• How to configure Link Aggregation Groups in EOS

 
 
Print Friendly, PDF & Email

This article describes the configuration of Link Aggregation Groups (LAGs) between two Arista 7050T-64 switches. The configuration examples are not specific to the switch model and this guide should apply to configuring LAGs on all Arista hardware.

Static Link Aggregation

Configuration of 7050-01

7050-01(config-if-Et17-20)#channel-group 200 mode on

Once the above sequence is entered, Ethernet interfaces 17 through 20 are bound in a LAG as port-channel 200:

7050-01#show int po200
Port-Channel200 is down, line protocol is lowerlayerdown (notconnect)
  Hardware is Port-Channel, address is 001c.731c.46f9
  Ethernet MTU 9214 bytes
  Full-duplex, Unconfigured
  Active members in this channel: 0
  Fallback mode is: off
  Fallback mode status: Unconfigured
  Fallback timeout is 90 seconds
  Down 3 minutes, 21 seconds
  1 link status changes since last clear
  Last clearing of "show interface" counters never
  5 minutes input rate 0 bps (- with framing overhead), 0 packets/sec
  5 minutes output rate 0 bps (- with framing overhead), 0 packets/sec
     0 packets input, 0 bytes
     Received 0 broadcasts, 0 multicast
     0 input errors, 0 input discards
     0 packets output, 0 bytes
     Sent 0 broadcasts, 0 multicast
     0 output errors, 0 output discards

Configuration of 7050-02

7050-02(config-if-Et17-20)#channel-group 200 mode on

Once the above sequence is entered, Ethernet interfaces 17 through 20 are bound in a LAG as port-channel 200:

7050-02#show int po 200
Port-Channel200 is down, line protocol is lowerlayerdown (notconnect)
  Hardware is Port-Channel, address is 001c.731c.54e5
  Ethernet MTU 9214 bytes
  Full-duplex, Unconfigured
  Active members in this channel: 0
  Fallback mode is: off
  Fallback mode status: Unconfigured
  Fallback timeout is 90 seconds
  Down 2 minutes, 45 seconds
  1 link status changes since last clear
  Last clearing of "show interface" counters never
  5 minutes input rate 0 bps (- with framing overhead), 0 packets/sec
  5 minutes output rate 0 bps (- with framing overhead), 0 packets/sec
     0 packets input, 0 bytes
     Received 0 broadcasts, 0 multicast
     0 input errors, 0 input discards
     0 packets output, 0 bytes
     Sent 0 broadcasts, 0 multicast
     0 output errors, 0 output discards

After connecting the cables the interface will be up, verification commands will show the status:

7050-01(config)#show int status connected
Port       Name              Status       Vlan        Duplex  Speed Type
Et17                         connected    in Po200    a-full  a-10G 10GBASE-T
Et18                         connected    in Po200    a-full  a-10G 10GBASE-T
Et19                         connected    in Po200    a-full  a-10G 10GBASE-T
Et20                         connected    in Po200    a-full  a-10G 10GBASE-T
...
7050-02(config)#show int status connected
Port       Name              Status       Vlan        Duplex  Speed Type
Et17                         connected    in Po200    a-full  a-10G 10GBASE-T
Et18                         connected    in Po200    a-full  a-10G 10GBASE-T
Et19                         connected    in Po200    a-full  a-10G 10GBASE-T
Et20                         connected    in Po200    a-full  a-10G 10GBASE-T
...
7050-01(config)#show int po 200
Port-Channel200 is up, line protocol is up (connected)
  Hardware is Port-Channel, address is 001c.731c.46f9
  Ethernet MTU 9214 bytes , BW 40000000 kbit
  Full-duplex, 40Gb/s
  Active members in this channel: 4
  ... Ethernet17 , Full-duplex, 10Gb/s
  ... Ethernet18 , Full-duplex, 10Gb/s
  ... Ethernet19 , Full-duplex, 10Gb/s
  ... Ethernet20 , Full-duplex, 10Gb/s
  Fallback mode is: off
  Fallback mode status: Unconfigured
  Fallback timeout is 90 seconds
  Up 4 minutes, 16 seconds
  2 link status changes since last clear
  Last clearing of "show interface" counters never
  5 minutes input rate 109 bps (0.0% with framing overhead), 0 packets/sec
  5 minutes output rate 387 bps (0.0% with framing overhead), 0 packets/sec
     34 packets input, 6129 bytes
     Received 0 broadcasts, 34 multicast
     0 input errors, 0 input discards
     160 packets output, 21627 bytes
     Sent 0 broadcasts, 160 multicast
     0 output errors, 0 output discards
7050-01(config)#show port-channel summary

                 Flags
------------------------ ---------------------------- -------------------------
  a - LACP Active          p - LACP Passive           * - static fallback
  F - Fallback enabled     f - Fallback configured    ^ - individual fallback
  U - In Use               D - Down
  + - In-Sync              - - Out-of-Sync            i - incompatible with agg
  P - bundled in Po        s - suspended              G - Aggregable
  I - Individual           S - ShortTimeout           w - wait for agg

