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					     Link Aggregation
Over View of the IEEE 802.3ad-2000
                        (clause 43)

     Authors: Anthony Mwingira, Jon
                            Sterritt
       Bridge Functions Consortium
Introduction
Link Aggregation (LA): The combination of
  multiple physical links to function as a single
  logical link.
Link Aggregation Group (LAG): A group of
  physical links that make up a single
  aggregation. Each physical port may be a
  member of a single LAG.
Link Aggregation Control Protocol (LACP): The
  protocol specified by IEEE 802.3.ad-2000 to
  outline standardized Link Aggregation.
Possible Problems and Issues
   By combining multiple physical links to form a
    single logical link two notable issues could
    occur:
       Frame duplication, “flooding”
       Frame disordering

    Both of these issues are addressed by LACP.
Goals and Objectives of LA
   Increased bandwidth – multiple links combined into one
    logical link
   Linearly incremental bandwidth – increase in unit
    multiples
   Increased availability – failure of a single link within aggr.
    Need not cause MAC client failure
   Load Sharing – MAC Client traffic may be distributed
    across links
   Auto Configuration – in even of changes in physical
    connection
   Rapid configuration and reconfiguration – also in the
    event of changes in physical connection
   Deterministic behavior – independent of
    algorithm chosen( implementer can choose
    internal algorithm). The configuration can
    be made to resolve deterministically i.e.
    resulting aggr. Can be made independent of
    the order in which events occur, and be
    completely determined by the capabilities of
    the individual links and their physical
    connectivity.
   Low risk of duplication or mis-ordering – during
    link reconfiguration or steady-state operation there
    is a high probability that frames are neither
    duplicated or mis-ordered.

   Backwards compatibility with aggregation-
    unaware devices - Link that can not take part in
    an aggregation operate as normal, individual links.

    Multipoint Aggregations – does not support
    aggregations among more than two systems;
    multiple aggregations are allowed, but 3 systems
    cannot share a single Link Aggregation Group.
Limitations:
 MACs – supported only on links using
  the IEEE 802.3 MAC
 Half-duplex operation – supported
  only on point-to-point links with MACs
  operating in full duplex mode.
 Multiple data rates – All Links in a
  Link Aggregation Group operate at
  the same data rate (e.g. 10 Mb/s, 100
  Mb/s or 1000 Mb/s )
LAG Operation
   Frame Distribution - Responsible for taking frames from MAC Client and
    submitting them for transmission on appropriate ports.
   Frame Collection – Responsible for passing frames received from the various
    ports to the MAC Client -> also includes Marker Responder ( Marker protocol
    – allows the distribution function of an Actor’s Link Aggregation sub-layer to
    request the transmission of a Marker PDU on a given link)
   Aggregator Parser/ Multiplexers. When transmitting these blocks pass frame
    requests to the appropriate port. When receiving, distinguish frames and pass
    them to appropriate entity.
   Aggregator – This is the combination of frame Distribution and Collection, along
    with the aggregator Parser/ Multiplexers.
   Aggregation Control – Responsible for configuration and control of the Link
    Aggregation.
   Control Parser/Multiplexers – On transmit -> pass frame transmission requests
    from the Aggregator and Control entities to the appropriate port. On receive,
    these blocks distinguish Link Aggregation Control PDUs from other frames,
    passing LACPDUs to the appropriate sub-layer entity, and all other frames to
    the Aggregator.
Principles of Link Aggregation
   Note: Link Aggregation allows a MAC Client to treat a set
    of one or more ports as if it were a single port.

   A Mac Client communicates with a set of ports through
    an Aggregator. An Aggregator binds to one or more
    ports within a System.

   It is the responsibility of an Aggregator to distribute
    frame transmissions from the MAC Client to the various
    ports, and to collect received frames from the ports and
    pass them to the MAC Client transparently.

   A given port will bind to (at most) a single Aggregator at
    any time. A MAC Client is served by a single Aggregator
    at a time.
   The binding of ports to Aggregators within a
    System is managed by the Link Aggregation
    Control function for that System.

   a unique, globally administered MAC address.
   Binding may be under manual control through direct manipulation
    of the state variables of Link Aggregation (e.g. Keys) by net
    manager. Automatic determination, configuration, binding, and
    monitoring my occur through the use of Link Aggregation Control
    Protocol (LACP)

   Frame ordering must be maintained. The distributor ensures that
    all frames of a given conversation are past to a single port. They
    are to be passed in order they were received from that port.

   Conversations may be moved among ports within aggregation,
    both for load balancing and to maintain availability in the event of
    a link failures.

