NCS 540 Insert SFP 1gb/s in interface 25gb/s

[a.auvinet]

Hello,

I test one NCS 540 in my lab.

I have 24 interfaces TenGiga , 8 twentyfiveGiga  and 4 100gb.

In documentation, i can see interface  twentyfiveGiga  are Ok for 1Gb.

https://www.cisco.com/c/en/us/products/collateral/routers/network-convergence-system-500-series-routers/datasheet-c78-740296.html

When I insert a SFP 1 Gbs in interface tengiga, It seems OK, the NCS540 create a gigabit interface.

Not When I insert in twentyfiveGiga.

Someone have a idea ?

[philclemens1835 · Accepted solution]

I suspect the documentation is incorrect.

As I understand it, the NCS platform is based on merchant silicon from Broadcom.

If you look at Broadcom's material for SFP28 interfaces, it only states backwards compatibility with SFP+ 10Gbps, and not 1Gbps.  I found this in a few different SFP28 educational-type articles as well.

If there is backwards compatibility to 1Gbps, it would likely be based on a specific SFP model.  Something along the lines of an SFP+ that is stepped down to 1Gbps.  Much like Cisco makes 100BaseFX SFP's for gigabit interfaces (GLC-GE-100FX vs GLC-FE-100FX).

[a.auvinet]

hi philclemens.

thank you for your reply.

I just find this link on the web

http://networkingbodges.blogspot.com/2019/03/how-to-use-25g-ports-in-110g-mode-on.html?m=1 

I try it asap

and reply to you for your information

best regard

[a.auvinet]

Hi Everybody,

I configured the Twentyfive   to ten .

The interface  25 to 31 is now 10g.

hw-module quad 0 location 0/0/CPU0
 mode 10g
!
hw-module quad 1 location 0/0/CPU0
 mode 10g

But when I insert a SFP  1g in Interface between 0 > 24 , it is OK, it's UP

But when I insert a SFP  1g in Interface between  25 > 31, it is NOK, it's still Down

Exemple of configuration of interface :

interface GigabitEthernet0/0/0/22
 speed 1000
 negotiation auto
!
interface GigabitEthernet0/0/0/28
 speed 1000
 negotiation auto