1. Link Aggregation
AT-8000S

2. Trunk/SmartTrunk/port-channel
Device #1 Channel Device #2
• Several physical ports are joined together to be one logical
port with a higher bandwidth.
• Link aggregation is defined and controlled by the
IEEE802.3ad standard.

3. Link Aggregation
• Providing higher bandwidth connections where and when
needed, without requiring higher bandwidth connections.
• Better bandwidth granularity – if a connection needs to
have a higher capacity than the standard link, it can be
achieved without requiring a link with a 10-fold speed
increase, which may well be an overkill (or may not exist) .
• The trunk has many terms: Trunks, Aggregated Links,
Link Aggregation Groups - LAG, Channel-group and Port-
channeling

4. LAG – Types and Attributes
• Aggregated Links may be set up manually, or automatically by
enabling LACP (Link Aggregation Control Protocol) on the
relevant links.
• An Aggregated Link is treated by the system as a single logical
port, in the same manner as any other port in the system.
• In particular, the Aggregated link has port attributes similar to a
“regular” port – Auto negotiation state, speed, Duplex setting,
etc.
• These attributes are applied to all ports in the LAG
• The system uses balancing rules to decide which frames will be
forwarded on which aggregate-link member.

5. Link Aggregation ports
• The user may aggregate ports into link-aggregation port-groups.
Each group is composed of ports of the same speed.
• Ports in a LAG may be of different media types (Copper/Fiber, or
different fiber types), provided they have the same speed
capabilities.

6. Aggregated Link Port Type
• Each Aggregated Link has an “Aggregated Link Port Type”
(e.g. Fast Ethernet, Gigabit Ethernet). This is defined as the
type of the first port to be added to this Aggregated link.
• A port may be added to an aggregated link only if it has the
same type as the “Aggregated Link Port Type”
• When a port is added to a LAG, it takes on the attributes of
the aggregated link.

7. Applications
WEB Server
Windows
Multimedia FTP Server
LAG Server
LAG
WEB Server
Linux
FTP Server
WEB server

8. AT-8000S
LAG
Implementation

9. LAG on the AT-8000S
• The AT-8000S supports 8 Aggregated Links each with up
to 8 member ports.
• The LAGs already exist on the device, and do not have to
be created. All that is needed is to add the ports to the
existing aggregate links.
• Features includes:
– aggregate throughput
– incremental bandwidth
– link redundancy
– traffic load balancing

10. LAG Configuration Rules
• If a VLAN is configured on a port it cannot be added to a LAG
(excluding the default VLAN VID#1)
• When a port is added to a LAG – it is removed from the
default VLAN
• All the ports who are members of a LAG automatically
implement the auto negotiation and speed configuration of
the LAG.

11. LAG Configuration Rules
• By default auto negotiation is enabled on the LAG, but user
can define it to full duplex and set speed.
– Ports may be configured for speed and auto negotiation when
they are members of a LAG, but the setting will not take effect
until they are removed from the LAG. That way the user may
set the port settings for the port to be implemented when/if it
is removed from the LAG.

12. LAG –Load Balance
• The Packet Processor performs load balancing for packets
to be transmitted on the LAG.
• Load balancing is performed for all types of packets
transmitted on the LAG (Unicast; multicast, broadcast and
unknown).
• The hash index is calculated so as to load-balance the
traffic evenly across all LAG members, at the same time
ensuring that packets of any given flow are not reordered.

13. LAG – User Setting
• Port level settings:
– Adding/removing from a channel group
– Defining the LAG member as static (on) or LACP (auto).
• Channel- port level settings:
– General port settings (e.g flow-control, back-pressure, auto-
negotiation, GVRP, STP, port speed etc), like any other port interface.
– Note that LAG can be either auto-negotiation or full duplex but not half
duplex

14. AT-8000S
LAG
CLI Configuration

15. CLI – Adding Ports to LAGs
• Use the following Interface Mode command to add a port
to a Channel-Port:
channel-group port-channel-number mode {on|auto}
• Mode “on” is static LAG and mode “auto” is LACP
• Note that the port cannot belong to a VLAN other than
the default VLAN.
• Use the “no” form of the command to remove the
channel group configuration
no channel-group

