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.
Contents
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