QSFP-100G-CU1M DAC link stays down between NCS55A2-MOD (IOS XR) and Catalyst 9500-48Y4C
3
The poster needs a 100GE link between a Cisco NCS55A2-MOD (NC55-MPA-4H-S MPA) and a Cisco Catalyst C9500-48Y4C using a QSFP-100G-CU1M DAC. Both platforms list the cable as supported, yet the link never comes up at the physical level. Because the Catalyst 9500 lacks 100G auto-negotiation (bug CSCvk07538), the poster disabled it on the NCS with 'interface HundredGigE 0/0/1/2' / 'no negotiation auto', to no effect. IOS XR 6.5.3, 6.6.3 and 7.0.2 were tested on the NCS with identical results. Per the NCS 5500 interface guide, 100G auto-negotiation is on by default on NCS 540 and NCS 55A2. The same DAC works NCS-to-NCS and Catalyst-to-Catalyst, so the poster suspects a platform interoperability problem.
- Hardware: Cisco NCS55A2-MOD with NC55-MPA-4H-S, Cisco Catalyst C9500-48Y4C
- Transceivers: QSFP-100G-CU1M
- Form factor: QSFP28, DAC
Symptoms / messages:
100G DAC link down between NCS55A2-MOD and Catalyst 9500
no negotiation auto has no effect
CSCvk07538 (no 100G auto-negotiation on Catalyst 9500)
same DAC works NCS-to-NCS and Catalyst-to-Catalyst
Comments 2
A respondent said they had seen several auto-negotiation problems with this particular DAC, asked which software version was in use and suggested trying with 'negotiation auto' enabled on both sides.
The poster replied that three IOS XR releases behaved identically and that the Catalyst side cannot negotiate at 100G, leaving the NCS 'no negotiation auto' knob as the only lever, whose effectiveness is unclear; the thread ended without a fix.