16. CLI – LAG Configuration
• Example – LAG (Static) configuration:
– Adding port range 1/e1- 7 to channel-group 1
console# configure
console(config)# interface Range ethernet 1/e(1-7)
console(config-if)# channel-group 1 mode on
12-Aug-2004 17:44:57 %TRUNK-I-PORTADDED: Port 1/e1 added to ch1
12-Aug-2004 17:44:57 %LINK-I-Up: ch1
12-Aug-2004 17:44:57 %TRUNK-I-PORTADDED: Port 1/e2 added to ch1
12-Aug-2004 17:44:58 %TRUNK-I-PORTADDED: Port 1/e3 added to ch1
12-Aug-2004 17:44:58 %TRUNK-I-PORTADDED: Port 1/e4 added to ch1
12-Aug-2004 17:44:58 %TRUNK-I-PORTADDED: Port 1/e5 added to ch1
12-Aug-2004 17:44:58 %TRUNK-I-PORTADDED: Port 1/e6 added to ch1
12-Aug-2004 17:44:58 %TRUNK-I-PORTADDED: Port 1/e7 added to ch1
console(config-if)# 12-Aug-2004 17:45:27 %STP-W-PORTSTATUS: ch1:
STP status Forwarding

17. CLI –LAG Show Commands
• Use the following EXEC Mode command to view the
members of a group-channel
show interfaces port-channel [port-channel-number]
• To view all port-channels – omit the channel number.

18. CLI – LAG Show Command
• Example – showing information for port-channel 1
– Ports who are members in the port-channel
console# show interfaces port-channel 1
Channel Ports
....... .....
ch1 active: 1/e(1-7)

19. AT-8000S
LACP

20. LACP - General
• Link Aggregation Control Protocol (LACP)
• The 802.3ad standard provides for the formation of a single Layer 2
link from two or more standard Ethernet member links via
automatic member link activation
• LACP provides a robust means of assuring that both ends of the
link are up and agree to be members of the aggregation before the
link member is activated
• LACP must be enabled at both ends of the link to be operational.
• It automatically determines which member links can be aggregated
and then aggregates them. It provides for the controlled addition
and removal of physical links to the link aggregation such that no
frames are lost or duplicated

21. LACP Operation
• LACP has no concept of “request and response” – the
protocol does not issue any “commands”
• LACP expects all devices to “make the right decision”
based on their own state and protocol distributed
information
• Devices compare their own information with that of
their neighbors and decide what action to take
• Information exchange is periodic and timely – so any
change in configuration is detected
• LACP messages are contained within the specific link

22. LACP Process – device ID
• Messages are sent between 2 attached devices
• Each device sees itself as the “actor”, and the other device as
the “partner”
• The “Actor” (i.e each device) compares its own information to
that of the partner and decides what actions to take
• LAGs are created only among links connecting the same pair
of devices
• Therefore, each device has a unique system ID. As in STP it
is 64 bits long containing a priority field (16 bits) + MAC (48
bits)
SysID=pr_field+MAC
• An Actor will consider aggregating links together only if the
parallel links on the other (Partner) device have the same
system ID, as indicated in their LACP information

23. LACP Process – System Key
• Another use for the system ID is to determine which device has the
lower ID (can be controlled by the priority field)
• For links to aggregate to one LAG – not only must they have the
same system ID, they also have to have the same system allocated
(LAG) key (16 bits).
• Links with the same device ID but different key values – cannot be
aggregated to the same LAG

24. LACP Process – System Key
• Keys are assigned by the system and can be based
on:
– Different speeds
– Physical limitation (of device) to aggregate ports
– User defined groups (i.e defined as a separate LAG group by
administrator)
Summary: for links to be join together in a LAG with
another device, they must have the following 3
identical values:
 System priority
 System MAC
 System allocated (LAG) key

25. LACP Process – Port Priority
• Each potential aggregate port has a port ID consisted
of a port priority (16 bits) and port number (16 bits)
• A Lower ID means a higher priority
• The port ID determines which ports will have
precedence over others to join the LAG
• The system with the LOWER SYSTEM ID is the one
who “rules” on port priority, and therefore which links
have precedence in joining a LAG (if there are more
links than LAG allows)