Number of channels in use: 3
Number of aggregators:3

  Port-Channel     Protocol    Ports
---------------- ------------- ------------------------------------------------
  Po200(U)         Static       Et17(P) Et18(P) Et19(P) Et20(P)

Dynamic Link Aggregation using LACP

In static Link Aggregation, each port-channel is created with no awareness of the port-channel on the other switch. This can cause packets to be dropped if the two switches are not configured for exactly the same static aggregate. Using the Link Aggregation Control Protocol, dynamic Link Aggregation Groups are aware of the state of the port-channel on the partner switch. (Note: In LACP terminology, the local interface is referred to as the ‘actor’ and the remote interface is referred to as the ‘partner’).

As part of LACP, each interface configured to be part of the channel-group must be designated as ‘active’ or ‘passive’. An active interface sends LACP Protocol Data Units (LACP PDUs) at a rate of one per-second in an attempt to form a channel with a partner interface on the other switch. A passive interface will only send LACP PDUs if it receives one from a partner. Therefore an actor set to ‘active’ will form a channel with a partner set to ‘passive’ or ‘active’, but if an actor and a partner are both set to ‘passive’ no channel will be formed.

Typically, the mode will be set to active on both ‘actor’ and ‘partner’. Our examples will show both passive and active configurations.

Configuring LACP with an active and passive port-channels

Configuration of 7050-01

7050-01(config-if-Et17-20)#channel-group 200 mode active

Configuration of 7050-02

7050-02(config-if-Et17-20)#channel-group 200 mode passive

In addition to ‘show’ commands we can inspect the logs:

7050-02(config-if-Et17-20)#show logging last 2 minutes
Jan 28 20:56:03 7050-02 Ebra: %LINEPROTO-5-UPDOWN: Line protocol on Interface Port-Channel200, changed state to up
7050-02(config-if-Et17-20)#show port-channel summary

                 Flags
------------------------ ---------------------------- -------------------------
  a - LACP Active          p - LACP Passive           * - static fallback
  F - Fallback enabled     f - Fallback configured    ^ - individual fallback
  U - In Use               D - Down
  + - In-Sync              - - Out-of-Sync            i - incompatible with agg
  P - bundled in Po        s - suspended              G - Aggregable
  I - Individual           S - ShortTimeout           w - wait for agg

Number of channels in use: 3
Number of aggregators:3

  Port-Channel     Protocol    Ports
---------------- ------------- ------------------------------------------------
  Po200(U)         LACP(p)      Et17(PG+) Et18(PG+) Et19(PG+) Et20(PG+)

Note that the show port-channel summary output now shows LACP(p) on 7050-02. The legend tells us that ‘(p)’ means passive. On 7050-01, we see LACP(a), which tells us it is configured as active:

7050-01(config-if-Et17-20)#show port-channel summary

                 Flags
------------------------ ---------------------------- -------------------------
  a - LACP Active          p - LACP Passive           * - static fallback
  F - Fallback enabled     f - Fallback configured    ^ - individual fallback
  U - In Use               D - Down
  + - In-Sync              - - Out-of-Sync            i - incompatible with agg
  P - bundled in Po        s - suspended              G - Aggregable
  I - Individual           S - ShortTimeout           w - wait for agg

Number of channels in use: 3
Number of aggregators:3

  Port-Channel     Protocol    Ports
---------------- ------------- ------------------------------------------------
  Po200(U)         LACP(a)      Et17(PG+) Et18(PG+) Et19(PG+) Et20(PG+)

The ‘show interface port-channel 200’ output is similar to our static port-channel example:

7050-01#show int po 200
Port-Channel200 is up, line protocol is up (connected)
  Hardware is Port-Channel, address is 001c.731c.46f9
  Ethernet MTU 9214 bytes , BW 40000000 kbit
  Full-duplex, 40Gb/s
  Active members in this channel: 4
  ... Ethernet17 , Full-duplex, 10Gb/s
  ... Ethernet18 , Full-duplex, 10Gb/s
  ... Ethernet19 , Full-duplex, 10Gb/s
  ... Ethernet20 , Full-duplex, 10Gb/s
  Fallback mode is: off
  Fallback mode status: Unconfigured
  Fallback timeout is 90 seconds
  Up 20 minutes, 15 seconds
  4 link status changes since last clear
  Last clearing of "show interface" counters never
  5 minutes input rate 330 bps (0.0% with framing overhead), 0 packets/sec
  5 minutes output rate 814 bps (0.0% with framing overhead), 1 packets/sec
     409 packets input, 65248 bytes
     Received 0 broadcasts, 409 multicast
     0 input errors, 0 input discards
     1274 packets output, 171623 bytes
     Sent 0 broadcasts, 1274 multicast
     0 output errors, 0 output discards

During the synchronization process, all configured interfaces transmit LACP PDUs at a rate of one per-second. Once synchronized, LACP PDUs are exchanged at a rate of one every thirty seconds.

