as well as some Foundry and IBM products.
    The algorithm used by this policy is not 802.3ad compliant.
  • 2 or layer2+3 — Uses a combination of layer2 and layer3 protocol information to generate the hash.
    Uses XOR of hardware MAC addresses and IP addresses to generate the hash. The formula is:
    (((<source_IP> XOR <dest_IP>) AND 0xffff) XOR
      ( <source_MAC> XOR <destination_MAC> ))
        MODULO <slave_count>
    This algorithm will place all traffic to a particular network peer on the same slave. For non-IP traffic, the formula is the same as for the layer2 transmit hash policy.
    This policy is intended to provide a more balanced distribution of traffic than layer2 alone, especially in environments where a layer3 gateway device is required to reach most destinations.
    This algorithm is 802.3ad compliant.
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