26. LACP Process – sending messages
• LACP ports have 2 modes of operation:
– Active mode – will generate LACP messages on a regular
basis
– Passive mode – will not generates messages unless first
“spoken to” (by an active mode port)
• Messages can be sent in a fast rate (1 sec’) or slow rate
(30 sec’). The rate used is determined by the partner.
• Each message contains information of both Actor and
identified Partner

27. LACP PDU (Actor and Partner)
LAG ID
Device #1 Device #2
• System priority – 16bits
• MAC – device MAC address
• Key – Key number of the dynamic LAG. (ifindex of the LAG)
Will be used only when ports exceed the
• *Port-priority number of allowed ports within the LAG
• *Port number

28. Actor/Partner state in the PDU
7 6 5 4 3 2 1 0
0x46 0 1 0 0 0 1 1 0
• ‘0’ – Activity 1=active mode; 0= passive mode
• ‘1’ – Time out 0=long 30 sec’; 1=short 1sec’
• ‘2’ – Aggregation 0=individual only; 1=can be aggregated
• ‘3’ – Synchronize 0=admin; 1=operative active state
• ‘4’ – Collecting 0=off; 1=on
• ‘5’ – Distribute 0=off; 1=on
• ‘6’ – Default
• ‘7’ – Experience

29. AT-8000S
LACP
Implementation

30. LACP – Implementation
• Layer 2 protocol
• LACP must be enabled at both ends of the link to be
operational
• Static and dynamic ports can not work at the same LAG
• Ports are in the Active mode.
• Each LAG has its own specific LAG key, which is the
“ifIndex” of the LAG interface.
• User can configure more than 8 ports as potential LACP
LAG members. However LACP will use only up to 8 ports
with “best” (lowest) port ID.

31. LACP – Implementation
• If several ports with different operative speed (due to
auto-negotiation…) are attempting to join a new or
existing LAG, only the higher speed port(s) will join,
and lower speed ports will not join/ will be removed
from the LAG
• The system will notify the user (log message, SNMP
trap, etc.) whenever a port is added/removed from an
Aggregated Link, or when it changes state to/from
standby, or changes its attributes due to auto
negotiation.

32. LAG ID and Port Priority
• When LACP is used, each LAG is uniquely identified by a
LAG ID.
• The value of the LAG ID is important to BOTH SIDES OF
THE LAG.
• All ports in a LAG (on a single device) must have the same
LAG ID.
• Ports have a per-port LAG priority. When an “Opening” for
an additional LAG member is available, and there are
inactive LAG members, they will be made Active in the
order of their port LAG priority.

33. LAG - Port Priority
• If the per-port LACP priority of the link is lower than
that of the currently active link members, and there is
already the maximum possible number of active
members, then the link will be made inactive.
• If the per-port LACP priority of the new link is higher
than that of one the currently active link members, the
new link will become active, and an existing link will be
made inactive.

34. Example 1
Device #1 Device #2
E1 100FE 100FE
Key E1 Key
E2 100FE 100FE
E2
25 E3 100FE 100FE 27
Key 29 E3
E4 10FE 10FE
E4
Key E5 10FE 10FE
E5 Key
E6 10FE 10FE 28
26 E6
Device #3

35. Example 2
Device #1 Device #2
Key E1 100FE 100FE E1
Key
25 E2 100FE 100FE E2
100FE 100FE E3 27
Key 29 E3
10FE 10FE
E4 E4
Key E5
10FE 10FE E5 Key
26 E6
10FE 10FE E6 28
100FE 100FE
Device #3

36. Example 3
Device #1 Device #2
Key E1 100FE 100FE E1 Key
25 E2 100FE 100FE E2
E3 100FE 100FE
27
Key 29 E3
E4 10FE 10FE
E4
Key E5 10FE 10FE
E5
Key
26 E6 100FE 100FE
E6 28
Device #3

37. LACP – User Setting
• Device Level Configuration:
– Assign system priority (1-65535; default is 1)
• Port-Channel Level configuration:
– The same as in regular LAG
• Port Level configuration:
– Adding a port to a LAG and defining it as LACP
– Assign port priority (1-65535; default is 1)
– Define short or long timeout (default is short)

38. AT-8000S
LACP
CLI Configuration

39. CLI – Adding Ports to LACP LAGs
• Use the following Ethernet Interface Mode command to add
a port to a LACP Channel-Port:
channel-group port-channel-number mode auto
• Mode “auto” is LACP type channel
• Note that the port cannot belong to a VLAN other than the
default VLAN.
• Use the “no” form of the command to remove the channel
group configuration
no channel-group