   Each port is assigned a unique , globally administered MAC
    address. ( Prospective of a MAC Client)

   Each Aggregator is assigned a unique, globally administered
    MAC address.
Link Aggregation Control
 Link Aggregation Control configures and
  controls the Link Aggregation sub layer using
  static information local to the function and
  dynamic information exchanged by means of
  the Link Aggregation Control Protocol.
For Each aggregatable port in the System:
 Maintains Configuration information to
  control aggregation
   Exchange configuration information with other
    with other Systems to allocate the link to a Link
    Aggregation Group. NOTE a given link is allocated
    to, at most, one Link Aggregation Group at a
    time.
   Attaches the port to the Aggregator used by the Link
    Aggregator Group, and detaches the port from the
    Aggregator when it is no longer used by the Group
   Uses information from the Partner Systems’ Link
    Aggregation Control entity to enable or disable the
    Aggregator or Distributor
   Checking that candidate links are actually be
    aggregated.
   Controlling link addition to Aggr. Group and
    the creation of a Group if necessary
   Monitoring the status of aggregated links
   Removing a Link from a Link Aggr. Group if
    its membership is no longer valid, and
    removing the group if it no longer has any
    member links.
Test Suite – General How To
   See Cisco Document, most devices work just
    like Cisco with different variations, all the
    following could port a port into LAG1 in active
    mode depending on the device.
        “channel-group 1 mode active” (Cisco)
        “channel-group 1 mode auto” (some Cisco)
        “port-channel” 1 mode auto
       “LACP mode auto”
        “LACP key 1” (Foundry uses keys, no LAG’s)
          How To Configure LAG’S
Different Strategies by Vendor
#1 Cisco - go into the interface prompt and put that
  interface into a LAG, i.e.,“channel-group”
#2 Dell - command line, almost identical to Cisco, Web
  Interface the ports are configured from the LAG
  menu
#3 HP, Nortel - LAG’s configured as “trunks” that run
  LACP as a protocol.
#4 3Com – From menu driven command line ports
  must be activated for LACP (port menu) and then
  added to an activated LAG (Link Agg. Menu).
#5 Other “odd” implementations require setting keys,
  most devices require ports assigned to a LAG, but
  some require setting the Key for each port, the result
  is equivalent.
        More About Configuration
   #1 Configure LAG’s, some tests require multiple LAG’s

   Complete Cabling/Setup

   Ensure that for the device you are working on there is
    not a way to configure the LAG as an interface – i.e.,
    sometimes you can configure the group as if it was a
    port – allow speed, enable/disable, and other
    configurations to be executed on the entire group of
    physical links that make up the LAG

       See the Dell web Interface:
        Ports->LAG Configuration
        See the Cisco Interface:
        int port-channel <PORT_CHAN>
Trouble-Shooting/Testing Continued
   Line Taps: Very useful when diagnosing
    issues with LACP
       Verify that LACP PDU’s are being transmitted
       Verify that both devices are correctly transmitting
        traffic
       Usually if inter-operability problems as suspect it
        will be determined that one device is not
        transmitting or receiving frames on it’s aggregated
        links
Trouble-Shooting/Testing
When a port is enabled for active LACP, PDU’s
must be transmitted from that port:
        MAC 01:80:C2:00:00:02
        Type/Length 8809

Also, check the status of the LAG’s on both devices; LAG status
should be “bundl” (Cisco) “oper”, “operational”, “active”, or
equivalent and NOT “indep” (Cisco), “down”, “dis”, etc..

With STP DISABLED traffic should be passed over a multi-port
LAG without flooding or duplication, with multiple LAG’s flooding
should occur unless there is a protocol in place to prevent loops.
  Note: Some devices will disable ports in the event of flooding.

Most LA testing is executed with STP disabled for this reason – if
LACP fails we want to note flooding.
       Specific Device Configuration
        Cisco – See My Cisco Document (word doc)
        The following is basic Dell CLI config.

       Note: Web Interface Config is very easy, simply use the web interface
         LAG menu and specify a LAG and “L” for LACP in the table.
                                                                      Console#show lacp port 1
                                                                      Port-Channel ch1
                                                                          Port Type Gigabit Ethernet
                                                Produces the following    Attached Lag id:
console# conf
                                                LAG configuration.        Actor
console(config)# int eth g1
console(config-if)# channel-group 1 mode auto                                  System Priority:1
console(config-if)# exit                                                       MAC Address: 00:30:ab:cd:66:55
console(config)# int eth g2                                                    Admin Key:     25
console(config-if)# channel-group 2 mode auto                                  Oper Key:     25
                                                                          Partner
console# show lacp port 1                                                      System Priority:0
                                                                               MAC Address: 00:00:00:00:00:00
                                                                               Oper Key:     0
                                                                      console# show lacp port 2
                                                                      Port-Channel ch2
                                                                          Port Type Gigabit Ethernet
                                                                          Attached Lag id:
                                                                          Actor
                                                                               System Priority:1
                                                                               MAC Address: 00:30:ab:cd:66:55
                                                                               Admin Key:     26
                                                                               Oper Key:     26
                                                                          Partner
                                                                               System Priority:0
                                                                               MAC Address: 00:00:00:00:00:00
                                                                               Oper Key:     0
3Com 4400 (RSTP) Config

Login: admin
Password:

Menu options: --------------3Com SuperStack 3 Switch 4400---------------
bridge        - Administer bridge-wide parameters
feature       - Administer system features
gettingStarted - Basic device configuration
logout        - Logout of the Command Line Interface
physicalInterface - Administer physical interfaces
protocol       - Administer protocols
security       - Administer security
system          - Administer system-level functions
trafficManagement - Administer traffic management