After synchronization is complete, LACP interfaces have a default timeout of 30 seconds with a failure tolerance of three. This means that if a LACP PDU is not seen from the partner interface after ninety seconds, the actor interface will record the partner interface as failed and remove the actor interface from the port-channel.

This timeout can be altered by configuring the interface to instruct the partner to transmit LACP PDUs at a faster rate:

7050-01(config-if-Et17)#lacp rate fast

Following this, the partner interface will begin sending LACP PDUs at a rate of one per-second, and the actor interface’s timeout will be changed to 1 second.

LACP show commands

The output of show lacp counters allows users to see both the send the receive counts of LACP PDUs:

7050-01#show lacp counters
                        LACPDUs       Markers       Marker Response
 Port      Status      RX     TX     RX     TX         RX          TX   Illegal
--------- ---------- ------ ------ ------ ------ ---------- ----------- -------
Port Channel Port-Channel200:
 Et17      Bundled     94    187      0      0          0           0         0
 Et18      Bundled     52    187      0      0          0           0         0
 Et19      Bundled     52    187      0      0          0           0         0
 Et20      Bundled     52    187      0      0          0           0         0

* - Only local interfaces for MLAGs are displayed. Connect to the peer to
    see the state for peer interfaces.

show lacp internal shows the LACP state of the actor interfaces on the local switch:

7050-01#show lacp internal
LACP System-identifier: 8000,00-1c-73-1c-46-e8
MLAG System-identifier: 8000,02-1c-73-1c-46-e8
State: A = Active, P = Passive; S=ShortTimeout, L=LongTimeout;
       G = Aggregable, I = Individual; s+=InSync, s-=OutOfSync;
       C = Collecting, X = state machine expired,
       D = Distributing, d = default neighbor state
                | Partner                                Actor
Port    Status  | Sys-id                  Port#  State    OperKey  PortPriority
------ ---------|------------------------ ------ -------- -------- ------------
Port Channel Port-Channel200:
Et17    Bundled | 8000,00-1c-73-1c-54-d4     17  ASGs+CD   0x00c8         32768
Et18    Bundled | 8000,00-1c-73-1c-54-d4     18  ALGs+CD   0x00c8         32768
Et19    Bundled | 8000,00-1c-73-1c-54-d4     19  ALGs+CD   0x00c8         32768
Et20    Bundled | 8000,00-1c-73-1c-54-d4     20  ALGs+CD   0x00c8         32768

* - Only local interfaces for MLAGs are displayed. Connect to the peer to
    see the state for peer interfaces.

show lacp neighbor shows the LACP state of the partner interfaces on the remote switch:

7050-01#show lacp neighbor
State: A = Active, P = Passive; S=ShortTimeout, L=LongTimeout;
       G = Aggregable, I = Individual; s+=InSync, s-=OutOfSync;
       C = Collecting, X = state machine expired,
       D = Distributing, d = default neighbor state
                 |                        Partner
Port     Status  | Sys-id                    Port#   State     OperKey  PortPri
------- ---------|------------------------- ------- --------- --------- -------
Port Channel Port-Channel200:
Et17     Bundled | 8000,00-1c-73-1c-54-d4       17   PLGs+CD    0x00c8    32768
Et18     Bundled | 8000,00-1c-73-1c-54-d4       18   PLGs+CD    0x00c8    32768
Et19     Bundled | 8000,00-1c-73-1c-54-d4       19   PLGs+CD    0x00c8    32768
Et20     Bundled | 8000,00-1c-73-1c-54-d4       20   PLGs+CD    0x00c8    32768

* - Only local interfaces for MLAGs are displayed. Connect to the peer to
    see the state for peer interfaces.

For example, here is what happens if the port-channel on 7050-02 is converted to active:

7050-02(config-if-Et17-20)#channel-group 200 mode active
7050-02(config-if-Et17-20)#show port-channel summary

                 Flags
------------------------ ---------------------------- -------------------------
  a - LACP Active          p - LACP Passive           * - static fallback
  F - Fallback enabled     f - Fallback configured    ^ - individual fallback
  U - In Use               D - Down
  + - In-Sync              - - Out-of-Sync            i - incompatible with agg
  P - bundled in Po        s - suspended              G - Aggregable
  I - Individual           S - ShortTimeout           w - wait for agg

Number of channels in use: 3
Number of aggregators:3

  Port-Channel     Protocol    Ports
---------------- ------------- ------------------------------------------------
  Po200(U)         LACP(a)      Et17(PG+) Et18(PG+) Et19(PG+) Et20(PG+)

Link aggregation hashing

The switch determines the forwarding path within a Link Aggregation Group by using a hashing algorithm. This hash takes the following factors into account:

  • source/destination MAC addresses
  • EtherType
  • source/destination IP addresses
  • IP protocol number
  • source/destination TCP/UDP ports
Follow

Get every new post on this blog delivered to your Inbox.

Join other followers: