Symptom
Control-plane traffic coming in standby Supervisor's port using multirate 40/100GE QSFP (e.g. QSFP-40/100-SRBD) on a C9400-SUP-1/XL/XL-Y Dual-Sup system will be punted to CPU with incorrect/Inactive ingress interface information.
Conditions
For example, interface Fo3/0/9 is enabled/Active, thus interfaces Te3/0/1-4 are disabled/Inactive:
SW1# sh int fo3/0/9 status
Port Name Status Vlan Duplex Speed Type
Fo3/0/9 connected 1 full 40G QSFP 40/100GE SRBD
CDP frames received on this interface will be then punted to CPU with interface Te3/0/4 as ingress port:
------ Punt Packet Number: 5, Timestamp: 2022/02/24 01:18:38.465 ------
interface : physical: TenGigabitEthernet3/0/4[if-id: 0x00000053], pal: TenGigabitEthernet3/0/4 [if-id: 0x00000053]
metadata : cause: 96 [Layer2 control protocols], sub-cause: 0, q-no: 1, linktype: MCP_LINK_TYPE_LAYER2 [10]
ether hdr : dest mac: 0100.0ccc.cccc, src mac: 3c13.cca3.a9b9
ether hdr : length: 34
As interface Te3/0/4 is Inactive, the CDP table is not updated with this neighbor's information.
Affects as well LACP (ports will be Suspended with no RX counter increase), and EPC capturing capabilities for the affected ports. Other punted traffic might be impacted too.
Workaround
Do not use multirate 40/100G QSPF.
Do not use standby Supervisor's port with multirate 40/100G QSPF.
Issue not seen with 10G SFPs and single-rate 40G QSFPs.
Further Problem Description
Seen with 17.5.x, 17.6.x and 17.7.x trains.
Affects only C9400-SUP-1/XL/XL-Y, C9400-SUP-2/XL is not affected.