40. CLI – LACP System Priority
• Use the following Global Mode command to set LACP
system priority (the “no” form resets value to default):
lacp system-priority value
no lacp system-priority

41. CLI – LACP port Parameters
• Use the following Ethernet Interface Mode command to
set LACP port priority (the “no” form resets value to
default):
lacp port-priority value
no lacp port-priority
• Use the following command to set LACP port timeout
value (the “no” form resets value to default):
lacp timeout { long | short }
no lacp timeout

42. CLI – LACP Configuration
• Example –LACP configuration:
– Adding port range 1/e11-18 to channel-group 3
– Defining system priority to 100
– Defining LACP port priority of port 1/e10 to 50
– Defining timeout of port 1/e10 to long
console(config)# interface Range ethernet 1/e(11-18)
console(config-if)# channel-group 3 mode auto
console(config-if)#
console(config)# lacp system-priority 100
console(config)# interface ethernet 1/e10
console(config-if)# lacp port-priority 50
console(config-if)# lacp timeout long

43. CLI – LACP Show Commands
• To view LACP parameters of a specific Ethernet port (omit
keyword to view all details):
show lacp ethernet interface [parameters | statistics | protocol-state]
• The can be displayed:
– Parameters: Actor and Partner parameters
– Statistics – PDU sent and received
– Protocol state: protocol state info
• If the port is not LACP, show command will state only that
the port is not LACP enabled.

44. CLI – LACP Show Commands
• Example –LACP command, show:
– port 1/e4 (doesn’t belong to LACP LAG)
– statistic for port 1/e11 (LACP LAG port)
console# show lacp ethernet 1/e4 parameters
LACP is not enabled on 1/e4
console# show lacp ethernet 1/e11 statistics
1/e5 LACP statistics:
LACP Pdus sent: 30
LACP Pdus received: 0

45. CLI – LACP Show Commands
• Example – show port 1/e6 LACP parameters:
console# show lacp ethernet 1/e6 parameters
1/e11 LACP parameters:
Actor
system priority: 1
system mac addr: 00:00:b0:11:22:99
port Admin key: 1004
port Oper key: 1004
port Oper number: 6
port Admin priority: 1
…..
…..

46. CLI – LACP Show Commands
• To view LACP parameters of a port channel:
show lacp port-channel [ port_channel_number ]
console# show lacp port-channel 1
Port Type 100 Ethernet
Attached Lag id:
Actor
System Priority:100
MAC Address: 20:06:12:03:10:00
Admin Key: 1000
Oper Key: 1000
Partner
System Priority:0
MAC Address: 00:00:00:00:00:00
Oper Key: 0

47. AT-8000S
Lag and LACP
Examples

48. Example #1
Vlan 33, 34, Vlan 33
35 (trunk) (Access)
GVRP CoS 7
enable (on
LAG)
AT-8000S #1 AT-8000S #2 AT-8000S #3
Regular LACP
LAG LAG

49. Example 1 - Configuration
• Configuration relates to AT-8000S #2
• Define ports 1/e(1-7) as Channel-Group 1, - regular LAG
• Define ports 1/e(16-23) as channel-group 2 - LACP LAG
• Before adding ports use show command to verify that
ports do not have configuration which does not allow
them to join a LAG (such as VLAN, GVRP, IP address, ACL
etc)

50. Example 1 - Configuration
• On channel group 1 – define it as a VLAN trunk mode
port, with VLANs 33,34,35. Enable GVRP on the LAG.
• On channel group 2 – define it as Access VLAN port
member of VLAN 33. Assign the LAG default COS of 7.

