Speed Groups, QSA Adapters, and Breakouts

References
https://www.arista.com/en/um-eos/eos-ethernet-ports
https://arista.my.site.com/AristaCommunity/s/article/25g-lane-speed-2-2

Multi-rate Optics

It is possible to use multi-rate optics such as a single mode SFP28 transceiver in an SFP28 port, and configure the transceiver to operate at 1G, 10G, or 25G. For example:

interface Ethernet1
   description Interface forced to 1Gbps
   speed forced 1000full
   transceiver media override 1000base-lx

interface Ethernet1
   description Interface forced to 10Gbps
   speed forced 10000full
   transceiver media override 10gbase-lr

interface Ethernet1
   description Interface forced to 25Gbps
   speed forced 25gfull
   transceiver media override 25gbase-lr

 

The output of "show interfaces transceiver hardware" will show that the media type matches the transceiver override type configured under the interface.

 

Speed Groups

Note: there are many caveats and limitations with using QSA adapters and configuring speed groups. Be sure to understand them all before using them.

 

One can see available speed groups using "show hardware speed-group configurations".

Example from a 7280CR3 running 4.31.2F:

#show hardware speed-group configurations 
Group Interfaces        Select Value Available Speed Configurations                
----- ----------------- ------------ ----------------------------------------------
1     Et1/1-4/3         10g          10G/full,40G/full                             
1     Et1/1-4/3         25g          25G/full                                      
1     Et1/1-4/3         50g          50G/full,100G/full       

Two speeds per speed group are support on this specific model.

The default is 10G and 50G which allows the QSFP28 ports to be used for 100G services or 10G services (when using a QSA adapter):

#show hardware speed-group status 
Group Interfaces        Supported   Default     Configured  Active     
----- ----------------- ----------- ----------- ----------- -----------
1     Et1/1-4/3         10g,25g,50g 10g,50g     default     10g,50g  

 

When configuring speed-groups, the SerDes speeds must be set under the global config.

The following command configures ports in speed group 7 to be used for 10G or 25G services (when using a QSA adapter):

hardware speed-group7 serdes 25g 10g

Then the ports in the speed group can be configured with their individual speeds.

Below we see that now ports Eth25 to 28 only run in 10G or 25G mode.

#show hardware speed-group status 
Group Interfaces        Supported   Default     Configured  Active     
----- ----------------- ----------- ----------- ----------- -----------
...  
7     Et25/1-28/3       10g,25g,50g 10g,50g     10g,25g     10g,25g 

Because this specific model has QSFP28 ports, each port then requires a QSA adapter. If a multi-rate optic is inserted into that adapter, the port speed needs to be set under the interface code.

The output of "show interfaces transceiver hardware" for a QSFP28 port with a QSFP28 optic inserted, would normally show four lanes for the QSFP28:

#show interfaces transceiver hardware
Name: Ethernet1/1
Media type: 100GBASE-LR4
Module presence: detected
Maximum module power (W): 4.0
Maximum slot power (W): N/A
Wavelength (nm): 1310.0

Name: Ethernet1/2
Media type: 100GBASE-LR4
Module presence: detected
Maximum module power (W): 4.0
Maximum slot power (W): N/A
Wavelength (nm): 1310.0

Name: Ethernet1/3
Media type: 100GBASE-LR4
Module presence: detected
Maximum module power (W): 4.0
Maximum slot power (W): N/A
Wavelength (nm): 1310.0

Name: Ethernet1/4
Media type: 100GBASE-LR4
Module presence: detected
Maximum module power (W): 4.0
Maximum slot power (W): N/A
Wavelength (nm): 1310.0

Now with a QSA adapter and a 25G optic inserted, Eth25/1 shows as one lane:

Name: Ethernet25/1
Media type: 25GBASE-LR
Module presence: detected
Maximum module power (W): 1.0
Maximum slot power (W): N/A
Wavelength (nm): 1310

And Eth27/1 has a 1/10/25G multi-rate optic configured to run at 10Gbps:

Name: Ethernet27/1
Media type: 10GBASE-LR
Module presence: detected
Maximum module power (W): 1.0
Maximum slot power (W): N/A
Wavelength (nm): 1310
Detected media type: 25GBASE-LR

 

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