• 25G Lane Speed

 
 
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Introduction

With the introduction of support for 25GbE on servers and switches we expect to see a rapid movement to server attachment at 25G, replacing the use of servers at 40G.

Even though 25G is becoming norm these days, most of the deployment is still carried out with 10G to servers with 25G as future state.

So when a 25G switchport is used, we can use them as 10G/1G/100M ports. But there are some limitations around how to configure them as they follow SerDes quartet, which means a group of 4 ports (eg:Et1-4, Et5-8, etc.) have to be configured in a compatible speed configuration.

Platform Compatibility

  • DCS – 7060X series

Configuration

Note when configuring the speed on a 25G Port, it follows the speed of the Master Port to their remaining 3 other ports (only in 25G speed mode). Which means when a Master Port(starting from Et1) is configured as a 25G Port then Et2-4 cannot be configured as 10G/1G ports, they can only be used as 25G ports. Configuring them to 10G/1G will result in switchport to be “err-disabled”.

The above limitation is only when configuring 25G on Master ports this is because the SerDes quartet can either be configured to run only at 25G or a mix of 10G/1G.

But saying that when we configure the Master port(Et1) as 10G port, then remaining (Et2-4) ports can be configured as either 10G or 1G ports.

Configure forced 25G speed

Arista(config)#interface ethernet 1-4
Arista(config-if-Et1-4)#speed forced 25gfull

Output from “show interface status” command

Interface  Speed   Status
Et1        25G     Connected
Et2        25G     Connected
Et3        25G     Connected
Et4        25G     Connected

Configure forced 10G/1G speed on Et2-4

Arista(config)#interface ethernet 2-3
Arista(config-if-Et2-3)#speed forced 10000full
Arista(config)#interface ethernet 4
Arista(config-if-Et4)#speed forced 1000full

Output from “show interface status” command

Interface  Speed   Status
Et1        25G     Connected
Et2        10G     errdisabled
Et3        10G     errdisabled
Et4        1G      errdisabled

Configure forced 10G speed

Arista(config)#interface ethernet 1-4
Arista(config-if-Et1-4)#speed forced 10000full

Output from “show interface status” command

Interface  Speed   Status
Et1        10G     Connected
Et2        10G     Connected
Et3        10G     Connected
Et4        10G     Connected

Configure forced 1G/100M speed on Et2-4

Arista(config)#interface ethernet 2-3
Arista(config-if-Et2-3)#speed forced 1000full
Arista(config)#interface ethernet 4
Arista(config-if-Et4)#speed forced 100full

Output from “show interface status” command

Interface  Speed   Status
Et1        10G     Connected
Et2        1G      Connected
Et3        1G      Connected
Et4        100M    Connected

Configure forced 1G speed

Arista(config)#interface ethernet 1-4
Arista(config-if-Et1-4)#speed forced 1000full

Output from “show interface status” command

Interface  Speed   Status
Et1        1G      Connected
Et2        1G      Connected
Et3        1G      Connected
Et4        1G      Connected

Configure forced 10G/100M speed on Et2-4

Arista(config)#interface ethernet 2-3
Arista(config-if-Et2-3)#speed forced 10000full
Arista(config)#interface ethernet 4
Arista(config-if-Et4)#speed forced 100full

Output from “show interface status” command

Interface  Speed   Status
Et1        1G      Connected
Et2        10G     Connected
Et3        10G     Connected
Et4        100M    Connected

Status

  • show interfaces <interface-range> status : displays the speed & status of interface.
  • show interfaces <interface-range> status errdisabled/connected/notconnect : displays the err-disabled/connected/notconnect interface status
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