51. Example 1 - Table
Config LAG VLAN Other
Interface
1/e1-7 LAG 1 mode on No VLAN on “Clean port”
ports
1/e16-23 LAG 2 mode No VLAN on “Clean port”
auto ports
LAG 1 ----- Trunk VID GVRP enable
33,34,35
LAG 2 ----- Access VID 33 Default COS = 7

52. Example 1 - CLI
console(config)#
console# configure
console(config)# vlan database
console(config-vlan)# vlan 33-35
console(config-vlan)#
console(config)# interface range ethernet 1/e(1-7)
console(config-if)# channel-group 1 mode on
L3 interface is defined on port 1/e1
console(config-if)#
console(config)# interface ethernet 1/e1
console(config-if)# no ip address
console(config)# interface range ethernet 1/e1-7
console(config-if)# channel-group 1 mode on
console(config-if)#

53. Example 1 – CLI Cont’
console(config)# interface range ethernet 1/e(16-23)
console(config-if)# channel-group 2 mode auto
console(config-if)#
console(config)# interface port-channel 1
console(config-if)# switchport mode trunk
console(config-if)# switchport trunk allowed vlan add 33-35
console(config-if)# gvrp enable
console(config-if)#
console(config)# interface port-channel 2
console(config-if)# switchport access vlan 33
console(config-if)# qos cos 7
console(config-if)#

54. Example 1 – CLI Cont’
console# show vlan
Vlan Name Ports Type
---- -------------------------------- --------------------------- ------------
1 1 1/e(8-15, 24), ch(1,3-8) other
33 33 ch(1-2) permanent
34 34 ch1 permanent
35 35 ch1 permanent
console# show interfaces port-channel
Channel Ports
....... .....
ch1 Active: 1/e(1-7)
ch2 Active: 1/e(16-23)
….
ch8

55. Example 1 – CLI Cont’
console# show lacp port-channel 2
Port-Channel ch2
Port Type 100 Ethernet
Attached Lag id:
Actor
System Priority:1
MAC Address: 20:06:12:03:10:00
Admin Key: 1001
Oper Key: 1001
Partner
System Priority:0
MAC Address: 00:00:00:00:00:00
Oper Key: 0
consconsole#

56. AT-8000S
LAG & LACP
Troubleshooting

57. Troubleshooting
The challenges for LAG can be divided into two main areas:
• Troubleshooting during the configuration phase, and
troubleshooting during the execution phase.
• Configuration errors usually occur because of mismatched
parameters on the ports involved (different speeds, different
duplex, and so on).
• But you can also generate errors during the configuration by
setting the channel on one side to “on” and waiting too long
before configuring the channel on the other side. This
causes spanning tree loops, which generate an error in the
network.

58. Troubleshooting
• Link aggregation and Spanning-Tree protocol.
– The port will be automatically configured to the LAG
parameters whenever joining the group. When the port is
removed from the group, the port will return to its own
“private” port configuration.
– Configuring two devices for LAG while already
connected. (disable ports, configuring, enable ports).
• Link aggregation and tagging.
– These are completely separate features. The same as
previous item: The port will be automatically configured
to the LAG parameters whenever joining the group.

59. Possible Problem Solution
problem description
There is Ping doesn’t 1. Use show interfaces port-channel command to check that
no traffic run between the configuration of the particular LAG is correct.
through devices 2. Use show lacp ethernet command to check whether lacp is
the LAG through the enabled on the particular port.
LAG 3. Use show lacp port-channel command to check LAG
attributes.
4. Use show interfaces configuration command to check that
the ports to be grouped have the same settings
5. Use show spanning-tree port-channel command to check
the LAG spanning-tree parameters

60. Possible problem Problem Solution
description
Traffic is not Some ports 1. If LAG is configured to auto-negotiation some of its
forwarded on where added links may have reduced speed to 100/10Mbps. In such
some of the to a LAG as a case lower speed ports will not be active in the LAG.
LAG ports members, but Use show interfaces status to view LAG ports speed.
when running 2. If LAG is LACP, there may be more ports defined to
traffic on the the LAG then actually operationally possible (on this
device they or neighbor device). Beyond the allowed number,
are not used ports with lower port priority will be set to inactive.
to forward Use show lacp ethernet X parameters to view specific
packets port priority. Use lacp port-priority command to set
port priority.
3. If LACP LAG port is connected to a regular port on
neighbor device – it will not function as a LAG
member.
4. Due to physical problems port has synchronization
problems and will not function properly. Disconnect
and reconnect port

61. Possible problem Problem Solution
description
There are no Ping doesn’t 1. Check that the device security parameters are
trap messages run between configured correctly.
neither on the devices 2. Check configuration of the SysLog Server
ASCII terminal through the 3. If needed perform set of operations presented on the
nor on the LAG previous slide.
SysLog server
regarding
dynamic port
joining the
LAG