Type ? for help
----------------------------------------- (1)---------------------------
Select menu option: bridge
Menu options: --------------3Com SuperStack 3 Switch 4400---------------
addressDatabase - Administer bridge addresses
broadcastStormCont - Enable/disable broadcast storm control
linkAggregation - Administer aggregated links
multicastFilter - Administer multicast filtering
port          - Administer bridge ports
resilientLinks - Administer resilient links
spanningTree        - Administer spanning tree
summary           - Display summary information
vlan          - Administer VLANs

Type "quit" to return to the previous menu or ? for help
----------------------------------------- (1)---------------------------
Select menu option (bridge): linkA

Menu options: --------------3Com SuperStack 3 Switch 4400---------------
detail      - Display detailed information
modify        - Modify aggregated links
summary          - Display summary information

Type "quit" to return to the previous menu or ? for help
----------------------------------------- (1)---------------------------
Select menu option (bridge/linkAggregation): mod

Menu options:    --------------3Com SuperStack 3 Switch 4400---------------
addPort           - Add a port to an aggregated link
linkState        - Enable/disable an aggregated link
partnerID         - Set the partner ID for an aggregated link
removePort           - Remove a port from an aggregated link

Type "quit" to return to the previous menu or ? for help
----------------------------------------- (1)---------------------------
Select menu option (bridge/linkAggregation/modify): addPort
Select aggregated link index (1-4): 1
Select ports (unit:port...,?): 1:1

Select menu option (bridge/linkAggregation/modify): q
Menu options: --------------3Com SuperStack 3 Switch 4400---------------
addressDatabase - Administer bridge addresses
broadcastStormCont - Enable/disable broadcast storm control
linkAggregation - Administer aggregated links
multicastFilter - Administer multicast filtering
port          - Administer bridge ports
resilientLinks - Administer resilient links
spanningTree        - Administer spanning tree
summary           - Display summary information
vlan          - Administer VLANs

Type "quit" to return to the previous menu or ? for help
----------------------------------------- (1)---------------------------
Select menu option (bridge): port
Menu options: --------------3Com SuperStack 3 Switch 4400---------------
defaultPriority - Sets the default 802.1D priority for untagged frames
detail        - Display detailed information
lacpState        - Enable/disable Link Aggregation Control Protocol
stpCost         - Set the Spanning Tree path cost parameter
stpFastStart       - Enable/disable Spanning Tree fast start
summary            - Display summary information

Type "quit" to return to the previous menu or ? for help
----------------------------------------- (1)---------------------------
Select menu option (bridge/port): lacpS
Select ports (unit:port...,?): 1:1
Enter new value (enable,disable)[enable]: en

Select menu option (bridge/port):
     HP Configuration

HP ProCurve Switch 4172GL               8-Jan-1990 0:35:50
==========================- CONSOLE - MANAGER MODE -==========================18
                  Main Menu

 1. Status and Counters...
 2. Switch Configuration...
 3. Console Passwords...
 4. Event Log
 5. Command Line (CLI)
 6. Reboot Switch
 7. Download OS
 8. Run Setup
 9. Stacking...
 0. Logout

Displays the event log.
To select menu item, press item number, or highlight item and press <Enter>.
     Enter 2 to get to the following menu:



HP ProCurve Switch 4172GL               8-Jan-1990 0:38:
==========================- CONSOLE - MANAGER MODE -==========================
             Switch Configuration Menu

 1. System Information
 2. Port/Trunk Settings
 3. Network Monitoring Port
 4. Spanning Tree Operation
 5. IP Configuration
 6. SNMP Community Names
 7. IP Authorized Managers
 8. VLAN Menu...
 0. Return to Main Menu...



Configures system-level information including system identification.
To select menu item, press item number, or highlight item and press <Enter>.
     Enter 2 to get to the following menu:

HP ProCurve Switch 4172GL                     8-Jan-1990 0:42:13
==========================- CONSOLE - MANAGER MODE -==========================18
         Switch Configuration - Port/Trunk Settings

 Port Type           Enabled         Mode        Flow Ctrl Group Type
 ---- --------- + ------- ------------ --------- ----- -----
 A1 100FX | Yes                100FDx           Disable                 Use the arrow keys
 A2             | Yes                 Disable
 A3             | Yes                 Disable                           and space bar to
 B1 10/100TX | Yes               Auto           Disable                 configure.
 B2 10/100TX | Yes               Auto           Disable
 B3 10/100TX | Yes
 B4 10/100TX | Yes
                                 Auto
                                 Auto
                                                Disable Trk1 LACP
                                                Disable Trk1 LACP
                                                                        Notice Two LAG’s of
 B5 10/100TX | Yes               Auto           Disable Trk2 LACP       Two ports each.
 B6 10/100TX | Yes               Auto           Disable Trk2 LACP
 B7 10/100TX | Yes               Auto           Disable
 B8 10/100TX | Yes               Auto           Disable
 B9 10/100TX | Yes               Auto           Disable

Actions-> Cancel         Edit    Save     Help

Cancel changes and return to previous screen.
Use arrow keys to change action selection and <Enter> to execute action.

				
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