lag man page on DigitalUNIX

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lag(7)									lag(7)

NAME
       lag - Link aggregation (also called trunking) introductory information

DESCRIPTION
       Link aggregation, or trunking, enables administrators to combine two or
       more physical Ethernet Network Interface Cards (NICs) and create a sin‐
       gle  virtual  link.   (Upper-layer  software sees this link aggregation
       group as a single virtual interface.) The single virtual link can carry
       traffic	at higher data rates than a single interface because the traf‐
       fic is distributed across all of the physical ports that	 make  up  the
       link aggregation group.

       Using  link  aggregation provides the following capabilities: Increased
       network bandwidth - The increase is incremental based on the number and
       type  of	 ports,	 or  Network Interface Cards (NICs), added to the link
       aggregation group. See the "Load Sharing" section for more information.
       Fault  tolerance	 -  If	a  port in a link aggregation group fails, the
       software detects the failure and reroutes traffic to the	 other	avail‐
       able  ports.  See  the  "Fault Tolerance" section for more information.
       Load sharing - Traffic is distributed across all ports of a link aggre‐
       gation group. See the "Load Sharing" section for more information.

       You  can use a link aggregation group virtual interface for the follow‐
       ing point-to-point connections: server-to-server and  server-to-switch.
       For server-to-switch connections, the switch must support link aggrega‐
       tion. See your switch documentation for information on configuring your
       switch.

       Link  aggregation requires an optional kernel subsystem (lag.mod).  You
       can verify the presence of the link aggregation	subsystem  by  issuing
       the  sysconfig -s lag command.  If the lag subsystem is not loaded, you
       can load it using either of the following methods: Dynamically load  it
       using  the  sysconfig  -c  lag  command.	  This method does not persist
       across system reboots.  Edit the	 system	 configuration	file,  add  an
       options LAG entry to it, and build a new kernel by issuing the doconfig
       command. Then, reboot the system. This method loads the subsystem  each
       time the system reboots.

       After  the  subsystem  is  loaded, you can configure a link aggregation
       group.

   Link Aggregation Configuration
       You can configure link aggregation groups either in multiuser  mode  or
       at boot time with the lagconfig command.	 When you configure the group,
       you can specify a virtual interface number, a key, a distribution algo‐
       rithm, and a Media Access Control (MAC) address.

       After  you  create  a link aggregation group, you can then enable ports
       (interfaces) for link aggregation.  The enabled	ports  attach  to  the
       link  aggregation  group with the corresponding key.  If the port fails
       in some way, the port detaches from the group and traffic  is  rerouted
       to the remaining port or ports.

       Any link aggregation configuration done in multiuser mode does not per‐
       sist across system reboots.  If you want link aggregation  groups  con‐
       figured	at  boot  time, you must include the appropriate lagconfig and
       ifconfig commands in the /etc/inet.local file.  See the Network	Admin‐
       istration: Connections manual for an example.

       On  platforms  where  I/O bandwidth may be a limiting factor, you might
       increase link aggregation performance by distributing the  NICs	across
       different  portions  of	the I/O infrastructure (for example, different
       PCI buses).

   Fault Tolerance
       The link aggregation subsystem monitors the link state  of  ports  that
       are  enabled  for link aggregation. When the link aggregation subsystem
       detects that a port's link state is down, the  subsystem	 detaches  the
       port  from  its	link aggregation group and redistributes traffic among
       the remaining ports.

       When the link aggregation subsystem detects that the port's link	 state
       is up, the subsystem reattaches the port to its link aggregation group.
       The port then starts handling part of  the  traffic  load  again.   The
       amount  of  time	 it  takes to detect a link state change and fail over
       depends on the device and driver in use. For DE60x devices using the ee
       driver, average failover times are typically 1 to 2 seconds. To achieve
       faster failover, reduce the value of the ee subsystem link_check_inter‐
       val  attribute.	A value of 20 (0.2 seconds) typically provides average
       failover times of 0.1 to 0.2 seconds.

       For DEGPA devices using the alt driver, average failover times are less
       than 1 second.

   Load Sharing
       A link aggregation group performs load sharing of both inbound and out‐
       bound traffic.  Distribution of inbound packets is  determined  by  the
       server  or  switch  to  which  the link aggregation group is connected.
       When transmitting packets, the system uses a  load  distribution	 algo‐
       rithm to determine on which attached port to transmit the packets.  The
       following load distribution algorithms are supported: For  IP  packets,
       the  port  is  selected	based on a hash of the destination IP address.
       For non-IP packets, the port is selected based on a hash of the	desti‐
       nation MAC address.  All traffic addressed to a specific destination IP
       address uses the same port in the link aggregation group.

	      This algorithm can utilize the  combined	bandwidth  of  a  link
	      aggregation group in environments where traffic is destined to a
	      large number of different	 IP  addresses	(for  example,	a  web
	      server).

	      However, this algorithm might not produce the expected bandwidth
	      utilization in environments where the  majority  of  traffic  is
	      destined	to a single IP address (for example, a private server-
	      to-server interconnect).	The port is selected based on  a  hash
	      of the destination MAC address.  All traffic addressed to a spe‐
	      cific destination MAC address uses the same  port	 in  the  link
	      aggregation group.

	      This  algorithm  can  utilize  the  combined bandwidth of a link
	      aggregation group in environments where traffic is destined to a
	      large  number  of different MAC addresses (for example, a server
	      that sends most of its traffic to clients on the same LAN).

	      However, this algorithm might not produce the expected bandwidth
	      utilization  in  environments  where  the majority of traffic is
	      destined to a small number of  MAC  addresses  (for  example,  a
	      server-to-server	interconnect,  or  a server that sends most of
	      its traffic through a router).  For TCP or UDP packets originat‐
	      ing  on  the system, the port is selected based on a hash of the
	      source and destination TCP or UDP port numbers.  For  all	 other
	      packets,	including  TCP	and UDP packets being forwarded by the
	      system, the Destination IP address (dstip)  algorithm  is	 used.
	      All traffic addressed to a specific source+destination port pair
	      uses the same port in the link aggregation group.

	      This algorithm can utilize the  combined	bandwidth  of  a  link
	      aggregation group in environments where traffic is destined to a
	      single IP or MAC address, but is exchanged between a  number  of
	      different	 TCP  or UDP port number pairs (for example, a server-
	      to-server interconnect).	The port is  selected  on  a  rotating
	      basis.

	      This  algorithm  can  utilize  the  combined bandwidth of a link
	      aggregation group in most environments.

	      However, this algorithm may  result  in  reordering  of  packets
	      belonging	 to  the  same	flow  (for example, a TCP connection),
	      which in turn may adversely affect performance.

RESTRICTIONS
       The following restrictions apply:  Supports  only  DEGPA	 (alt),	 DEGXA
       (bcm),  and  DE60x  (ee) network interface cards (NICs).	 Supports only
       Ethernet (802.3 CSMA/CD) links.	NetRAIN virtual interfaces  cannot  be
       included	 in  link aggregation groups.  Ports must be operating in full
       duplex mode.  Ports in the same link aggregation group must operate  at
       the same data rate.  Ports in a link aggregation group must be attached
       to the same system, either server-to-server or server-to-switch.

SEE ALSO
       Commands: lagconfig(8)

       System Attributes: sys_attrs_ee(5), sys_attrs_lag(5)

       Files: inet.local(4)

       Technical Overview

       Network Administration: Connections

									lag(7)
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