Can the 10G Twinax cables work in 1G mode on 1G ports?

[ronit]

So we use ASR920-12CZA and ASR920-24SZ-M on our networks. Recently we started doing the cabling between different routers of the same cabinet using Twinax cables; however, I am seeing very inconsistent compatibility issues

1. In my lab, a Twinax cable (SFP-H10GB-CU2M) between 1G SFP ports on the ASR920-12CZA working in 1G mode
2. In my lab, a Twinax cable (SFP-H10GB-CU2M) between dual rate 1G/10G SFP ports on the ASR920-12CZA working in 1G mode
3. In the field, a Twinax cable (SFP-H10GB-CU1M) between dual rate 1G/10G SFP ports on the ASR920-12CZA failing to negotiate at 1G and failing to come up because we don't have a 10G license on these routers (Don't have 10G license in point 2 above, either)

Points 2 and 3 are baffling to me, because the router model, IOS image (16.9.3), config are virtually identical; only difference is length of the cable. Still, for point 3, there's an error that the port cannot operate in 10G mode because of a lack of license and stays administratively down.

We also have some ASR920-24SZ-M coming up and now I fear the Twinax won't come up on these routers on the 1G ports in 1G mode.

The datasheet itself doesn't mention 1G compatibility anywhere, but I went ahead because of success in the lab (Points 1 and 2).

Is there any official information about this available?

[ronit · Accepted solution]

Did some more tests and the cables on-site work fine on 1G ports, they work fine on 10G ports, but then don't work on 1G/10G dual-rate ports without a 10G license.

My lab cables work fine in all situations. The only difference I can see is that my lab cables are version V02 and the ones on site are V03. Seems like they broke the 1G/10G negotiations in V03.

Anyways, I have learnt my lesson and will use Twinax for 10G links only.